MD Helicopters MD Explorer - Fault Isolation; Main Rotor System Troubleshooting

CSP−900RMM−2MD Helicopters, Inc.
Rotorcraft Maintenance Manual
Page 101
Revision 15
18-00-00
VIBRATION AND NOISE ANALYSIS
FAULT ISOLATION
1. Main Rotor System Troubleshooting
Rotor Vibrations
The following troubleshooting procedures are a
brief summary of main rotor system faults,
which may be encountered (Ref. Table 101).
Troubleshooting tables should be used with
system schematics, electrical wiring diagrams,
serviceability checks and other detailed
procedures in this and other chapters of the
manual.
Table 101. Main Rotor System Troubleshooting
Fault Probable Cause Corrective Action Ref. Section
Unusual or excessive
vibration.
Main rotor blades damaged. Inspect blades. 62−10−00
Vertical or lateral vibration. Main rotor hub or hub
components damaged.
Inspect main rotor hub
assembly.
62−20−00
One−per revolution lateral
beat in hover and cruise.
May also occur on ground
during warm up or shutdown.
Defective main rotor hub
damper.
Replace defective main rotor
hub damper(s).
62−20−00
One−per revolution vertical
beat. Beat may appear
throughout entire flight
regime, becoming more
pronounced at higher
airspeeds.
Main rotor blades out of
track.
Track main rotor blades. 18−00−00
Autorotation rpm low. Blade pitch is too high
(Pitch links are too short).
Lengthen pitch links equally. 18−00−00
Autorotation rpm high. Blade pitch is too low
(Pitch links are too long).
Shorten pitch links equally. 18−00−00
Five−per revolution or
medium−frequency beat.
Worn pitch control bearings. Replace pitch links. 62−30−00
Lateral feedback (beat) in
cyclic control stick with no
longitudinal.
Rotor blades out of track. Track main rotor blades. 18−00−00
High frequency vibrations. Loose or defective
component in Anti−torque
System.
Inspect and replace damaged
components.
64−00−00
Erratic track and balance
readings.
Incorrect azimuth to sensor
gap.
Verify azimuth sensor gap. 62−30−00
Cross−over rotor instability
High vertical, roll or pitch
vibration felt by the pilot
which occurs between
35%−40% Nr on startup or
shutdown.
Cyclic control not centered at
low rotor speed.
Damaged flexbeam.
Perform flexbeam inspection.
Perform flexbeam inspection.
62−20−00
62−20−00
WARNING