FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsHard
An aircraft's rate of climb decreases linearly with altitude above FL350 at a rate of 50 fpm per 1,000 feet. At FL350, the rate of climb is 300 fpm. Using the standard definition of service ceiling (rate of climb = 100 fpm), what is the approximate service ceiling for this aircraft?
- AFL430
- BFL410
- CFL390
- DFL370
Show answer & explanationAnswer & explanation
Correct answer: C. FL390
The rate of climb must decrease from 300 fpm to 100 fpm, a reduction of 200 fpm. At 50 fpm per 1,000 feet, this requires 200/50 = 4,000 feet of climb above FL350, giving a service ceiling of FL350 + 4,000 ft = FL390.
Why the other options are wrong
- A. This exceeds the calculated absolute ceiling and is not achievable given the climb rate trend.
- B. At FL410, climb rate would be 0 fpm, which defines absolute ceiling, not service ceiling.
- D. This altitude would still have a climb rate above 100 fpm (200 fpm), not meeting the service ceiling definition.
Service Ceiling vs Absolute Ceiling
Service ceiling is the altitude where maximum rate of climb decreases to 100 fpm; absolute ceiling is the altitude where climb rate reaches 0 fpm.
- Service ceiling standard: 100 fpm rate of climb
- Absolute ceiling standard: 0 fpm rate of climb (theoretical max altitude)
- Both derived from thrust/power available vs required curves diminishing with altitude
Memory trick: Service = still climbing a little (100 fpm); Absolute = all climb gone (0 fpm)