FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsMedium
An airplane is flying at 8,000 feet MSL on a standard day with an indicated airspeed of 100 knots. Using the rule of thumb that true airspeed increases approximately 2% per 1,000 feet of altitude, what is the approximate true airspeed?
- A108 knots
- B124 knots
- C116 knots
- D100 knots
Show answer & explanationAnswer & explanation
Correct answer: C. 116 knots
At 8,000 feet, the correction is 2% × 8 = 16%. 100 knots × 1.16 = 116 knots true airspeed.
Why the other options are wrong
- A. This uses only 8% correction, an incomplete calculation.
- B. This overestimates the correction beyond the 2%/1,000 ft rule.
- D. This ignores the altitude correction entirely.
True Airspeed vs Indicated Airspeed
True airspeed (TAS) exceeds indicated airspeed (IAS) as altitude increases because air density decreases; a common rule of thumb is a 2% increase in TAS per 1,000 feet of altitude.
- TAS = IAS approximately corrected for density altitude
- Rule of thumb: add ~2% per 1,000 ft MSL
- Used for flight planning and fuel calculations
Memory trick: Higher you fly, faster the true speed flies.