Mr Roy King
Mr Gary Kendell
During the past two years Cormorant CH149907
has consumed a large number of tail rotor half hubs
and under specific taxi conditions exhibited excessive
vibrations that could not be duplicated or rectified
by applying procedures identified in the approved maintenance
program. Crews reported severe vibrations; however,
these unbalanced conditions referred to as “cobblestoning”
could not be verified through routine rotor analysis
diagnostic system (RADS) functional checks. In each
of these cases RADS was unable to detect the excessive
vibrations. This engineering/design condition has severely
restricted Cormorant operations, and continues
to this day.
Perplexed by the problem, Mr. Gary Kendell (Production
Supervisor Comox) and Mr. Ray King (Crew Chief Comox)
conducted an in-depth study of the issue and the associated
RADS procedures. Realizing that the “cobblestoning”
effect, while evident to the crew, did not register
on the RADS equipment under normal operations, they
proposed that additional measurements be taken utilizing
the standard RADS kit, albeit under an unused menu mode.
Using their extensive knowledge of the aircraft and
vibration equipment, the duo surmised that during the
“cobblestoning” phenomena, vibration readings might
be detectable using the 135 V1, 135 V2 screen on the
control and display unit. In an effort to prove their
theory, Mr. King arranged to have Cormorant 907
taxi under similar conditions to those noted when the
vibrations were detected. Once the “cobblestoning” became
evident Mr. King reverted to the 135 V1 and 135 V2 screen,
recording vibrations well beyond the allowable limits.
As many as nine readings were recorded, all in excess
of the allowable limit, even though these readings were
not evident on the normal RADS menu screen. Armed with
this previously unrecorded evidence, the investigating
team, supported by the Technical Airworthiness Authority,
is utilizing these new readings to assist in their ongoing
investigation. The capturing of this data provided the
first concrete evidence that clearly demonstrated that
the CH-149 Cormorant was susceptible to the “cobblestoning”
effect that had previously only been identified with
Merlin aircraft variants of the EH-101.
Mr. King and Mr. Kendell demonstrated concern and
effort well beyond the call of duty. Their work will
undoubtedly be a key factor in the ultimate resolution
of the CH-149 tail rotor half hub problem. They are
highly commended for their commitment and diligence
in ensuring the safety of flight for the entire Cormorant
community.
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