FAA Commercial Pilot Airplane (CAX)Aerodynamics and PerformanceMedium
A pilot climbs an airplane toward its absolute ceiling. As altitude increases, what happens to the best angle-of-climb speed (Vx) and best rate-of-climb speed (Vy)?
- AThey converge and become the same speed at the absolute ceiling
- BThey diverge further apart as altitude increases
- CBoth remain constant regardless of altitude
- DVx becomes greater than Vy at high altitude
Show answer & explanationAnswer & explanation
Correct answer: A. They converge and become the same speed at the absolute ceiling
As altitude increases, available excess power/thrust decreases, narrowing the range of speeds that produce a positive rate of climb. Vx increases and Vy decreases with altitude until they converge at a single speed at the absolute ceiling, where climb rate is zero.
Why the other options are wrong
- B. The opposite occurs — the speeds converge, not diverge, with altitude.
- C. Both speeds change with altitude due to decreasing excess power and thrust available.
- D. Vx does not exceed Vy; they converge but Vx approaches Vy from below.
Vx/Vy Convergence with Altitude
As altitude increases, Vx increases and Vy decreases until they meet at the same speed at the absolute ceiling.
- Excess thrust and power decrease with altitude.
- At absolute ceiling, only one speed produces zero rate of climb.
- This convergence point defines the airplane's absolute ceiling.
Memory trick: Climb speeds shrink together like a V closing into one point at the top.