At first glance, this week’s crash of Cirrus N89423 at Truckee looks like yet another “high density altitude” accident. Such accidents are, after all, perhaps the most common type of accident at Truckee airport. Due to the thin air, the aircraft cannot climb fast enough to clear rising terrain or to maintain altitude in
downdrafts. Sometimes the climb performance might be adequate but the pilot, growing impatient, asks more of the aircraft than it can then provide, usually with lethal results.
Certainly, this accident has many of the earmarks of the typical high-density altitude crash:
- Truckee is at altitude – 5890 feet.
- The weather was warm, meaning the air was even thinner thus further degrading climb performance.
- Breezy conditions were conducive to generating downdrafts on the lee side of the surrounding terrain.
- The Cirrus SR20 is of low horsepower for its weight and thus has little climb performance to spare
But there seems to be more to it than that. High density altitude accidents often catch those who are unfamiliar with high density altitude operations, or at least are unfamiliar with the terrain surrounding an airport. When the pilot asks of the aircraft more climb performance than the aircraft can deliver, the aircraft gets too slow to continue flying, the wing stalls, and the aircraft crashes.
But this was an instructional flight. The flight school, Mountain Lion Aviation, was based at Truckee airport. The school boasts experience in Cirrus aircraft and so, presumably, the instructor was well familiar with the modest climb performance capabilities of the Cirrus Sr20 and familiar with the airport, the surrounding terrain, and the effects of high density altitude as they then existed. Further, per the air traffic control tapes, the plan was not to depart the area, but rather stay within the relative safety of the traffic pattern.
Definitely not the usual “high density altitude” accident profile.