Plane & Pilot
Tuesday, March 27, 2012

Living Large

Transitioning from a piston to a turbine

Phenom 100
The second is avoiding CB build-ups. One inadvertent trip through a building cumulus, and you'll figure out why—the turbulence and ice can be scary to say the least. If airline captains go around this stuff, you should too, so hone your negotiating skills. Some of the worst widespread icing can happen at the top of the clouds between 16 and 25 thousand feet. Understanding icing reports, the limitations of your ice protections systems, how to judge icing rates, the effects of icing, and how to get to better conditions quickly are key to dealing with these altitudes.

Another obvious hazard of traveling in the flight levels is the lack of air pressure. At FL 180, atmospheric pressure is half that of sea level, and at FL 410, it falls to less than 1⁄5 of sea level. An unexpected depressurization is serious business, so understanding and monitoring the pressurization system is critical. At FL 280, the time of useful consciousness is two to three minutes—plenty of time to don a mask and head down; however, at FL 410, useful consciousness decreases to 15 seconds and about half that in a rapid decompression. So, it's vital to recognize and attend to any problem rapidly. This is why turbines are equipped with quick-donning masks, and training is so important. If you're a single pilot, regulations require that you wear an oxygen mask full time above FL 350. Above FL 410, at least one crewmember has to have a mask on at all times.

Another high-altitude issue is reduced vertical separation minimums or RVSM, which requires the use of precision altimeters above FL 280 to permit 1,000 vertical feet of traffic separation. You'll need an approved RVSM manual for the aircraft, and the pilot will require special training, which takes an hour or two to complete online. It's important to understand that each time an aircraft changes hands it requires new RVSM approval from your local FSDO. Until you submit an application and receive a letter of authorization, you're restricted to flying your new plane below FL 290.

Phenom 100
Two other weather issues of importance in the flight levels are winds and temperatures. You learned it in primary training, but now you get to actually experience the jet stream, and it's a big deal. All turbines achieve their best range at high altitude so like it or not, you are stuck with the high altitude winds. Going eastbound, a 100-180 knots tailwind becomes a real nuisance when you are headed in the other direction. Most of the time, the fuel savings gained by going high overrides wind considerations (up to around 100 knots), so wind calculations always go into turbine flight planning.

In all turboprops, but especially in light jets, the other little "gotcha" is the temperature at altitude, which can have a big effect on engine power. The temperature at your desired cruising altitude will determine how fast and maybe even how high you can go. On the ADDS website, the data that counts is the temperature difference map on the winds page showing temperatures normalized to ISA conditions. If it's hot up high (like over ISA+10 degrees), it will be a slow climb, and cruise speed could be as much as 20 to 30 knots slower than normal.

What Happens If Something Breaks?

FAR 91.213 prohibits flight in a turbine aircraft with inoperative instruments or equipment unless an approved, aircraft-specific minimum equipment list (MEL) exists. Without an MEL, something as simple as a burned- out post light grounds the aircraft. Remember that a MEL specifies operational limitations for inoperative equipment. So, as a turbine operator, you'll need to make sure your airplane has an approved MEL. For airplanes operating in RVSM airspace, the MEL and the RVSM manual may be the same document.

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