>High Density Altitude Takeoffs Be Aware of Density Altitude
October 1995
Takeoff in any aircraft on a hot day from an airport located at a high elevation, is not to be taken lightly. You, as Pilot-in-Command, should always check the density altitude, and most control towers at airports where high density altitude is prevalent will remind you to check "density altitude." This should trigger a mental alarm and you should calculate the density altitude and look up your flight manual takeoff performance estimate. You need this information before you decide to take off. Flight manual performance data, if accurate, should predict the takeoff capability of a properly flown aircraft. "Properly-flown" is very important as it is possible to greatly extend a takeoff if the pilot does not smoothly fly the correct speeds. Density altitude is a function of pressure altitude (altimeter set at 29.92) and outside air temperature. For example, at Flagstaff, Arizona (elevation 7000 feet) on a hot summer day, 100 degree F, the density altitude is over 11,000 feet.
This means that your airplane performs just as it would for standard temperature at 11,000 feet! High altitudes require that you accelerate to higher true speed to attain adequate wing lift. High altitude also reduces the power output of your engine and prop. Also, when your performance is low, a modest uphill runway slope will greatly extend takeoff roll. Add all of these factors together and you have an airplane that may roll two or three times as far down the runway before reaching lift-off speed. If you try to rotate early (maybe at about the normal distance down the runway) you will extend the take-off roll even further, due to the drag of the airplane at a high angle of attack, at too low an airspeed. Thus, you will find yourself in a classic "behind the power curve" situation. If you have tried to lift-off at too-low speed you have greatly extended your distance required to clear an obstacle. Your only option is to chop the power and land.
Do not wait too late to be able to safely exercise this last option. As pilots we are all trained about the dangers of heavy, hot, and/or high conditions for takeoff, and how to avoid the "backside" performance problem. Also, your pilot's handbook instructs you to fly faster when heavy or at high density altitude. In general, the EZ pilot community is very familiar with the limitations of their airplanes. However, since these recent accidents occurred, we are compelled to add further emphasis to the pilot's handbooks.
Following are some unfortunate results of High Density Altitude Accidents and Incidents
As always, the following reports are published for the sole purpose of helping others to avoid the same problems that caused the accidents. A VariEze crashed in Illinois recently, and unfortunately the pilot was killed. The passenger survived with severe burns. After this VariEze landed on the 2300-foot paved landing strip, the two occupants complained that they smelled fuel fumes in the cockpit. They spent considerable effort trying to locate a fuel leak. No leak was found, so they purchased fuel and took off. At least four eyewitnesses saw the crash. The VariEze reportedly used nearly the entire 2300-foot runway before breaking ground. It did not climb out of ground effect, and struck the corn in a field off the end of the runway before crashing on the runway centerline a quarter of a mile from where they broke ground.
Witnesses reported that the engine sounded normal, and there was no sign of an in-flight fire. The VariEze was destroyed, and a fire broke out shortly after impact. The passenger was able to evacuate the aircraft, but received severe bums trying to get the pilot out. This VariEze was known locally as a "heavy" aircraft, and routinely used lots of runway to take-off. The pilot did not build this aircraft, but purchased it three years previously. He was a proficient pilot, and flew his VariEze often. The pilot was a large man, weighing between 270 and 280 pounds. The weather was clear with temperatures in the high 80's. The pilot's home base runway was 4,000 feet long.
CONCLUSION
This was a heavy example of a VariEze, and had a reputation of needing a long take-off roll. The day was hot (upper 80's) and the pilot was a heavy man. With a load of fuel and a passenger, this aircraft was undoubtedly over gross. Even a lightweight VariEze (630 lbs) would be at the maximum allowable gross weight just with this pilot (270 lbs) and full fuel, not including a passenger! An over gross weight take-off from a 2300-foot strip on a hot day is simply a recipe for disaster.
A LONG-EZ crashed on take-off in Arizona. The pilot was killed but the passenger survived with serious head injuries.
The aircraft was attempting to take off on a 7,000-foot-long runway with an 1% uphill grade. The Long-EZ was loaded to more than 150 pounds over the maximum allowable gross weight. The temperature was 85 degrees F, and density altitude was over 8,000 feet. It was almost dark. 8:30 pm in August 1995, and the tower operator reported that the aircraft initially broke ground at the 4800-foot mark, but settled back onto the runway. The pilot continued the take-off attempt, lifting off briefly twice more before finally chopping the power and steering around the approach light system.
Unfortunately there was a six-foot chain link fence around the airport perimeter. The Long-EZ crashed into this fence, striking two fence posts, and breaking through the chain link. It crossed a road, broke through a wood-pole fence and came to rest upright on a golf course. There was no fire, but the chain link fence and/or fence posts severely injured the passenger and fatally injured the pilot.
CONCLUSION
This was yet another example of an attempted take-off at over gross weight! Add to that, a hot, high density evening, plus an uphill runway! This pilot might have been successful with any one of these problems individually, but was unable to overcome them all.
EDITORS COMMENT
The above accidents were preventable and unnecessary. The pilot-in-command is responsible to check the gross weight and to make a "go" or "no go" decision based on the available runway and density altitude. An uphill runway, even an 1% grade, is a lot. A 7,000-foot-long runway, with an 1% grade is 70 feet higher at one end than the other.
Think of this as a seven-story building sitting at the end of the runway. It is hot, it is dark, you are over gross with a high-time Lycoming 0-235 engine. The wind is calm, so no help from the wind (although a downhill take-off should have been an option with no wind). Would you attempt a take-off in these conditions, particularly if you think of the uphill grade as a seven story building you would have to clear!?
Hopefully not. For most pilots this situation would be unacceptable. Recently we read in the Cozy newsletter of an attempted over gross weight take-off from a short runway. 'Me take-off attempt was aborted, but the brakes failed to stop the aircraft and it broke through a fence and hit a berm, failing the canard, both wings and the landing gear. Fortunately both occupants survived with minor injuries.
How can accidents such as this be prevented? Know your aircraft's limitations, and know your own limitations. Never try to operate outside of this envelope. Use your common sense. If you don't like the look of a situation, STOP and REEVALUATE what you are trying to do. NEVER allow yourself to be driven by schedule- much better late in this world than early in the next!