united (ual) performance manual

7/30/2019 United (UAL) Performance Manual

1/64

INTRODUCTION

United Airlines employs a Fleet Standard system of defining, calculating, and using performance data. Thismeans only onesystem of performance procedures must be learned, regardless of seat or airplane. The factsand definitions learned from this manual, indoctrination academics, and in the CBT (Computer Based Trainer) will

carry over directlyinto your first, and all subsequent fleet transition courses. The time to acquire a thoroughandcompleteunderstanding of United Fleet Standard performance is now. There is little time allotted in transition

training to learn the basics of performance. Learn it now. Learn it well.

DEFINITIONS

The calculation and use of Fleet Standard performance data depends on a complete and uniform understanding ofcertain terms. The following basic definitions are the basis for all performance calculations.

PRESSURE ALTITUDE

Pressure altitude is actual field elevation corrected for variations from standard pressure. At sea level on aStandardDay an altimeter setting of 29.92 makes the altimeter read correctly; i.e., zero. If the pressure is not

standard, then the altimeter must be adjusted in order to read correctly. This concept is true at all elevations.The adjustment is the altimeter setting we receive from the tower.

To find the pressure altitude at any time, just set 29.92 in the altimeter. If the local altimeter setting is greater than29.92, pressure altitude is lower than field elevation. And the opposite, of course, is also true.

Arithmetically, pressure altitude can be determined using the relationship of ten feet of altitude change for each.01 inch of altimeter change. For example:

If field elevation = 5333, andaltimeter setting = 30.02, then

pressure altitude = 5233.

In this case, the altimeter setting has increased by .1 inch from standard. Therefore, pressure altitude is 100 feet

less than field elevation.

Pressure altitude is an entry parameter for performance procedures such as V speed corrections.

DENSITY ALTITUDE

Density altitude is pressure altitude corrected for variations from standard temperature.

An airplane always performs based on density altitude. Drag, lift, power available, and true airspeed are all

affected by the number of air molecules per unit of time that hit the airframe, flow over the wing, and areprocessed through the engines. As density altitude decreases (more dense air), drag, lift, and power available allincrease, but true airspeed decreases. As density altitude increases (less dense air), drag, lift, and power

available all decrease, but true airspeed increases.

STANDARD PERFORMANCE 02/01/94Page 1

MN111

REFERENCE HANDBOOK


2/64

CHORD LINE

A chord line is an imaginary straight line from the very front of the leading edge of the wing to the very back of thetrailing edge. The line does not necessarily remain entirely inside the wing, nor does it necessarily remainconstant at a given wing section. For instance, the chord line changes continuously as flaps are lowered. For

purposes of defining the chord line, the flaps are considered part of the wing.

Figure 1

RELATIVE WIND

Relative wind is simply the direction from which the airstream strikes the chord line as the airplane moves throughthe air. Normally, the relative wind strikes the airplane from somewhat below the chord line. (Figure 2)

ANGLE OF ATTACK

Angle of attack is the angle between the chord line and the relative wind. Angle of attack is notthe same thing aspitch attitude. The angle of attack for a particular combination of weight and speed may be changed by altering

the shape of the wing; i.e., changing flap setting. Angle of attack is one of the parameters affecting airplaneperformance (along with weight, altitude, temperature, airspeed and configuration).

Figure 2

RELATIVEWIND

ANGLE OFATTACK

STANDARD PERFORMANCE02/01/94Page 2

MN111

REFERENCE HANDBOOK


3/64

LIFT

Lift is the force, perpendicular to the relative wind, that opposes weight and keeps the airplane airborne.

There are four ways a pilot can change the amount of lift being produced by the wings:

1. Change density Altitude. Normally, this is done by changing actual altitude. Density altitude couldalso be changed by flying into a region of warmer or colder air, or a region of higher or lower

pressure, while maintaining a constant actual altitude. As density altitude increases, lift decreases,and as density altitude decreases, lift increases.

2. Change angle of attack. As angle of attack increases, lift increases, up to the point where the wingstalls, resulting in a massive loss of lift. For a given weight and configuration, the angle of attack at

which this loss of l ift occurs corresponds to a certain speed, which is stall speed of the airplaneunder those conditions. In normal airline operations, we dont fly the airplane anywhere near the

maximum angle of attack, exceptduring max performance windshear recoveries.

3. Change the shape of the wing. This is usually done by extending trailing edge and/or leading edgedevices, which increases wing area and camber, thus increasing lift. The more devices extended,the greater the lift of the wing. Drag, of course, would also increase.

4. Change speed. Increased airspeed at a constant angle of attack produces greater lift.

THRUST

Thrust is the product of two things: the mass of air that flows through an engine and the increase of velocityimparted to the air as it exits the engine.

Thrust produced by a jet engine results when a mass of air entering the intake is compressed, then heated bycombustion. This enables the air mass to be accelerated through the turbine section to be exhausted at a much

higher velocity.

The engines on Uniteds airplanes are turbofans. A turbofan is an engine that has a fan mounted ahead of thecompressor. The fan accelerates a large mass of air which bypasses the core of the engine to be mixed with the

jet exhaust. The thrust of this engine is the combination of the thrust produced by the fan section and that

produced by the core. Some of the advantages of a turbofan are lower noise and increased fuel efficiency.

The factors a pilot can change to affect thrust are:

1. Fuel flow and RPM. Within limits, the higher the fuel flow and greater RPM, the more thrust the

engine will produce. As long as the operating limits of the engine are not exceeded, the faster itturns, the more air and fuel it can process, so the more thrust it produces.

2. Density altitude. This factor has a huge effect on thrust. As the density of the air entering the enginechanges, the mass flow rate, and therefore thrust, change.

4. Airspeed. As airspeed increases, thrust decreases. This is because the mass flow rate out of theengine remains relatively stable, while the mass flow rate into the engine increases. Since thrust is

proportional to exhaust mass flow rate minus inlet mass flow rate, as airspeed increases thrustactually decreases, and vice versa.


MN111

REFERENCE HANDBOOK


4/64

DRAG

Drag is the force, parallel to the relative wind, that opposes movement in the direction of flight. The total dragacting on the airplane is the sum of three primary components: parasite drag, induced drag, and compressibilitydrag.

Parasite drag, sometimes referred to as form drag, barndoor effect or the flat plate effect is drag that resultsfrom trying to push the airplane shape through the air. There are four ways to influence parasite drag:

1. Change the shape of the airplane, usually with flaps, slats, spoilers, speed brakes, or landing gear.

2. Change the speed. Parasite drag is negligible at low speed, but increases dramatically as speedincreases. In fact, parasite drag varies with the squareof the airspeed.

3. Change angle of attack. Parasite drag increases as angle of attack increases because the airplane

presents a larger shape to the relative wind.

4. Vary density altitude. As density altitude increases, drag decreases, and vice versa.

Induceddrag is drag that results from the production of lift. Induced drag varies with angle of attack, weight,altitude, temperature, configuration and airspeed. At low speeds, induced drag is quite high. At the design cruise

speed, induced drag is low.

Compressibility drag is caused by the compression of air in front of the onrushing airplane, and the resultingshockwavebuildup. It begins to be a factor at about .75 mach, depending on wing design. As speed buildsbeyond this point, compressibilitydrag increases rapidly.

Figure 3 shows how parasite drag, induced drag and compressibility drag all combine to produce a total drag

curve. From this plot it is evident that at some given airspeed, total drag is at its minimum. This is importantwhen determining holding speed because when drag is at a minimum, the thrust required to maintain an altitude

for a given weight is at a minimum. Fuel flow at this point is also very close to being at a minimum which servesto maximize endurance. (See Holding Speed Section for further discussion)


MN111

REFERENCE HANDBOOK


5/64

Velocity

Drag risedue to

compressibility

Total DragParasite Drag

Stall

Induced Drag

MinDrag

Speed

MaxRangeSpeed

Total Drag Curve Figure 3

The point where a straight line drawn from the lower left corner of the graph tangent to the total drag curve definesthe speed that gives the best mileage the max range speed. Any deviation from this speed requires additionalfuel for every mile traveled through the air.

Each total drag curve is specific to weight, configuration, altitude and temperature. Generally, the lower the

weight, the lower the minimum drag and max range speeds. As far as configuration goes, the best minimum dragand max range speeds are both achieved with the airplane as clean as possible.

When lift equals weight and thrust equals drag, the airplane is neither accelerating nor decelerating.Unaccelerated flight can be level flight or a constant speed rate of climb or descent. If an airplane has more thrust

(power) than is required for level unaccelerated flight, the excess thrust (power) can be used to climb oraccelerate.


MN111

REFERENCE HANDBOOK


6/64

LOAD FACTOR

Load factor is the ratio of the lift the wings must generate to keep the airplane in stabilized flight to the actualweight of the airplane. In straight and level flight, the load factor is one. As Figure 4 shows, as the airplane isbanked, the load factor starts to increase. For example, a 100,000 pound airplane must generate 115,000 pounds

of lift to maintain level flight in a 30 degree bank. At 45 degrees of bank, it will take 142,000 pounds of lift to holdup the 100,000 pound airplane.

L

2.00

1.90

1.80

1.70

1.60

1.50

1.40

1.30

1.20

1.101.00

0 5 10 15 20 25 30 35 40 45 50 55 60

Bank Angle ()

Relation of Bank Angle to Load Factor

Figure 4

oad

Factor

g

Load factor isnt the only thing that increases in a bank. Since the wings must generate additional lift, induceddrag and stall speed also rise. Using Figure 5, note that if a 100,000 pound airplane has a wings level stall speed

of 100 knots, at 30 degrees of bank the stall speed will be about 107 knots. At 45 degrees of bank, the stall speedrises to about 118 knots. The maneuvering and reference speeds shown on all United takeoff and landing datacards provide a stall margin of at least 1.3 or for more recently certified airplanes, 1.23 times the One G stall

speed (VS 1G). Both certification methods provide about the same amount of stall margin. The purpose of this

margin is to provide for overbank protection, and to account for turbulence, which can instantaneously raise bothload factor and stall speed without warning.

I1.45

5 10 15 20 25 30 35 40 45 50 55 60

Bank Angle ()

Relation of Bank Angle to Stall Speed

1.40

1.35

1.30

1.25

1.20

1.15

1.10

1.05

1.00

0

Figure 5

ncrease

in

st

all

speed


MN111

REFERENCE HANDBOOK


7/64

HYDROPLANING

An article in Boeing Airlinerexplains hydroplaning: As a tire rolls along a wet runway, it is constantly squeezingthe water from the tread. This squeezing action generates water pressures which can lift portions of the tire offthe runway and reduce the amount of friction the tire can develop. This action is called hydroplaning. The loss of

friction can be partial or complete. There are three types of hydroplaning: Viscous, Dynamic and RevertedRubber.

Viscous hydroplaning is the loss of friction due to thin film lubrication. It is most often caused by a very thin filmof water over the rubber deposits in the touchdown zone or the runway. Although friction loss does occur, there is

normally enough to cause wheel spinup in order to initiate the antiskid system.

Dynamic hydroplaning occurs when the surfaces of the tires lose contact with a wet runway and ride up on thelayer of water covering the runway. This effect is exactly the same as water skiing. When is occurs tire friction is

lost and wheel spinup may not occur. High speed, standing water, tire condition, tread depth, and runway surfacetexture and condition are all factors contributing to Dynamic hydroplaning. The speed at which hydroplaning willbegin can be figured out by multiplying the square root of the tire pressure for your airplane by 7.7. As an

example, on the 737300/500, the speed is about 110 knots.

Reverted Rubber hydroplaning is the loss of friction due to a tire skidding on a smooth wet or icy surface. Theheat due to friction generates steam which lifts the tire off the runway. The heat generated by the steam revertsthe rubber to a black gummy substance. It can be initiated at any speed above about 20 knots and results in tire

friction levels equivalent to an icy runway.


MN111

REFERENCE HANDBOOK


8/64

N1 / N2

N1 is the percent RPM of the low pressure section of the engine. It consists of the fan, the first few stages of thecompressor section, the aft most stages of the turbine section, and the shaft which connects them.

N2 is the percent RPM of the high pressure section of the engine. It consists of the majority of the compressorsection stages and the forward stages of the turbine section.

N1 and N2 are indicated in percent of a nominal value of actual revolutions per minute of the respective section.For this reason it is not uncommon for N1 and N2 limits to be greater than 100%.

EPR

EPR stands for Engine Pressure Ratio. It is the ratio of the total air pressure at the exhaust section of the

engine to the total air pressure at the intake. As such, it is an indication of the thrust being produced by theengine. Always crosscheck the N1 gauges to see if the RPM is correct for the EPR shown. On some modernairplanes, the EPR gauges have been eliminated, and N1 is used to set thrust.

VmcgVmcg stands for Velocity, Minimum Control, Ground. It is the lowest speed at which directional control of the

airplane can be maintained on the ground after an engine failure withoutthe use of brakes or nosewheel steering.In other words, it is the minimum speed at which the control surfaces are effective on the ground (rudder pedalnosewheel steering is disconnected for certification testing).

Vmca

Vmca stands for Velocity, Minimum Control, Air. It is the lowest speed at which control of the airplane can be

maintained in the air, after an engine failure. Banking slightly into the good engine usually enhances engine outcapability. The conditions under which Vmca is determined for an airplane limit this bank angle to five degreesduring the certification process.

For determining Vmcg/a, it is assumed that the operating engine(s) remain at maximum thrust and the takeoff iscontinued.


MN111

REFERENCE HANDBOOK


9/64

Vminimum

Some airplanes have V minimum tables given in the Flight Manual and the Flip Cards, which provide for V1minimum, Vr minimum and V2 minimum speeds, as applicable. They are defined as follows:

V1 minimum = VmcgVr minimum = 1.05 Vmca

V2 minimum = 1.10 Vmca

The 727 is not effected by Vmca or Vmcg because of the proximity of the pod engines to the centerline of the

airplane, and does not have V minimum tables. On some airplanes, Vr minimum and V2 minimum may not limitany of the flip card speeds and are not provided.

Vmbe

Vmbe stands for Velocity, Maximum Brake Energy. It is the maximum speed at which the brakes can absorb allthe energy required to stop the airplane at a given weight. The certification process for Vmbe consists of

considerable taxiing and stopping to warm up the brakes, and then a max effort stop from the proposed Vmbe

speed. The brakes may catch fire. All that is required is that any brake fire remains confined to the wheel area fora period of five minutes with no fire retardant applied. This is to accommodate evacuation of the airplane.

V1 must always be less than Vmbe.

BRAKE ENERGY LIMIT WEIGHT

Brake Energy Limit Weight is the maximum weight at which a max effort stop can be made from the planned V1

(defined on page 10) without exceeding the certification requirements of Vmbe. Brake Energy Limit Weight andVmbe are closely tied together, but unlike Vmbe, Brake Energy Limit Weight is runway specific.

REJECTED TAKEOFF BRAKE COOLING

A Rejected Takeoff Brake Cooling Table is published in each Flight Manual which must be consulted following a

rejected takeoff. The charts indicate required ground cooling time, as a function of indicated airspeed and grossweight. The purpose of the ground cooling time is to allow heat, which has built up in the brakes, to dissipate tothe wheels and tires. This ensures that the peak temperature of the fuse plugs has been reached before anyfurther operation.


MN111

REFERENCE HANDBOOK


10/64

MAXIMUM PERFORMANCE STOP

Many line pilots have expressed the opinion, based on their everyday experience, that it would be impossible toget the airplane stopped from V1 in a Runway Limited situation. This perception comes from the normal stoppingperformance experienced on each landing. The vast majority of pilots will never experience a true max

performance stop from high speed. A properly performed max performance stop requires maxbraking to bemaintained throughout the maneuver. The airplane may buck or vibrate. The brakes may even begin to burn.

The bottom line is that the airplane and stopping performance is dramatic when a Max Performance stop isperformed. A properly executed Max Performance stop results in an amazingly short stopping distance. The pilot

must apply full leg and back strength standing on the brakes and use the full capability of the antiskid system toaccomplish this maneuver. Brake pressure must be maintained until the airplane comes to a complete stop.

TIRE LIMIT SPEED

Tire Limit Speed is the maximum speed at which the tire can safely operate during takeoff or landing roll, ascertified by its manufacturer. The certification process does not take into account the impact forces of a high sink

rate landing. At United, takeoff runway limit weights protect tire speed. Since Tire Limit Speeds are based onground speed and not airspeed, it is possible on a hot day at a high altitude airport to exceed the Tire Limit Speed

with the indicated airspeed showing below the limit.

CLUTTER

Clutter refers to standing precipitation on a runway surface that can be expected to impede airplane acceleration.

As used in United performance calculations, clutter is standing water or slush of at least 1/8 inch depth, wet snowof at least 1/4 inch depth, or dry snow of at least one inch depth. The various types and depths of clutter are

classified into clutter levels according to a table printed in the United Flight Operations Manual and reprinted ineach airplane Flight Manual. The classification of clutter levels is the same for all fleets.

Clutter has little effect on initial acceleration, but becomes significant as speed increases. The effects of clutterare not taken into account when calculating landing performance because clutter, by definition, deals with the

impedance of acceleration.

BRAKING ACTION

The normal method of accounting for the effects of runway contamination on stopping performance is with Braking

Action Advisories. They may come from Pilot Reports or FAA testing equipment, and may be issued on ATCfrequencies or by ATIS. The United Flight Operations Manual contains extensive guidance on Braking Action.


MN111

REFERENCE HANDBOOK


11/64

CLEARWAY

Clearway is an area beyond the runway, not less than 500 feet wide, centrally located about the extendedcenterline of the runway, and under the control of the airport authorities. The clearway is expressed in terms of aclearway plane, extending from the end of the runway with an upward slope not exceeding 1.25 percent, above

which no object nor any terrain protrudes. Threshold lights may protrude above the plane if their height above theend of the runway is 26 inches or less and if they are located to each side of the runway. Clearway extends the

available takeoff distance of a given runway.

STOPWAY

Stopway is an area beyond the takeoff runway, no less wide than the runway and centered upon the extendedcenterline of the runway, able to support the airplane during an aborted takeoff, without causing structural damageto the airplane, and designated by the airport authorities for use in decelerating the airplane during an aborted

takeoff. Stopway extends the available AccelerateStop Distance of a given runway.

United considers clearway and stopway to increase takeoff weight capability on an extremely limited basis. In allother cases where clearways and stopways exist, they provide increased takeoff margins.

TAKEOFF PERFORMANCE

All United airplanes are certified under FAR Part 25, and must meet specific takeoff flight path criteria. Thetakeoff flight path extends from a standing start to the point at which the airplane reaches 1500 feet above the

takeoff surface, or when the transition from the takeoff configuration to the enroute configuration is complete,whichever is higher. When reduced thrust is used, all FAR Part 25 criteria must be met at that reduced thrust.

Takeoff data, obtained in certification by the airplane manufacturer, is presented in the FAA-approved AirplaneFlight Manual (AFM). Our Operational Engineering Department uses the AFM to develop the Performance Data

presented in our Flight Handbooks, Flip Cards, and the computer generated Planned Takeoff Data Message,which are tailored specifically to our operation.

MAXIMUM TAXI WEIGHTMost airplanes are certified to taxi at a weight slightly greater than Takeoff Structural Limit Weight. This is toprovide a taxi fuel allowance. Therefore, Maximum Taxi Weight is Takeoff Structural Limit Weight plus Taxi Fuel

Allowance.


MN111

REFERENCE HANDBOOK


12/64

ALLOWABLE TAKEOFF GROSS WEIGHT ATOG

(Takeoff Limit Weight)

ATOG is the most restrictive (lowest) of:

Structural Limit Weight.

Runway Limit Weight.

Performance Limit Weight.

Enroute Limit Weight (some airplanes).

Landing Limited Takeoff Weight.

STRUCTURAL LIMIT WEIGHT: Structural Limit Weight is found in the Limitations section of the Flight Handbook.It is determined by the manufacturer and ensures that the airplane will meet maximum inflight weight restrictions

once airborne. It is the most restrictive of certified maximum takeoff weight or maximum taxi weight minus theplanned taxi fuel.

RUNWAY LIMIT WEIGHT: At United, Runway Limit Weight is the most restrictive (lightest) of:

FAR Field Length limit weight.

Obstacle clearance limit weight.

Brake energy limit weight.

Tire speed limit weight.

FAR FIELD LENGTH LIMIT WEIGHT: FAR field length limit weight is determined by the most restrictive

(longest) of the following field lengths:

All Engine Takeoff Field Length.

One Engine Inoperative Takeoff Field Length (AccelerateGo Distance).

AccelerateStop Distance.

Note: FAR Part 25 allows the use of stopways and clearways during the calculation of required runway

lengths.

United Airlines uses stopways and clearways in developing performance data on a very limited

basis. (See definition of Stopway/Clearway, this section.)

ALL ENGINE TAKEOFF DISTANCE: The total distance required to accelerate on all engines, rotate at Vr,

liftoff, and reach 35 feet at a speed equal to or greater than V2.

ALL ENGINE TAKEOFF FIELD LENGTH: 115% of the All Engine Takeoff Distance.


MN111

REFERENCE HANDBOOK


13/64

ALL ENGINE TAKEOFF FIELD LENGTH

ALL ENGINE TAKEOFF DISTANCE TO 35 FT

ALL ENGINE TAKEOFF FIELD LENGTH

15%

V1

Figure 6

Vr Vlof V2 or greater

35 FT

MARGIN

ACCELERATEGO DISTANCE: The total distance required to accelerate from a standing start to V1, andassuming the critical engine failure is recognized at V1, to continue the takeoff and be at V2 at 35 feet using

only aerodynamic controls and average piloting skills. (This is also called One Engine Inoperative TakeoffField Length.)

ACCELERATESTOP DISTANCE: The total distance required to accelerate from a standing start to V1,and assuming the critical engine failure is recognized at V1, to bring the airplane to a full stop using brakes

and spoilers only with engines at idle thrust.

Note: In the certifications applicable to our airplanes, maximum brake application was simultaneous with

V1. For this reason, the V1 callout must be initiated so that it is completed, and stop action

initiated (application of maximum braking) no later than computed V1 speed. The technique that

United uses is to initiate the callout as the airspeed needle approaches within 5 kts. of V1 to

ensure completion by V1. (See V1 discussion which follows.)

OBSTACLE CLEARANCE LIMIT WEIGHT: The maximum weight at which the airplane can clear allobstacles in the takeoff path. Since any obstacle (and therefore the weight restriction) is runway specific, it

is always included as a runway limit weight consideration. The margin of obstacle clearance is 35 ft at theend of the takeoff distance. The margin increases with distance from the end of the takeoff distance (the

farther the obstacle is from the runway, the greater the margin of clearance).

BRAKE ENERGY LIMIT WEIGHT: The maximum weight at which a stop can be made from V1 without

exceeding the allowable brake energy.

TIRE SPEED LIMIT WEIGHT: The maximum weight at which liftoff speed would not exceed the maximum

tire speed.

PERFORMANCE LIMIT WEIGHT: The maximum weight at which the airplane can achieve the minimumFAR-specified climb gradient usually limited at beginning of Second Segment climb. The climb gradient requireddepends on the number of engines installed. (See CLIMB SEGMENTS, page 19.)

ENROUTE LIMIT WEIGHT: That weight (applicable to some airplanes) which ensures the airplane meets specificenroute performance criteria as specified under FAR 121.191. (See METHOD I/METHOD II DISPATCH, page21.)

LANDING LIMITED TAKEOFF WEIGHT: Destination allowable landing weight plus planned trip fuel burnout.


MN111

REFERENCE HANDBOOK


14/64

V1

The definition of V1, as published in the FARs, has changed several times over the years, resulting in someconfusion among pilots. A knowledge of the history of the FARs, and the changes that have taken place, is not asimportant as understanding the operational significance of V1.

Transport category airplanes certificated in the United States, in the last 25 years, use a method similar to the

following to determine the balanced runway limit weight and its associated V1:

The airplane is assumed to accelerate with all engines operating from a standing start to the point

where the critical engine fails (Vef). The airplane continues to accelerate, with one engine inoperativeto the point where the engine failure is recognized (V1). If the takeoff is to be continued, using only

aerodynamic controls and average piloting skills, the airplane can accelerate, with one engineinoperative, to the point at which V2 is achieved at 35 feet above the end of the runway. If the takeoff is

to be rejected, maximum braking is applied at V1, throttles are retarded, and the spoilers areextended. A short time delay is included after V1 to account for thrust reduction to idle, and spoilerdeployment. The details of how the manufacturer applies these time delays, during the certification

process, varies from airplane to airplane. It is assumed that maximumeffort braking at V1 is used to

bring the airplane to a stop at the end of the runway. No credit is taken for reverse thrust.

The most important concept, common to all rejected takeoffs, is that V1 is the brakes on speed, not thedecision speed. The decision to abort must be made, and the abort initiated, at or before V1, to ensurethe likelihood of stopping on the remaining runway.

V1 -- ADDITIONAL INTERESTING FACTS

The adjusted V1 speed obtained from the Flip Cards is a Balanced Field V1. This means simply that with anengine failure at this speed, it would take an equal distance to abort, or to continue the takeoff. Since mosttakeoffs made at United Airlines are made at considerably less than Runway Limit Weight, the available runwaylength is greater than the Balanced Field Length. This additional length would be beyond, in most casesconsiderably, that required to stop or go from V1. This additional runway length, when available, is what allowsunbalancing V1 through such procedures as Optional V1, or the AntiSkid Inoperative procedure. It also allowsReduced Thrust operations.

Conditions which could adversely effect stopping distance, such as runway composition, runway contamination

(i.e., rubber build up), and crosswind effect, are not accounted for in certification.

Since reverse thrust is not used in certification, it provides a measure of conservatism.


MN111

REFERENCE HANDBOOK


15/64

BALANCED FIELD LENGTH

A balanced field condition exists when AccelerateStop Distance equals AccelerateGo Distance. This isdetermined by selection of V1 speed. For a given set of ambient conditions and airplane weight, only one V1speed would cause these distances to be equal. The associated runway length is called the Balanced Field

Length, and is the minimum runway length required for takeoff. Selecting a lower V1 decreases AccelerateStopDistance, but increases AccelerateGo Distance. Conversely, selecting a higher V1 decreases AccelerateGo

Distance, but increases AccelerateStop Distance. Either increases required Takeoff Field Length. (See V1 ADDITIONAL INTERESTING FACTS, page 17).

ACCELERATESTOP DISTANCE

Figure 7

V1

V1ACCELERATEGO DISTANCE


AVAILABLE RUNWAYLENGTH

The V1 speed determined from the Flip Card is Balanced V1. United uses Balanced Field Length rather thanRunway Length as the basis for V speed calculations. (See V1 ADDITIONAL INTERESTING FACTS, PAGE17.)


MN111

REFERENCE HANDBOOK


16/64

The figure below illustrates Balanced Field Length in another way. It is readily apparent that increasing anddecreasing V1 from the Balanced V1 increases runway required.

Figure 8


All engine operating acceleration distance to V1

One engine inoperative acceleration distance from V1 to V2 at 35

Distance to stop from V1

BalancedField Length

Runway Available

BalancedV1

V1


MN111

REFERENCE HANDBOOK


17/64

UA TAKEOFF SAFETY POLICY

In the high speed regime, especially at speeds near V1, a decision to stop should be made only if thefailure involved would impair the ability of the airplane to be safely flown.

The 80 knot thrust set callout should alert the crew that they are approaching the high speed phase of takeoff. In

the high speed regime, the Captains bias should be to continue the takeoff, unless there is a compelling reason toreject. Conditions that may validate a stop decision include, but are not limited to, engine failure, fires, or anymalfunction where there is doubt that the airplane will fly.

Any malfunction that does not impair the ability of the airplane to be safely flown does not warrant an abort in thehigh speed phase of takeoff. During the departure briefing, the Captain should clearly communicate this to the

flight crew.

This Takeoff Safety Policy does not advocate that a GO decision be made at or just after the 80 knot thrust setcallout. Even though the airplane is approaching the high speed regime, the Captain must make the decision tostop or go based on the nature and severity of the malfunction and its proximity to V1. At or beyond V1, takeoffshould be continued due to the possibility of insufficient runway available to stop the airplane if a STOP decisionis made. Finally, this Takeoff Safety Policy is intended to call attention to the variable and changing decision

making challenges presented during the takeoff phase of flight.

V1 CALLOUT PROCEDURES

Recognizing that V1 is the speed by which the GoNo Go decision must be completed, and, in the case of anaborted takeoff, maximum braking applied, procedures in all Fleets specify:

The V1 callout must be made by the PilotNotFlying such that any decision to abort can be made, and

the stop initiated by, and not after V1.

Since the airplane is accelerating at 35 kts/second as it approaches V1, the accepted technique is to initiate the

callout as the airspeed needle approaches within 5 kts of the set V1 bug. This allows time for the call to be made,heard, and acted upon by V1.

V1 ADJUSTMENTS

Required adjustments to the basic V speeds on the Flip Cards vary slightly according to airplane type. Requiredadjustments are always found on the Adjustments tab of the Flip Card deck and in the Flight Handbook.


MN111

REFERENCE HANDBOOK


18/64

Vmu

Vmu is Minimum Unstick Speed. It is the lowest possible speed at which the airplane can lift off. To certify Vmu,the takeoff roll is begun with the control yoke held full aft. The yoke is held in that position until the airplanebreaks ground. This is a certification flight test maneuver to determine Vr speed.

Vr

Vr is the speed at which rotation to normal takeoff attitude must begin to reach V2 by 35 feet (with an engine

inoperative). It must ensure adequate margin above demonstrated all engine and engine inoperative MinimumUnstick (Vmu) Speeds and Minimum Control Speed Air (Vmca). It assumes the pilot rotates at a normal rate.

The following restrictions apply:

Vr must not be less than V1.

Vr must be 5 percent greater than Vmca.

Since these speeds are predicated on losing an engine at V1, on a normal takeoff the airplane should reach V2 atless than 35 feet.

V2

V2, Takeoff Safety Speed, must be at least 110% of Vmca and 120% of Vs. It is the speed at which it is assumedthe airplane will be flown to meet climb gradient criteria with an engine inoperative.

CLIMB GRADIENT

When pilots talk about climb performance, they are normally talking about climb ratein feet per minute. However,airplane climb performance with regard to takeoff and approach certification requirements is calculated using

Climb Gradient, which is distance climbed per distance traveled across the ground, expressed in percentage. Aone percent climb gradient would be 10 feet of altitude gained for every 1000 feet traveled.

CLIMB SEGMENTS

The takeoff profile, as defined by the FARs, is composed of four segments. The first segment is from liftoff to thepoint at which the landing gear are fully retracted. The second segment is from gear retraction to level off. The

third (acceleration) segment is from level off through acceleration to cleanup and final climb speed. The fourth(final) segment begins with the thrust reduction from Takeoff Thrust to Maximum Continuous Thrust and ends

when the airplane has reached 1500 AFE. Minimum climb gradient capabilities are established for each segment,with one engine becoming inoperative at V1. This is the basis for all takeoff performance data provided by

United.

United addresses the takeoff profile as five segments, providing a more detailed illustration of airplane

performance.

First segment: From liftoff to gear retracted. The climb gradient required for all airplanes in this segment is thatwhich will allow the airplane to reach V2 (takeoff safety speed) and35 feet AGL no later than the end of thetakeoff distance.


MN111

REFERENCE HANDBOOK


19/64

Second segment: From gear retracted to the first level off, which must be at least 400 AFE, or higher if specialterrain clearance requirements exist at that airport. The minimum climb gradient required during this segment isas follows:

Two engine airplanes 2.4 percent.

Three engine airplanes 2.7 percent.

Four engine airplanes 3 percent.

Third segment: From the first level off to flaps up. Although the airplane is in level flight during this segment, the

minimum climb gradient availableduring this and all subsequent segments must be as follows:

Two engine airplanes 1.2 percent.

Three engine airplanes 1.5 percent.

Four engine airplanes 1.7 percent.

Fourth segment: From Flaps up to the first power reduction.

Fifth segment: From the first power reduction to 1500 AFE.

Figure 9

VR VLOF

V2 and35 ft AGL

V1 Engine failure occursand takeoff continues

FIRSTSEGMENT

LIFTOFF TO

GEAR

RETRACTED

SECONDSEGMENT

GEAR

RETRACTED

TO THE FIRST

LEVEL OFF

THIRDSEGMENT

FIRST LEVEL

OFF TO FLAPS

UP

FOURTHSEGMENT

FLAPS UP TO

FIRST POWER

REDUCTION

FIFTHSEGMENT

FIRST POWER

REDUCTION TO

1500 AFE

GEARRETRACTED

Takeoff Distance(AccelerateGo Distance)


MN111

REFERENCE HANDBOOK


20/64

METHOD I / METHOD II DISPATCH

During the flight planning process, all transport category airplanes are required by FAR 121.191 to account forenroute performance limitations in the event of an engine failure. All flights must plan a route and/or limit themaximum allowable takeoff gross weight (MTOG) so that the airplane will have sufficient performance to clear

enroute terrain if an engine becomes inoperative. Most airplanes in Uniteds fleet can either dump fuel to reduceweight, or they have sufficient engine inoperative performances so that MTOG is not restricted. However, the

B737 and the A320 cannot dump fuel to reduce weight. As a result, their MTOG may be limited on routes overmountainous terrain. In case the Takeoff Enroute Limit Weight becomes too restrictive, there are two alternate

dispatch methods for the called Method I and Method II.

Method I is the more weight restrictive of the two methods, and is not normally used by Dispatch unless nosuitable alternate airport is available. Its use is based on the following assumptions and requirements:

1. The engine failure occurs sometime during the climb.

2. The airplane will have adequate engine out performance capability to clear all obstacles within five

statute miles of the planned route of flight to the destination by 1000 feet and still have a positive

(300 footperminute) climb capability.

3. The APU will be used for pressurization and air conditioning below 17,000 MSL (B737 only).

4. Antiice penalties will be applied if PIREPS or forecasts indicate icing below FL 180 along the route

of flight.

If a flight has been dispatched Method I, the phrase FAR 121.191A1 Method I will appear near the top of thecomputerized flight plan. If your maximum takeoff weight is limited by Takeoff Enroute Limit Weight, then a

phrase like ENRT T+05 AI will appear in the remarks section. T+05 means standard temperature plus five isthe forecast temperature at the planned single engine cruise altitude, and AI means antiice is forecast to benecessary. Enroute weight limits will be printed for a variety Temperatures/Antiice configurations near the

bottom of the flight plan.

Method II is not enroute weight limiting. It breaks the planned route of flight down into segments, with eachsegment having a suitable enroute driftdown alternate with weather at or above alternate minimums. Method IIplanning is based on the following assumptions and requirements:

1. One engine fails at or above FL 240.

2. The airplane will perform a max range driftdown to the designated driftdown alternate for that sector.The flight planning for this driftdown uses worst case conditions: 100 knot headwinds, temperature

10C above standard, engine and wing antiice on.

3. The airplane has adequate performance during the driftdown maneuver to clear all obstacles along

the flight path by 2000 feet.

4. The airplane will be able to arrive over the alternate airport and have a positive (300footperminute) climb capability at 1500 ft AFE.

5. The APU will not be available for pressurization (B737 only).

6. If an engine didfail below FL 240, the airplane would return to the departure airport or its alternate, if

required.


MN111

REFERENCE HANDBOOK


21/64

If a flight has been dispatched Method II, near the top of the computerized flight plan, the phrase FAR 121.191A2ENRTE ALTN XXX XXX XXX XXX .... will appear. The XXXs are the enroute alternates for each segment ofthe route. A description of the Method II segments and alternates will appear near the bottom of the flight plan.

The Weather Briefing Message portion of the flight plan will contain the appropriate weather and NOTAMS foreach of the designated enroute alternate.

Remember, Method I/Method II is a dispatch function. Once the flight is airborne, and an engine fails, nothinginMethod I or Method II relieves the crew of the FAR requirement to proceed immediately to the nearest suitable

airport in point of time at which a safe landing can be made.

MAXTAKEOFF THRUST

Max Takeoff Thrust is the maximum thrust which may be set for takeoff, adjusted for density altitude, which willnot exceed any engine limitations or design parameters. It is shown on the N1/EPR/ATOG section of the Planned

Takeoff Data Message as Max EPR/N1 or Max N1, depending on airplane type. The design parameters mostlimiting to this thrust setting are usually RPM and turbine inlet temperature. The time limit normally associatedwith this thrust setting is five minutes for U.S. operators.

Max Takeoff Thrust is normallynotthe maximum thrust available from the engine. On some airplanes, additionalthrust is available beyond Max Takeoff Thrust, but using it on takeoff would exceed engine limitations or designparameters, and require that the engine be grounded and inspected prior to flying again.

MAXIMUM THRUST

Most turbojet engines are capable of producing more thrust than maximum certified takeoff thrust simply by settingthe throttles to their maximum forward position. On airplanes so equipped, the engine control system may prevent

thrust from increasing beyond certified limits. Maximum thrust is not legal to use in any phase of flight. However,in case of an emergency situation, such as a windshear encounter close to the ground, use of maximum thrustmay be justified. The engines will need to be inspected by Maintenance any time any limit is exceeded.

MAX CONTINUOUS THRUST

Max Continuous Thrust is approved for unrestricted periods of use. Thus, the throttle setting for Max Continuous

Thrust is somewhat less than that for Max Takeoff Thrust. Max Continuous Thrust is normally used afteracceleration and cleanup following an engine failure on takeoff, or following an enroute engine failure.

MAX CLIMB THRUST

Max Climb Thrust is intended for use with all engines operating normally. The throttle setting is usually less thanMax Continuous Thrust, and is intended to provide required climb performance while maximizing engine life. On

some engines, Max Climb Thrust may be slightly greater than Max Continuous Thrust at low altitudes.

MAX CRUISE THRUST

Max Cruise Thrust is determined by the engine manufacturer to meet cruise performance requirements and

maximize engine life, with thrust available as a secondary criteria.


MN111

REFERENCE HANDBOOK


22/64

GO-AROUND THRUST

Go-around thrust is the same thrust used for takeoff but the EPRs/N1s are different because of the effect ofairplane velocity.

Go-around thrust is also time-limited to 5 minutes. It is to be used in the event of a missed approach, whenneeded for safety.

REDUCED THRUST

10% 20%

COST/FAILURE RATE

REDUCTION

AVERAGE % THRUST REDUCTION

Figure 10

Figure 12 illustrates that each percent of thrust reduction from maximum takeoff thrust realizes a significant

reduction in engine operating cost/engine component failure rate for about the first 810 percent of thrust

reduction, then becomes a case of diminishing return.

If reducing takeoff thrust enhances safety through reduction in engine failures, and also significantly reducesoperating costs, it would seem prudent to reduce whenever possible. But, it is a well known fact that there is no

free lunch. So, lets ask a couple of questions first. One, why is the relationship depicted in Figure 10 true? And,is it necessary to sacrifice safety margins to reap the benefits of using Reduced Thrust for takeoff?

Why does reduced thrust work?

The positive effect of reduced thrust is so dramatic that engine manufacturers base their guarantee and warrantyprograms on a Severity Factor determined by careful monitoring of the average number of reduced thrust

takeoffs, and magnitude of thrust reduction, at each airline. Their analyses show that while completion of thetakeoff run at reduced thrust may actually use slightly more fuel than at maximum thrust, the positive tradeoffs,

that is, reduction in the potential for engine failure, and reduction in overall engine operating cost, are far moresignificant. As a rule of thumb, an average thrust reduction of 1% provides a 5% reduction in operating cost, witha like effect on engine failure rate.


MN111

REFERENCE HANDBOOK


23/64

The reason reduced thrust is so beneficial is that it minimizes the effect of four of the most significant factors inengine deterioration and/or failure: Tip Clang & Splatter, Creep, InterGranular Oxidation (IGO), andThermal Stress.

Tip Clang & Splatter is a function of the centrifugal forces on engine components at high RPM. The blades on

the compressor rotor can contact the compressor case. This results in damage to the blade tips, making thecompressor less efficient, and in molten metal splattering on components farther back in the engine. Thiscauses reduced efficiency of the airfoils in the compressor and turbines (similar to ice on a wing). It can also plug

the internal cooling ports in the turbine blades of modern engines, and can, and in fact has, resulted incatastrophic engine failure on a United airplane.

Creep describes the metallurgical effect of the centrifugal forces which stretch the components resulting inunrecoverable and progressive deformation.

InterGranular Oxidation (IGO) describes the oxidation (deterioration) which takes place between the grains ofthe metal of the components. A significant factor is temperature.

Thermal Stress describes the action which takes place within a piece of metal when it it heated or cooled. It is

most severe in the turbine section where the blades and buckets are subject to the blow torch effect of thecombustor. The center portion of the blade is heated faster than the ends when power is added, and the opposite

is true when power is reduced. The effect is most dramatic when setting takeoff thrust, then reducing to climbpower. The impact is similar to repeatedly bending a piece of sheet metal.

Does reduced thrust sacrifice required safety margins?

The FARs require that all takeoff flight path criteria be met at the thrust set for takeoff. If reduced thrust is set fortakeoff, all flight path criteria can be met at that reduced thrust. Increasing to maximum thrust would provide

increased margins. Before learning how to estimate reduced thrust takeoff margin lets review some basic takeoffperformance information.

Most takeoffs at United are made with excess runway and/or climb performance available; i.e., actual weight is

less than runway or performance limit weight. This excess margin can be used in a number of ways:

1. Compensate for inoperative equipment (Antiskid Inop., PMC Inop.)

2. Compensate for runway conditions (Cluttered Runway & Optional V1)

3. Reduced Thrust

Inoperative equipment and less than optimum runway conditions have specific UAL procedures that make takeoffmargins readily apparent. Simply look at the difference between the procedurally calculated limit weight and the

actual weight of the airplane.

The N1/ATOG reduced thrust calculation provides a weight margin (1000 lbs. for 737s to 10,000 lbs. for 747s) to

allow for a weight increase above planned. However, simply comparing actual weight to ASMD ATOG does not

give an accurate picture of real margins, because the ASMD ATOG corresponds to the ASMD TEMP, not actualambient conditions.


MN111

REFERENCE HANDBOOK


24/64

True Airspeed Effect

Reduced thrust provides a margin of safety which is often overlooked due to True Airspeed (TAS) Effects. Given

the fact that the actual temperature is lower than the assumed temperature, true air speed (and therefore groundspeed) is actually lower as well.

What this means is that it will take a shorter time and distance to reach V1 at the lower actual temperature than atthe higher assumed temperature. This effect along with improved engine and aerodynamic performance can be

looked at as an added safety margin since credit is not taken for it while calculating the required parameters for areduced thrust takeoff.

There are two methods which can be used to approximate the actual margins available when making a reducedthrust takeoff. One method approximates margin in terms of weight, the other in terms of excess available

runway.

Estimating Reduced Thrust Margins

To estimate the excess runway available, take the difference between the ASMD Temperature and the Actual

Temperature and multiply by 15 (15 feet per degree F). This indicates approximately how much less runway isused (in feet, without using reverse thrust) for Accelerate Stop (or Accelerate Go) at actual ambient conditions

versus ASMD TEMP conditions, using Reduced Thrust corresponding to ASMD TEMP.

The following example uses a 737300. The relationships are true for all airplanes:

Conditions:

ACTUAL TEMP 60F. . . . . . . . . . . . . . . . . . . . . . . . .ASMD TEMP 120F. . . . . . . . . . . . . . . . . . . . . . . . . .ACTUAL RUNWAY LIMIT WEIGHT 130.0. . . . . . . . .

ASMD ATOG 100.0. . . . . . . . . . . . . . . . . . . . . . . . . .ACTUAL WEIGHT 99.0. . . . . . . . . . . . . . . . . . . . . .

Excess runway approximation:

Step 1Step 2

Estimated runway margin

120 60 = 6060 X 15 = 900 feet900 feet (without reverse thrust)

In this case, the AccelerateStop (or Go) could be performed in 900 ft less at actual temperature because of thetrue airspeed effect and the greater net thrust produced at ambient temperature.


MN111

REFERENCE HANDBOOK


25/64

It is important to remember that this is an approximation that works for all airplane, airport, and temperaturecombinations. It is generally conservative. For example, excess runway can vary from about 14 feet per degreeF, to almost 25 feet per degree F, depending on airplane type, ambient temperature, and pressure altitude. This

procedure may notbe used to determineany ATOG weight. Its only purpose is to provide the flight crew with arule of thumb assessment of the performance capabilities of their airplane when deciding whether or not to use

Reduced Thrust.

In the above example, it was assumed that the ASMD ATOG for 120F was based on the FAR field length

(acceleratego/acceleratestop) part of the runway limit weight equation. This, of course, represents the worstcase scenario regarding the amount of excess runway margin available. That is to say, if these numbers are in

fact limited by the FAR field length, there would still be at least 900 feet of additional runway margin available.

However, this may not be the case. The assumed temperature and weight for a given takeoff not only considers

the FAR field length, but it must also consider the other factors that would normally go into a runway limit weightsuch as obstacle limit criteria. Additionally, performancelimit criteria must also be met. The ASMD ATOG/TEMP

is based on whichever factor is the most restrictive. This means that the excess runway available in the aboveexample may be far in excess of 900 feet, since the ASMD ATOG of 100.0 may in fact be based on a

performance limit weight, nota runway limit weight.

OPTIONAL V1

The purpose of the Optional V1 procedure (also referred to as Slippery V1) is to unbalance (reduce) the

Balanced Field Length V1 to enhance stopping performance. (If there is Clutter on a runway, thatis a separateproblem with its own procedure for determining adjustments to weights and V speeds.) If, however, there is

runway contamination that does not fit the definition of Clutter, or any other time enhanced stopping capability isdesirable, the Optional V1 procedure may be used.

Use of the Optional V1 procedure is only possible when runway length exceeds Balanced Field Length, that is,when the takeoff is not runway limited. Actual weight is compared to Runway Limit Weight and the difference is

converted to an airspeed adjustment that can be applied to reduce V1. Remember, this whole process only worksif there is runway available beyond Balanced Field Length.


MN111

REFERENCE HANDBOOK


26/64

MINIMUM UNBALANCED V1

Minimum Unbalanced V1 is the minimum V1 speed which is published in the FAA Approved Flight Manual for aspecific runway limit condition.

The manufacturer has simply chosen a minimum value for V1 to provide takeoff speed information down to Vmcgfor the weight range of the airplane

FLAP RETRACTION SPEED

The figure below shows a typical fleet standard Takeoff and Landing Data card. This one happens to be from a

737300 weighing 113,000 pounds with B2 engines. The flap retraction schedule is at the left side of the card.The published Flap Retraction Speeds are designed to accomplish the following:

Optimize engine out acceleration by minimizing drag.

Maintain adequate stall margin during the retraction sequence.

Protect against flap asymmetry during retraction.

Assure FAR required climb margins.

These speeds are minimum speeds for retraction, which protect against worst case conditions, optimize

acceleration, minimize the distance required to accelerate to climb speed, and assure climb gradient capability.

Notice that the schedule speed for raising the flaps from 15 to 1 is higher than the speed for 5 to 1. This is not a

misprint. On some United airplanes, including this one, the minimum control speed (Vmca) with a full flapasymmetry on retraction from 15 to 1 is higher than the minimum control speed with full asymmetry on retraction

from 5 to 1.

To insure adequate buffet margins exist during flap retraction, if bank angles greater than 15 are required, delay

flap retraction until reaching the maneuvering speed for the next flap configuration.

Figure 11

V 2 146 141 134

136 131 124

135 130 123

Clean

1 to 0

5 to 1

184

173

156

Maneuvering / REF

0

1

15

25

30

40

184160153147

140136133

15 to 1 162

V r

V 1

Flap 1 5 15

5


MN111

REFERENCE HANDBOOK


27/64

MINIMUM MANEUVERING SPEED AND

LANDING REFERENCE SPEED

These speeds, displayed on the right hand side of the Flip Cards, are the minimum operating speeds for thecorresponding Flap configuration. They provide adequate buffet margin for an inadvertent 15 overshoot beyond

a nominal 25 bank angle.

BEST ANGLE OF CLIMB SPEED

Best Angle of Climb speed is the speed that results in the most altitude gained for the distance covered across the

ground. It is achieved when the ratio of thrust available to total drag is the greatest. This normally occurs at L/Dmax speed.

BEST RATE OF CLIMB SPEED

Best Rate of Climb speed is the speed that results in the most altitude gained per unit of time. It is achieved whenmaximum excess power exists. Since velocity is a factor in the rate of climbequation, Best Rate of Climb speedis always faster than Best Angle of Climb speed.

OPTIMUM CLIMB SPEED

Optimum Climb Speed is the speed that yields the best overall fuel economyfor the climb segment of the flight. Itis normally close to Best Rate of climb speed. It provides the best compromise between three competing goals:

Getting to altitude as quickly as possible.

Using the least fuel possible.

Traveling as far as possible during the climb.

On United airplanes not equipped with a flight management computer, Optimum Climb Speed is shown for eachweight on the Takeoff and Landing Data cards.

ECON CLIMB SPEED

Econ Climb speed considers block hour operating cost, maintenance, and hourly crew costs. At a cost index ofzero, it closely approximates Optimum Climb. However, as time costs increase (cost index increases), Econ

Climb speed increases to reduce trip time, thus optimizing total cost of operation.

Additional Interesting Facts related to Airplane Climb Performance

Airplanes climb due to excess power or thrust.

True Airspeed always increases with altitude if indicated airspeed remains constant.


MN111

REFERENCE HANDBOOK


28/64

BUFFET

There are two kinds of Buffet to consider in flight; Low Speed Buffet and High Speed Buffet.

Low Speed Buffet, also sometimes called Load Factor Buffet or G Buffet, is caused by the beginnings of

separation of airflow over the wing. It can occur in stable, unaccelerated flight at low speed, or be caused by anincrease in angle of attack due to maintaining level flight in a bank, by a turbulence encounter, or by otherwise

pulling more than 1g. As altitude increases the airspeed at which Low Speed Buffet occurs increases.

High Speed Buffet, also sometimes called Mach Buffet, is caused by the separation of smooth airflow over anyportion of the airframe due to the formation of shock waves. This can happen at speeds as low as .77 Mach onsome airplanes. The reason is that the air must accelerate to get around the airplane as it passes by. Although

the airplane is only traveling through the air .77 Mach, the air near the surface of the airframe is movingconsiderably faster. This causes shock wave buildup and flow separation. High Speed Buffet causes a huge

increase in drag and is annoying to the passengers.

High Speed Buffet becomes a concern as altitude increases because high speed buffet speed decreases as

altitude increases.

At a given weight, as altitude increases, the margin between Low and High Speed buffet decreases. Each flight

manual has an Initial Buffet Speeds chart that shows the spread between Low Speed Buffet and High SpeedBuffet for a given weight and altitude. An example is shown in Figure 12, which happens to be from a 737300

with B1 engines. At 105,000 pounds and FL 370, for instance, there is only a 35 knot spread between the twoBuffet limits. The airplane must be operated in this 35 knot range, or a different altitude selected.

BUFFET PROTECTION CRUISE WEIGHT

The Buffet Protection Cruise Weight is limited by various levels of buffet protection. The chart provided in eachflight manual has a range of G level margins (normally 1.2 to 1.6) and shows the maximum weight that will

provide that G margin at cruise speed and the given altitude. On some airplanes the performance limited andBuffet Protection Maximum Cruise Weight charts are combined, with both weight limits shown on the same chart.


MN111

REFERENCE HANDBOOK


29/64

Figure 12

1.3G BUFFET BOUNDARIESHIGH

LOW(KIAS)

GROSS WEIGHT (1000 POUNDS)

FL

370

80 85263

173

90 95 100 105 110 115 120 125 130259

182

255

188

253

197

250

204

247

212

244

220

350279

170

277

179

273

185

270

192

267

198

264

206

262

214

259

221

257

228

251

238

340286

168

286

177

283

183

279

190

276

196

273

204

271

211

268

218

266

224

263

233

259

241

330292

166

292

176

292

181

288

188

285

194

282

202

279

208

277

217

274

222

272

228

270

235

320299

164

299

174

299

178

299

186

295

193

291

200

288

206

285

214

283

220

281

226

279

232

310306

163

306

172

306

177

306

184

306

192

305

197

301

204

298

212

295

216

292

224

290

230300

312

161

312

171

312

176

312

183

312

188

311

196

308

202

304

209

301

215

299

222

297

228

290319

160

319

169

319

174

319

180

319

187

319

194

318

200

314

207

311

213

308

219

306

225

280326

159

326

166

326

173

326

178

326

186

326

193

326

198

325

205

322

211

318

216

316

222

270333

158

333

165

333

172

333

177

333

184

333

190

333

196

333

203

332

208

328

215

325

221

260340

157

340

164

340

171

340

176

340

183

340

188

340

194

340

202

340

206

339

213

336

218

250347

156

347

163

347

170

347

175

347

181

347

187

347

193

347

200

347

205

347

211

347

216

MAXIMUM CRUISE WEIGHT

Maximum Cruise Weight is the lesser of two weights. The first is the Performance Limited Maximum Cruise

Weight. It provides at least 300 foot per minute rate of climb capability at a given altitude and temperature atmaximum climb thrust. The second is the weight at which Maximum Cruise Thrust will provide level flight at a

cruise speed of either Long Range Cruise (LRC) or standard cruise Mach.

Each flight manual has a Maximum Cruise Weight chart which shows the performance limited weight at a given

altitude and temperature. The basic purpose of this chart is to show the highest usable altitude at a given weight.It does not consider most efficient operating altitude.

The weights may be further restricted to avoid buffet upset problems.


MN111

REFERENCE HANDBOOK


30/64

ROUGH AIRSPEED

Rough Airspeed, also called Turbulent Air Penetration airspeed, is the speed to be flown when encounteringturbulence. It is determined by the manufacturer and based on a number of factors. It is greater than Vmin andlow speed 1.3 G buffet and less than Vmo and the high speed 1.3 G buffet. It is selected to allow quick

acceleration from Rough Airspeed to optimum climb speed and is sufficient for a range of weights. On someairplanes, one speed is used for all weights.

OPTIMUM ALTITUDE

For a given weight and cruise speed the altitude which yields the most nautical air miles per pound of fuel

consumed (Specific Range) is called Optimum Altitude. As weight decreases optimum altitude increases. Stepclimbs approximate an optimum altitude profile. The Wind Altitude Trade Tables account for the effect of wind onspecific range, providing the flight crew with guidance for selecting the best cruise altitude for given conditions.

MINIMUM DRAG SPEED

Minimum Drag Speed is the low point on the Drag Curve; the L/D Max speed. This is where the airplane requires

the minimum amount of thrust to stay in the air. Distance traveled is not considered. Going any faster or slowerrequires additional thrust. The Indicated Airspeed (IAS) for L/D Max speed does not change with altitude.

HOLDING SPEED

Technically, the speed of a turbojet associated with minimum fuel flow is less than the speed used for minimumdrag. The reason for this is that a jet engine is more efficient at the slower speed. See Figure 13.

SPEED

Speed ForMinimum Fuel

Speed ForMinimum Drag

Figure 13

It would be ideal to maintain this airspeed when a maximum endurance profile such as holding is desired.However, this speed falls on the back side of the drag curve where speed instability is likely to develop. It is

therefore more desirable to hold at speeds closer to minimum drag. For practical reasons, the holding speedsfound in our flight manual fall on, or slightly faster than, the minimum drag point. This provides speed stability with

negligible effect on fuel consumption.


MN111

REFERENCE HANDBOOK


31/64

MAX RANGE CRUISE

For any given set of flight conditions, one speed will give the greatest nowind specific range (nautical air milesper 1000 pounds of fuel). This speed is known as Maximum Range Cruise (MRC). Unfortunately on manyairplanes MRC is often speed unstable (meaning that it is difficult to find and maintain in flight).

LONG RANGE CRUISE

Long Range Cruise (LRC) is defined as a speed greater than MRC which provides 99% of the specific range of

MRC. LRC provides almost the same specific range as MRC but is much more speed stable. This makes LRCmuch easier to find and maintain.

ECON CRUISE

Econ Cruise, associated with FMC-equipped airplanes, is dependent on Cost Index to generate a cruise speed. Acost index of 0 yields max range speed. A larger value results in a faster cruise speed. Econ Cruise speeds are a

function of Cost Index, weight, altitude and wind.

NORMAL DESCENTFor each United airplane, a normal descent speed schedule has been defined to reflect UALs time/fuel policy

and comply with ATC restrictions. For airplanes equipped with a flight management computer, this schedule canbe adjusted by changing Cost Index.

ECON DESCENT

Econ Descent calculates a descent speed that yields the lowest total trip cost. It is a function of Cost Index, andapplicable only to airplanes equipped with a Flight Management Computer.

REFERENCE SPEED

At United, Reference Speed, usually called Ref Speed, is the basis for determining approach speed for the

selected flap setting. It comes from the right side of the Takeoff and Landing Data card. Ref speed provides a 1.3stall margin for the selected landing flap setting. Corrected for wind and gust, it becomes Target Speed.

Certain irregularities, such as flap malfunctions, require procedural adjustments to Reference Speed. Once thecorrected Reference Speed is determined, it must then be corrected for Wind and Gust to determine Target

Speed.


MN111

REFERENCE HANDBOOK


32/64

TARGET SPEED

Target Speed is the speed at which an approach should be flown. It is Ref Speed plus onehalf the steady stateheadwind component plus the full gust component, up to a maximum of 20 knots correction. In addition, TargetSpeed must not be less than Ref plus five. Thus, Target Speed is always between Ref plus five and Ref plus 20.

AUTOLAND AND AUTOTHROTTLE TARGET SPEED

On airplanes that have Autoland and Autothrottle capability, if bothAutoland andAutothrottle are being used for

landing, Target Speed is Ref Speed plus five regardless of wind. Otherwise normal wind corrections must beapplied.

THRESHOLD SPEED

Threshold Speed is the minimum speed at which an airplane should cross the runway threshold. It is Ref Speedplus the full gust component up to a maximum of 20 knots correction, but no steady state headwind component

correction. Reduction from Target, to threshold speed occurs normally, during the flare. Target speed should bemaintained until the normal transition to landing.

LANDING DISTANCE

Landing Distance is the total distance from 50 feet AGL through the flare, touchdown, and braking to a completestop. It is calculated and demonstrated for the following conditions:

1. A dry, hard surface, level runway with braking action good or better (a wet but grooved runway isconsidered good).

2. No wind.

3. Ref Speed and normal descent rates from 50 feet AGL over the threshold to the flare.

4. Five knots of airspeed loss during the flare.

5. Touchdown 1000 feet down the runway.

6. Spoilers deployed upon touchdown.

7. Reverse thrust not used.

8. Max braking applied two seconds after touchdown.


MN111

REFERENCE HANDBOOK


33/64

There are three areas where pilot technique has a major impact on total Landing Distance. They are:

1. Threshold crossing height. Of course, its not safe to come in low, butcrossing the threshold above50 feet AGL will significantly lengthen total Landing Distance. For instance, crossing the threshold at100 AGL and maintaining a normal three degree glide path will add about 1000 feet to the Landing

Distance. (However, if you find yourself in this position, do notdump the nose to try to make anormal touchdown point. This is extremely dangerous, and is absolutely forbidden by United policy.Basically, if youre too high to make a normal landing, youre committed to a goaround.)

2. Flare Technique. Crossing the threshold on speed on a three degree glide path at 50 feet

determines a touchdown point about 1000 ft. down the runway. Stretching out the flare trying tomake that perfect grease job landing, increases landing distance and increases the potential for atail strike.

3. Touchdown speed. Once on the ground, stopping consists of dissipating the kinetic energy of the

airplane. In the kinetic energy equation, velocity is squared, weight is not. Therefore, a ten percentincrease in weight causes a ten percent increase in landing roll, but a ten percent increase intouchdown speed causes a 20 percent increase in landing roll. Proper speed control is perhaps the

most critical factor in stopping performance.

A final word on landing distance. Accident records show that most runway departures on rollout did not occurunder runway limited conditions. They happened where there was plenty of runway available. So, what caused

them? Crew complacency or distraction on final, resulting in landing long.

FAR LANDING FIELD LENGTH (DRY)

FAR Landing Field Length (Dry) is Demonstrated Landing Distance plus a specified safety margin. According to

the definition, of the total FAR Landing Field Length (Dry), 60 percent is Landing Distance and 40 percent is therequired safety margin. If you think that a 40 percent margin is overkill, consider this example: Crossing the

threshold only 30 feet high and five knots fast uses up onehalf the 40 percent margin.

Demonstrated Landing Distance

FAR Landing Field Length (Dry)

Additional Margin

Figure 14

50HAT

60% of total 40% of total

DEMONSTRATED LANDING DISTANCE WITH MAXIMUM BRAKING

The Demonstrated Landing Distance with Maximum Braking as shown in the Landing Runway Limit Weight

tables, is available for use inflight to evaluate landing options during abnormal situations. This landing distance is60% of the FAR Landing Field Length and is the minimumstopping distance demonstrated during certification, as

illustrated above.


MN111

REFERENCE HANDBOOK


34/64

FARLANDINGFIELDLENGTH(WET)

FAR Landing Field Length (Wet) is 115 percent of FAR Landing Field Length (Dry). No one is saying that it onlytakes 15 percent more runway to stop on a wet runway on a dry. Its just that the dry distance already includes a40 percent margin, and now another 15 percent is added to that.

Demonstrated Landing Distance

FAR Landing Field Length (Dry)

Additional Margin

Figure 15

50HAT

60% of total 40% of total

Additional Margin15%

FAR Landing Field Length (Wet)

A word of caution here. Real world experiences have shown that the number of variables involved in landing on a

wet runway is so large, it is extremely difficult to predict actual landing distance. Things like tire condition, treaddepth, runway texture and condition, and rubber deposits all have an exaggerated effect on a wet runway. TheLanding Distance (wet) charts in the flight manual include some allowance for these variables. However, they are,

like the dry charts, based on maxbraking.

LANDINGSTRUCTURALLIMITWEIGHT

Landing Structural Limit Weight is the maximum weight demonstrated by the manufacturer and certified by theFAA at which the airplane can land at a specified high sink rate without structural damage. Blown tires are not

considered structural damage for the purposes of this limit. The exact sink rate used during the certificationprocess varies from airplane to airplane.

Often the same models of airplanes flown by different airlines have different Landing Structural Limit Weights.This is because some airlines reduce their Landing Structural Limit Weight in order to reduce weightbased

landing fees charged at many airports. United does this on some airplanes.

Keep in mind that nothing precludes the crew from landing the airplane at a weight above the Landing Structural

Limit Weight if this is a safer course of action than remaining airborne with a problem or emergency. The airplanewould, of course, have to be inspected prior to flying again.


MN111

REFERENCE HANDBOOK


35/64

LANDING RUNWAY LIMIT WEIGHT

Landing Runway Limit Weight is tied very closely to Landing Distance and FAR Landing Field Length. It is,however, adjusted for runway length, pressure altitude, and wind. It is the maximum weight at which the airplanecan cross the threshold at 50 feet AGL at Ref Speed, land 1000 feet down the runway, stop using max braking

with spoilers but no reverse thrust, and still have 40 percent of the runway length remaining. The calculation isbased on the runway being dry with braking action good or better. However, if the runway is wet, or visibility is

less than three quarters of a mile or 4000 RVR, an additional weight penalty is taken. If the runway is both wetand below 4000 RVR, a second additional weight penalty is taken. These weight penalties vary with runway

length, pressure altitude, and airplane type.

The Landing Runway Limit Weights may exceed the Landing Structural Limit Weight. Any procedural adjustments

should be made to Landing Runway Limit Weight.

APPROACH CLIMB LIMIT WEIGHT

FARs require that an airplane on final approach retain the ability to perform a missed approach if one engine fails.After engine failure, the airplane must perform as follows:

1. Goaround thrust selected on the remaining engine(s).

2. Goaround flaps.

3. Landing gear up.

4. Goaround speed must not be greater than 1.5 times the stall speed at the goaround flap setting.

5. The stall speed at the goaround flap setting must not be greater than 1.1 times the stall speed at thelanding flap setting.

6. The minimum climb gradient required on the goaround is 2.1 percent for two engine airplanes, 2.4percent for three engine airplanes, and 2.7 percent for four engine airplanes.

Approach Climb Limit Weight is the maximum weight that will allow the airplane to perform in accordance withthese requirements. On airplanes that cannot dump fuel, Approach Climb Limit Weight can also limit Allowable

Takeoff Gross Weight. This is due to the possibility of an engine failure on takeoff, an emergency return to thedeparture airport, and then a required goaround.

Approach Climb Limit Weight is automatically included under the category: Landing Performance Limit Weight.


MN111

REFERENCE HANDBOOK


36/64

LANDING CLIMB LIMIT WEIGHT

FARs also require that a landing airplane retain the ability to go around from the flare on all engines. Theassumptions made in this calculation are as follows:

1. The throttles will be moved from idle to goaround thrust, and the engines will take eight seconds torespond fully.

2. No configuration changes. The goaround will be made, with gear down and landing flaps.

3. The maximum speed on the goaround will be Ref Speed.

4. The climb gradient must be at least 3.2 percent for all airplanes.

Landing Climb Limit Weight is the maximum weight at which the airplane can perform as described above.

LANDING PERFORMANCE LIMIT WEIGHT

Landing Performance Limit Weight is the more restrictive (lower) of Approach Climb Limit Weight and Landing

Climb Limit Weight.

ALLOWABLE LANDING WEIGHT

Allowable Landing Weight is the most restrictive (lightest) of Landing Runway Limit Weight and LandingPerformance Limit Weight. This is the number listed on the flight plan.

Notice that Landing Structural Limit Weight is not one of the factors considered in Allowable Landing Weight.

Since the structural limit does not change from flight to flight, it is assumed that you have this number in mind andwill not land at a heavier weight unless a greater hazard exists by remaining airborne.

Do not confuse Allowable Landing Weight with Landing Limited Takeoff Weight, which doesinclude LandingStructural Limit Weight.

FLIGHT PAPERS

There are two documents needed prior to every flight. They are:

1. Planned Takeoff Data Message which is comprised of the DPWM (Dispatch Planned WeightManifest) and the EPR (N1)/ATOG message.

2. The FPF. This is the Flight Plan for the planned route of flight.

This manual covers the first two parts of the flight papers in detail. The FPF is thoroughly covered in the Flight

Operations Manual.


MN111

REFERENCE HANDBOOK


37/64

DPWM

DPWM stands for Dispatch Planned Weight Manifest. The example shown below is the one you will use inPerformance Training class.

PLANNED TAKEOFF DATA MESSAGE

DPWM 67916 MAR DEN 1373 373UA IAW AUTO DEN02 KRAS

OEW

PITS

F

R

ZFW

FOB/TAXI

TOG

* SECURITY: NORMAL *

72023

3301

714

15762

91800.......

21500/700 (:16)

113300.......

4....

89....

MTOG

PCT MAC

TRIM

125400

24.3

3.9..........

67916 MAR DEN means this DPWM is for Flight 679 of March 16th departing Denver.

1373 is the United nose number and 373UA is the FAA designated tail number.

IAW AUTO means this DPWM was generated in accordance with the automatic weight and balance computerprogram.

DEN02 KRAS means this DPWM was generated by Denver Load Planner number 2, whos name is Kras.

OEW means Operating Empty Weight. It includes everything on the airplane except passengers, cargo, andfuel. If there is a jumpseat rider, either in the cockpit or in the cabin, their weight is included here along with therest of the crew. In this case, the OEW is 72,023 pounds.

PITS is the weight of cargo in the belly of the airplane. This includes checked baggage. In this case, the total

cargo weight is 3,301 pounds.

F 4.... means that four passengers are planned in the front, or first class section of the airplane. The planned

weight per passenger is based on historical data and varies with airplane type, trip length, city of origin,destination, and time of year. The weight always includes carryon baggage. In this case, the first class cabin

weight is 714 pounds.

R 89.... means that 89 passengers are planned in the rear, or coach section. In this case, aft cabin weight is

15,762 pounds.

ZFW stands for Zero Fuel Weight. It is the weight of the airplane and everything on it, except fuel. In this case,

the ZFW will be 91,800 pounds, which is the sum of the four previous weights.


MN111

REFERENCE HANDBOOK


38/64

FOB/TAXI stands for Fuel On Board and Taxi fuel. The Fuel On Board is the legal minimum fuel required fortakeoff. Taxi fuel is the extra fuel over and above FOB that is expected to be used during ground operations priorto takeoff. The two amounts are shown separately so that you will know exactly how much fuel you need to

legally take off, but the total fuel boarded must be at least equal to the total of the two amounts. In this case, thefuel required for takeoff is 21,500 pounds and the fuel boarded for ground operations is 700 additional pounds,

which should last for 16 minutes.

TOG stands for Takeoff Gross Weight. It is the planned weight of the airplane at the point of takeoff. Taxi fuel is

not included in this number, so if your ground time has been significantly different than planned, your actualtakeoff weight will be significantly different also.

SECURITY: NORMAL means there are no unusual security considerations for this flight. If something other thanNORMAL appears here, you need to contact Station Operations. An example of other than normal security

would be armed guards escorting a prisoner.

MTOG stands for Maximum Takeoff Gross Weight. The basic definition of MTOG is identical to ATOG (seeDefinitions). The difference, and it is a critical difference, is that MTOG is the predicted ATOGbased onconditions that exist at the time the N1/EPR/ATOG message is generated. The performance program uses the

most optimistic runway and field conditions expected to exist at takeoff time. Thus, MTOG is the highest ATOGyou can reasonably expect to see. If, using the takeoff data portion of the N1/EPR/ATOG message and current

field conditions, you come up with an ATOG that is higher than MTOG, you need to contact Dispatch to resolvethe discrepancy. In line operations, it is normal to come up with a final ATOG that is less than the predicted

MTOG. This is normal, and no further communication is required.

PCT MAC stands for Percent of Mean Aerodynamic Chord. It is the location of the planned center of gravity of

the airplane in terms of a percentage of the total length of the Mean Aerodynamic Chord Line. It is derived fromthe weight and location of the various items loaded on the plane including fuel, crew, galleys, cargo, and

passengers. The number crunching involved in this calculation is done automatically by Uniteds weight andbalance computers, and is not shown on any paperwork ava

united (ual) performance manual

Documents