Mountain Operations

REFERENCES

FM 1-202, Environmental Flight, February 1983

TC 1-218, Aircrew Training Manual Utility Aircraft, March 1993

Aircraft Operator’s Manual

OUTLINE

• Mountain Weather and Climate• Winds• Density Altitude

• Flight Techniques

Definitions

Prevailing Winds - Upper-level winds; flowing predominantly from West to East.

Local Winds - (Valley Winds) created by convection heating and cooling.

Surface Winds - Winds close to the ground. Less turbulent than both prevailing and local winds.

Demarcation Line - The point which seperates the upflow from the downflow of air.

Types of Mountain Wind Flow

DEMARCATION LINE

Turbulence and Downflow

Prevailing Winds

Surface Winds

Local Winds (Upflow)

Light Winds

WIND DEMARCATION LINE

Light Winds

• 1 to 10 Knots• Gentle updraft as wind accelerate uphill• Wind will follow the slope of the terrain• After the crest the wind will turn into a gentle downdraft

Moderate Winds

WIND DEMARCATIO

N LIN

E

UPDRAFT

Moderate Winds

• 11 to 20 Knots• Increase in the up and downdrafts will create moderate turbulence• There will be an updraft on the leeward side near the crest• The demarcation line will form closer to the crest and will be steeper

Strong Winds

WIND

DEMARCATIO

N LIN

E

Strong Winds

• Above 20 Knots• Demarcation line will move to the forward side of the hillcrest.• Updrafts, Downdrafts and turbulence will increase.

Mountain Wave

WIND

Stable Air

Unstable Air

Mountain WaveConditions

•Stable layer of air above a unstable of air•Wind directoin fairly constant with increasing speed with altitude•Mountain is perpendicular to the airflow

Effects

•Updrafts of 2,000 FPM to 5,000 FPM•Moderate to Severe Turbulence•Altimeter errors as much as 1,000 Ft when penetrating a wave•Icing can be expected in clouds when below freezing

Mountain Wave Cloud Formation

WIND

Stable Air

Unstable AirLenticular Clouds

Rotor Clouds

Cap Cloud

When weather conditions are favorable, the following visual indicators can exist: Cap clouds, Rotor clouds and Lenticular clouds

Mountain Wave Cloud Formation

Lenticular Clouds - Lens shaped clouds normally found between FL250 and FL400. They may form downwind from the mountain ridge. Turbulence will exist below the clouds.

Cap Cloud - Consist primarily of updrafts. They will develop updrafts and downdrafts as it passes over the mountain

Mountain Wave Cloud Formation

Rotor Clouds - Clouds of short duration will a rapid onset and dissapation. They can have updrafts in excess of 5,000 FPM.

- Found downwind of mountain- Bases found below the ridge with tops up to the lenticular

clouds

Mountain Wave Cloud Formation

DENSITY ALTITUDE

• Pressure altitude corrected for non-standard temperature.

• Altitude at which your aircraft will perform at.

• As DA increases-------air density decreases

Effects of DA on aircraft performance?

• Reduced horsepower (Torque) available.– As DA incr. - air molecules spread out - less air

going into the engine = less horsepower (Torque) being produced.

• Reduced wing efficiency– Less air molecules acting on the wings to produce

lift.

RESULTS• Increased takeoff roll

• Reduced climb performance (ft./min.)

• Increased landing distance (higher TAS, higher GS)

• Decrease in the “excess power available”

• Aircraft response----more sluggish

• Deceleration effects (ability to slow down, and not fall through)

Flight Techniques

Preflight. Complete a detailed performance evaluation to determine if any operating limitations will be encountered.

Starting engine(s). Use normal starting procedures.

Taxiing. Use normal taxiing procedures.

Before takeoff. If a takeoff is made from an airport located at a

high elevation--

In Pressurized aircraft. Place the bleed air valves in the ENVIRO-

OFF position to provide more power for the takeoff.

Takeoff. Use normal takeoff procedures. NOTE: Many mountain landing strips or runways are not level. Unless local conditions dictate otherwise, always take off downhill.

Flight Techniques

During flight. Use normal procedures. Be alert for clear air turbulence that may be encountered because of uneven terrain and wind variations.

Landing. Use normal landing procedures. NOTE: Many mountain landing strips or runways are not level. Unless local conditions dictate otherwise, always land uphill.

Before leaving the aircraft. Use normal procedures. Ensure that the aircraft is properly secured. (In mountainous areas, the possibility of severe and rapidly changing weather is greater than normal.)

SUMMARY

• Mountain Weather

• Density Altitude

• Flight Techniques

QUESTIONS?

QUESTIONS?