The tip of the iceberg?

The quantitative recording of Fume Events and the lessons we draw from them

by Stefan Thielemann

In September 2017, our association member Arie Adriaensen was a speaker at the International Cabin Air Conference in London, a global forum for the exchange of information and views on cabin air quality on board of aircraft. Recently his article "Fragmentation of Information in International Data Gathering from Aircraft Fume Events"[1] based on this speech in the "Journal of Health & Pollution" was published and I would like to give an insight into its content. The scientific work analyses the incomplete data situation and its effects on decision-makers in aviation as well as on flight crews.

Since the introduction of bleed air technology, by means of which air is extracted from the engines to generate cabin pressurrization and air conditioning, there have been incidents in which cockpit and cabin personnel have reported health impairments or even incapacitation on board. It is not uncommon for the findings of the technical examination of affected aircraft to reveal traces of engine oil or hydraulic fluid in the cabin air system [2-6].

Nevertheless, there is still no global database for the recording of so-called Fume Events, which is why there is hardly any reliable knowledge about the dimension of the problem and investigations of toxicological effects are more difficult. In addition, reports of the events reported to the aviation accident investigation authorities of the respective countries are generally not publicly accessible and existing data from internal analyses of manufacturers and airlines are not shared.

The author sums up that the "share-your-experience"-principle of aviation in the field of Fume Events, which is recognized and respected across industries, suffers from a phenomenon which is called "organization without a memory" in science. Organisational barriers prevent the storage and processing of the experience already gained across institutions.

Despite the hurdles to data collection mentioned above, 55 investigation reports from various authorities from the period 1996 to 2017 could be evaluated for this scientific work. In 27 cases, the presence of engine oil or other aviation-specific fluid (hydraulic oil, de-icing fluid) was determined. This means that in almost half of the incidents investigated, leakages or contamination of the cabin air system were proven.

It should be emphasised that many of these investigation reports reveal that the manufacturers concerned had knowledge of hundreds of other documented incidents at the time which have not yet been mentioned in any other database or investigation.

Two examples are given:

"The aircraft manufacturer continuously follows-up submitted reports of disturbances from operators of the BAe 146 type of aircraft. The following information has been provided by the manufacturer. During the period from June-92 until January-01 a total of 22 cases were reported where the flight crew's capacity had been impaired. Of these, seven have been judged as serious since they affected flight safety negatively. During the period from January-96 until September-99, 212 reports were submitted by a specific airline to the aircraft manufacturer concerning tainted cabin air. Of these, 19 reports concerned the impairment of the crew's capacity. Seven of the reports were submitted directly by the crewmembers. From another 36 operators of the aircraft type a total of 227 occurrences relating to contaminated cabin air were reported during the period from May-85 until December-00. Of these, 11 reports concerned the impairment of the crew's capacity".

In 2007 the British Air Accidents Investigation Branch [2] (AAIB) writes:

"A search of the CAA database revealed that in the three-year period to 1 August 2006 there had been 153 cases of fumes, abnormal odor or smoke or haze in the flight deck and/or cabin of UK registered public transport aircraft of various types. Details on a number of the cases were limited but the available information suggested that around 119 of the cases had probably resulted from conditioned air contamination. This had commonly been caused by oil release from an engine, APU or air conditioning unit or ingestion of de-icing or compressor wash fluid by an engine or APU, with consequent smoke and/or oil mist in the conditioned air supply to the fuselage. It appeared that in many of the cases the crew members had found it difficult or impossible to establish the source of the contamination."

However, the article also compares the numbers of cases of the official investigation reports with other data sources. A query of the AAIB's [8] database of reportable aviation incidents revealed 37 confirmed cases of engine leaks and a further 26 cases of overfilled oil reservoirs in auxiliary power units (APUs) or engines of a total of 227 cases of suspected Fume Event of varying severity from 2001 to 2005. Within five years, the AAIB alone had recorded more proven cases of contaminated cabin air than had been investigated worldwide by the air accident authorities of all countries over several decades.

In Germany, too, there seems to be a discrepancy in the officially reported figures. The "Study on reported events in connection with the quality of cabin air in commercial aircraft" [9] of the Federal Office for Aircraft Accident Investigation (BFU) covers an eight-year period from 2006 to 2013. 659 events of this category were identified. Only in 50 cases the cause reported by the aircraft operator was related to overfilling or leakage of engine oil or penetration of de-icing fluid.

The internal evaluation of a medium-sized German airline included 167 entries in the fleet's technical logbooks, which contained complaints about contaminated cabin air and were recorded and evaluated within 18 months. Aircraft maintenance found oil residues in the bleed air system at 58 events, in a further 79 cases the manufacturer's specifications for the cause analysis after a Fume Event were not followed, so that the source of the impairment could not be determined. Thus a higher number of engine oil-related cabin air pollutants occurred in a period of 1.5 years for a single German airline alone than the total number of cases of the German aviation industry reported to the BFU over eight years. The date of this evaluation, the year 2009, falls within the period of the BFU study and should therefore also include all these events. It remains unclear how many of the airline's findings mentioned above were reported to the BFU. In any case, they would massively alter the statistical significance of engine oil leakages as the cause of the cases of contaminated cabin air recorded by the BFU. It is therefore questionable whether the available figures from the BFU study have any valid significance.

The risk to flight safety and health arising from Fume Events is not negligible. The study shows that the difficult access to already collected data, but also the generally rather incomplete collection, suggest that the exact extent of the cabin air problem is rather underestimated. As the first link in the information chain, we are also in demand here.

The author further comes to the conclusion that the knowledge gained from research reports, following the principle of "share-your-experience", should be better communicated to the pilots.

The withholding of the lessons learned from these studies not only influences the actions of the pilots, but also has effects on the regulatory authorities. They are recommended to expand the range of their information sources for decision-making processes and to be vigilant in the event of discrepancies.

The full article is available for download as PDF file.


  1. Adriaensen, A., ‘Fragmentation of Information’ in International Data Gathering from Aircraft Fume Events in Conference Proceedings, Sessions presented at the 2017 International Aircraft Cabin Air Conference 19-20 September 2017. J Health Pollution, 2019. 24.
  2. AAIB, Report on the Incident to BAe 146 G-JEAK during the descent on Birmingham airport on 5 November 2000. 2004, Air Accidents Investigation Branch, Department for Transport, United Kingdom: UK.
  3. Montgomery, M.R., et al., Human intoxication following inhalation exposure to synthetic jet lubricating oil. Clinical Toxicology, 1977. 11(4): p. 423-426.
  4. Swiss Federal Department of Transport, Investigation Report concerning the serious incident to aircraft AVRO 146-RJ 100, HB-IXN operated by Swiss International Air Lines Ltd. under flight number LX1103 on 19 April 2005 on approach to Zurich-Kloten Airport. 2006, Federal Department of Environment, Transport Energy and Communications: Bern.
  5. ATSB, British Aerospace Plc BAe 146-100, VH-NJX. Occurrence brief no. 200205865. 2003, Australian Transport Safety Bureau: Canberra, Australia.
  6. GPIAA, Air Incident Investigation – Final Report Airbus A-330-322, CS-TMT. 2009, Gabinete De Prevenção E Investigação De Acidentes Com Aeronaves.
  7. SHK, Incident onboard aircraft SE-DRE during flight between Stockholm and Malmö, M county, Sweden, on 12 November 1999. 2001, Statens haverikommission (SHK) Board of Accident Investigation: Stockholm, Sweden. p. 36.
  8. CAA, UK, CAA Mandatory Occurrence Reporting (MOR) - Engine Oil Fume Events – UK AOC Aircraft. 2011. p. 91.
  9. BFU, Studie über gemeldete Ereignisse in Verbindung mit der Qualität der Kabinenluft in Verkehrsflugzeugen. 2014, German Federal Bureau of Aicraft Accident Investigation.

Fragmentation of Information in International Data Gathering from Aircraft Fume Events (PDF)

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