Ryanair B738 near Stansted on Sep 18th 2014, unusual odour in cockpit

Last Update: September 27, 2016 / 15:00:53 GMT/Zulu time

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Photo of Ryanair EI-EFB, Boeing 737-800 — Ryanair EI-EFB, Boeing 737-800 (Photo credit: Cha già José / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Sep 18, 2014

Classification
Report

Airline
Ryanair

Flight number
FR-8352

Departure
Almeria, Spain

Destination
London Stansted, United Kingdom

Aircraft Registration
EI-EFB

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Ryanair Boeing 737-800, registration EI-EFB performing flight FR-8352 from Almeria,SP (Spain) to London Stansted,EN (UK) with 174 passengers and 6 crew, was descending through about FL200 towards London when the commander (26, ATPL, 3,250 hours total, 3,100 hours on type) became aware of an unusual odour in the cockpit, describing the fumes as chemical type, felt "something in the back of his throat" during the discussion of the fumes with the first officer, and suggested that both flight crew should don their oxygen masks. The crew subsequently declared emergency and continued for a safe landing on Stansted's runway about 15 minutes later. The commander checked with the cabin, was advised everything was okay in the cabin, and decided to taxi to the apron advising emergency services that no assistance was needed. However, the commander was on sick leave following the occurrence until Oct 2nd 2014.

Ireland's AAIU released their Synoptic Report concluding the probable cause of the serious incident was:

Residual contamination in the air conditioning system, leading to fumes/smells in the aircraft.

Contributory Cause(s)

An internal oil leak in a previously installed Auxiliary Power Unit, due to an unsuccessful workshop repair.

The aircraft had been involved in a tail strike event, see Accident: Ryanair B738 at London on Jul 29th 2014, tail strike on landing.

The AAIU reported that prior to the occurrence flight there had been a number of reports of unusual odours during descent on a number of previous sectors. The commander therefore instructed cabin crew and first officer to report any unusual odours as soon as noticed. The commander also briefed on what to do in case of unusual odours.

Pilot flying for the sector was the first officer, the commander was pilot monitoring.

The AAIB reported medical findings:

The Commander noted in his written statement provided to the Investigation that during the event flight, he noticed “chemical type fumes” in the flight deck and felt an “irritation/tingling sensation” at the back of his throat. On the direction of the Operator, he attended a doctor the following day. Medical examination found his lungs to be clear with no bronchospasm6 and no focal signs7. A lung function (spirometry) test was performed, with normal results. The medical report noted “the history is of inhalation exposure” and concluded that “one day later there is no evidence of any medical effects to this exposure”.

The Commander reported to the Investigation that, three days later, his throat irritation was still present. He spoke to the doctor via telephone and made another appointment for 25 September 2014. He did not return to work during this time. He said that when he visited the doctor on 25 September, he was granted a further week’s sick leave. The Commander reported to the Investigation that during this week he had headaches and throat irritations that eased by 2 October 2014, when he returned to flying duties.

On the direction of the Operator, the FO also attended a doctor subsequent to the event and no adverse medical findings were reported. There were no reports of smoke or unusual smells in the aircraft cabin during the event flight and the Operator informed the Investigation that the Cabin Crew did not attend a doctor following the event.

The AAIU reported that the APU had been replaced on Sep 1st 2014 due to hot section distress. After landing later the same day an entry was made in the tech log reporting an electrical smell after starting the APU in auto and bleed on. The APU was tested, no odour was detected, however the APU was declared inoperative and the aircraft was dispatched under minimum equipment list requirements.

The following night the APU was tested, again no fumes were found even though a different smell was noticed, that maintenance personnel believed was associated with replacement of the APU, and the aircraft and APU were released to service with the request to flight crews to monitor further developments.

On Sep 3rd another tech log entry was made reporting a strong smell of oil during descent. A borescopic inspection of the #1 engine was performed with no wettings found, an engine run was conducted with no findings and the aircraft was returned to service.

During the following days further troubleshooting tasks were performed including checks for APU oil contamination with no findings.

On Sep 9th 2014 a "serious obnoxious smell" during descent was noted. Maintenance noted: "On selection of L/H pack to auto using APU as bleed source, slight smell of oil fumes noted with very fine mist evident in flight deck only. Unable to reproduce smell on any further attempts. Cabin pressurised […]. Nil findings. #1 and #2 eng idle runs c/out independently using both packs and single pack only. Nil findings […]" The APU was declared inoperative and the aircraft was dispatched under minimum equipment list requirements.

Additional troubleshooting found evidence of oil on the "clamps attaching duct between bleed valve and A/C [aircraft]". The duct was removed but nothing was found.

On Sep 10th 2014 another note was written up reporting "slight smell on engine #1 start". The APU was replaced again, an oil contamination removal task was instructed, however, there was no evidence of this task having been performed.

On Sep 11th 2014, six flights after the APU replacement, maintenance noted: "APU bleed duct inspected – found mild oil in joints. Same cleaned. ACM [Air Cycle Machine] and water separator ducts insp. No fault found. Recirc filters insp. Found clean. # 1 pack func[tion] check carried out – ops normal, no smell apparent"

On Sep 12th 2014 a flight crew made following tech log entry:

During gnd ops with APU running, and even after APU off, eng running during taxi, t/o [take-off], crz [cruise], slight cheesy smell, same as explained on prev. occasions in this tech log. During final descent, strong heavy cheesy smell, first in f/d [Flight Deck] only, then reported in cabin by all 4 cabin crews. After landing, crews reported of slight headache and layer on tongue. Maintrol [Maintenance Control] contacted, who told us to check on return flight if agreed. During return flight, crew informed us of disorientation, which disappeared. No smell on ground in […] or during crz. During descent into […] passing FL150, idle thrust, smell returned, but much lighter.

The aircraft was withdrawn from service and extensive maintenance troubleshooting actions were taken in consultation with the aircraft manufacturer, both engines underwent borescopic inspections, the #1 engine was replaced, a good number of components in the air conditioning path were replaced, an oil contamination removal procedure was performed on both engines. Following engine runs with no smells observed the aircraft was returned to service on Sep 16th 2014.

The AAIU described maintenance actions following the occurrence flight of Sep 18th 2014:

Following the incident, numerous maintenance actions were performed at the request of the Operator’s Engineering department and with the assistance of the Aircraft Manufacturer. The APU bleed and surge valves were removed to permit inspections of the bleed air ducts. No contamination was found. The bleed air check valve was also inspected and no contamination was found. Borescope inspections were performed on both engines. A scavenge tube on the number one engine was found to be leaking oil and was replaced. This scavenge tube is located in the turbine section of the engine and therefore a leak in this tube could not adversely affect the air conditioning system.

Possible oil streaking was found on the number two engine at the stage one guide vanes of the high pressure compressor. The stage two blades exhibited signs of wetting on all blades with discolouration noted on the stage three casing. This resulted in the number two engine being replaced.

Borescope inspections were performed on the ducting at the number one and number two engine pylon bleed valves and at the L/H and R/H wing leading edge ducting for evidence of oil contamination and none was found.

The following components were replaced:

- The hydraulic air charging manifold and hydraulic quantity transmitters
- The number one engine PRSOV
- Both engine pre-coolers
- Both ACMs
- The L/H and R/H water separators
- The L/H and R/H condensers
- The primary and secondary air conditioning pack heat exchangers on the L/H an R/H sides
- The recirculation filters
- The bleed air isolation valve
- The flight deck muffler

An oil contamination removal task was performed and inspections were carried out to verify that contamination was removed.

The air conditioning ducting from the heat exchanger to the mix manifold and from the condenser to the flight deck muffler was inspected on the left hand and right hand systems, with no evidence of oil contamination found. The three-zone trim air valve and the temperature control valves were inspected and no oil contamination was found.

Engine runs were carried out at various power settings matching the last flight profile and at various air conditioning settings with no smells noted. The cold air outlets on both air conditioning packs were inspected for oil contamination following the engine runs, with no contamination noted.

The aircraft was operated on a positioning flight on 24 September, following which it was reported that there were “nil fumes/smells evident in cabin and flight deck through all phases of flight. Verbal report from flight crew concurs”. It was returned to service on 25 September 2014. At the time of writing, no further reports of smells or fumes on the aircraft have been reported since the subject event.

The APU, that had been installed on the aircraft on Sep 1st 2014 and was replaced on Sep 10th, was sent for analysis. The AAIU reported:

The APU was disassembled. The load compressor seal was found to be in “fair condition” and there was no indication that oil had by-passed the seal. Nevertheless, oil traces were noticed on the back face of the compressor impeller. A detailed inspection of the load compressor housing revealed that a previous workshop repair of the bearing carrier seat area had been unsuccessful and had “allowed oil to bypass the mating surface of the liner and load compressor housing”.

The AAIU analysed:

The workshop report for the APU noted that “the outer shell of the load compressor housing and the bleed air ducts were found to be covered by traces of oil” which was attributed to an unsuccessful workshop repair, which had been previously performed on a bearing carrier seat area. This APU had been installed on 1 September 2014 and following its installation, smells on board the aircraft began to be reported. It is likely that the oil leak, identified in the workshop report, contaminated the air-conditioning system following its installation until the APU was declared unserviceable by maintenance personnel on 9 September 2014. This APU was replaced on the night of 10 September. However, it is likely that the now-contaminated air conditioning system continued to cause unusual smells in the aircraft. Considering the numerous inspections performed by maintenance personnel, during which no contamination was found, it is possible that the nature of the contamination was such that it was not readily visible and was therefore difficult to detect.

The AAIU further analysed:

... extensive troubleshooting and maintenance actions were carried out on the aircraft following the reports of unusual smells, from the time that the first report was made until the incident occurred. In addition, assistance was requested from the Aircraft Manufacturer when reports continued to be raised. Furthermore, following the report of a “cheesy smell” on 17 September 2014, the day before the subject event, several maintenance tasks were performed. These included engine borescope inspections and the performance of an engine run with a similar profile to the last flight. No adverse findings were reported and the aircraft was released to service. This highlights the difficulty in positively identifying the cause of such reports.

The AAIU did not release any safety recommendations as result of the investigation.