Boeing 787-8 - Page 749

787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Engines, APU -
Engine System Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 7.20.23
Airborne Vibration Monitoring System
[Option – GE engines]
The engine monitor unit tracks engine vibration levels. The vibration indications
are displayed on the secondary engine display. The vibration source indication
(N1, N2, or BB) is also displayed. If the vibration monitoring system cannot
determine the source, BB (broadband) is displayed for the affected engine.
Broadband vibration is the average vibration detected.
[Option – RR engines]
The engine monitor unit tracks engine vibration levels. The vibration indications
are displayed on the secondary engine display. The vibration source indication
(N1, N2, N3, or BB) is also displayed. If the vibration monitoring system cannot
determine the source, BB (broadband) is displayed for the affected engine.
Broadband vibration is the average vibration detected.
[Option – GE engines]
The airborne vibration monitoring feature is primarily intended to track rotor
imbalance, but is also a useful tool for isolating and determining corrective action
for engine anomalies. There is no certified vibration limit, but when a vibration
value of 4 units is reached, the secondary engine parameters are automatically
displayed and the digital vibration readout is displayed in reverse (black digits on
white background). Since there are no operating limits, there are no specific flight
crew actions (or procedures) based solely on vibration indication. High N1
vibration would most likely be accompanied by tactile vibration where as high N2
vibration may not be felt. Both N1 and N2 high vibrations may be accompanied
by anomalies in other engine parameters and usually respond to thrust lever
adjustment.
[Option – RR engines]
The airborne vibration monitoring feature is primarily intended to track rotor
imbalance, but is also a useful tool for isolating and determining corrective action
for engine anomalies. There is no certified vibration limit, but when a vibration
value of 4 units is reached, the secondary engine parameters are automatically
displayed and the digital vibration readout is displayed in reverse (black digits on
white background). Since there are no operating limits, there are no specific flight
crew actions (or procedures) based solely on vibration indication. High N1
vibration would most likely be accompanied by tactile vibration where as high N2
or N3 vibration may not be felt. N1, N2 and N3 high vibrations may be
accompanied by anomalies in other engine parameters and usually respond to
thrust lever adjustment.
Engine Failure Alert System
The engine failure alert system provides alerts when actual engine performance is
less than commanded engine performance during a part of the takeoff and for other
phases of flight.
February 15, 2010