Which of the following is NOT a valid limit?

• A. Fuel temperature -37 C to 57 C
• B. Wing Ice protection maximum temperature 15 C
• C. STAB ICE continuous operation maximum temperature 30 C
• D. Ground PITOT STATIC button ON limit 2 minutes

Answer: (C)

The main idea is that limits describe the safe envelope for a system as a clear value or duration. They’re typically given as a temperature range, a maximum/minimum, or a maximum time for a condition.

The line about STAB ICE with a continuous operation maximum temperature of 30 C is not a valid limit because it merges a time-based concept (“continuous operation”) with a temperature cap in a way that isn’t how icing-system limits are normally stated. Anti-ice systems are limited either by temperature envelopes that define when they should operate or by time-on limits, not by a standalone “continuous operation maximum temperature” value.

The other options fit common formats: fuel temperature -37 C to 57 C mirrors a typical allowable fuel temperature envelope; wing ice protection maximum temperature 15 C reflects a defined operational constraint for that subsystem; and the ground PITOT STATIC button ON limit 2 minutes is a plausible on-ground time limit for a system operation.