Vueling A320 near Alicante on Feb 21st 2017, both air conditioning systems failed

Last Update: June 4, 2019 / 21:06:09 GMT/Zulu time

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Photo of Vueling EC-HTD, Airbus A320 — Vueling EC-HTD, Airbus A320 (Photo credit: Anna Zvereva / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Feb 21, 2017

Classification
Incident

Airline
Vueling

Departure
Malaga, Spain

Destination
Barcelona, Spain

Aircraft Registration
EC-HTD

Aircraft Type
Airbus A320

ICAO Type Designator
A320

A Vueling Airbus A320-200, registration EC-HTD performing VY-2116 from Malaga,SP to Barcelona,SP (Spain) with 179 passengers and 7 crew, was climbing through FL100 out of Malaga when the crew received a "AIR ENG BLEED ABNORM PR" and a "AIR PACK 1 FAULT" message. The crew decided to continue the flight and limited the maximum altitude to FL300. However, after levelling off at FL300 the crew received a "AIR PACK 2 FAULT" message, initiated an emergency descent to FL110, passenger oxygen masks did not deploy, and diverted to Alicante,SP (Spain) for a safe landing about 30 minutes after leaving FL300.

Spain's CIAIAC reported the occurrence was rated a serious incident and is being investigated. Following the first almost simultaneous messages "AIR ENG BLEED ABNORM PR" and "AIR PACK 1 FAULT" the crew attempted a reset of the affected system, which however went "unsatisfactorily", then decided to continue the flight and limited the aircraft to FL300. At FL300 the crew received an "AIR PACK 2 FAULT" message, declared Mayday and performed an emergency descent. The cabin altitude did not increase above 6700 feet, the passenger oxygen masks were not released.

On Mar 9th 2018 Spain's CIAIAC reported in an interim note, that the aircraft had been dispatched with the APU deferred under minimm equipment list requirements. While climbing through FL100 out of Malaga the crew received "AIR ENG 1 BLEED ABNORM PR" and "AIR PACK 1 FAULT" messages. The crew attempted to reset the left hand pack however without success. With the right hand pack still providing air conditioning the crew continued the flight and was enroute at FL300 - the flight was limited to FL300 due to single pack operation - when the crew received a "AIR PACK 2 FAULT" message, declared emergency and performed an emergency descent to FL100. The cabin altitude climbed to a maximum of 6700 feet, the release of passenger oxygen masks was thus not necessary. The crew diverted the aircraft to Alicante for a safe landing. The investigation has been completed and a draft final report is being report as of current.

On Jun 4th 2019 the CIAIAC released their final report concluding the probable causes of the incident were:

The investigation has determined that the most likely cause of the incident was the undetectable and undetected degradation of the bleed regulation in the aircraft.

It was also determined that the correct model of pressure regulating valve (PRV) was not installed in the aircraft’s no. 1 engine due to a component identification error in the IPC.

The CIAIAC analysed:

The crew were on the fourth scheduled flight that day on aircraft EC-HTD. The aircraft had been dispatched with the auxiliary power unit deferred, as per the operator’s MEL, since the start of their duty period.

During the departure maneuver from the Malaga Airport (1600 ft and climbing), the aircraft issued an abnormal pressure alert for the bleed system in the left engine, accompanied by a warning that the pack associated with that engine had failed. After resetting the fault, it reappeared as they were climbing through 12000 ft.

Since the APU was not available to supplement the engine bleed to the packs, and in keeping with the instructions issued by the operator in its information note “DUAL BLEED FAULT version 2”, the crew decided to limit the flight level to FL300, which was authorized by ATC.

The captain stated that his intention was to analyze the initial situation and apply the OEB PROC-40 “AIR ENG 1 (2) BLEED ABNORMAL PR OR AIR ENG 1 (2) BLEED FAULT” once level at their cruise altitude, in an effort to solve the indicated fault.

They did not have time to execute this procedure because shortly after reaching the set flight level, the aircraft issued an abnormal pressure alert for the bleed system, this time for the right engine, along with a warning that the pack associated with this engine had failed. This new indication implied that the aircraft would be unable to maintain the differential pressure in the cabin.

The QRH “AIR ENG 1 + 2 BLEED FAULT” procedure requires closing the crossfeed valve and reset both bleed valves. If neither one is recovered, the procedure instructs descending to FL100 or to the MEA/MORA (whichever is higher), though it does not explicitly call for an emergency descent.

The flight crew informed both ATC and the cabin crew that they were doing an emergency descent and carried out the memory items for this procedure, but without donning the oxygen masks.

In his statement, the captain indicated his intention to make a rapid, not emergency, descent, since he saw that the cabin altitude was rising slowly and there was no risk that the masks would automatically deploy. In fact, the maximum cabin altitude recorded was 6700 ft.

The information note “DUAL BLEED FAULT version 2” refers to the required descent in the following terms:

“Although each situation is different, a slow and/or controlled depressurization (in the event of a DUAL BLEED FAULT and/or DUAL PACK FAULT) should not be confused with an EMERG DESC and its associated memory items. One of the goals in this situation is to avoid, to the extent possible, the automatic dropping of the passenger masks or avoid activating them manually when not necessary”.

This paragraph indicates to crews that in case of a fault, such as those that occurred in this incident, the aircraft will depressurize slowly, meaning that an emergency descent is not required, as specified in the manufacturer’s abnormal procedures.

In any event, depending on the depressurization rate and on how long the cabin pressure is estimated to remain above FL100, the flight crew must consider using the oxygen masks to avoid the effects of hypoxia and the consequent reduction in their time of useful consciousness.

Although they initially requested to return to the airport of origin (Malaga), the captain’s decision to divert to the Alicante Airport, the topography of the terrain around which would allow them to fly at levels that would not require assisted breathing if the aircraft were to depressurize (FL100 or lower), is judged to have been correct.

While en route to Alicante at FL070, the crew managed to reset the bleed system on the right engine and its associated air conditioning pack, which remained operational until landing.

The CIAIAC analysed that the aircraft had been dispatched with the APU inoperative which deprived the crew of a backup system to supply the packs. 18 months prior to the occurrence the PRV in the left hand engine was an g-type with an incorrect part number instead of the initial e-type. The CIAIAC wrote with respect to the PRV replacement:

The investigation into the incident conducted by the operator and the maintenance services provider determined that the left engine had a type-G PRV installed, which, according to the IPC, is a conditional spare for the type-E PRV it should have had.

This component was verified not to comply with the condition required for installation in aircraft EC-HTD, since the required modification (MOD 31261) was not implemented on this aircraft.

Since a year and a half had elapsed between its installation by the maintenance services provider, at the completion of the A4 check, it was not possible to trace the error, which probably occurred as a result of a misinterpretation of the IPC.

In any event, this faulty installation could not be established as the direct cause of the incident since, as mentioned, the aircraft had been flying with the component installed for 18 months without any failures, which makes it unlikely that it was solely responsible for the incident. The type-G PRV installed in the #1 engine probably had its cover in place since after its erroneous installation, when it was placed into operation, no problems occurred during any other flights.

The CIAIAC complained: "The data from the cockpit voice recorder (CVR) were not available to the investigating team since the recordings were not preserved after the incident flight. Following the incident, the aircraft was taken on a ferry flight to the Barcelona-El Prat Airport, and it was only the recordings from this flight that were available on the CVR."