Page 42 - June 2015 Volume 19 Number 6

PERSPECTIVES
By Kevin R. Dingman
One of several hilarious, flying- related Far Side cartoons is the classic goat-in-the- clouds. We all hope to never see such a thing in the clouds, or any other solid object for that matter. Most often encountered during arrival and approach, CFIT–Controlled Flight Into Terrain, is a serious subject. Pilots can avoid CFIT and goats by installing a TAWS (Terrain Avoidance and Warning System), commonly known by Honeywell’s trademark name: EGPWS – Expanded Ground Proximity Warning System. GPWS and EGPWS are essentially the same system except that EGPWS includes a terrain database that adds a “predictive” function to the traditional GPWS.
Studies conducted after a rash of CFIT accidents in the late 60’s concluded that some type of automatic warning system, alerting pilots to the proximity of the ground, could have prevented the accidents. As a result of the studies and recommendations by the NTSB, in 1974 the FAA and, in 1979, ICAO, required all large turbine-powered aircraft to install GPWS. In 2002, the rule was amended to include all jets and all aircraft with a MTOW greater than 12,500 lbs. There is a further distinction in the type of TAWS required (Class A or B, and with or without a visual display), based on the number of passenger seats configured and whether the airplane is used in commercial air transport or general aviation. For TAWS neophytes, and those like me that have trouble remembering the rules for who needs a TAWS, or the eleven or so alerts and warnings presented by TAWS, I offer this brief dissertation on terrain avoidance and warning systems.
Who Needs ‘em
There are three categories of TAWS: Class-A, B and C. Class-C is simply a Class-B custom-modified for use in smaller GA airplanes that have no mandated requirement to have a TAWS. Class-A is at the top of the food chain in cost and capability, Class-C is at the bottom. The Class-A TAWS must have both an aural and visual output to the crew. Class-B has the option of having a display or not having a display – Class-C has no display. The “who needs ‘em “ question is answered by the FAR “Part” under which you operate, the type of motor propelling your vehicle, your MTOW and the number of “configured” passenger seats in your plane. Here’s a summary:
Part 91.223 – Piston powered – no TAWS mandated. Turbine powered with less than six passenger seats and less than 12,500 lbs., no TAWS mandated. Turbine powered
with six or more passenger seats, regardless of MTOW, Class-B TAWS, no display mandated.
Part 135.154 – Piston powered over 12,500 and ten or more passenger seats, Class-B with no display mandated. Turbine powered with six to nine passenger seats, Class-B with no display mandated, Turbine powered with ten or more passenger seats, Class-A with display required.
Part 121 – Class-A with display mandated for all operators.
For a Class-A TAWS, you need additional equipment to provide input to the system: Gear and flap position, radar/radio altitude, CADC, GPS, glideslope and SAT (static air temperature), for example.
CFIT happens most often when flying non-precision approaches. Continuous Descent Final Approach (CDFA) is one of the initiatives to address the problem in this phase of flight. In industry parlance, the previous method of flying a non- precision approach such as VOR, NDB, LOC-BC or GPS/RNAV approach was called “Dive-and- Drive.” The phrase describes the technique of diving from the FAF to the MDA, and then, once level, driving to the MAP. This means we’re cruising at a very low altitude, relatively slow and often several miles from the runway. We would then calculate a VDP, Visual Descent Point, from which to descend to the runway. This type of approach descent differs greatly in stability, consistency, predictability and pilot workload from a constant rate-of- descent approach, such as on an ILS glideslope. Most non-precision approaches now incorporate some form of a CDFA. Combining a TAWS with a CDFA goes a long way in
Too Low - Goat
40 • TWIN & TURBINE
JUNE 2015