Idle Operation
The EEC automatically selects ground minimum idle, flight minimum idle, and approach
idle. Ground minimum idle is selected for ground operations and flight minimum idle is
selected for most phases of flight. Approach idle is selected in flight if flaps are in landing
configuration or engine anti–ice is ON for either engine. At the same airspeed and
altitude, N1 and N2% RPM will be higher for approach idle than for flight minimum idle.
This higher% RPM improves engine acceleration time in the event of a go–around.
Approach idle is maintained until after touchdown, when ground minimum idle is selected.
In flight, if a fault prevents the EEC from receiving flap or anti–ice signals, approach idle
schedule begins below 15,000 feet MSL.
Option - Takeoff bump thrust
Takeoff bump thrust is available when increased thrust is needed for takeoff, above the
normal maximum takeoff thrust setting. When selected using the FMC N1 LIMIT page,
takeoff thrust is increased by either the flight crew or the autothrottle positioning the thrust
levers to set N1 to the reference N1 bug. Bump thrust applies only to the takeoff rating;
maximum climb, maximum continuous and go-around thrust ratings are not affected.
Airplanes equipped with a takeoff thrust bump have a reserve thrust capability which is
greater than the standard values listed under the EEC Normal Mode listed above.
Use of this reserve thrust capability is intended for emergency use only in the event of
wind shear or impending ground contact. FMC selection of takeoff bump thrust can be
configured as either “Bump Option” or a “Full-Rate Option.” When configured as a FMC
“Bump Option”, the default takeoff rating is lower then takeoff bump, and the takeoff bump
must be activated via the FMC-CDU. With this “Bump Option” configuration, assumed
temperature engine derates are not available from the bump. When configured as a FMC
“Full-Rate Option”, the default takeoff rating is the takeoff bump. With this full-rate option,
the assumed temperature engine derate method may always be used. With this “Full-Rate
Option” configuration, the ability to select the lowest normally offered takeoff fixed derate
is lost.
