During door disarming of the Boeing 747SP aircraft after landing, the cabin crew notified the flight crew that although the levers of main cabin doors L3 and L4 had been moved to the disarm position, the doors failed to disarm. The captain directed the flight attendants to remain at the doors and advised ground engineering to limit catering access. The flight engineer was directed to ensure a safe disarm. The flight engineer found the door slide girt bars still partially engaged into the girt bar receivers. He then used tools to safely disengage the girt bars and disarm both doors.

Line maintenance personnel examined the doors and, after repeated arm/disarm cycles, were unable to duplicate the anomaly. The flight crew elected to continue operations with additional precautions, referred to as "girt bar disengagement inspection", taken to ensure the operational status of the doors. That action included the flight engineer confirming arming of the doors before departure and disarming following arrival. That precaution was taken to prevent inadvertent activation of the slide during normal door opening.

Following landing at the next sector airport, the cabin crew again could not disarm main cabin doors L3/L4. The flight engineer again used tools to physically disengage the girt bars from the girt bar receivers in order to disarm both doors. A maintenance entry was made in the aircraft technical log requiring visual confirmation of the door arming/disarming during each transit. The Master Minimum Equipment List (MMEL) was reviewed and the aircraft returned to service without restrictions.

Over the next three days, the aircraft completed twelve sectors with the girt bars of main cabin doors L3/L4 requiring the girt bar disengagement inspection. Following the last of those twelve sectors, the operator's maintenance department issued an Authority to Proceed (ATP), stating a requirement that the doors not be opened from the outside or left unattended until maintenance personnel confirmed the girt bar was completely disengaged from the girt bar receiver. The ATP was applicable for two sector overwater flights only. Upon completion of those sectors, maintenance personnel corrected the girt bar discrepancy by adjusting the escape slide skirts and returned the slides and doors to normal operation.

B747SP main cabin door configuration

The aircraft's main cabin was configured with four doors per side. The doors were arranged in sequential order, with numbering starting at the nose of the aircraft. The doors were identified by lettering indicating `L' for the left side of the cabin looking towards the nose, and `R' for right.

Discrepancy history of main cabin doors L3/L4

Five days prior to girt bar disengagement inspection implementation, the technical log noted an entry that said, "L4 unable to move mode select to auto". Corrective action stated that an obstruction was found in the girt bar and had been removed, with door operations now normal.

Four days prior to disengagement inspection implementation, the technical log noted an entry, "Door L4 selector switch handle will not engage arm position or sweep seal is remaining outside the door sill". Corrective action stated that the lower skirt aft side was found fouling the girt bar, and that the skirt appeared to be distorted. The skirt was repositioned and operations reported as normal.

Two days prior to girt bar disengagement inspection implementation, the technical log noted an entry, "L4 lower bustle has skirt damage". Corrective action stated that the lower bustle sweeper seal was trimmed.

Door mounted escape slide normal operation

When the crew selected the door to the armed mode (automatic), the girt bar mechanism positioned the girt locks into the floor brackets. As the door handle was moved towards the open position (at approximately 45 degree's of rotation) it lifted the lower gate and girt lift mechanism. When the girt lift mechanism separated from the girt lock, the girt bar springs protruded, locking the girt bar to the floor brackets. The escape pack was then attached to the floor. The door was then forced open by use of an emergency pressure cylinder. That opening of the door, with the girt still attached to the aircraft, caused the slide to release from the door and initiate the inflation sequence of the slide.

Authority to proceed

The Civil Aviation Safety Authority (CASA) issued authorisation under Civil Aviation Regulation (CAR) 37 to delegates of the operator permitting those individuals to authorise continued operation of aircraft with known discrepancies. That authorisation was designed to address aircraft discrepancies not covered by the MMEL or other documentation and was subject to the conditions outlined in the ATP. Such discrepancies must not constitute a concession against an operational requirement of a CAR nor conflict with the design standard of the aircraft. An authorised delegate of the operator who annotated the discrepancy, signed the ATP. A copy of that ATP was provided to the local CASA office.

The crew of a departing Boeing 737 (B737) reported that as they were climbing to 5,000 ft on a standard instrument departure from runway 27 at Melbourne, they saw an arriving B737 on descent in their 12 o'clock position, passing from right to left. The departing aircraft's traffic alert and collision-avoidance system indicated that there might have been less than the required radar separation standard of 3 NM between the two aircraft. The crew was not alerted by air traffic control regarding the arriving B737.

Radar data and air traffic control automatic voice recordings were reviewed to establish the sequence of events. The investigation found that the Departures controller had assigned responsibility for separation to the pilot of the arriving B737, which was tracking for left downwind runway 34. The transmission from air traffic control to the crew of the descending B737 included the statement "...clear of the 737 out to your left, descend to 3000".

Airservices Australia advised that the procedure was used when separating runway 27 departing aircraft from arriving aircraft tracking on left downwind for runway 34. The aim was to release the climb and descent restrictions of both aircraft as soon, and as efficiently, as possible. The procedure of one aircraft sighting and confirmed past the other aircraft was considered to be a legitimate technique in such situations.

Visual separation of air traffic may have been a valid method to use in those circumstances. However, the criteria for its application were clearly detailed in the Manual of Air Traffic Services (MATS) Part 4 Section 5. In particular, MATS 4.5.1.11 stated: "In circumstances where an aircraft has been instructed to maintain separation from, but not follow, an IFR aircraft, traffic information shall be issued to the IFR aircraft, including advice that responsibility for separation has been assigned to the other aircraft". The departing B737 was an IFR aircraft but was not provided with the required traffic information.

Sequence of events

As the crew of the Boeing 747-438 applied take-off thrust to begin a flight from Sydney to Los Angeles, a noise described as "similar to an engine stall" was heard by all on the flight deck. After an immediate check of engine parameters revealed no abnormal indications, the crew elected to continue the take-off and subsequently heard no similar noises.

During the climb phase of the flight, the Cabin Services Director advised the flight crew of a small area of damage to the right outboard trailing edge flap. The first officer then inspected the area and reported that he believed that the damage was the partial delamination of the composite flap section. All engine parameters, including vibration levels were subsequently rechecked and found to be normal. After discussions with ground maintenance personnel, the crew decided to continue the flight.

On landing at Los Angeles, inspection of the aircraft by ground staff revealed the loss of both left and right combustion fairing panels from the number-three engine. Indentation and scraping damage was found on the internal surfaces of the bypass airflow nozzle behind the combustion fairing. The damage to the trailing edge flap was limited to the area immediately behind the number three engine.

On the morning following the departure, while conducting a routine runway inspection, Sydney airport staff recovered four large aircraft parts from the undershoot area of runway 34L. Further items, including small fragments of composite material, clevis couplings and metal strips, were subsequently found during a walking inspection of the runway undershoot area.

Inspection of the items by the operator's engineering personnel confirmed the items to be the missing fairing panels from the Boeing 747.

Technical examination

The ATSB examined the items recovered from the runway to determine how they separated from the aircraft. The left and right combustion fairing panels were both extensively damaged, with the larger right panel having broken into two sections. Both panels showed evidence of having forcibly struck the internal surfaces of the engine nozzle assembly before being ejected to the rear by the bypass airflow of the accelerating engine.

The fairing panels were mounted onto the engine by a row of three hooks that engaged with recessed pins on the upper panel section. When mounted, the panels latched together at the base of the engine using an adjustable hook and clevis. A study of the fairing panel mounting and latching points showed evidence that the right panel was not engaged with the upper panel at the time it was ejected from the engine. All three mounting hooks were undamaged and showed no sign of having been forcibly pulled away from the upper fairing pins. In comparison, both latches and the forward hook from the left panel showed damage consistent with the connections being overloaded and pulled apart.

Damage to the trailing edge section of the right centre wing flap was consistent with an impact with the ejected combustion fairing panels. Witness marks pointing to a forceful impact surrounded the area of damaged composite material along the edge of the flap section.

Technical analysis report number 18/01 refers to this part of the investigation and is available on the ATSB website or from the Bureau on request.

Assembly examination

The engine from which the fairing panels were lost was a Rolls-Royce RB211-524 model. The panels were part numbers UL26239 (right) and UL26237 (left), with the manufacturers illustrated parts catalogue identifying both items as made to incorporate service bulletin RB.211-72-4647. The manufacturer introduced bulletin 4647 in 1977 to combat combustion (gas-generator) fairings detaching because of incorrect fitting.

Examination of the fairing assembly during installation confirmed that it was possible to place the fairing panels in position around the engine without engaging the upper mounting hooks. The clamping action of the interlocking fire seal along the rear edge of the fairing panels allowed the items to stay in position without the support of the hooks. Latching action between the fairing panels was also unaffected.

When the panels were installed incorrectly, inspection of the upper connection points clearly showed a large gap between the upper and side fairings. Inspection of that area was difficult because of the restricted confines of the cold stream duct surrounding the panels. Platforms for use within the cold stream duct were available, however comment from maintenance personnel suggested they were rarely used. Testing the platforms showed a degree of instability in use and further restricted the access to the lower areas of the duct. Latching the fairing panels together with the platforms in place was difficult. The time taken to load, fit and then unload the platform sections, was also cited as a problem for maintenance personnel. The Boeing maintenance manual for the 747-400 aircraft requires the use of access platforms within the cold stream duct.

Maintenance records

Documents provided by the operator showed that the flight from Sydney to Los Angeles was the first flight of the aircraft following release from scheduled maintenance. That maintenance (described as an `A' check) involved several tasks that required the removal and reinstallation of the combustion fairing panels from all engines. A further review of the records relating to the work conducted on the number-three engine showed that a "panels and fairings final fitment check" line item was present in the work instructions. That action was signed-off as completed by a licensed maintenance engineer. The engine had been subsequently ground run for five minutes at idle speeds, with no noted anomalies. Check sheets for the examination of engines after ground running incorporated eight specific inspections, including a check for correct installation and latching of the fairing panels. Those checks had also been signed-off as being satisfactorily completed.

Fitting the combustion fairing panels to RB211-524 engines was the subject of several work instructions produced by the operator. The instructions referred to the operator's minor maintenance manual and the manufacturer's maintenance manual, which provided both written and visual illustrations of how the panels were to be fitted. The need for inspection of mounting hook engagement after installation was also clearly stated, with clear warnings of the potential for incorrect installation and the damage that may result. Requirements for the use of INA (integrated nozzle assembly) access platforms were also included in the latest revisions of the manual, which were issued on February 18, 2001.

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.

A Boeing 737-476 aircraft was in the final stages of preparation for an 0810 EST scheduled departure from Melbourne. It was the aircraft's first flight of the day. The ground engineer had completed the pre-flight and other assigned pre-departure tasks. There was little else for him to do prior to his duties for the pushback which included assisting the ramp towmotor driver to connect the towbar to the towmotor and walk out with the aircraft. The flight crew had started the Auxiliary Power Unit (APU) and were completing the Before-Start Checklist in preparation for pushback.

The towbar was delivered by ramp personnel at 0803 and was connected to the aircraft nose landing gear by the engineer. At 0805, cargo loading was still in progress in both the forward and rear cargo bays. The engineer was aware that the towmotor should only be driven by the rostered ramp towmotor driver who was still involved with the loading of the aircraft. Concerned that the departure of the aircraft was about to fall behind schedule, he decided to connect the towmotor to the towbar himself.

The engineer moved the towmotor close to the towbar, but stopped when he noticed that the towbar was at the wrong height for connection. He then left the cab, with the towmotor's engine running, to correct the towbar height. While re-adjusting the towbar, he heard the towmotor engine shut down. He reported that he then climbed back into the towmotor, restarted the engine, and attempted to drive forward the remaining 10 cm required for connection.

At that time the towmotor appeared to him to move forward "...relentlessly..." and collided with the aircraft. He indicated that he had applied the brakes and selected reverse gear, without success. He then vacated the cabin of the towmotor across the deroofed front of the vehicle.

The flight crew indicated that they heard and felt a "...big thump..." which continued and shook the aircraft for about 4-5 seconds. The pilot in command advised the cabin crew to "...brace..." and noticed the towmotor wedged under the aircraft nose. He assessed that there was no danger to the aircraft and ordered that the passengers be disembarked normally through the forward door via the aerobridge, which was still in place. He shut down the flight deck systems, set the park brake, but left the APU running to power the hydraulics and disembarked to view the extent of the damage.

The aircraft had sustained substantial damage to the radome, forward pressure bulkhead, forward fuselage skin and nose landing gear doors.

The engineer had been employed by the operator for more than 26 years and was highly regarded as a Licensed Aircraft Maintenance Engineer (LAME) and company employee. Supervisors indicated that the engineer was very cooperative and willing to assist ramp staff at all times to despatch aircraft on schedule.

At the time of the accident, the engineer was on the first day of a shift rotation, having been off-duty for the preceding three weeks.

The engineer held a current ramp driver's licence and had considerable recent experience towing aircraft using another towmotor type. He had last driven the accident towmotor about 6 months previously.

Towmotor and towbar information

The towmotor was designed specifically for B737 use. It had last undergone maintenance action on 5 March 2001. According to the operator's maintenance staff, the accident towmotor was used only on the ramp as it was unsuited for maintenance purposes. It was the only one of its type used by the operator.

The design of the towmotor was such that the towbar and connection point at the front of the vehicle could not be seen from the driver's seated position. Towbar connection was a two-person operation. Any attempt by a single person to connect the vehicle and the towbar, involved the driver having to stand up and lean over the steering wheel to view the operation. From a standing position, it was possible for the driver to place a foot over both the accelerator pedal and the brake pedal simultaneously.

The cabin forward structure had been torn upwards and rearwards during the initial contact with the aircraft. The rear left corner of the cabin structure was forced down through the vehicle's upper body panel by the weight of the aircraft's nose. Inspection of the towmotor found no mechanical fault that could have contributed to the accident.

The towbar for the Boeing 737 aircraft underwent a complete service on 28 March 2001 and had been correctly connected to the nose landing gear strut of the aircraft. Impact from the towmotor sheared the towbar's rear shear pin, which allowed the bar to swivel out of the way, pivoting on the remaining shear pin, as the towmotor drove forward into contact with the aircraft. The towbar was inspected and found to have been serviceable at the time of the accident.

Aircraft pushback procedures

Aircraft pushback procedures at the time of the accident were contained in the operator's Ramp Standard Operating Procedures (SOP). The SOP stated that the towbar was to be delivered to the aircraft by ramp personnel, then connected to the nose landing gear by the engineer. Connection to the towmotor was to be accomplished by the rostered ramp towmotor driver, with the assistance of the engineer. Line engineers normally towed the aircraft for maintenance purposes only. In addition, the SOP stated:

"Use a marshal (usually the engineer) when manoeuvring for hook up to the tow bar when it is attached to the aircraft. Do not stand up to see the hitch point."

The operator's Engineering and Maintenance Procedures Manual stated that:

"...Prior to push-out operation, the engineer will...(2) Connect the towbar and towmotor by front or rear connection as appropriate..."

A ramp driver's licence was valid for a 12 month period. Renewal was devolved to airline operators by the airport owner and consisted of a written examination covering rules, procedures, airfield speed limits and ATC communications and light signals. No driver refresher training was conducted. Company towmotor drivers who were qualified to tow aircraft on the ramp were to conduct towing operations in accordance with their respective company SOP.