ENGINE START CONTROL SYSTEM
to the cockpit turbine inlet temperature indicator.
The second circuit supplies the temperature datum
Learning Objective: Recognize operating
control with temperature signals for the electronic
fuel trimming circuit. As the gases heat the
parameters and characteristics of aircraft
thermocouples, they generate an electromotive
engine starting systems.
force that goes to the cockpit indicator and
In this section, you will learn about engine
the temperature datum control. Because the
starting, engine ignition, and engine fuel tempera-
thermocouple connections are in parallel, the
ture starting systems. By combining these systems,
signal they send is the average temperature of the
thermocouples. If one parallel circuit fails, the
you will understand how they interrelate. The
engine start control system covered in this section
other circuit continues to operate normally.
is the one found in the P-3C aircraft.
TEMPERATURE DATUM SWITCHES
The left and right engine temperature datum
(TEMP DATUM) switches are on the engine con-
trol panel in the cockpit. Each switch has AUTO
Major components of the engine start control
and NULL positions. When the switch is in AUTO,
system include the air turbine starter, the
the engine RPM is above 94 percent, and the engine
speed-sensitive control, the ignition exciter, the
coordinator is above 66 degrees, the temperature
engine fuel pump and filter, the fuel control, the
datum control compares the turbine inlet tempera-
fuel nozzles, the fuel control relay, the starting
ture to a reference temperature. If the temperatures
fuel enrichment valve, the temperature datum
differ, the temperature datum control electrically
signals the temperature datum valve to bypass
more or less fuel from the engine to bring turbine
table 5-1 as you read about these components.
inlet temperature to the selected value.
If the electronic fuel trimming circuit malfunc-
tions, position the TEMP DATUM switch to
Air Turbine Starter
NULL. The circuit de-energizes and the fuel
control, through movement of the power lever,
You have learned that the air turbine starter
controls turbine inlet temperature. Overtempera-
is pneumatically driven and mechanically
ture protection is not available.
connected to the engine through a gearbox. The
air turbine starter operates on compressed air
internal auxiliary power unit (APU), or bleed air
REVIEW SUBSET NUMBER 3
from an operating engine. The compressed air
Q1. List the four positions of the E-2 aircraft
goes through a manifold, an engine isolation bleed
air valve, and a starter control valve into the
starter's turbine. The engine start switch, located
in the cockpit, controls the opening of the starter
Q2. When is the temperature datum control in
control valve, which allows compressed air to
enter the air turbine starter. The speed sensitive
the temperature controlling range?
control, through a holding solenoid, holds the
engine start switch on until engine speed reaches
65 percent RPM.
Q3. At what RPM is the engine limiting
The speed-sensitive control, located on the
Q4. Thermocouple leads are made of
engine, contains internal switches that activate at
three predetermined intervals. These intervals are
relative to the engine's normal speed--16 percent,
65 percent, and 94 percent of engine RPM.
Activation of these switches controls many
Q5. List the main components of an engine
operations in the engine start cycle.