What defines the differential pressure range?

• A. The range where cabin altitude equals outside altitude
• B. The operating range that extends from where the isobaric range stops
• C. The range where cabin pressure is 1 atm
• D. The range where bleed air is heated

Answer: (B)

Differential pressure range describes how much cabin pressure can differ from outside air pressure over the flight envelope. The cabin is kept at a set pressure by controlling this delta pressure. There’s a zone called the isobaric range where cabin pressure is held nearly constant (a fixed differential). Once you pass beyond that zone, the system varies the differential within its safe limits to maintain the desired cabin pressure as outside pressure drops with altitude. So the differential pressure range is the operating span from where the isobaric range ends up to the maximum differential pressure the system can safely sustain.

The other options describe situations that don’t define this range: zero differential when cabin and outside pressure are equal, cabin pressure at 1 atm which is a specific condition rather than a range, and bleed air heating which relates to temperature, not pressure difference.