Following the Boeing 767 (B767) aircraft's second flight after
scheduled maintenance, a pilot maintenance log entry noted that the
cabin door L1 slide bustle was hanging down. A line engineer on
duty examined and certified that the cause was a weak cable spring.
The discrepancy was then placed on deferred maintenance as it was
not considered to be an airworthiness defect. The following day,
prior to departure, the cabin crew of the aircraft reported the
cabin door L1 (forward entry door) bustle was lower than normal.
Inspection revealed that the girt bar was not attached to the
escape slide girt bar carrier, but was instead in the stowed for
maintenance position, rendering the slide inoperative. The line
engineer on duty correctly installed the girt bar, thereby
returning the L1 door escape slide to operational capability. No
maintenance log entry was made concerning the discrepancy, or of
the corrective actions.
When maintenance personnel conferred following the L1 door
escape slide girt bar rectification, a decision was made to inspect
the remaining aircraft door slides for condition. The inspection
revealed that cabin doors R1 (forward service door), R2 (rear
service door), and L2 (rear entry door) emergency escape slides
were inoperative, with the door girt bars also in the stowed
position.
Consequently, during 8 and 9 April 2001, the aircraft was
operated seven sectors with four cabin door mounted escape slides
inoperative. During 9 April 2001, the aircraft was operated one
sector with three slides inoperative. If required, the cabin crew
could not have successfully activated the escape slides of those
doors, nor the automatic opening of the doors during those flown
sectors.
B767 cabin door configuration
The cabin door configuration of this aircraft was one forward
door and one rear door per side. The doors were arranged in
sequential order, numbered from the nose of the aircraft. The doors
were identified as per side by lettering indicating `L' for the
left side of the cabin looking towards the nose, and `R' for
right.
Previous maintenance
Further investigation revealed that the last known maintenance
of the escape slides, bustles, and girt bars of doors R1, R2, L1,
and L2 was performed sixteen days earlier, during a recent 2C
scheduled maintenance check. The C check on B767 aircraft, a major
scheduled maintenance check, was performed at 6,000 flight hour
intervals, and normally planned for 30 days elapsed time (total
days out of service). The incident aircraft was out of service for
the 2C check for 41 days.
During that maintenance, the escape slide bustles of doors L1,
L2, R1, and R2 were disabled and removed by an apprentice Aircraft
Maintenance Engineer (AME) under supervision, to allow repainting,
other maintenance in the area, and zone inspections. During
disabling and removal of the bustles, the girt bars were removed
from the carriers and stowed using special straps on the side of
the slide packs.
Door mounted slide normal operation
During normal operation, door arming by the cabin crew would
lock the girt bar carrier to the aircraft floor fittings. The girt
bar would engage the girt bar carrier, whether the slide was ARMED
or DISARMED. The ARMED or DISARMED status of the door-mounted
slides was indicated to the cabin crew by witness marks, visible at
floor level. The arming witness marks reflected the girt bar
carrier position in the floor fittings, not the location of the
girt bar itself. Thus, the ARMED indication presented to the cabin
crew was the same, whether the girt bar was properly installed in
the girt bar carrier or stowed on the slide pack.
When a cabin door was unlocked from the inside while in the
ARMED condition, the girt bar (engaged with the carrier) initially
caused the slide to release from the door. The unladen door would
then open under the influence of heavy springs. The subsequent
action of the slide pack falling out of the doorway activated the
slide inflation sequence.
Door mounted slide operation with girt bar stowed on the
slide pack
With the girt bar stowed on the slide pack, each door would have
unlocked if opened from the inside in the ARMED condition, however
the girt bar carrier would have remained (disconnected from the
door) in the floor fittings. The slide pack would have remained
intact and attached to the door. The doors would have needed
opening manually (as though disarmed), as the emergency
auto-opening feature of the cabin door, before slide deployment,
relied on the weight of the slide releasing from the door as the
door was unlocked. Manual operation was only applicable if the
slide had released from the door, but failed to inflate.
Maintenance documentation (removal of the escape
slide)
The maintenance facility's normal practice was to use the
company's Maintenance Supplementary Report (MSR) form to document
tasks involving removal of items from an aircraft for access and
inspection purposes. The removal of four escape slide bustles was
noted on the aircraft's MSR form for the maintenance event,
however, the apprentice who completed the removal of the bustles
did not personally document details of the removal in the MSR form.
The apprentice did annotate on a Supplementary Report Card (SRC)
the bustles removal in accordance with the company's maintenance
manual procedures.
The senior Licensed Aircraft Maintenance Engineer (LAME)
responsible for the cabin during the scheduled inspection, and
supervising the apprentice, stated that his normal practice was to
annotate in the Heavy Maintenance Discrepancy Report (HMDR) form,
deactivation of the escape slides. On that occasion, he noted the
removal of the slide bustles but not the deactivation of the escape
slides. There was no evidence that a hand-over log was employed
documenting the work.
Installation of the escape slide
Following completion of the zone maintenance in the area of the
slides, another apprentice was tasked with reinstallation of the
slide bustles to allow the aircraft to be moved outside for engine
runs. The engine runs were normally performed three days before
maintenance check completion to identify and resolve any engine
related anomalies. Normal Heavy Maintenance practices required the
slides be installed and operational during engine runs. The slide
bustles, including the girt bars, were not completely installed
because of on-going work in the area. It was reported that the
aircraft's inspection completion was behind schedule by
approximately one week.
The bustles of the four doors were partially installed by a
second apprentice and annotated on the SRC as completed in
accordance with the applicable maintenance manual section. The
installation was not completed as per the maintenance manual at
that time, as the girt bars were still stowed and the inflation
cylinder regulator safety pins were still fitted. No other
documentation was utilised to annotate the partial
installation.
Post maintenance inspection of the escape
slide
According to aircraft maintenance documentation, two LAMEs
conducted independent inspections of the slides following
maintenance to the slide during the scheduled check. Both conducted
and certified the inspection with the knowledge that slide R1 was
not yet fully operational. An independent inspection was not
carried out for maintenance actions performed on escape slide
bustles at the L1, L2 and R2 doors. No additional entries were
annotated in the aircraft documentation to note the non-operational
condition of the slides.
Prior to release from the 2C check, the B767 Flight Readiness
Schedule, an engineering check list, was used to ensure aircraft
completion. The check list contained a requirement to check
over-wing emergency exits for correct arming, but for door mounted
slides the inspection was only to verify that the escape slides
were installed.
Human factors issues
The LAME responsible for cabin certification during the 2C
check, reported that this was the first time he had been tasked
with such duties.
