Flying is a wonderful adventure, but unfortunately, many of our most important “lessons” come from surprise “experience” after certification (if we survive the “lesson”). It is critical to remember that all our new pilots are “hot house plants,” raised in a very controlled environment (but their certificate permits them the whole country). Our obligation as educators is to safely expose them to as many potential real-world “surprises” as possible so they have the tools to cope and the awareness to avoid these hidden hazards. “Chalk talk” is great but lacks the power of meaningful demonstrations. Density altitude operation is a perfect example of an insidious killer that is seldom taught but actually remarkably easy to demonstrate.
Most educators are failing their students here. The ground school discussion does not reveal the true surprises and hazards of high density altitude operations. This environment is easy to demonstrate, even for flatlanders, but must be conducted very with careful preparation to stay safe.
Combine a tailwind take-off with slightly reduced power (carb heat on?) on a long, unobstructed runway to provide the exact same surprise as “Telluride on a hot day.” At the usual lift-off groundspeed (60K?) in this condition, your plane refuses to fly. This is “the surprise that kills” when a pilot encounters it solo for the first time (cognitive dissonance). In this condition – simulating thin air – a plane needs another 10-15 knots groundspeed to achieve the indicated airspeed for flight. The combined surprises of the longer take-off roll, faster GS for lift-off, and a pathetic climb angle is what creates accidents.
Just like in Telluride on a hot day, you will be going remarkably fast over the ground before your plane gathers enough air molecules under the wings to go flying. The disparity between groundspeed and airspeed (TAS/IAS in real thin air conditions) is remarkably unsettling the first time you see it. This simulation is even more surprising for experienced pilots with a deeply embedded TLAR (That Looks About Right) sense of performance. If a pilot forces a plane into the air too early, this slow-flight (behind the power curve) demonstration can get “very exciting.” Only by carefully lowering the nose, to reduce induced drag, will your wing get enough air lift to fly (think “soft-field T/O technique).
When demonstrating this maneuver as a CFI, practice carefully solo first, and select a very long runway with no obstacles for an adequate safety margin. Watching a learner mishandle this experience reveals why there are so many craters at the end of high-altitude runways. Be especially vigilant dual because your learner *will* mishandle this simulation. Thoroughly brief the expected operation (and surprise) and proceed with great caution. Brief and practice a positive exchange of controls too. The “reduced power take-off” (POH says “full power?”) might be controversial, but how many pilots comply with preflight regulations (91.103) and calculate their performance on *every* take-off.
Reduced power is important for two reasons (just pulling carb heat works to drop 200rpm). One is to demonstrate the insidious loss of performance every plane experiences during high/hot operations (expect to use LOTS of runway). The other reason is that this extra power margin will be available when your learner mishandles this simulation (almost guaranteed). It is essential to fly the IAS not just what you see out the window; the angle of climb with a tailwind can be shocking (I own a 7AC Champ though…) Landing with a 10K tailwind is also tricky and can be visually confusing. Every pilot will initially drop in the landing – getting slow from the (TLAR) view out the window. This simulates the high density altitude trap.
This demonstration shows the disparity between take-off and landing “appearance” (TLAR). How fast the plane is actually moving over the ground in both cases is the shocker. You can talk about this all you want, but you have to see it to appreciate it. Reduced climb rate and angle of climb are the second takeaways here. As in all training, acquired humility and respect are important take-aways here. This demonstration also debunks the myth that a high-power machine will fix the density altitude problem (plenty of wrecked Big Cubs litter the high country too). Thin air operations are not (entirely) a power problem. At their root density altitude accidents are a misperception problem (surprise!) followed by a lack of operating experience. A full mountain flying course is recommended for every pilot if you plan real mountain operations. Fly carefully out there (and often)!
Thanks to everyone that was able to attend #OSH21 and visit our SAFE booth – or attend our amazing “SAFE Gathering!” What a wonderful experience after a year of quarantine. Tune-up your flying chops and join SAFE for more resources and savings. Our SAFE Toolkit app is free and brings ideas and tools to your daily flying.