For a few years now, all King Airs with six or more installed passenger seats are required to have a Terrain Awareness and Warning System (TAWS) onboard and operational. This is a stand-alone system in some installations and is integrated into the GPS navigator in other installations. I have a homework assignment for you: Go to the Supplements section of your King Air’s POH and find, then read, the supplement dealing with your exact system. After doing this, I bet you will discover a few things you did not know or had forgotten. There’s good info there!
If TAWS is a part of your latest, greatest, factory-installed Pro Line or Fusion system, its description can be found in the Systems section of the POH, not in the Supplements section.
Thanks to space shuttle flights, the entire earth has been mapped in great detail and that detail can now be included on a tiny chip in your TAWS unit. Amazing! GPWS – Ground Proximity Warning System – a system that preceded TAWS, was primarily based on radar altimeter readings so it knew your height above the ground right beneath you and it could calculate your rate of closure to terra firma. But it had no look-ahead capability – it couldn’t see that cliff looming up ahead – and it also lacked an airport database. But by combining a chip with knowledge of all terrain and airports with an exceedingly accurate GPS navigator that knows the airplane’s exact position both horizontally and vertically, as well as the track and speed of the airplane, it is now possible to look well ahead and to accurately predict whether the existing flight path is safe or not safe. EGPWS – Enhanced GPWS – is the name Honeywell assigned to their version of this advanced system. The FAA and other manufacturers use the moniker TAWS.
There would be absolutely no reason for a TAWS system if pilots never made mistakes! It’s only when scud-running suddenly turns into solid IMC, or when a pilot misreads a chart and descends too soon, or when a pilot fails to follow the assigned flight path that TAWS is a necessary life-saver. Let’s face it, we are human and humans can and do make mistakes. CFIT – Controlled Flight Into Terrain – has been a consistent leader of reasons for aviation-related fatalities and TAWS is a Godsend that helps reduce the likelihood of this cause of death. Will it ever completely eliminate CFIT? I doubt it because mistakes will still be made, but it surely improves the odds of survival by a huge amount.
How about giving yourself a little educational fun? On your next deadhead leg in excellent visual conditions, head directly for a convenient mountain. Oh, you don’t have one of those in Kansas, you say? In that case, just casually descend toward a wide open wheat field with no farmer nearby. I want you to actually experience both a TAWS Caution and a TAWS Warning in your exact airplane. This will always include verbal calls and in most installations it will include a visual presentation of the dangerous terrain. The caution you will hear probably is this: “Caution, Terrain! Caution, Terrain!” If we ignore that and continue toward the danger, then we should hear a warning: “Terrain ahead! Pull Up! Terrain ahead! Pull Up!” Now remember, we are doing this in good weather with plenty of visibility and we have an easy escape route, right? Right!
Descending toward the Kansas wheat field, the Caution we hear may be “Too Low! Terrain!” Continuing our descent will then lead to the “Terrain ahead! Pull Up!” warning as before.
Your system’s instructions will tell you that using the visual display to steer toward lower ground is not the correct procedure. Sometime you may have a system without a visual display or else it is malfunctioning. So the proper procedure is to climb like a homesick angel! Now is the time to use your four friends – Power, Props, Flaps, Gear – and get the heck away from the terrain. In the majority of the cases, your airspeed will likely be quite high … cruising or descending. Also, your prop levers will probably be set for cruise RPM and your flaps and gear will be retracted. But not always. So always do all four steps: Power levers aggressively forward to torque or temp limits. Prop levers smoothly forward to the stops for maximum propeller speed. Flaps: Make sure they’re up. Gear? Same thing.
And as you are doing these steps be honking back on the control wheel to get the airplane into an optimum climb profile. Now is not the time to bring the nose up to 12 or 15 degrees and to wait for Vx to be achieved. No! Pull that sucker up to 25 degrees! Only when you see the airspeed approaching 120 KIAS should you drop the nose to maintain that speed … probably the 12 to 15 degrees I mentioned before.
Now if you are exceptionally sharp and know the exact Vx number that is correct for your airplane, your weight, and your existing altitude, wonderful! Go for that number! But, dear readers, if you target 120 KIAS for every King Air ever built, you won’t be too far off. It’s simple, it works, and it provides a comfortable margin above stall speed.
Yes, there may be that one-time-in-a-hundred in which the caution or warning activated when airspeed was not high. If you are already near 120, then obviously you cannot convert a lot of kinetic energy into potential energy by zoom-climbing out of trouble. Now the nose will indeed need to stay near 12 degrees as you complete the four friends procedure.
If you are uncomfortable experiencing this practice scenario by yourself, then seek an experienced instructor to fly with you and/or request a TAWS scenario during your next simulator session.
I believe that practicing the terrain evasion maneuver is important to ingrain the proper steps into your memory and to experience the actual zoom-climb. However, knowing what’s to come and being prepared to conduct the proper steps bears very little resemblance to the state of mind that will likely exist when you hear that caution for the first time while in IMC. It is common to have an initial reaction of “Wait, that can’t be right! I know I am at a safe altitude according to this approach plate. I wonder why it’s squawking at me?!” That reaction, friends, can get you killed.
Remember: Humans make mistakes. Maybe today you are making one of yours, and maybe it is about to have a tragic ending. The proper, safe, reaction is always to quickly and properly execute the terrain evasion maneuver. Analyze why the caution or warning occurred later … and, yes, maybe it was indeed an error. But now, climb like a space shuttle launch!
TAWS includes some neat features that are not always dependent upon imminent terrain impact. It announces when you are 500 feet above the landing runway or the terrain below you. It chastises you if you deviate too much below a glideslope. It has a “Don’t sink” call if the after takeoff flight path starts going down instead of up. It also includes cautions caused by being close to landing without gear and flaps extended. You should know how to disable the flap caution when you are executing a low ILS approach to a long runway and have decided to land with approach flaps.
In fact, you should know how to disable the entire system! There are two cases in which this is so desirable as to be nearly mandatory. First, landing at some private ranch strip that is not in the TAWS airport database will yield a myriad of cautions and warnings that are nothing but distracting to you and scary to your passengers. Second, giving your passengers a nice, calm air tour of some alpine mountaintops or deciding to cruise down a remote isolated coastline only a few hundred feet above the sand … the pleasure of these types of airborne adventures is rapidly lost when all you hear are incessant cautions and warnings!
One last comment: The earth’s surface – the terrain map that the TAWS contains – does not change much (at least we hope that’s the case!) so the need for regular and often database updates for new terrain does not exist. On the other hand, many items in the database do indeed change: perhaps a new airport is built, existing airports change as runways are added or removed, previous database errors are corrected, obstacles – also in many databases – can and do change as new towers are erected or old ones are demolished. Thus, updating the TAWS database in accordance with the POH Supplement’s instructions is important. If no guidelines are given, I recommend getting it done no less than annually.
TAWS is indeed a lifesaver … but only if pilots heed its messages and execute the correct procedures. Fly safe!
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