In an emergency extension, where does the 2B pressure come from?

• A. From the main hydraulic system pressure.
• B. From the APU and emergency brake accumulators.
• C. From external ground supply.
• D. From the environmental control system.

Answer: (B)

In an emergency extension you rely on a dedicated backup hydraulic source for the landing gear. The 2B pressure isn’t drawn from the main hydraulic pumps, but from the 2B emergency circuit. This pressure is supplied by the APU-driven hydraulic pump and by the emergency brake accumulators, which store hydraulic energy for just these kinds of situations. If the engines aren’t driving pumps, the APU can pressurize 2B to extend the gear; if that isn’t available, the emergency brake accumulators provide the stored pressure needed for the emergency extension. External ground supply isn’t the normal source for this in flight, and the environmental control system doesn’t provide hydraulic pressure.