The Emergency Power System system fitted on the IDS comprises a one shot battery. The purpose of the EPS is in the event of a double Engine Flameout with consequent loss of hydraulic and electrical AC power, the system supplies hydraulic power via the No 1 Protected hydraulic system to the taileron actuators. This is to enable the pilot to maintain control and place the aircraft in a nose down attitude to attempt engine re-light. The system will also supply fuel pressure via an emergency DC Fuel pump to the engines during an aircraft AC failure. This is to compensate for the loss of fuel pressure caused by the aircraft fuel pumps going off line.
The system has two modes of operation,
1. If during flight a double engine flame out occurs the emergency power system will supply hydraulic power via the No 1 protected hydraulic system to the taileron actuators and also fuel pressure to the engines.
2. If during Flight a double Integrated Drive Generator failure occurs the emergency power system will supply fuel pressure only. In these circumstances the hydraulic systems are still operational and are therefore unaffected.
The battery provides 28V DC to power the following,
The Electro-Hydraulic Pump is located in the left hand secondary power supply compartment. It consists of a variable delivery, positive displacement pump driven by a DC electric motor. The pump is of the axial piston type and a pressure sensing control mechanism provides a variable output flow depending on aircraft system demand. The pump is of similar design to the main aircraft hydraulic pumps.
An Emergency DC fuel pump is mounted in fuel cell No 6. The pump delivers pressurised fuel from the rear fuselage tanks via a feed system to the engines during certain emergency conditions. This allows one engine to be relit subsequent to a failure of the aircraft fuel boost pumps due to AC power failure.