Start Switch Functions
AMM - SDS 80-00-00
All
positions on the start switch represent several important functions toward
starting engines and controlling the mighty CFM’s in case of unwanted or
uncommanded decay in N2, and/or flame-outs. The start switch position is
monitored by the EEC (through the DEU’s) to activate the several functions and
related actions of the switch, together with igniter selection.
OFF
a. Neither igniter is activated when the start lever is in the cutoff position.
b. On ground, when N2 drops below 57% until 50%, both igniters will activate when the start lever is in the Idle position.
c. In flight, when N2 drops below Flight Idle RPM until 5%, both igniters will activate when the start lever is at Idle.
a. Neither igniter is activated when the start lever is in the cutoff position.
b. On ground, when N2 drops below 57% until 50%, both igniters will activate when the start lever is in the Idle position.
c. In flight, when N2 drops below Flight Idle RPM until 5%, both igniters will activate when the start lever is at Idle.
GRD
a. The engine bleed valve (solenoid) is commanded to close the valve.
b. The starter valve opens.
c. On ground, the selected igniter(s) will activate.
-----Powered by Xfr bus 1 for engine #1 left igniter, AC stdb bus for the right igniter.
----- Powered by Xfr bus 2 for engine #2 left igniter, AC stdb bus for the right igniter..
d. In flight, both igniters will activate.
----- You do not want to be bothered by a failed selected igniter when you need to start an engine in-flight. There must be a reason why you want to start a shut-down engine like a greater problem on the (only) operating engine.
e. The EEC is powered from its XFR bus (1 for eng #1, 2 for eng #2) below 15% N2 where after an AC alternator mounted on the gear box takes over;
-----> 15% N2 (gearbox RPM) it’ll produce enough AC power to operate the EEC.
----- On a battery start you won’t see EGT, FF, Oil press & oil temp until the EEC becomes powered after reaching 15% N2.
f. ECU (APU) receives a signal to open the APU IGV’s.
----- To provide maximum air capacity and pressure for starting.
g. At 56% N2, the starter switch is commanded to move to the OFF position. (AMM says 55%)
----- This is the AUTO position with newer switch features.
a. The engine bleed valve (solenoid) is commanded to close the valve.
b. The starter valve opens.
c. On ground, the selected igniter(s) will activate.
-----Powered by Xfr bus 1 for engine #1 left igniter, AC stdb bus for the right igniter.
----- Powered by Xfr bus 2 for engine #2 left igniter, AC stdb bus for the right igniter..
d. In flight, both igniters will activate.
----- You do not want to be bothered by a failed selected igniter when you need to start an engine in-flight. There must be a reason why you want to start a shut-down engine like a greater problem on the (only) operating engine.
e. The EEC is powered from its XFR bus (1 for eng #1, 2 for eng #2) below 15% N2 where after an AC alternator mounted on the gear box takes over;
-----> 15% N2 (gearbox RPM) it’ll produce enough AC power to operate the EEC.
----- On a battery start you won’t see EGT, FF, Oil press & oil temp until the EEC becomes powered after reaching 15% N2.
f. ECU (APU) receives a signal to open the APU IGV’s.
----- To provide maximum air capacity and pressure for starting.
g. At 56% N2, the starter switch is commanded to move to the OFF position. (AMM says 55%)
----- This is the AUTO position with newer switch features.
CONT
a. On ground, activates the selected igniter(s) when the start lever is at Idle.
b. In flight, activate both igniters when N2 drops below idle also with the start lever at the Idle position.
c. Selected for;
------Take-off.
------Landing.
------Before TAI is selected.
FLT
a. Activate both igniters.
b. Selected for;
------ Adverse weather.
a. Activate both igniters.
b. Selected for;
------ Adverse weather.
AUTO (when installed)
a. Ignition is OFF.
b. Both igniters activate when engine start lever is in IDLE and:
------ An uncommanded rapid decrease in N2 occurs
------ On ground, N2 is between 57% and 50% or,
------ In flight, N2 is between idle and 5%.
c. Activates selected igniters when:a. Ignition is OFF.
b. Both igniters activate when engine start lever is in IDLE and:
------ An uncommanded rapid decrease in N2 occurs
------ On ground, N2 is between 57% and 50% or,
------ In flight, N2 is between idle and 5%.
------ Below 18000 feet altitude and flaps extended.
------ TAI is selected.
