FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsHard
A transport aircraft at FL410 experiences low-speed buffet onset at 1.3g and high-speed (Mach) buffet onset at 1.5g at the current weight and Mach number. Regulations require a minimum buffet margin of 0.3g above 1g level flight for cruise. Is the aircraft's buffet margin adequate, and which boundary is limiting?
- AAdequate; the margin is 0.3g, limited by low-speed buffet
- BAdequate; the margin is 0.5g, limited by high-speed buffet
- CInadequate; the margin is 0.3g, limited by low-speed buffet
- DInadequate; the margin is 0.2g, limited by high-speed buffet
Show answer & explanationAnswer & explanation
Correct answer: A. Adequate; the margin is 0.3g, limited by low-speed buffet
Low-speed buffet margin = 1.3g − 1g = 0.3g; high-speed buffet margin = 1.5g − 1g = 0.5g. The smaller (limiting) margin is 0.3g on the low-speed side, which exactly meets the 0.3g minimum requirement, so the aircraft's buffet margin is adequate at this weight/altitude/Mach combination.
Why the other options are wrong
- B. 0.5g is the high-speed margin, but it is not the limiting (smaller) margin.
- C. The margin calculation is correct, but 0.3g meeting the minimum requirement means it is adequate, not inadequate.
- D. Miscalculates the margin; 1.5g − 1g = 0.5g, not 0.2g, and high-speed buffet is not limiting here.
Buffet Margin
The difference in load factor (g) between 1g level flight and the onset of either low-speed (stall) buffet or high-speed (Mach) buffet; the smaller value is the limiting margin.
- Low-speed buffet margin = g at stall buffet onset minus 1g
- High-speed buffet margin = g at Mach buffet onset minus 1g
- Regulations require a minimum margin (commonly 0.3g) for cruise maneuvering capability
Memory trick: Take the smaller gap — that's your real safety cushion.