A dispatcher plans a departure well below the airplane's maximum structural takeoff weight, so the crew elects to use the assumed temperature method to compute a reduced-thrust takeoff. What is the primary operational benefit of this technique?
- AIt increases the maximum allowable takeoff weight for the runway
- BIt reduces engine wear and extends engine service life while still meeting all takeoff performance margins
- CIt allows the crew to disregard obstacle clearance requirements for the departure
- DIt permits takeoff on a contaminated runway without additional performance penalty
Show answer & explanationAnswer & explanation
Correct answer: B. It reduces engine wear and extends engine service life while still meeting all takeoff performance margins
The assumed temperature (flex/reduced-thrust) method calculates a fictitious higher outside air temperature to derive a reduced thrust setting that still satisfies all required performance margins at the actual (lower) weight and temperature. This reduces engine operating temperatures and stress, extending engine life, but it does not increase allowable weight, is prohibited on contaminated runways, and does not waive obstacle clearance requirements.
Why the other options are wrong
- A. Reduced thrust does not increase maximum allowable weight; it is only usable when weight is below the limit.
- C. All obstacle clearance and climb gradient requirements must still be satisfied at the reduced thrust setting.
- D. Reduced thrust takeoffs are generally prohibited on contaminated or slippery runways per AFM limitations.
Assumed Temperature (Flex Thrust) Method
A reduced-thrust takeoff technique that uses a fictitious higher temperature to compute lower thrust settings, valid when actual weight is below the performance-limited maximum.
- Reduces engine wear and extends engine life
- Only usable when weight margin exists below max takeoff weight
- All performance and obstacle clearance requirements must still be met
- Not permitted on contaminated or slippery runways
Memory trick: Pretend it's hotter outside to save your engines' insides