Final answer:
The single engine service ceiling is the altitude at which an aircraft can maintain a 50 FPM climb rate on a single engine.
Step-by-step explanation:
The aircraft's single engine service ceiling refers to the highest altitude at which the aircraft can maintain a specified minimum rate of climb. The correct definition is (a) Highest altitude the aircraft can maintain 50 FPM climb rate when single engine. At that altitude, the aircraft can sustain a climb rate of 50 feet per minute (FPM) on a single engine under standard atmospheric conditions. Beyond this ceiling, the aircraft would not be able to climb at this minimum rate due to the thinning air and decreased engine performance.