ENGINE MASTER CONTROL - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. HP Fuel Shut OFF Valve Control

A. General

HP and LP Fuel Valve Power Supplies ** ON A/C NOT FOR ALL

The HP fuel shutoff valve control is fully electrical (the HP shutoff valve is a part of the HMU described in Ref. 73-20-00). It is performed from the engine panel in the cockpit as follows :

opening of the HP fuel SOV :
it is controlled by the ECU : the ECU receives the commands from the ENG/MASTER control switch and ENG/MODE/CRANK/NORM/IGN START selector switch.
closure of the HP fuel SOV :
it is controlled directly from the ENG/MASTER control switch in OFF position (Ref. 73-20-00 and 80-00-00).

B. Valve Operation

HP Fuel Shutoff Valve Control ** ON A/C NOT FOR ALL

The FADEC control system contains two fuel shut-off means, which act through pilot valves to close the pressurizing valve :

(1) A fuel shutoff which is directly hardwired to the ENG/MASTER control switch.
This solenoid operated pilot valve is powered by the 28VDC.
It is closed when powered.

(2) When the main metering valve is positioned below a minimum fuel flow position : a mechanically operated pilot valve in the HMU closes the pressurizing valve. This function is software logic inhibited to prevent operation at and above idle operation.
The fuel shutoff valve meets the following concepts.

The pressurizing valve does not actuate open with boost pressure (even if both pilot valves call for ON) until the HP fuel pump provides sufficient pressure to open it.
Loss of power supply does not lead to change the selected HP fuel shutoff valve position.
When HP fuel shutoff valve is selected closed (open) a spurious transient voltage to open (close) does not lead to a permanent opening (closure) of the fuel valve.
The cockpit commanded OFF coil has priority over the ECU command.

The cockpit control interfaces directly with the HP fuel shutoff solenoid. The valve contains a coil which operates the HP shutoff closed when energized. The solenoid is of a latching type. It latches either open or closed until a reversing signal is applied. The open function is a hydraulic trip with a magnetic latch. A closed signal has priority.

** ON A/C NOT FOR ALL

2. LP Fuel Shut Off Valve Control
(Ref. ATA 28)

A. General
The function of the LP fuel shutoff valve is to control the fuel supply at engine-to-pylon interface.
The valve is located on the engine supply system in the wing leading edge.

B. Valve Operation

HP and LP Fuel Valve Power Supplies ** ON A/C NOT FOR ALL

The LP fuel shutoff valve is controlled :

From the cockpit overhead panel by means of the ENG FIRE pushbutton switch
From the cockpit center pedestal by means of the ENG/MASTER control switch on engine control panel.

[Rev.10 from 2021] 2026.04.01 03:15:35 UTC