Austrian DH8D at Vienna on May 6th 2015, smoke in cabin due to oil contamination
Last Update: September 27, 2016 / 18:44:34 GMT/Zulu time
Passengers reported haze in the cabin that reduced visibility.
The airline reported a defect in an engine, the haze/light smoke was then distributed into the cabin through the air conditioning system. The cause of the defect is being investigated. The flight was cancelled, the return flight was performed by a replacement aircraft.
On Sep 23rd 2016 Austria's Accident Investigation Commission (SUB), part of Austria's Civil Aviation Authority (VERSA), signed off their final report in German concluding the probable causes of the serious incident were:
The serious incident has been caused by damage in a seal of bearing 2.5 of the right hand engine, which resulted in bleed air leakage and oil entering the bleed air system via the Inter Compressor Case and bleed air connector 2.7 and further the air conditioning system.
VERSA reported that the captain (40, ATPL, 6,631 hours total, 3,717 hours on type) was pilot monitoring, the first officer (31, CPL, 3,837 hours total, 3,837 hours on type) was pilot flying.
Shortly after departure, when the crew operated the switches for bleed air #1 and #2, smoke appeared in the cabin and shortly afterwards in the cockpit, a lavatory smoke detector activated and could not be silenced. The first officer instructed the flight crew to don the oxygen masks and to work the "fire/smoke on flight deck" check list. The flight crew decided to return to Vienna. The captain contacted the cabin via "normal call" to prepare the cabin for emergency arrival, estimated landing in 15 minutes. The crew started to work the emergency procedures, however, did not declare emergency with Air Traffic Control but reported the nature of the occurrence to ATC. While working the checklists the crew recognized the smoke originated from the bleed air of the right hand engine, the aircraft was about 12nm before the runway 34 threshold. The crew performed an ILS approach to runway 34 and landed safely, smoke was still present in the cabin. The aircraft stopped on the runway, emergency services inspected the aircraft and apart from seeing some smoke from the inboard side of the right hand engine no damage was visible. With this information the crew decided to taxi the aircraft to the apron, where the passengers disembarked normally.
The SUB reported that neither flight crew nor cabin crew nor 3 passengers, that could be reached for comment, complained about any health impact following the occurrence.
The SUB reported after landing a massive oil leak was detected at the right hand engine. Oil was found on the right hand main gear, right hand flaps, at the right hand side of the aft fuselage as well as the right hand horizontal stabilizer/elevator.
A first inspection of the right hand engine revealed a crack in the inter compressor case (ICC) at about the 6 o'clock position. The ICC transports compressed air from the low pressure compressor to the high pressure compressor.
A borescopic inspection determined the crack was the sole source of the oil leakage onto the gear, fuselage and tail plane. However, engine oil was also found in the bleed air ducts towards the Nacelle Shut Off Valve (NSOV). Oil contamination was further found along the lines towards the air conditioning systems raising doubts that the crack at the ICC could be responsible for this kind of contamination. Therefore the engine was sent to the engine manufacturer for further investigation, this examination was supervised by Canada's TSB.
When the engine was disassembled it was found that all blades of the low pressure compressor were oily. Subsequently carbon sludge and metallic particles were found at the inner barrel of the first low pressure compressor stage and the flange and seal of bearing 2.5. Bearing 2.5 itself was undamaged.
The seal showed damage to the wave springs and sheets of carbon seal. Therefore the seal could no longer seal off pressurized air, which resulted in oil entered the bleed air system via bleed air connector 2.7 within the ICC and further into the environmental control system.
The crack at the ICC was identified to be the result of fatigue.
An examination of the smoke detector, which had triggered and could not be silenced, did not reveal any malfunction.
The SUB analysed that there had been a number of cases already, where bearing 2.5 received damage resulting in smoke in the cabin, 4 cases were documented between March 2014 and February 2015.
The SUB analysed that the smoke probably was too dense to silence the smoke detector.
The SUB reported that the certification of engines is done according to standard CS-E510, which requires risk assessments, that are to be done by the engine manufacturer. Those risks include amongst others:
…“(iv) Toxic products.
CS-E 510 (g)(2)(ii) concerns generation and delivery of toxic products caused by abnormal Engine operation sufficient to incapacitate the crew or passengers during the flight. Possible scenarios include:
- Rapid flow of toxic products impossible to stop prior to incapacitation;
- No effective means to prevent flow of toxic products to crew or passenger compartments;
- Toxic products impossible to detect prior to incapacitation.
The toxic products could result, for example, from the degradation of abradable materials in the compressor when rubbed by rotating blades or the degradation of oil leaking into the compressor air flow.
No assumptions of cabin air dilution or mixing should be made in this Engine-level analysis; these can only be properly evaluated during aircraft certification. The intent of CS-E 510 (g)(2)(ii) is to address the relative concentration of toxic products in the Engine bleed air delivery. The Hazardous Engine Effect of toxic products relates to significant concentrations of toxic products, with “significant” defined as concentrations sufficient to incapacitate persons exposed to those concentrations.
Since these concentrations are of interest to the installer, information on delivery rates and concentrations of toxic products in the Engine bleed air for the cabin should be provided to the installer as part of the Engine instructions for installation.
The SUB further analysed that the air conditioning filters were not designed and chemically unable to filter out oil fumes.
The SUB analysed that although there is guidance by the aircraft manufacturer of how to clean up the environmental control system following a fumes event, there is no guidance for cleaning cabin and/or cockpit following a fumes event.
The SUB analysed that the manufacturer of the engine oil in use provided following warning in the safety and hazard instructions:
„WARNING ! While no significant adverse effects on health are expected when properly handled and used, this product contains tricresyl phosphate (TCP) which, if taken internally, can cause paralysis.“
The SUB analysed that working the fire/smoke in cockpit checklists is primarily geared towards fighting a fire, however, gives no concern to protecting the cockpit and cabin against fumes. The checklist thus contributed to increase oil fumes to invade cabin and cockpit because the bleed air was selected to ON/MAX in accordance with the checklist.
The same applies to the checklist "Fire/Smoke in cabin" checklist. However, this checklist enabled the crew to identify the right hand engine and its bleed air system as cause of the fumes resulting in the right hand bleed air system being shut down.
The SUB analysed that both pilots used their oxygen masks, however, not the smoke goggles. In addition the crew did not declare Mayday and did not communicate with cabin crew via the emergency calls but normal calls. Further, the captain removed his oxygen masks on several occasions for better communication.
The SUB analysed that the oxygen masks mounted on the aircraft were not the same type that the crew had been trained on during their simulator training. Other than in the simulator which featured a combined oxygen mask and smoke goggle the aircraft featured a oxygen mask and separate smoke goggles.
The SUB analysed that cabin crew did not use their protective equipment. Cabin crew did not perceive any aggressive/dangerous odour and described the smoke as dense haze. The SUB complained that the risk of incapacitation of a cabin crew member should not be taken by such judgement, the toxic nature of gases can only be assessed by chemical analysis and according equipment, neither of which is present on board of the aircraft.
The SUB analysed, using the largest part of the entire analysis, that engine oils, hydraulic fluids and other materials contain toxic substances, in particular organo phosphates, due to the outstanding properties as softener in plastic as well as lubricant even at high temperatures. Therefore all engine oils contain 3 to 5 percent of tricresyl phosphates (TCP), the ortho isomer of which can cause neuropathies.
The SUB wrote (in German Original, translation below):
Zu den bekannten Symptomen nach einem solchen Öldampf-Vorfall bei Passagieren und Besatzungsmitgliedern zählen Beklemmungen, Leistungsminderung, Sprachstörungen, gereizte Schleimhäute, brennende Augen, Husten, Speichelfluss, erhöhte Bronchialsekretion, Bronchospasmus (Krampfzustand der Bronchialmuskulatur), Atemnot, oberflächliches Atmen, bis hin zu Lähmungen und plötzlich auftretendes Zittern in den Gliedmaßen, Übelkeit, Erbrechen oder auch starke (migräneartige) Kopfschmerzen.
Eine beträchtliche Anzahl von Messungen der Flugzeugkabinenluftverunreinigung mit mehr oder weniger toxischen Substanzen wurde bisher weltweit durchgeführt. Jedoch gibt es signifikante Unterschiede zwischen den berichteten Ergebnissen. Dies kann eine mögliche unterschiedliche Realität zwischen verschiedenen Luftfahrzeugtypen in verschiedenen Stadien der Triebwerkswartungszyklen reflektieren. Unglücklicherweise geben die meisten Berichte nicht ausführlich genug Information in dieser Hinsicht wider. Auf der anderen Seite sind Messungen an sich schwierig durchzuführen und die fehlende Übereinstimmung kann systematische Fehler durch falsche Messmethoden reflektieren.
The known symptoms of passengers and crew following oil fume events include feel of anxiety, drop in performance, speech impediment, irritations of mucuous membranes, burning eyes, coughing, flow of saliva, increased bronchial secretion, bronchial spasm (spasm of the bronchial muscles), shortness of breath, shallow breathing up to paralysis, shaking of limbs, nausea, vomitting and strong (migraine like) head aches.
A substantial number of measurements of cabin air contamination with more or less toxic substances has been done worldwide so far. The results however show significant differences, which could reflect a possible different reality between various aircraft types and different stages of engine maintenance. Unfortunately most of those reports do not provide sufficient detail. On the other hand those measurements are difficult and the lack of agreement can indicate systematic errors in the measurement methodes.
The SUB analysed that following the occurrence neither crew nor passengers were offered medical assistance. There is no standard established in Austria of how to handle crew and passengers following fume events.
This article is published under license from Avherald.com. © of text by Avherald.com.
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