An “extremely bad fumy smell” in the cabin and cockpit that caused an Aer Lingus Airbus A320 to declare an emergency immediately after takeoff from Dublin in October 2015 was caused by a flawed engine-wash operation in maintenance the night before, according to investigators.
The incident, which ended safely when the A320 returned to Dublin, prompted Aer Lingus to develop an engine-wash training program for maintenance engineers and CFM, to change its engine wash procedures for the CFM56, according to the final report by Ireland’s Air Accident Investigation Unit (AAIU).
Despite Aer Lingus’s statement that the fumes were so bad that many of the passengers had to cover their mouths with “items of clothing and handkerchiefs” by the time they left the aircraft via the jet bridge, medical examinations of the crew—including blood tests and lung function tests—did not show any ill effects. “The operator also advised that there were no subsequent reports of associated illnesses from any of the crew members involved or from any of the passengers,” states the AAIU.
The cause of the smell was traced back to the bleed air coming from engines, which had received a “compressor wash” the night before. The flight in question was the first of the day.
The high-pressure engine wash, a mandatory task every 1,500 flight hours, removes deposits that build up on the engine’s compressor blades and stator vanes, decreasing performance. The airline has several wash and after-wash procedures available but did not have a dedicated engine-wash training program for maintenance technicians.
In this case, the maintenance engineers chose to use a process in which 8 oz. of corrosion inhibitor would be added to each engine, with the engines then washed with high-pressure water from a mobile engine-wash rig cart, followed by a post-wash check using low engine power.
By mistake, one of the engineers added the corrosion inhibitor to the water tanks on the engine wash rig rather than to the oil tanks of the CFM56 engines.
Investigators determined that the probable cause of the fumes was the presence of the corrosion inhibitor in the intermediate pressure bleed ducts, which contaminated the air conditioning system when the engines were running at high-power settings on takeoff.
After the incident, CFM determined that the corrosion inhibitor was not necessary and in fact was reducing engine bearing life.