Swiss RJ1H enroute on Sep 3rd 2016, fumes in cockpit and cabin

Last Update: March 14, 2023 / 16:08:12 GMT/Zulu time

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Incident Facts

Date of incident
Sep 3, 2016



Flight number

Aircraft Registration

ICAO Type Designator

A Swiss Global Airlines Avro RJ-100, registration HB-IYU performing flight LX-2813 from Geneva to Zurich (Switzerland) with 88 passengers and 4 crew, was climbing out of Geneva, when just after having cleaned up the flaps the crew switched to engine bleed air supply for the air conditioning systems. Shortly afterwards an acrid odour was observed on board of the aircraft without haze or smoke. The crew switched air conditioning to APU bleed air supply, which improved the situation, however, after 10 minutes the acrid odour became stronger again. The flight crew donned their oxygen masks and requested priority for landing in Zurich. The aircraft landed safely on Zurich's runway 14 about 20 minutes after requesting priority.

Switzerland's SUST rated the occurrence a serious incident and opened an investigation.

On Mar 14th 2023 the SUST released their final factual report without a conclusion, however the following analysis:

After take-off, a fume smell became noticeable when the air supply was switched to engine bleed air. The flight crew immediately turned off the engine bleed air and, after the APU had been restarted, again supplied the air conditioning packs with its bleed air. These actions were appropriate for the situation and both logical and justified, as the APU bleed air had conditioned the cabin’s air on the ground without any problems. It was not foreseeable that the fume smell would return after a certain period of time.

When the fume smell again became noticeable and also had physical effects on the flight crew, they immediately put on their oxygen masks. This behaviour was safety-conscious. Involving the cabin crew in the assessment of the situation and repeatedly enquiring about the air quality in the cabin was prudent.

However, the serious incident has once again demonstrated that it is virtually impossible to either identify the source of the contaminated air or to predict its further development. Therefore, flight crews would be well-advised to classify any occurrence of contaminated air that requires oxygen masks to be put on as an emergency and to act accordingly.

The report describes the following medical findings:

As stated earlier in the report, the pilots had noted a fume smell shortly after take-off which was clearly not normal. In order to improve the air supply, several changes were made to it and approx. 2-3 minutes passed during which contaminated air was inhaled. It is not clear if the changes definitely improved the air quality. However, to begin with, the pilots felt that they experienced an improved situation. But after another 6 minutes or so, the first symptoms appeared. The pilot felt an unpleasant pressure in his head. The co-pilot experienced a headache and sore throat. Therefore, the decision to put on their masks with 100% oxygen was safetyconscious. This made the situation tolerable and the flight crew was able to complete the flight without experiencing any additional symptoms.

After the flight, the two pilots went to the Airport Medical Centre (AMC) for a medical checkup. The main reason for this was that the co-pilot was experiencing a severe headache and an extremely sore throat.

Both pilots were examined at the AMC. These examinations did not produce any causal findings that could definitively have pointed towards an exogenous intoxication as described by the pilots.

Over the course of the following days, both pilots reported to their Aviation Medical Examiners (AME). The pilot was signed off as healthy within a short period of time and was certified as fit to fly on 4th September 2016. The co-pilot had a somewhat longer recovery period and did not return to flying activities until 14th September 2016.

The pilots mentioned that they considered the medical care following the serious incident to have been suboptimal.

The report describes the following technical findings:

Maintenance documentation shows that the aircraft registered as HB-IYU had previous history with regards to smell.

During flight LX 1613 from Milan Malpensa to Zurich on 11th July 2016, the flight crew already complained about an odour reminiscent of dirty socks. The air conditioning packs and the APU were examined and no abnormalities were found.

During flight LX 2813 from Geneva to Zurich on 26th August 2016, the flight crew reported a strong fume smell after they had switched the supply for the air conditioning packs from APU bleed air to engine bleed air. The following work was subsequently carried out:

- the torque values of the air cycle machines were checked;
- the APU was checked for faults;
- all four engines were examined for potential leaks;
- all four engines underwent a test run;
- as a preventative measure, the cockpit and cabin air filters were replaced.

In this case, too, the maintenance company could not determine the source of the fume smell that had been detected.

As in both instances the maintenance company did not produce any findings and the flight crew neither put on their oxygen masks nor sent an urgency message to air traffic control, the STSB had no reason to investigate these two cases.

After the serious incident on 3rd September 2016, additional experts from the MCC3 troubleshooting department and from the power plant and system engineering division were consulted for the investigation. As a result, the measures taken included inspections of all four engines and the APU using a borescope to find a potential oil leak. No such leak was found.

The extensive checks showed smaller discrepancies that could possibly have led to a fume smell. Most notable, however, was a leak in engine 1’s IDG4 oil system. The IDG oil system works independently of the engine oil system and its components are arranged around the engine compressor. The temperature control valve is situated exactly in the twelve-o’clock position directly above the engine compressor. It was found that the oil pipe connections for this temperature control valve had not been tightened using sufficient torque. Oil was therefore able to drip onto the engine compressor and get through the bleed band openings into the engine compressor, therefore also reaching the engine bleed air and the air conditioning circuit.

Another possible contributory factor was recorded: instead of flowing overboard, the contaminated air was able to get into the air conditioning circuit because the APU breather and the engine oil cooler ventilation pipes had not been correctly aligned.

On completion of all of these checks, a test flight was carried out during which all possible air and air conditioning configurations were tested. All of these tests showed no abnormalities.
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Incident Facts

Date of incident
Sep 3, 2016



Flight number

Aircraft Registration

ICAO Type Designator

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