CH12422 SEA KING
23 June 2000
150 NM South of Honolulu, Hawaii, USA
Approximately 25 minutes after launching from HMCS
PROTECTEUR, a hot Main Transmission Gearbox (MGB) was
noted. As the crew returned to land, cockpit indications
were assessed as severe enough to require a controlled
ditching. After the crew successfully egressed uninjured,
the aircraft sank, suffering "A" category
damage.
The investigation eliminated all possible MGB malfunctions
as causal to this accident with the exception of an
over-temperature condition similar to previous 21000
Series MGB overtemps. Only this inherent overtemp condition,
that previously had neither been satisfactorily explained
nor caused any known damage, offered a plausible explanation
of the indications experienced by the crew.
The CF Sea King fleet has, since 1994, documented a
phenomenon of inherent overtemp in all regimes of operation
in which MGB temperature rapidly increases above the
normal operating range up to and exceeding the maximum
operating limit. Through informal trial, the "#1
SSL Procedure" was developed in which the #1 Speed
Select Lever was retarded to the ground idle position.
This action was known to work with not only CF Sea Kings,
but also with USN Sea Kings despite the lack of the
original equipment manufacturer's engineering data to
support the theoretical cause of internal overtemp conditions.
CF flight safety data showed that in all 27 overtemp
occurrences when the #1 SSL procedure was employed,
it was 100% effective in not only arresting further
MGB temperature, but also in reducing that temperature
regardless of maximum value reached. Furthermore, a
significant number of these occurrences indicated that
MGB pressure fluctuations were evident with the overtemp
indications. Despite this data, the procedure remained
a discretionary one in the Sea King AOI; it was not
included for reference in the Pilot Checklist.
Analysis concluded that had the #1 SSL procedure been
mandated for use in instances of MGB overtemp, it is
highly probable that the high temperature condition
and all its associated indications would have been reduced
or eliminated, thus reducing the severity of indications
from Land As Soon As Possible to Land As Soon As Practicable.
Given lack of guidance and resulting non-use of the
#1 SSL procedure, the crew decided to enter the hover
with only Land As Soon As Possible criteria in evidence.
Once in the hover, significant pressure fluctuations,
strong welding-like metallic odours and radiant heat
from the MGB developed. These new indications led the
crew to conclude that MGB failure was imminent. Had
the aircraft continued (as suggested by the Land As
Soon As Possible criteria in the AOI and checklist)
instead of coming to the hover, the aircraft may have
successfully returned to land on the nearest flight
deck.
As a result of this accident, the AOI and Checklist
were updated to accurately reflect the mandated use
of the #1 SSL procedure in instances of inherent MGB
overtemp. The requirement for this procedure has subsequently
been overcome by events with the introduction of the
new 24000 Series MGB. It was further recommended that
emergency procedures be reviewed to give aircrew specific
direction with respect to the notion of coming to the
hover for MGB emergencies.
Other preventative measures included staff work to
address both the experience levels and training offered
to HELAIRDET senior NCMs. 12 Wing also initiated a training
program to ensure that line maintenance personnel are
aware of torquing procedures in accordance with the
CFTO and that the techniques are uniformly applied.
Finally, due to some confusion over ditching and egress
SOPs, it was recommended that the AOI and Pilot Checklist
be amended to give aircrew a logically flowing sequence
of reactions to water operations emergencies. It was
also recommended that current aircraft egress training
be reviewed to ensure that correct procedures are adequately
emphasized and that the hazards posed by non-standard
actions are understood by all aircrew.
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