MD-11 Flight Crew Operations Manual
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Engines -
Description and Operation
Eng.10.6
Actuation of the ENG IGN OVRD switch will bypass the MSC to simultaneously
provide power to both the A and B ignition systems for as long as the override is
selected. Selection of the ENG IGN OVRD switch provides power to the ENG
START switches to allow starter assisted air starts.
The ignition system has no time limit although excessive use will reduce ignitor
service life.
Two IGN TRANSFER switches on the upper maintenance panel allow ignition
transfer for engines 1 and 3 as follows:
• Ignitor B power source can be changed from the R emergency ac bus to
the L emergency ac bus, or
• Ignitor A power source can be changed from the L emergency ac bus to
the R emergency ac bus.
The switches are intended for use on the ground, prior to engine start, if system A
ignition is inoperative.
If the engine flames out, the MSC will turn on the respective ignitor for an engine
relight attempt. The ignition lightning symbol will be displayed during the auto
relight attempt.
Starting System
The starting system consists of an air turbine starter and a starter air valve.
The starter air valve is a butterfly valve that controls the flow of air (supplied by
APU, engine crossbleed, or ground power unit) to the engine air turbine starter. It
is powered from the battery bus.
The starting system is energized by pulling the ENG START switch on the
forward pedestal. Pulling out the ENG START switch will:
• Energize a coil that holds the switch out.
• Energize the engine starter valve open which will illuminate the light in
the switch.
• Supply power to the ECU.
Normal engine starts can be done with pneumatic pressure greater than 25 psi.
Optimum engine acceleration to idle and lowest EGT peak is obtained with a
pressure of 40 psi and above. Conditions may necessitate the use of pressure
below 25 psi. Extended time to idle and higher EGT peaks may result. Under these
conditions, the start cycle must be closely monitored so that action can be taken to
prevent a hung or hot start.
If starter air pressure drops during start, the START AIR PRES LO alert will
appear at 25 psi.
October 02, 2006
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