Lingus A320 At Dublin on Oct 3rd 2015, fumes in cockpit and cabin
Last Update: February 14, 2017 / 14:27:31 GMT/Zulu time
Ireland's AAIU released their final report reporting that the fumes had worsened so much "that by disembarkation, many passengers had [their] mouths covered with items of clothing and handkerchiefs." The AAIU concluded the causes of the serious incident were:
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.
- Corrosion inhibitor was erroneously added to the water tanks of the engine wash rig.
- The Operator did not have an engine wash training program in place prior to the occurrence and therefore neither Engineer had received training in engine wash procedures.
- 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.
The AAIU reported that the flight was the first of the day. The previous night scheduled compressor washes on both engines were done. The compressor wash took about 4 hours without time pressures, two licensed aircraft maintenance engineers (LAMEs) carried out the engine wash, completed the required post wash tests without any observation of odours in cockpit or cabin and returned the aircraft to service. Only after first reports of an inflight return due to fumes became known the following day, one of the LAMEs realized, that inhibitor fluid had been placed into the wash rig tanks instead of the oil tanks of the engines.
The AAIU analysed: "A scheduled engine wash was performed on the aircraft when it was undergoing maintenance on the night before the occurrence. Prior to the engine wash being carried out, one can, containing eight US fluid ounces (236.6 millilitres) of corrosion inhibitor, was erroneously added to each of the 115 litre water tanks of the engine wash rig. This likely resulted in the inhibitor, which is insoluble in water, being deposited within the compressor sections of each engine during the engine wash procedure. The design of the aircraft’s engine bleed air and air conditioning systems is such that any contamination of this nature in the compressor sections of the engines, APU or associated bleed ducting can lead to fumes or unusual odours entering the aircraft cockpit and cabin."
With respect to the fumes becoming noticeable only after takeoff the AAIU analysed:
The Engineers who performed the engine wash task reported that following the wash, they carried out a post wash test in accordance with the AMM and that no fumes were noticed in the aircraft cockpit or cabin. The test performed was the ‘Alternative procedure - Post Engine Wash Test’, which permits the engines to be operated at idle power only.
During this test, bleed air would have been supplied through each engine’s High Pressure (HP) bleed valve, by the ninth stage of each engine’s high pressure compressor, which is the final stage of compression. However, as no fumes were noticed during the engine run, which was reported to have lasted for approximately half an hour, it is unlikely that there was any corrosion inhibitor trapped in the HP bleed ducts and HP engine chambers. Because only 1% of the core engine air is extracted by the bleed system, it is likely that the majority of any corrosion inhibitor residue remaining on the compressor blades and stator following the engine wash, passed through the engine during the idle run, without entering the HP bleed system.
Fumes only became apparent after take-off, when the engine power setting was such that bleed air would have been supplied by the fifth (Intermediate Pressure - IP) stage through the IP bleed check valve of each engine. Only then would any corrosion inhibitor trapped in the IP engine bleed chambers or the associated bleed ducting be purged. Pressurised air in the engines’ high pressure compressors reaches temperatures in excess of 400o C. The corrosion inhibitor’s flash point is 218o C and the quickly clearing “smoke-like effect” observed in the cabin after take-off, could have been due to vaporisation or heating of the remaining fluid, with the persisting fumes likely resulting from the now-contaminated air conditioning system.
According to the AMM, the purpose of the ‘Alternative procedure - Post Engine Wash Test’ is to “ensure that the bleed system is free from contamination”. This test permits the engines to be operated at idle power following an engine wash using pure water, which was not the case in this event. It would not be effective in ensuring that the bleed system was free from contamination; ordinarily, when a wash is performed with anything other than pure water, the AMM requires engine runs to be performed at higher power settings (60% N1).
Regarding effects on health of humans the AAIU analysed:
Regarding potential hazardous effects, the corrosion inhibitor Manufacturer noted that the conditions, circumstances and thermodynamics in this scenario were complex and could not be fully understood due to the number of variables involved and the fact that the corrosion inhibitor was used incorrectly. Post-event medical examination of the Flight Crew resulted in no adverse findings. The Flight Crew Members donned their oxygen masks and therefore were no longer breathing air from the air conditioning system. However, the Cabin Crew Members, similar to the passengers, were breathing cabin air throughout the event. Subsequent medical tests on the Cabin Crew Members also resulted in no adverse findings and, at the time of writing, there have been no reports of associated illness from any of the Crew Members involved or from the passengers.
With respect to human factors leading to the inhibtor erroneously added to wash rig tanks the AAIU analysed:
When the aircraft was in the maintenance hangar, Engineer B assisted Engineer A in preparing the engines for washing, which involved disconnecting and blanking several air pressure pipes. Regarding the corrosion inhibitor, Engineer B said he had read in the AMM that it was to be added to the oil tanks of the engine. However, although he had performed the engine wash in the past, he had never used the corrosion inhibitor and before using the engine wash rig, which is fitted with two fluid tanks, he needed to re-familiarise himself with its operation by reading the instructional placards and booklet affixed to the rig.
While trying to assimilate this information and with “tank” in his mind and the visual cue of the cans of inhibitor on top of the engine wash rig, he sought clarification from Engineer A as to where the cans were to be added, asking “one in each tank?”, meaning at this stage, the wash rig tanks. Engineer A replied, saying “yeah, one in each tank”, meaning the engine oil tanks. This was interpreted by Engineer B as confirmation that he was to add the inhibitor to the wash rig tanks. From an engineering perspective, the addition of corrosion inhibitor into the wash rig tanks would not seem unreasonable; for example, the AMM requires anti-freeze to be added to the wash rig tanks if temperatures are below 5o C. Engineer A was performing other tasks on the aircraft in preparation for the engine wash and did not see the inhibitor being added, but believed that the corrosion inhibitor had been added to the engine oil tanks as required.
With respect to the delay operating the gangway the AAIU analysed:
The Investigation notes that the aircraft arrived at the parking stand approximately six minutes after landing, and approximately 11 minutes from when the parking stand was allocated. A further three minutes approximately elapsed before movement of the air bridge was commenced. The Investigation therefore considers 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.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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