Swiss A320 near Marseille on Sep 12th 2013, loss of cabin pressure
Last Update: December 9, 2015 / 16:16:55 GMT/Zulu time
Date of incident
Sep 12, 2013
Loss of cabin pressure
Swiss International Airlines
ICAO Type Designator
A listener on frequency reported that the crew, audibly on standard cockpit microphone but with some urgency in the voice, reported a pressurization problem and requested lower, ATC cleared the aircraft to FL350. Another request to lower was not granted by ATC, the crew declared PAN PAN and again requested lower, ATC did not acknowledge the PAN call and confirmed FL350. The crew attempted to get ATC acknowledge the PAN, ATC now acknowledge the PAN and cleared the aircraft to FL300. The crew requested FL140, ATC did not approve FL140, the crew now audibly on oxygen masks declared emergency. ATC instructed to squawk emergency, cleared the flight to FL140 and handed the aircraft off.
The aircraft was able to depart Valencia with a delay of 30 minutes and performed return flight LX-2141 climbing up to FL350.
The airline confirmed that the aircraft suffered a cabin pressure lower than normal but not yet low enough to release the passenger oxygen masks, when the crew attempted and finally succeeded to descend the aircraft to FL100. After about 20 minutes the crew was able to restore air conditioning and cabin pressure and continued the flight.
On Oct 5th 2013 the Swiss SUST reported that the aircraft had been dispatched under minimum equipment list requirements with one bleed air system inoperative, while in cruise at FL370 over France the second bleed air system failed and an emergency descent was initiated. The occurrence was rated a serious incident, the SUST is investigating.
On Dec 9th 2015 the Swiss SUST released their final report concluding the causes of the serious incident were:
The serious incident is due to the fact that during cruise a loss of cabin pressure occurred on the passenger aircraft which required an emergency descent.
The investigation has determined the following causal factors:
- The flight commenced with only one functional pneumatic system;
- A lack of clarity in the procedures meant that the use of this system was not optimised;
- This pneumatic system had characteristics that led to overheating and the system switching itself off;
- An optional improvement provided by the manufacturer (service bulletin) had not yet been implemented;
- A revision of the MEL procedure provided by the manufacturer was not available to the operator at that time.
The following contributing factor was determined for the occurrence and the history of the serious incident:
- The necessary information and procedures for handling a system fault during the flight are not clearly presented to the flight crew.
The SUST reported that the aircraft had encountered a #1 bleed air fault on the previous evening while on a flight to Hamburg. In Hamburg maintenance determined a pre-cooler fault, it was decided to deactivate the #1 bleed air system and release the aircraft under minimum equipment list requirements for the return flight. Maintenance in Zurich did not have the thermostat needed availabe on stock and therefore decided to put the aircraft back into service still under minimum equipment list requirements with the #1 bleed air system inoperative.
The incident crew was aware of the MEL requirement and after studying the minimum equipment list decided that the flight could be performed as planned.
In flight at FL370 the crew contacted Marseille Center, some time later they noticed a pressure on their ears and detected the cabin altitude was climbing at approximately 1700 fpm. The #2 bleed air valve was shown closed, shortly afterwards an AIR ENG 2 BLEED FAULT activated together with a chime and the master caution. While working the related checklists the crew was handed off to the next Marseille sector, on reporting with that sector the crew reported being at FL370 and requesting descent, the controller cleared the flight direct to waypoint BISBA but did not reference the descent request, the crew therefore read back "Direct BISBA, request descent to FL320 initially." The controller communicated with another aircraft, the crew repeated their request, the controller transmitted "descend level" but did not complete the transmission. The crew therefore declared PAN PAN requesting a descent to at least FL300 and was now promptly cleared to descend to FL350 initially. The crew explained they had got a pressurization problem and needed further descent, the controller responded "roger", the flight crew queried "did you copy PAN?" to which the controller replied "call you back".
The SUST continued to write:
Since the flight crew wished to descend to a lower flight level without delay, they intervened immediately as follows: „Did you copy my PAN PAN Miss, Swiss two one four ze-ro?” Since the ATCO responded with „Say again your request”, the flight crew now transmitted a message with emphasis as follows: „Swiss two one four zero PANPAN PANPAN PANPAN requesting lower”, which the ATCO acknowledged with „Roger”.
As the ATCO issued the following instruction to the flight crew at 05:53:46 UTC: „Swiss two one four zero, squawk two zero zero zero” the latter initiated their de-scent and responded with: “Thank you two thousand Swiss two one four zero ap-proaching flight level three five zero requesting lower.” There was no response to this message from the ATCO.
The flight crew then wanted to give additional emphasis to their descent requests and at 05:54:10 UTC transmitted: „Swiss two one four zero MAYDAY MAYDAY MAYDAY request descent!” The ATCO then responded promptly at 05:54:16 UTC with „Swiss two one four zero squawk seven seven zero zero, descend flight level three zero zero”, which the flight crew confirmed without delay.
In the intervening time the cabin pressure altitude had risen further, and at 05:54:18 UTC the alert CAB PR EXCESS CAB ALT was displayed in the cockpit at the same time as the aural master warning sounded. The flight crew donned their oxygen masks without delay and initiated an emergency descent.
At 05:55:23 UTC the ATCO enquired as to the flight crew’s intentions: „Swiss two ... Swiss two one four zero, what are yourintentions?” The flight crew of SWR 2140 answered at 05:55:33 UTC as follows: „Marseille Swiss two one four zero, request further descent”, to which the ATCO gave the following clearance: „Swiss two one four zero, descend flight level two five zero.” The flight crew responded to this with: „We need to descend at least flight level one four zero Swiss two one four zero, descending flight level two five zero for now.” At 05:55:49 UTC the ATCO immediately gave further clearance to descend to FL 140, which the flight crew promptly confirmed.
The crew was handed off to the next Marseille sector who immediately offered to decend to FL110, which was accepted by the crew and subsequently offered FL100, again accepted by the crew. The crew advised they were still continuing into the direction of Valencia but were also considering a diversion to Barcelona. The controller advised Marseille Airport was available as well, the crew had already verified their fuel would be sufficient to continue to Barcelona and thus decided to continue. The Mayday status was cancelled.
The crew started the APU and contacted their maintenance control center (MCC), the operator expressed preference to continue to Valencia, the MCC recommended to attempt a bleed system #2 reset, which returned the system to operation, two bleed air sources were now online (APU and engine #2) and the cabin pressure was under control again. The crew therefore decided to climb the aircraft to FL210 and continue to Valencia where a normal landing occurred.
Maintenance in Valencia determined that there had been no fault with the #2 bleed air system and released the aircraft to service again under the MEL requirements with the #1 bleed air system inop. MCC recommended to keep the APU running for the return flight, the crew took on additional fuel in case the return flight would need to commence at a lower flight level. The return flight was able to climb to FL340 and completed without further incident.
It was subsequently found that both bleed air systems showed the same problem, the temperature control thermostat intermittently failed to regulate the pre-cooler outlet temperature resulting in the temperature climbing above 240 degrees C, which also occurred on the return flight for several minutes. At 257 degrees C the pressure regulator valve would close automatically. It was further found that maintenance in Valencia did not check the functionality of the thermostat or the fan air valve.
The subsequent replacement of the thermostat on both bleed air systems resolved the issues.
The problem of dual bleed air faults had been known for a long time, Airbus had developed a solution, involving a new temperature control thermostat, a temperature limiting thermostat and new fan air valve, and offered an option to include that solution with service bulletin A320-36-1061, this option had been planned but not yet been implemented on HB-IJU however.
5 months prior to the occurrence Airbus in addition reworked the Minimum Equipment List to clarify that the OEB40 procedure, intended to be used in case of a single bleed air fault in flight, is to be applied as well if the aircraft is being dispatched under MEL requirements. This modified MEL became available to the operator only after the occurrence, however.
The SUST analysed: "After completion of the flight planning procedures and flight deck preparations the flight crew addressed the study of the minimum equipment list (MEL) and the cor-responding consequences. They were therefore of the view that if the remaining pneumatic system 2 would fail they had to use the procedure published in the operations engineering bulletin (OEB). This meant that when the alert AIR ENGINE 2 BLEED FAULT appeared on the electronic centralised aircraft monitor (ECAM), the commander immediately turned to the procedure in the aircraft manufacturer’s operations engineering bulletin (OEB). However, since he did not find this relevant to the situation, he decided to undertake a descent. This decision was accurate to the situation because neither the OEB procedure nor the ECAM procedure could lead to success. In both procedures a single fail-ure is assumed, in which the remaining system is able to overtake the bleed air demand. In case of a dispatch according to the MEL the result of this single failure however results in a double failure because only one system is available from the very beginning.
The flight crew was thus confronted with a dual bleed loss, which according to the appropriate checklist (cf. Annex 9) requires at least a rapid descent to FL 200 and the starting of the auxiliary power unit. Even an emergency descent to FL 100 is not ruled out; this would be appropriate for a dual bleed loss scenario. The request for clearance to descend without giving reasons or a particular flight level was not appropriate to the situation. As a result the ATCO was not aware of an abnormal situation and therefore did not react immediately. Only the declara-tion of the transmitted message as an urgency message with the words PAN PAN finally led to a clearance to descend. An immediate declaration of an emergency situation aids an appropriate assessment of the situation by air traffic control. Thus the flight crew did receive full support from the ATCO when they gave further emphasis to their descent re-quest with the distress message wording MAYDAY MAYDAY."
With respect to the Air Traffic Control performance the SUST analysed:
As the radiocommunication transcripts confirm, the air traffic control officer on the Marseille M123 Sector frequency answered the first „request descent” call of the flight crew with only clearance for a direct course to waypoint BISBA. The ATCO gave an incomplete response to the second call and answered the call from an-other aircraft. This behaviour is comprehensible insofar as the pilots, up to this point in time, gave no indication that they were in an abnormal situation.
When the flight crew transmitted the urgency message PAN PAN and requested descent to at least FL 300, they received clearance to descend to FL 350. The flight crew persisted with their urgency message and the ATCO once again requested a repetition of the message. To the repeated requests by the flight crew to descend to a lower FL the ATCO merely responded with „Roger”, which indicated little situational awareness. Although the flight crew in the first instance only requested a descent, it is astonishing that the ATCO did not listen attentively, at the latest by the transmission of the PAN PAN message and the reference to pressure problems. The behaviour of the ATCO provided little assistance to the flight crew in this phase. Apparently the ATCO only became conscious of the situation when the flight crew gave further emphasis to their request for further descent by using the distress message MAYDAY. The behaviour of the ATCO altered immediately and the flight crew then received optimal support.
After the change in frequency to the Marseille ML Sector the flight crew also was well supported by the ATCO.
Aircraft Registration Data
Date of incident
Sep 12, 2013
Loss of cabin pressure
Swiss International Airlines
ICAO Type Designator
This article is published under license from Avherald.com. © of text by Avherald.com.
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