Regarding stall speed and altitude for a given configuration, which is true?

• A. Indicated stall speed remains the same with altitude
• B. Indicated stall speed increases with altitude
• C. Indicated stall speed decreases with altitude
• D. Indicated stall speed becomes unpredictable with altitude

Answer: (A)

Stall speed is determined by the lift needed to balance weight at a given configuration, which depends on the stall lift coefficient and the dynamic pressure q = 0.5 ρ V^2. For a fixed weight and wing, the stall occurs at a fixed dynamic pressure, so the indicated airspeed—which translates that dynamic pressure into IAS using standard sea‑level density—stays essentially the same regardless of altitude. As you climb, the air is thinner, so the true airspeed needed to reach that same dynamic pressure increases, but the indicated stall speed remains about constant. Small deviations can occur due to changes in Reynolds number or compressibility at very high altitudes, but for typical conditions it’s effectively unchanged.