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1 In certain emergency conditions the typical aircraft power generation system

may meet all the airworthiness authority requirements.

2 The aircraft battery offers a long-term power storage capability, typically up to

60 minutes. 3 However for longer periods of operation the battery is sufficient.

4 The operation of twin- engined passenger aircraft on ETOPS flights now means

that the aircraft has to be able to operate on twin-engined while up to 280

minutes from an alternative or diversion airfield.

5 This has led to modification of some of the secondary aircraft systems.

6There are five standard methods of providing back-up power on civil transport

aircraft.

7 RAT is deployed when most of the conventional power generation system has

worked.

8 The RAT is an air driven turbine, normally stowed in the aircraft ventral or nose

section that is extended either automatically or manually when the emergency

commences.

9 The passage of air over the turbine is used to power a small emergency generator

of limited capacity, usually enough to power the crew’s essential flight

instruments and a few other critical services.

10 Typical RAT generator sizing may vary from 15 to 25 kVA depending upon

the aircraft.

11 The RAT is intended to furnish the crew with sufficient power to fly the aircraft

while attempting to restore the primary generators or carry out a diversion to

the nearest airfield. It is not intended to provide significant amounts of power

for a lengthy period of operation.