April 6, 2010
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Flying in the mountains By BILL SCHROEDER While departing a high-density altitude airport, a Cessna 177RG, with four people on board, climbed about 50 feet but did not accelerate. The airplane was observed descending before hitting trees about ½ mile off the departure end of the runway. Weight and balance computations placed the airplane over maximum allowable gross weight. Density altitude was computed at 8,493 above mean sea level. The airport, at 6,264 feet MSL, is known for its high-density altitude and downdrafts at the end of the departure runway. Probable cause of the accident, according to the NTSB, was the pilot’s decision to take off, over maximum allowable gross weight, from a high-densityaltitude airport. Other factors? The high-density altitude, down drafts and the pilot’s lack of familiarity operating from high-density altitude airports. The pilot’s logbook revealed that his only experience operating at an airport with a field elevation over 3,000 feet above sea level was one takeoff and landing at an airport with a field elevation of 3,996 feet. As a result of this pilot’s actions — and inexperience — he and his three passengers were killed. When it comes to high-density altitude training, one takeoff and one landing does not meet any acceptable standard of performance. That’s why all pilots planning to fly in mountainous regions should go through a comprehensive training program. The checkout should consist of a combination of ground and flight training that takes at least eight hours to complete. During ground training, the aircraft’s operations manual should be used to review performance for takeoff, climb, cruise and landings. Compare the sea level performance with performance at higher density altitudes. Also compare gross weight performance with weights less than gross. It is recommended that a plane taking off from a high-density altitude airfield weigh at least 10% less than gross weight for better performance. Most takeoff and climb performance figures are determined during test flights at airfields that are close
Photo courtesy Bill Schroeder
For General Aviation News
Bill Schroeder to sea level elevations, which means that much of the higher altitude performance figures are interpolated, especially takeoff distances and climb rates. Be aware of the importance of using the “red knob” (mixture control) to obtain maximum performance from the engine. Become familiar with the KOCH Chart, which is used to show what percentages a pilot should add to the sea level takeoff distance and sea level rate of climb based upon temperature and pressure altitude. (You can download a KOCH Chart at FlightSafetyCounselor.com.) Follow the directions at the bottom of the chart and compare the KOCH Chart performance figures to those in the aircraft operating handbook. Next look at terrain along planned routes and in the vicinity of airfields. Keep in mind that the “direct to” route is not always the safest route when flying in the mountains. Plan routes that do not exceed the capabilities of the aircraft or the pilot and, of course, provide adequate mountain top clearances. Also become familiar with oxygen requirements. Your instructor should take some time to talk about weather in the mountains and how to obtain information where weather reporting stations are non-existent.
Calling a local radio station, an FBO or even a local law enforcement agency can provide weather information that can be useful in planning a flight if ASOS or AWOS information is not available. The Area Forecast should be included in the pre-flight weather briefing, as it will provide information needed to safely conduct the flight over the entire route. Your instructor also should explain how winds can funnel through mountain passes, increasing speed dramatically (venturi effect), causing turbulence and downdrafts. Always carry extra water and other provisions when flying in the mountains. A basic survival kit is also recommended. Take some warm clothing for those cool mountain nights should you have to make an off-field landing in high terrain. Always file a flight plan. Radar service for flight following may be impossible to obtain due to mountainous terrain. It is nice to know that 30 minutes after the expected closure time of the flight plan, the FSS will start the process of looking for overdue aircraft. The flight portion of your training should consist of cross-country flying to each of the airfields identified during the flight planning phase and then doing several takeoffs and landings at each field. Compare performance calculations with actual performance at each of the fields. If an FBO is located at the field, stop and talk with them about specific operations at their field and some of the problems faced by pilots flying into and out of their airport. Once it’s complete, your instructor should review the flight and answer any questions you might have concerning the entire day of training. One last thing: Select a nice VFR day for training. If the weather is forecast to be marginal, cancel and reschedule.
“When it comes to high-density-altitude training, one takeoff and one landing does not meet any acceptable standard of performance.”
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Bill Schroeder is a Master CFI who gives mountain flying training in the Reno-Lake Tahoe area. For more information: FlightSafetyCounselor.com.
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