Engines - Vibration Procedures

BOEING Flight Operations REVIEW
A MESSAGE TO FLIGHT CREWS FROM THE BOEING COMMERCIAL AIRPLANE GROUP
727-11
737-13
747-11
757-10
767-10
December 10, 1990
ENGINE VIBRATION PROCEDURES
Boeing continues to receive inquiries from operators regarding recommended procedures for high engine vibration. The following information summarizes the Boeing position on this subject.
Current FAR's require that AVM systems be installed in all large transport airplanes and, except for short periods allowed by the Master Minimum Equipment List (MMEL), they must be operative.
AVM limits, if any, are provided by the engine manufacturer in their engine Operating Instructions (O.I.). However, except in a few cases, the engine manufacturers have not defined "hard" AVM
limits, i.e. amber bands, red lines, lights or EICAS messages where crew procedures or an engine shutdown is required solely on the bases of high AVM indications and without other abnormal
engine parameters. Instead, the engine manufacturers have provided AVM operating "guidelines" which were used to provide AVM procedures on three crew and 737 airplanes. Currently, flight crews on 707, 727, 737, and three crew 747 airplanes monitor engine and system indications and take actions based on observed trends to prevent exceeding engine operating limits. This sometimes includes precautionary engine shutdowns. AVM indications are included as one of the engine parameters to be used in judging the condition of the engine. Relative changes in AVM readings, as well as absolute values, are used as a cue to cross-check other engine parameters to determine the procedure to be used. This requires a continuous monitoring or awareness of the AVM indications. With the introduction of EICAS equipped 757, 767 and 747-400 airplanes, procedures were re-evaluated and all monitoring functions were placed in EICAS. Only parameters with published
operating limits were programmed to generate crew alert messages or indications. Procedures were written so that flight crews are not required to monitor, analyze or troubleshoot engine indications to diagnose problems or initiate procedures. The EICAS monitors designated engine parameters and alerts the crew when published limits are exceeded. Flight crew procedures are accomplished in response to these alerts. On some of the EICAS equipped airplanes, an AVM "pop-up" is provided at a predetermined value. However, with exception of the Rolls Royce powered 757, there are no associated high AVM procedures in the Operations Manual. The reason for the "pop-up" is for crew awareness and for entry in the airplane log book for maintenance trend monitoring. No crew action is required for an AVM "pop-up" unless there are other abnormal engine indications in these airplanes.
Since there are no published or defined AVM limits on EICASequipped airplanes (except on Rolls Royce powered 757's), EICAS only indicates existing AVM values but does not generate crew
alert messages based on these values. Because of this and because there are no defined "high" AVM limits, flight crews are not expected to respond to AVM indications without other abnormal
engine indications. On airplanes with AVM procedures, flight crews should also be made aware that AVM indications are not valid while at takeoff power settings, during power changes, or until after engine thermal stabilization. High AVM indications can also be observed during operations in icing conditions. For the above reasons, Boeing proposes no changes to the AVM procedures on EICAS equipped airplanes unless the engine manufacturers provide "hard" (not guideline) AVM limits. Boeing recommends that the AVM system be used for long-term engine condition trend monitoring. This can be accomplished by the flight crew recording the AVM values in the airplane log book
during stabilized cruise or by automatic recording as appropriate. In line with the above, flight crews should be instructed, in the absence of published AVM procedures, not to shutdown engines due
to high AVM indications unless there are other abnormal engine indications or other engine limits are exceeded.