Secondary Power System
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The secondary power system (SPS) comprises of two airframe mounted main gearboxes driven by its retrospective engine or the auxiliary power unit (APU). The gearboxes are connected by a cross drive shaft to enable either engine can be started by the APU. This also allows each engine to drive both gearboxes in emergencies.

Each gearbox drives a hydraulic pump, an integrated constant speed drive an electrical generator and a fuel pump. the starboard gearbox also carries the APU.  The APU is a small gas turbine engine which draws fuel from the engine supply system.

The APU can be started from the aircraft battery and used for ground maintenance purposes or to start the main engines.  The APU also Tornado to be operated and serviced in remote locations.  It also allows also servicing without ground power units.

Some advantages of this system,
            - APU can be run for up to four hours for maintenance purposes,
            - APU supplies ground electrical and hydraulic power,
            - Enable engine starting,
            - SPS control unit incorporates Built in Test Equipment (BITE) and is easily accessible,
            - Gravity & pressure re-oiling points,
            - optical fibre system for checking gearbox oil level,
            - All gearbox driven accessories use V-clamp attachments are are orientated using dowel pins,
            - Guard tubes on all drive shafts,
            - APU fuelled from main engine supply.