DH8D, Manchester UK, 2016
DH8D, Manchester UK, 2016
On 14 December 2016, soon after a Bombardier DHC8-400 took off from Manchester, an unfastened engine access panel detached and struck and damaged the aircraft's vertical stabiliser before falling onto and alongside the departure runway. The Investigation found the panel had been left unsecured after routine overnight maintenance which required it to be opened and that this condition had not then been detected during the pilot-performed pre-flight external check. An identical event was found to have occurred to the same aircraft a month earlier. The Operator-provided pilot training on pre departure inspections was found to be inconsistent.
On 14 December 2016, an engine access panel fell from a Bombardier DHC8-400 (G-PRPC) being operated by Flybe on a scheduled international passenger flight from Manchester to Hannover soon after it took off in night VMC. The crew were unaware of this until after the flight had arrived at destination where damage to the vertical stabiliser was also found. The departure airport were then advised and the missing panel and pieces of its hold-open strut, which had remained undetected on and near the runway for over two hours, were only then recovered.
An Investigation was carried out by the UK AAIB. The access panel involved was found to have been the outboard main engine bay access panel on the left engine, one of two such panels on each engine, one on each side.
The aircraft's vertical stabiliser skin was found to have been punctured on both sides. Impact marks were also present on the stabiliser leading edge de-icing boot and both VOR/LOC antennas had sustained damage.
The panel was subsequently found in a grass area alongside the runway approximately 440 metres from the runway threshold and "sections of the panel hold-open strut were also recovered from the runway and adjacent paved areas in the same vicinity" (see the illustration below). All four latches on the recovered panel were in the closed position.
It was noted that the departure involved was the first flight of the day and that the aircraft had been remotely parked away from the gate used overnight. Whilst it was so parked, the operator’s contracted maintenance organisation had carried out a routine 'Daily Check' on the aircraft that included checking the oil level in the left engine which required opening the nacelle panel - which was subsequently lost.
Forty minutes prior to departure, the crew who were to operate the aircraft arrived at the gate to which it had positioned and 20 minutes after that, with 20 minutes remaining until the STD, the 45 year-old Captain - who had 7,120 hours total flying experience but only 142 hours on type after joining the Company five months previously - conducted the pre flight external check. As it was still dark, he used a torch to supplement the area lighting but "did not identify any issues with the aircraft". Airport CCTV footage of this inspection being conducted showed that it lasted three minutes in total and had included the access panel area being illuminated by torchlight.
The push back crew subsequently "conducted their own walk-around check of the aircraft, also identifying nothing of note" and the aircraft departed the gate on time and taxied to Runway 23R for takeoff. Once airborne, the apparently uneventful 90 minute flight to Hannover was completed.
Once the passengers had disembarked, the attending ground crew advised that a panel was missing from the left engine. Having inspected the aircraft, the crew then contacted Flybe Maintenance Control who in turn informed Manchester Airport Operations staff who then, over two hours after the aircraft had taken off from Manchester, conducted an inspection of runway 23R which led to the discovery of the missing panel and its attachments.
The Investigation found that an identical but previously unreported event had occurred in respect of the same panel on the same aircraft just over a month previously just after it had taken off from runway 22 at Belfast in darkness on the first flight of the day. In this case, the preceding overnight stop at Belfast had also involved the same Daily Check being carried out by a different contracted maintenance organisation to the one used at Manchester. On this occasion, the crew of another Flybe aircraft departing from the same runway 15 minutes later reported "a foreign object" on it and a runway inspection requested by ATC found the engine access panel 300 metres from the threshold of the runway. The panel was subsequently found missing after the aircraft it came from had arrived in Glasgow. This panel too had been found with all its latches closed and it was found to have caused damage to the left wing leading edge de-icing boot and the wing skin as a result of its detachment.
The Flybe response to the Belfast event had been to issue a 'Notice to Engineers' which required that "following completion of all work either an independent person carries out a walk-round inspection to verify all access panels are fitted/secure, or the certifying engineer must return after a notable period of time for a double check of the security of the disturbed panel security" and stated that "the independent person could be a technician or a pilot, and the notable period of time could be after completion of paper work". The Investigation found that this Notice "did not require the additional walk-round inspection to be recorded in the maintenance paperwork or the aircraft Technical Log". It also noted that Flybe 'Notices to Engineers' were not being copied to their contracted maintenance organisations and so the Manchester personnel were unaware of the previous Belfast event. In addition, a Flybe "expectation" that each item on the Daily Check Task Sheet would be signed for and the individual pages would each then be certified complete before the corresponding 'Daily Check completed’ entry was made in the aircraft Technical Log was done, and the Flybe procedure requiring that signed hard copies of the task sheets and Technical Log pages should then be posted to the their HQ, were being universally ignored.
It was found that the way in which the maintenance personnel in both events had inadvertently not secured the access panel they had had to open to accomplish the oil check was considered in some detail. It was concluded that in the absence of a AMM procedure detailing how this should be done, it was found from interviewing contractor engineers at both Belfast and Manchester that a common technique was being used to secure the engine access panel which meant it was occasionally possible for the panel locking pins not to be engaged in the receiving fixtures on the nacelle side. Once this had happened, the only evidence of the unlatched condition would be a very small gap between the access panel and the surrounding nacelle panels which would not be easily noticed when on steps looking down from above in darkness and relying on a head torch to supplement area lighting. It was also observed that the difficulty in seeing any gap "would have been further exacerbated on the incident aircraft as the surrounding panels were painted purple rather than white, providing much less contrast to the shadow cast by the access panel". This situation was reproduced in trials and demonstrated by photographic evidence in representative lighting conditions.
The Flight Operations requirements for pilot pre flight external inspections included in the Operations Manual Part 'B' were noted to include the need to pay "particular attention....to ensure that all panels, equipment bay doors (and) engine cowlings are properly closed and secure" with "the inboard and outboard engine access panels....highlighted as a specific checklist item". However, evidence assembled during the Investigation indicated that there was no effective and universally applied pilot training and familiarisation on these 'panel closed and secure checks'.
The Investigation noted that the pushback crew had also not detected the unsecured hatch during their pre push back walk-around but accepted that they could be expected to detect more than obvious impediments to departure. However, it was noted that they had not been provided with any relevant safety information by Flybe and that it would be in any aircraft operator’s interest to ensure that ramp crews had access to and understood safety-specific information relevant to their walk-round task.
Bombardier advised the Investigation that over a period of 12 years, they were aware of "nine other incidents of engine access panel loss in-flight" in the type world fleet, with the evidence available in each case indicating that, as in the two Flybe cases, all the panel latches had been closed.
The overall Conclusion of the Investigation was that "(although) the aircraft sustained limited damage which did not compromise its ability to complete the flight safely....there was the potential for more serious damage to occur and the departure of such a large panel from the aircraft could also have endangered people on the ground".
Safety Action taken as a result of the event during and known to the Investigation included the following:
- Flybe revised their procedure for maintenance personnel to require that a sticker must be placed over the bottom of the panel when it is closed in order to provide a visual and tactile confirmation to the engineer that the panel is correctly closed and their pilots were advised of this new procedure. They also introduced a new requirement for their in-house 'Notices to Engineers' to be copied to their various contracted maintenance organisations.
- Bombardier "commenced development of a modification" which will add a pictorial advisory label to each engine access panel to provide guidance on how to ensure that it is correctly closed and latched. They also issued an "AMM Temporary Revision" which included instructions on how to correctly close the engine nacelle access door.
. The Cause of the panel loss was formally stated as "following overnight maintenance work, the outboard engine main access panel on the No 1 engine was not securely closed by the engineer, due to the latch bolts not engaging in the nacelle receiving features when the latches were closed".
Possible Contributory Factors were identified as:
- the technique used by the engineer of closing the top latches first which resulted in a gap around the panel which was not subsequently identified, possibly as a consequence of the angle at which he was looking down on the closed panel and the lack of contrast of the shadow cast on the dark coloured engine nacelle.
- a lack of consistency in the way flight crew were instructed on completing pre-departure inspections during their training.
Two Safety Recommendations were made as follows:
- that Flybe Ltd introduces defined and consistently delivered flight crew training on pre-departure inspections for the DHC-8-402 (Q400), compliant with the inspection procedure documented in its Operations Manual. This should include a practical element on the aircraft and a demonstration of correctly secured main engine access panels. [2017-014]
- that Flybe Ltd considers introducing a means of disseminating pertinent safety information to ground operations staff in an appropriate format. [2017-015]
The Final Report of the Investigation was published on 13 October 2016.