GATE 2022 AE – Question 18

Flight Mechanics & Space Dynamics · Airplane performance: drag polar, take-off and landing, climb and descent, ceilings, range and endurance, load factor, turning flight, V-n diagram, winds · 1 mark · Multiple choice

The service ceiling of an airplane is the altitude

at which maximum rate of climb is 100 m/min
beyond which theoretically the airplane cannot sustain level flight
at which maximum power is required for flight
at which maximum rate of climb is 100 ft/min

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Correct answer: (D) at which maximum rate of climb is 100 ft/min

Explanation

Aircraft ceilings are defined by the **maximum rate of climb** (ROC) the aircraft can still achieve at that altitude. The maximum ROC falls as altitude increases (less excess power), reaching zero at one limit altitude.

**Absolute ceiling:** the altitude where the maximum rate of climb is **zero**. Above it the airplane cannot sustain level flight.
**Service ceiling:** the altitude at which the maximum rate of climb has dropped to a specified small value. For propeller and subsonic jet aircraft this value is conventionally **100 ft/min** (about 0.5 m/s). It is the practical operating limit.

So the service ceiling is the altitude where the maximum rate of climb is **100 ft/min** (option D). Option A uses 100 m/min, which is a different number, and option B describes the absolute ceiling.