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High Density Altitude Takeoffs
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.
Be Aware of Density Altitude
From CP82, Page 10, October, 1995
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
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.
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
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
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
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
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.
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
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
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
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!