An airplane's maneuvering speed (Va) is published as 120 KCAS at maximum gross weight, regardless of altitude. A pilot flying at 20,000 feet notices that the true airspeed corresponding to 120 KCAS is significantly higher than it would be at sea level. What is the correct interpretation for turbulence penetration procedures?
- AThe pilot should fly the sea-level true airspeed value at altitude to maintain equivalent stall margin
- BVa increases with altitude because reduced air density requires a faster calibrated airspeed to protect the airframe
- CVa is only valid at sea level and provides no structural protection at higher altitudes
- DThe pilot should maintain 120 KCAS at altitude, since Va is defined in calibrated airspeed and provides equivalent structural protection regardless of true airspeed
Show answer & explanationAnswer & explanation
Correct answer: D. The pilot should maintain 120 KCAS at altitude, since Va is defined in calibrated airspeed and provides equivalent structural protection regardless of true airspeed
Maneuvering speed is published as a calibrated (essentially indicated) airspeed because it reflects the dynamic pressure at which the wing will stall before exceeding the airplane's limit load factor, regardless of altitude. Although true airspeed at a given CAS increases with altitude, the structural protection provided by flying at Va depends on CAS, not TAS, so the pilot should maintain 120 KCAS at any altitude for the same protection.
Why the other options are wrong
- A. Using sea-level TAS at altitude would result in a much higher CAS, exceeding safe structural limits.
- B. Va does not change with altitude; it is fixed by weight, not air density.
- C. Va remains valid at altitude precisely because it is defined in calibrated airspeed.
Maneuvering Speed and Altitude
Va is published as calibrated airspeed and provides the same stall-before-overstress protection at any altitude, even though the corresponding true airspeed increases with altitude.
- Va is defined in CAS, not TAS
- TAS for a given CAS increases with altitude
- Pilots should fly the published CAS value for turbulence penetration at any altitude
Memory trick: CAS stays the boss, no matter how high you toss.