FAA Airline Transport Pilot (ATM)Aircraft Performance and Weight and BalanceHard
A dispatcher is using a buffet-boundary chart to select the maximum cruise altitude for a turbojet, ensuring the airplane retains a 1.3g buffet margin at the planned weight and Mach number. This 1.3g margin approximately equals the load factor produced during a level turn at what bank angle?
- AAbout 40 degrees
- BAbout 25 degrees
- CAbout 15 degrees
- DAbout 60 degrees
Show answer & explanationAnswer & explanation
Correct answer: A. About 40 degrees
Load factor in a level turn equals 1/cos(bank angle). Solving 1.3 = 1/cos(θ) gives cos(θ) = 1/1.3 ≈ 0.769, so θ ≈ 40°. This means a 1.3g buffet margin ensures the aircraft can maneuver up to roughly a 40° banked turn (or an equivalent gust load) at the selected cruise altitude without reaching initial buffet onset.
Why the other options are wrong
- B. A 25° bank produces about 1.10g, still below the 1.3g requirement.
- C. A 15° bank produces only about 1.04g, far less than the 1.3g margin.
- D. A 60° bank produces 2.0g, well above the 1.3g buffet margin value.
Buffet Margin (1.3g)
A required load factor margin above 1g level flight that a turbojet must maintain at cruise altitude/weight/Mach before encountering aerodynamic buffet, roughly equivalent to a 40° banked turn.
- Load factor = 1/cos(bank angle)
- 1.3g margin corresponds to about a 40° bank angle
- Used to set maximum cruise altitude on buffet-boundary charts, protecting against high/low speed buffet and gusts
Memory trick: 1.3g is your 40-degree bank cushion before the buffet bites.