FAA Commercial Pilot Airplane (CAX)Aerodynamics and PerformanceEasy
An airplane, at a given weight and configuration, stalls at 60 KIAS at sea level. The same airplane, same weight and configuration, is flown to 10,000 feet density altitude and stalled again. What indicated stall speed should the pilot expect?
- AApproximately 60 KIAS, essentially unchanged from the sea level value
- BLower than 60 KIAS, because the thinner air reduces the load on the wing
- CHigher than 60 KIAS, because reduced air density requires more speed to generate lift
- DCannot be determined without knowing the outside air temperature
Show answer & explanationAnswer & explanation
Correct answer: A. Approximately 60 KIAS, essentially unchanged from the sea level value
Indicated airspeed is derived from dynamic pressure, which already accounts for air density. For a given weight and configuration, the wing always stalls at the same critical angle of attack and therefore the same indicated (calibrated) airspeed, regardless of altitude — although true airspeed at the stall increases with altitude.
Why the other options are wrong
- B. IAS does not decrease with altitude; it stays essentially constant for a given weight/config.
- C. This confuses IAS with TAS — TRUE airspeed increases with altitude, not indicated airspeed.
- D. Temperature affects TAS, not the indicated stall speed for a given weight and configuration.
Stall Speed and Altitude (IAS vs TAS)
Indicated stall speed remains essentially constant with altitude for a given weight/configuration because it reflects dynamic pressure; true stall speed increases with altitude due to decreasing air density.
- Critical AOA is reached at the same IAS regardless of altitude
- TAS at stall increases with altitude (thinner air)
- Pilots reference IAS/CAS for stall margins, not TAS
Memory trick: The gauge doesn't care how thin the air is — IAS stays the same.