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Cumulogranite
cu·mu·luo-/gran-ite/ /’kyoomy lo/'gran t/
noun
pilot slang:
mountains obscured by clouds
One of many hilarious flying-related Far Side car- toons 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 departures, arrival and approach, or if situational awareness is lost, CFIT – Controlled Flight Into Terrain – is a serious subject. Pilots can avoid CFIT, and any resident 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 which adds a “predic- tive” function to the traditional GPWS.
Studies were conducted after a rash of CFIT accidents in the late 1960s that concluded some type of automatic warn- ing system, alerting pilots to the proximity of the ground, could have prevented the accidents. As a result of the stud- ies and recommendations by the NTSB, the FAA (in 1974) and ICAO (in 1979) required all large turbine and turbojet 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. or 5,700 kg. 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 in commercial air transport or GA. For TAWS neophytes and those like me who have trouble remembering the rules for who needs a TAWS or can’t remember the 11 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 with no mandated requirement to have a TAWS. Class A is at the top of the food chain in both 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 hav- ing 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. (5,700 kg) no TAWS mandated. Tur- bine powered with six or more passenger seats regardless of MTOW, Class B TAWS, no display mandated, which infers Class C.
Part 135.154 – Piston powered over 12,500 (5,700kg) and 10 or more passenger seats, Class B with no display man- dated. Turbine powered with six to nine passenger seats,
From the Flight Deck
by Kevin R. Dingman
February 2023 / TWIN & TURBINE • 23
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