A Vueling Airbus A320-200, registration EC-MDZ performing flight VY-1431 from Bilbao,SP to Barcelona,SP (Spain) with 114 passengers and 6 crew, departed Bilbao's runway 12 when the left engine (V2527) dropped two bonnets. In the absence of any abnormal indications and unaware of the separation the crew continued the flight to Barcelona for a safe landing.
On Nov 8th 2018 Spain's CIAIAC reported they opened an investigation into the occurrence. Although a part of the engine cowling became stuck in the left main gear, the gear retracted normally after takeoff and extended in Barcelona without problems. The aircraft received minor damage at the left main gear and the left side of the fuselage where debris hit, however all persons on board disembarked normally, no medical attention was needed.
On Sep 5th 2020 the CIAIAC released their final report concluding the probable causes of the incident were:
The investigation has determined that the incident was caused by flying the airplane without closing and properly latching the cowls on the airplanes left engine, which was in turn caused by an improper maintenance operation and by the incorrect performance of the walk-around check prior to the flight.
The following factors contributed to the incident:
- The improper performance of the maintenance task before the flight, after which the cowls were left open and unlatched, and without the relevant entries being made in the logbook documenting the opening and closing of the fan cowls on the left engine.
- The incomplete performance of the visual inspections before the flight, during which the fan cowls were not identified as not having been properly closed and latched.
The CIAIC released following findings:
- On Wednesday, 25 October 2018, an Airbus A-320-232, registration EC-MDZ, operated by Vueling Airlines, S.A., was making the first flight of the day with a total of 120 persons on board from Bilbao to Barcelona.
- The crew of the aircraft had the licenses and medical certificates required for the flight and they were valid.
- The aircrafts documentation was valid and the aircraft was airworthy.
- The weather during the incident flight was not limiting and did not adversely affect the flight.
- On the night of 24 to 25 October, during the night stop, maintenance tasks had been performed on aircraft EC-MDZ that required opening and closing the left engine fan cowls.
- The personnel who performed the maintenance on aircraft EC-MDZ had the licenses and certificates required to perform said tasks, and they were valid.
- The maintenance technicians did not make the relevant entries in the aircraft logbook to document the opening and closing of the left engine fan cowls.
- The maintenance technicians did not close and secure the four latches on the cowls.
- During the walk-around inspection, the aircraft captain did not notice that the left engine fan cowls were not properly closed and latched.
- Ground personnel informed the pilots that all the covers were closed and latched before starting pushback.
- The visibility conditions did not limit the performance of the nighttime tasks prior to the flight.
- At 05:07 UTC, during the takeoff run on runway 12, the two fan cowls detached from the left engine. The crew did not realize this until they arrived at the Barcelona Airport, where they landed normally at 05:55 UTC on runway 25R.
- After aircraft EC-MDZ took off, ten additional aircraft took off from the same runway (the chocks-off time for the last one was 06:15 UTC). None of their crews reported seeing any objects on the runway or having any problems during the takeoff run or after takeoff.
- At 06:16 UTC, the operations department at the Bilbao Airport was notified from Barcelona of the possibility that the fan cowls that had detached from EC-MDZ could be inside the airfield at the Bilbao Airport.
- At 06:18 UTC, a marshaller at the Bilbao Airport double checked runway 12/30 (once in each direction) and only found two pieces on the runway, which were much smaller than a fan cowl.
- Landings on runway 12 at the Bilbao Airport (after the departure of EC-MDZ) began at 05:21 UTC. Seven were uneventful, but during the eighth, at 06:46 UTC, the crew of the aircraft reported seeing large pieces on the shoulders of runway 12.
- At 06:19 UTC, a marshaller at the Bilbao Airport again checked runway 12, and this time was able to locate large pieces (fan cowls) on the shoulders of runway 12. The runway was closed at 06:51 UTC.
- The runway was opened at 07:17 UTC following an inspection and removal of debris (about 40 pieces from the engine nacelle and another 50 smaller parts).
- In terms of the latches on the engine fan cowls, EASA AD 2016-53 mandated the implementation of Airbus SB A320-71-1069 by 28 March 2019 on affected aircraft (EC-MDZ was one of them). On the date of the incident, it had not been implemented on EC-MDZ.
- On the date of the incident, SBN71-0325, which corresponded to the condition prior to the issue of SB 71-1069, had been implemented on EC-MDZ.
- Vueling finished implementing EASA AD 2016-53 on its affected airplanes on 15 January 2019.
- After takeoff, an LGCIU2 FAULT was received on the ECAM in the cockpit. The crew did the relevant procedure and considered the implications of this fault on the operation of the aircraft. Since no further warnings were received, after weighing its consequences, they decided to continue to their destination.
- The indications in the cockpit were normal at all times. There were no messages warning of a malfunction, fault or abnormal operation in the left engine.
- One passenger in seat 9A informed the purser that the left engine seemed to be missing a cover.
- The purser looked at the engine from the aisle and saw nothing unusual. The pilots were informed of this.
The CIAIAC analysed:
Maintenance tasks prior to the incident flight
Several hours before the incident, during the night of 25 October 2018, two maintenance technicians performed tasks that required opening the engine fan cowls on both aircraft where SB 71-1069 had been implemented (using the key and tethered flag) and on aircraft where it had not (such as EC-MDZ, where the fan cowl flag was used instead).
The above notwithstanding, in both cases, the maintenance technicians should have documented the opening and closing of the cowls in the aircrafts logbook, as required by the Aircraft Maintenance Manual (AMM Task 71-13-00-010-010-A and AMM Task 71-13-00-410-010-A). In the case of EC-MDZ, the maintenance technicians did not make these entries.
When asked about this later, they recalled having gone to the aircrafts cockpit to make three entries in the logbook, but the technician in question recognized that he had forgotten to document the opening and closing of the cowls in the logbook, as is required.
The maintenance technicians who had worked on the left engine of EC-MDZ hours before the incident flight also stated that when they lowered the two cowls, they did not lie down face up on the floor to close them, though they could not remember why. Even though lying down to close them is second nature after lowering the cowls, they could not explain why this time they did not do it, as was their habit, and they acknowledged that the cowls were not properly locked using the four latches.
They also stated that they had been very close to the engine after lowering the cowls on several occasions that night and did not see anything unusual.
Based on these findings, it may be concluded that the cowls were not properly closed and locked using the four latches. It is very likely that the safety gap that exists between the lowered cowl and the nacelle was very small (or practically non-existent) such that despite walking by the engine on several occasions afterward, they did not see anything unusual.
The fact that EASA AD 2016-53 was fully implemented on the Vueling fleet two and a half months before the deadline is considered a positive, as it significantly reduces the risk of improperly latched cowls in the future.
Actions taken by the crew before the incident flight
From the point of view of the aircrafts operation and the crews actions, the crew had three sources of information to determine the condition of the cowls:
1) The aircraft logbook, in which the tasks to open and close the fan cowls should have been documented.
2) The visual check of the status of the cowls during the exterior inspection, and
3) The confirmation from ground personnel that all doors and covers are closed and locked before pushback.
The first involves checking the aircraft logbook for the maintenance tasks performed, and specifically the opening and closing of the cowls. This entry informs the crew that the cowls were operated during maintenance activities, and focuses their attention to check the condition of the cowls during the external inspection. These entries were not made, meaning the crew did not have this indication to inform them that the cowls had been opened and closed.
The second involves the crew checking the condition of the cowls during the exterior inspection. This inspection was done by the captain, who did not notice anything on the engines that made him question whether the latches on the cowls were properly secured. This reinforces the idea that the cowls, once lowered, left a very small gap with the engine fairing, being practically flush with it. However, if the pilot who did the exterior inspection had crouched to see if the latches were flush with the nacelle, he would have noticed that they were not (see Figure 19), and would have therefore realized that they were open.
The third and final source involves the check by ground personnel that all the doors and covers are closed and locked, which was the message relayed to the crew before pushback. In light of the previous paragraph, it can be deduced that the ground personnel had the same problems as the crew identifying the condition of the cowls.
Even though the sun was not yet up when the maintenance tasks and exterior inspections of the airplane were carried out, in light of the eyewitness statements and of the lighting conditions evident in Figure 10, the visibility conditions are not deemed to have been a limiting factor in conducting these tasks.
Situation after the cowls detached
Once airborne, the detaching of the cowls triggered the ECAM LGCIU2 FAULT alert.
An analysis of the flight recorders shows that the crew carried out the relevant procedure and considered the impact of this fault on the aircrafts operation. Since there were no other alerts, after assessing its consequences, they decided to continue to the destination.
The engine parameter readings in the cockpit were normal at all times and there were no warnings indicative of a malfunction, fault or abnormal operation in the left engine. This is confirmed by the analysis of the FDR data, which show no sign of any malfunction in the left engine during the flight, or any operating parameters that differed from those for the right engine.
The only issue that the pilots discussed was the aerodynamic noise at high speed that the aircraft was making, which they did not consider to be unusual, and the specific noise they heard at the moment of rotation, which they also dismissed as nothing unusual or very different from the noise made when running over a runway centerline light.
There was one later indication that could have helped them identify the situation: the comment made by the purser to the pilots about what a passenger seated in 9A involving the engine cover. However, the purser told the pilots that he had not seen anything out of the ordinary when he looked at the engine (from the aisle) after the passengers comment. While the dark conditions outside did make it difficult to see the engine, the purser could have tried to get a clearer view from a window, since there were unoccupied seats behind the passenger in 9A. And he could even have asked the pilots to turn on the external lights on the airplane.
The above indicates that the only source of information that could have alerted the crew to the loss of the cowls was a visual confirmation of said loss. In light of the warnings received in the cockpit and of the information provided by the cabin crew, the flight crew did not have any indications that would have made them think that they had lost the cowls.
Based on the information available to the pilots, their decision to continue flying to Barcelona, as well as the measures taken by the pilots in response to the ECAM LGCIU2 FAULT message and its potential implications, are deemed to have been correct.