FAA Airline Transport Pilot (ATM)Aircraft Performance and Weight and BalanceHard
At a high-elevation airport with a long, obstacle-free runway, a dispatcher finds that the maximum allowable takeoff weight is restricted to less than the field-length-limited weight, even though climb and obstacle limits are not restrictive. Which factor is most likely responsible for this additional restriction?
- AWind component crediting limitations
- BSecond-segment climb gradient requirement
- CTire speed or brake energy limit due to higher true airspeed at high density altitude
- DRunway gradient correction factor
Show answer & explanationAnswer & explanation
Correct answer: C. Tire speed or brake energy limit due to higher true airspeed at high density altitude
At high density altitude, true airspeed at a given calibrated/indicated V1 or VR is higher than at sea level, which can approach the certified tire speed limit or maximum brake energy speed (VMBE). Since obstacles and climb are not limiting in this scenario, the tire speed/brake energy limit becomes the governing restriction, independent of runway length.
Why the other options are wrong
- A. Wind crediting affects distance calculations but wouldn't uniquely explain a weight restriction below field limit here.
- B. Climb gradient was stated as not restrictive in this scenario.
- D. Runway gradient correction was not identified as a factor in this scenario.
Tire Speed / Brake Energy Limit
A weight limit imposed when ground speed at rotation/rejected takeoff would exceed certified tire speed or brake kinetic energy limits, common at high elevation/high temperature airports.
- High density altitude raises TAS for a given IAS
- VMBE = maximum brake energy speed
- Can limit takeoff weight even with long, obstacle-free runways
Memory trick: High and hot means fast feet on the ground — tires and brakes can only take so much.