Script Document

Terrain, Traffic, TCAS Script Writer: Michael Pittman

Lesson Introduction Terrain, terrain, whoop, whoop, pull up! Darn, you spill your fresh cup of coffee all of your pants but miraculously save the day by yanking the flight controls back to bring the huge 777 out of the edge of catastrophe. The terrain as well as the Traffic Alert and Collision Avoidance System (TCAS) often operate silently; however, they are always ready at a moments notice to save the day, and your life! In the Terrain, Traffic, and TCAS Groundwork section by Angle of Attack, we will teach you how to identify and properly respond to traffic and terrain alerts. In this section, well cover:

Ground Proximity Warning System (GPWS) Operation

GPWS Alerts and Warnings

Traffic Alert and Collision Avoidance System (TCAS) Operation

TCAS Alerts and Warnings

Buckle your seatbelt, we are about to dive into this lesson!

Ground Proximity Warning System (GPWS) Operation The Ground Proximity Warning System (GPWS) has evolved greatly throughout the years. When it first debuted on transport airplanes, GPWS protection was very limited. You were alerted of imminent doom moments before impact, not even giving the savviest pilots time to react. Thanks to modern technology installed on the 777, the enhanced GPWS greatly increases your safety awareness, even giving the laziest pilots plenty of time to react to impending danger. The fundamental element to any GPWS is the radio altimeter. This instrument gives the aircraft height above ground in real time so the GPWS computer can analyse the aircrafts terrain closure rate. If this rate becomes excessive, an appropriate alert will sound. The aircrafts height above ground also signals other configuration alerts, like if you forget to put the gear down when you are short final, yikes! In addition to the brand new, nervous captain yelling at you to get back on the glideslope during an instrument approach, the GPWS also monitors the glideslope to tell you if you start to excessively dive below it. One of the newer features standard on the 777 is look-ahead terrain alerting. This is made possible from an enhanced GPWS terrain database working together with the current aircraft GPS position. As long as the new mayor hasnt erected a billboard of himself since the last database update, this system is very accurate, especially close to airport areas. For your viewing pleasure, this system produces computer generated terrain data on your Navigation Display (ND). To activate the terrain display, press the TERR map switch on the EFIS control panel. Keep in mind that terrain data is only displayed on the expanded MAP, CENTER MAP, expanded VOR, and expanded APP navigation modes. A cyan TERR annunciation will appear on the ND when the terrain mode is selected and active. If you want to switch to weather radar, you can do so but you will no longer be able to display terrain data

Script Document

Terrain, Traffic, TCAS Script Writer: Michael Pittman

on your ND. It would be hard to tell which is weather or terrain if you were to combine these displays. Your friendly captain might display terrain data on his ND if you ask nicely. So you are departing out of Vail, Colorado with poor visibility. Your terrain display is seemingly filled with every color of the rainbow. Lets decode what you see on this screen:

Blank- Terrain is more than 2000 feet below the aircraft.

Dotted Green- Terrain is 2000 to 500 feet below the aircraft. This changes to 250 feet with gear down.

Dotted Amber- Terrain is 500 feet below, or 250 below with gear down, to 2000 feet above current altitude.

Dotted Red- Terrain is more than 2000 feet above the aircraft. You better climb or turn quickly.

Magenta- No terrain data is available. This does not mean that there is no terrain! Now that we know how the terrain system works, lets talk about the loud blaring alarms that warn you of impending terrain impact.

GPWS Alerts and Warnings Since the GPWS is a piece of the Master Caution and Warning system, it must have both visual and aural alerts to help wake you up when you start drifting towards the ground unexpectedly. Below are some of the basic warning and alert modes that have been around for some time:

Mode 1: Excessive descent rate- You will get an aural Sink Rate voice and the GND PROX light will illuminate.

Mode 2: Excessive terrain closure rate- You will get an aural Terrain voice as well as GND PROX and Master Warning lights will illuminate.

Excessive terrain closure rate continues or descent rate becomes severe- If the aural Sink Rate or Terrain alerts did not get your attention, the Whoop Whoop, Pull Up alert will sound. You will also get a PULL UP message on both Primary Flight Displays (PFDs) and Master Warning lights will illuminate. You can press the Master Warning lights to reset them; however, this will not deactivate the GPWS. You will still receive the loud aural alerts. Just do what the airplane says; trust me, it will be a lot easier.

Mode 3: Excessive altitude loss after takeoff or go-around- In these critical phases of flight it is very easy to get distracted, especially if your engine catches fire right after takeoff. If you start sinking back to the ground after takeoff, you will get a Dont Sink aural alert and the GND PROX light will illuminate.

Mode 4A: Unsafe terrain clearance at low airspeed with gear not down- You will get a Too Low Gear aural alert and GND PROX light. There is a GEAR OVRD switch to inhibit this alert.

Mode 4B: Unsafe terrain clearance at low airspeed with flaps not in landing position- You will get a Too Low Flaps aural alert and GND PROX light. This can be a really annoying alert if you have a flap failure and have to make a zero flap landing. To disable this alert, press the FLAP OVRD switch to inhibit this alert.

Mode 4C: Unsafe terrain clearance at high speed while not in landing configuration This could follow the Dont Sink alert if you have not made any corrections. You will get a Too Low Terrain aural alert and the GND PROX light will illuminate.

Mode 5: Deviation below glideslope- You will get a GND PROX light as well as an aural Glideslope alert which increases in frequency and volume as you deviate further from the vertical path. If this alert is

Script Document

Terrain, Traffic, TCAS Script Writer: Michael Pittman

acting up or you have the runway made, pressing the G/S Inhibit switch cancels or inhibits this alert below 1000 feet AGL.

Mode 7: Excessive Windshear condition below 1500 feet, after rotation- You will get a red WINDSHEAR message displayed on both PFDs as well as a two tone siren followed by an aural Windshear alert.

With the look-ahead terrain system, come three additional enhanced alerts that help give the pilot more time to respond to the issue.

Look-ahead caution alert- This alert starts 40-60 seconds from projected impact. You will get an aural alert and amber TERRAIN annunciation on your ND regardless of what mode you are in.

Look-ahead warning alert- This alert starts 20-30 seconds from projected impact. You will get an aural alert and a red TERRAIN annunciation on your ND regardless of what mode you are in.

Terrain floor clearance alert- Most Controlled Flight Into Terrain (CFIT) accidents are caused by aircraft that land short of the runway. This system stores the location of over 30,000 runways at over 12,000 airports. From these runways, the GPWS makes an imaginary clearance floor extending from each of these runways. If a descent is initiated below one of these floors, the Too Low Terrain aural alert will sound regardless of aircraft configuration.

If you were paying close attention, you would have noticed that we never mentioned Mode 6 terrain alerts. These are simply miscellaneous callouts and advisories that are nice to know. Examples of these callouts are Approaching Minimums and Fifty for 50 feet above the ground. These are in no sense warning alerts, unless of course you dont start flaring before the Ten callout. Your passengers will in that case be asking if you did most of your flying pounding fighters down on aircraft carriers. Now that you know how to avoid the obstacles on the ground, lets talk about avoiding the other airplanes in the air. Even though you fly a huge 777, you still have to make room for the weekend warrior flying a little single-engine propeller aircraft.

Traffic Alert and Collision Avoidance System (TCAS) Operation Most of the time, Air Traffic Control (ATC) will take great care of you. They will make sure you have a comfortable ride as well as separate you from other air traffic. Most people, even ATC and 777 pilots, make mistakes. You could get too close to an aircraft that is slowing down to its final approach speed 15 miles from the runway, or a weekend warrior could be buzzing his little aerobat around not talking to anyone on the radio. In any case, the Traffic Alert and Collision Avoidance System installed on the 777 will alert the crew to possible conflicting traffic, also known as a Traffic Advisory (TA). If the other aircraft gets too close for the TCASs comfort, it will issue a Resolution Advisory (RA) commanding you to climb or descend to avoid collision with the intruder aircraft. Now its not too nice for that other airplane to intrude on your personal space, now is it? The key for all this magic to happen is the simple aircraft transponder. When turned on, the TCAS constantly interrogates operating transponders in other aircraft. With each transponder interrogation, it analyses and predicts other aircrafts flight paths and positions. Airplanes that do not have transponders will not show up on your TCAS display and you will not receive RAs for these aircraft. Aircraft that have a transponder but do not

Script Document

Terrain, Traffic, TCAS Script Writer: Michael Pittman

have altitude encoding operating will still show up as TCAS targets but the system will not know their altitude so RAs cannot be issued. Around your fancy aircraft, the TCAS constructs several three dimensional bubbles defining your personal space. The more bubbles another aircraft penetrates, the more serious alerts you will receive from the TCAS. These comfort space bubbles change size depending on how fast another aircraft is closing in on your current and predicted position. Obviously, the bubbles will be much larger for a fighter jet coming at you head-on than a single-engine piston aircraft climbing towards your altitude. The TCAS is operated mostly from the transponder panel. The Transponder Mode Selector TCAS Controls knob operates the TCAS when in the TA ONLY or TA/RA positions. TA ONLY will only display traffic targets. You might use this position at a congested airport where multiple parallel approaches are being conducted to prevent a nuisance RA. The TA/RA position is the normal setting pilots select when cleared for takeoff. Depending on whos flying, you can switch the selected transponder by moving the transponder select switch. Now that weve talked about how the TCAS works and operates, lets proceed with caution as we enter the TCAS Alerts and Warnings section.

TCAS Alerts and Warnings If you havent figured it out yet, TCAS target information is displayed on the ND as long as you in either the map, map centered, VOR or APP modes. The cyan TFC message will display on the ND if you are in one of these modes and the TCAS mode is in either TA ONLY or TA/RA. The most basic and least stressful traffic alert is the Proximate Traffic Display. When an aircraft is within 6 miles and 1200 feet vertically, a filled white diamond will appear on your ND. A data tag will appear next to the diamond showing the aircrafts relative/absolute altitude and whether it is climbing or descending. There will be no aural alert in this case. A blank white diamond symbolizes the Other Traffic category which is an aircraft detected by TCAS with a transponder but no altitude information. Usually, these are low flying aircraft such as crop dusters, but they will get your blood pressure going as technically they could be at your same altitude and within 6 miles. Make sure to keep your eyes open and query ATC. There will be no aural alert. As the intruder aircraft penetrates more of the TCASs 3-D bubbles, it will alert you with more authority that another aircraft is getting close. A TA alerts the pilot that another aircraft will enter its critical conflict airspace in 35 to 45 seconds. You will get an aural Traffic, Traffic alert and the amber TRAFFIC message is displayed on the ND. The traffic target will also transform into a filled amber circle with an altitude, vertical motion, and distance data tag. This basically tells you to stop reading your favorite magazine and look outside for the other aircraft. Sometimes, you might get the TCAS amber message OFFSCALE. This simply means that you need to change your ND range to a larger scale to see the TA target. The most serious TCAS alert that will require you to do something is the RA. When the TCAS issues an RA, it predicts that the intruder aircraft will enter your conflict airspace within 20 to 30 seconds. You will receive a

Script Document

Terrain, Traffic, TCAS Script Writer: Michael Pittman

TCAS voice alert, vertical guidance on the PFD, vertical guidance on the vertical speed indication, and a red TRAFFIC message on the ND. The traffic symbol on the ND will be a filled red square with an identical data tag to the TAs. You must do whatever the RA tells you to do, regardless of ATC instructions. Disengage the autoflight and follow the aural and visual commands. Inform ATC of your RA as soon as you can. Note: While an RA is a serious situation that requires a timely maneuver by the pilot, it should not be an overly abrupt control yank. You have 20-30 seconds before the intruder aircraft will enter your conflict airspace. While you shouldnt delay your action to read another page of your Ops Manual, you should immediately but not abruptly pitch the aircraft to around 1000 feet per minute. The reason for this is you probably have at least flight attendants out of their seats. You probably will not get that filet mignon when all of the flight attendants are unconscious. There are a variety of TCAS voice alerts you will receive for an RA depending on the actual situation. Each of the voice commands is pretty self-explanatory. If you are told to climb, then pitch for the TCAS PFD commands. If you are told to maintain something, then do not make any abrupt changes to your current pitch. You should however avoid the red PFD pitch command. When separation is increasing and the RA will no longer occur, you will hear the relaxing Clear of Conflict voice alert. In this case, vertical guidance is removed from the PFD and the traffic symbol returns to an amber circle. You can now breathe normally again! The 777s TCAS system has some built in inhibits to help prevent distractions in the cockpit during critical phases of flight. Any kind of descent RAs are inhibited below 1200 feet AGL for obvious reasons. All RAs are inhibited below 1100 feet AGL when climbing and 900 feet AGL when descending. Those loud annoying voice alerts are inhibited below 500 feet radio altitude. If there is ever a conflict between the GPWS and TCAS, the GPWS always takes priority. Think about it, which is a bigger target to hit: another aircraft or the ground?

Lesson Summary Whether its the ground or another airplane, the 777 has quite a few safeguards to keep you out of harms way. The easiest and safest thing to do is follow what the airplane commands. It will stop yelling at you so you will have time for more important things, like greasing this landing to impress your passengers. You will have more time to explore this warning and alert system during Flightwork. For now, lets review the topics we discussed in this section:

Ground Proximity Warning System (GPWS) Operation

GPWS Alerts and Warnings

Traffic Alert and Collision Avoidance System (TCAS) Operation

TCAS Alerts and Warnings We hope you have enjoyed the Terrain, Traffic, and TCAS section by Angle of Attack. Feel free to explore more of our Safety Sections. Until then, Throttle On!

Script Document

Terrain, Traffic, TCAS Script Writer: Michael Pittman