Description

On 3 October 2015, an Airbus A320 (EI-DVJ) operating a scheduled international passenger flight from Dublin to Munich had just taken off when noxious fumes became apparent throughout the aircraft and a 'smoke-like effect' was observed in the cabin. The effects fluctuated but continued and a PAN for an air turnback was declared to ATC with the pilots donning oxygen masks as a precaution. The aircraft landed back at Dublin just over 20 minutes later and after an unexpected delay due to absence of ground staff, the doors were opened and all occupants were disembarked. The episode had no identifiable injurious effects on the 148 passengers or 6 crew members.

Investigation

The event was investigated by the Irish AAIU.

It was noted that the 40 year-old male aircraft commander, who had been PF for the flight, had 10,523 total flying hours which included 6,691 hours on type. The 27 year-old female First Officer had 2,067 total flying hours which included 1,771 hours on type. Both pilots held licences issued by the Irish Aviation Authority.

Immediately after take-off, the flight crew detected a "strange smell" in the flight deck which was followed by a corresponding call from the senior cabin crew and then by the further information that a "smoke-like effect" had been experienced in the aft cabin after take-off although it had subsequently cleared. ATC permission to enter a temporary holding pattern whilst a further cabin assessment was made was obtained. A cabin report was then received advising that, although the smell had dissipated, it was still present and as it then also seemed to be getting worse again in the flight deck, it was decided to return to Dublin as a matter of relative urgency. Both pilots donned their oxygen masks as a precaution, a PAN was declared to ATC due to fumes in the flight deck and ATC advised the Operator as well as the AFS.

The aircraft landed after 22 minutes airborne and after an expeditious taxi in facilitated by ATC reached the gate 4½ minutes later. No Operator personnel were available to position the air bridge and since the aircraft was not fitted with integral air stairs, opening of dis-armed doors was not permitted under Standard Operating Procedures (SOPs). Concerned at the non-appearance of operator personnel and in the light of cabin crew concern to "get the (cabin) doors open straight away, to get some fresh air", the flight crew contacted their Company to stress the need to attend which eventually occurred. By the time the forward door was opened, the Operator subsequently reported that the smell/fumes in the cabin were such that "many passengers had (their) mouths covered with items of clothing and handkerchiefs”.

No passengers or crew required medical attention on disembarkation and medical examination of all crew members including blood and lung function tests "resulted in no adverse findings". Thereafter "there were no subsequent reports of associated illness from any of the Crew Members involved or from any of the passengers".

The Investigation found that overnight prior to the early morning departure of the occurrence flight, both of the aircraft's CFM 56-5B4/3 engines had been routinely pressure washed using a procedure which only required idle power engine ground running after the wash process. At low power, engine bleed air for the air conditioning system is extracted from the fifth stage of each high speed compressor rather than from the ninth stage used for this purpose at the higher power settings used for take-off and climb. It was noted that the Operator scheduled this non-mandatory task every 1,500 flight hours.

The pressure wash task is specified in the AFM and was carried out by two licensed engineers, both of whom had previously carried it out - although not specifically trained for it - one more recently than the other. The AMM was found to state that when the pressure wash task was performed for EGT margin recovery, which was the purpose in this case, "it was recommended to perform the engine gas path water wash with pure water only". The AMM also noted that the purpose of this post-wash ground run was "to ensure that the bleed system is free from contaminant” which, the subtask notes, has the potential to cause “smoke/smell in the cabin”.

In this case, the two engineers involved had noted from the AMM that as part of the preparations for a pressure wash, "the engine oils should normally receive a specified quantity of a corrosion preventative additive" but that if none of the approved products were available "the engine must resume revenue service operation within 24 hours following the post engine wash (ground run)". Whilst they were aware that the aircraft was planned to depart within a few hours of the time of completion of the engine washes, the engineers involved said that as corrosion inhibitor was available, they had decided to use it "to cover any unforeseen event that could prevent the aircraft from flying within the 24 hour period". It was also decided that the engineer who had the least experience of carrying out the task would man the rig required to accomplish it (see the illustration below). He stated that he had never used a corrosion inhibitor before but had "read in the AMM that the corrosion inhibitor was to be added to the oil tanks of each engine". He had “re-familiarised" himself with the engine wash rig by reading the instruction placards on the rig and the attached instruction booklet. Then, "with the cans of corrosion inhibitor sitting on top of the wash rig and the word 'tank' in his mind, he checked with his colleague as to where the inhibitor was to be added - one in each tank?" (meaning, at this stage, the wash rig tanks) and received the response "yeah, one in each tank" (meaning the engine oil tanks). He then poured one can of inhibitor into each of the two water-filled tanks of the wash rig. At this time, his colleague was not present "as he was carrying out other preparatory tasks on the aircraft/engines" and as a result was unaware that the corrosion inhibitor had not been added to the engine oil tanks. After both washes had been completed, the permissible low power engine ground run was carried out.

The engineer who had made the error became aware of media reports about an air turnback and when he discovered that the aircraft involved was the one the engine washes had been performed on, he contacted his colleague and advised him that he thought that it may have been caused by the “water/inhibitor mix that hadn’t burnt off or got trapped in the bleed system”. The other engineer involved then "realised that the inhibitor had been placed in the wash rig tanks and not the oil tanks of the engines and immediately notified the Technical Shift Supervisor and advised him what had happened and requested him to remove the engine wash rig from service".

Once the cause of the event had been identified, the Engine Manufacturer was consulted for guidance and "a water wash with an added cleaning agent was performed on both engines, followed by a wash with pure water [and] a decontamination of the aircraft’s air conditioning system was carried out". In addition, "an inspection for oil wetting of the forward sump pressurisation tube on both engines was performed, as was an inspection of the engine bleed ducts [with] no adverse findings". Also, "the air conditioning recirculation filters and the avionic equipment cooling air filter were replaced" and following release to service "repetitive visual inspections of the engines and the master chip detectors were scheduled to be performed every 50 to 75 flight hours, for a total of three inspections" again all with no adverse findings reported.

The Investigation noted that in accordance with mandatory requirements, the Operator's maintenance personnel had received Company Procedure/Continuation and Human Factors training within the past two years. The Human Factors element of this training "referred to the Dirty Dozen factors" which have been identified as affecting human performance including "communication", "lack of knowledge" and "lack of awareness", as well as "the safety nets to combat them". However, it was found that there was no engine wash training program in place at the time of the investigated event and neither Engineer had received any other training directly relevant to engine wash procedures.

It was noted that the corrosion inhibitor involved in the contamination was insoluble in water and that "the engine washing procedure may have resulted in the corrosion inhibitor leaving a residual coating on the engine compressors". The fact that the corrosion inhibitor was used at all was found, according to an article in a CFM technical information document "CFM Fleet Highlites" published five months prior to the event, to be unnecessary. This article stated that the post wash engine run as defined in the AMM had been found to be effective in reducing water concentration in engine oil to pre-wash levels, so that use of "an oil corrosion inhibiting additive is not necessary”. The article advised that a corresponding AMM amendment would be forthcoming. This action has now been taken.

The delay in positioning the air bridge to the aircraft given the need to get its occupants clear of the contaminated environment was also examined. It was stated by the Airport Authority that the parking gate to be used by the returning aircraft had been allocated "approximately five minutes before the aircraft landed" with Operator personnel responsible for positioning it and the Operator aware of the return by ATC notification 11 minutes prior to the gate arrival. The Investigation "considered that sufficient time was available to ensure the prompt positioning of an air bridge or mobile passenger steps, which due to the presence of fumes on board the aircraft, would have been appropriate".

The Investigation formally determined that the Probable Cause of the occurrence was "the presence of corrosion inhibitor in the Intermediate Pressure (IP) bleed ducts and IP engine bleed ducts following an engine wash procedure, leading to contamination of the air conditioning system".

Three Contributory Factors were also identified as follows:

1. Corrosion inhibitor was erroneously added to the water tanks of the engine wash rig.
2. The Operator did not have an engine wash training programme in place prior to the occurrence and therefore neither Engineer had received training in engine wash procedures.
3. The alternative post engine wash test did not result in any adverse findings; this test was only applicable if the engines were washed with pure water.

Safety Action taken as a result of the occurrence included the following by the Aircraft Operator, both of which meant that Safety Recommendations were not made in either regard:

• An engine wash training programme for its engineers was developed and introduced and the circumstances of the investigated event were added to their engineers' Human Factors Training.
• A review of the delay in positioning the air bridge was followed by action to "enhance the efficacy of their response to aircraft returning due to fumes or other situations where a prompt disembarkation would be desirable".

The Final Report was published on 14 February 2017.

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