Criticism of the SCHINDLER-Study 2013: B. K. Schindler, T. Weiss, A. Schütze, St. Koslitz, H. Chr. Broding, J. Bünger, Th. Brüning: Occupational exposure of air crews to tricresyl phosphate isomers and organophosphate flame retardants after fume events

The following text is closely related to another documentation: "The Hunt for TCP (Tricresylphosphate)", available at, and can be accessed and linked directly via the short (perma)link

These are arguments regularly put on the table by BG Verkehr (German Statutory Accident Insurance for Transportation), which are of little use.

Regularly quoted - concerning the alleged irrelevance of a potential exposure / influence of TCP or ToCP (tricresyl phosphate from the chemical family of organophosphates, which are contained in engine oil) - the so-called SCHINDLER et al study from 2013 (bibliography see appendix):

This so-called SCHINDLER et al study is characterized by considerable weaknesses, namely: 

  • in their scientific statement as well as
  • related to the applied scientific standards.

Following, the most important points of criticism are compiled as a result from several individual criticisms (ANDERSON, Vereinigung Cockpit, XB, RFB), which are listed in the appendix.

The central points of criticism and the pointing out of the methodical weaknesses originate from several scientists and institutions:

  • Judith ANDERSON MSc, Association of Flight Attendants, USA
  • Association Cockpit, Frankfurt/M.
  • Prof. Dr. med. Xaver BAUR, Berlin
  • Prof. Dr. med. Rainer FRENTZEL-BEYME, Bremen

Summary by Prof. Dr. Johannes LUDWIG (communication scientist).

Summary of points of criticism of the "SCHINDLER et al study 2013" regarding the consequences of ToCP exposure in aircraft

Re 1: The scientific output

The study does not reveal any significant new findings: TCP could not be detected in its toxic variants (isomers).

Such a negative result in science is not uncommon. It only means that one could not find what one was looking for. So far the fact.

The interpretation of this fact leads to 2 options:

  • Option 1: What one had been looking for de facto does not exist. Fullstop.
  • Option 2: What one had been looking for exists. But one could not find or prove it. For example because the search method was unsuitable.

For SCHINDLER et al the matter is clarified: only option 1 is possible. Probably because it was a study commissioned by the DGUV (head of all German Statutory Accident Insurances) or the DGUV's own IPA Institute: they wanted scientific proof that there was "nothing to it" in the criticism of the dangerousness of Fume Events and the claims of injured parties that were based on it.

Exactly in such a fashion SCHINDLER et al writes:

  • "The lack of data on TCP in cabin air during fume events makes it currently difficult to assess the exposure of air crews to TCP" (p. 646)
  • "The reported health effects in air crews can hardly be attributed to an o-TCP exposure" (p. 647).

Another explanation, option 2, is not addressed at all. For example, the questions are not discussed, whether

a) the correct metabolite has been selected as measuring size

b) the quantities to be measured were sufficient,

c) or the 'minimum level of detection' was set adequately. And

d) and not at all that there are known genetic differences in the metabolism of humans.

However: "significantly higher values" were found, i.e. measured, for TBP and TPP, for example, regardless of the other strains with which this is compared. TBP and TPP are also potential hazardous substances that are used, for example, as flame retardants in hydraulic fluids. 

In the PubChem database, TBB (tributyl phosphate) is classified as a suspected carcinogen (section 12.1.1.): The significantly higher values for flight personnel are only mentioned as a minor issue in the study.

Re 2) Methodological procedure

Scientific honesty begins with an exact description of what you have studied and analyzed or experimented on.

  • Example: Size of a sample. According to SCHINDLER et al, urine samples were analyzed for TCP isomers from 332 pilots and cabin crew members on joint flights who had reported "fume/odour". It does not mention that (only) 51 flights were involved.
    With a suspected and officially conceded frequency of serious "fume/odour" incidents of 1:2000 this sample size is much too small. In other words: statistically unusable.

  • Neither was it discussed whether the observations or measurements after these 51 flights or 332 persons referred to were either outward or return flights in one and the same aircraft. Or possibly For aircraft whose relevant seals of the turbine shafts are working more or less well, for example because they have just been maintained, the probability of a serious "fume event" occurring is low. There is not a single word about this.

  • No statements are made about the use of additional performance requirements of the engines and/or the APU, nor about corresponding weather and environmental conditions during the flights.
    It is known that seals leak especially when the aircraft has to enter the high performance phase (take-off and landing, aggravated weather conditions during flight).

  • It is also not possible to find out which aircraft types were involved. It is well known that serious fume events occur primarily in certain aircraft types (BAe 146, Airbus 319 and 320, Boeing 757).

  • The SCHINDLER et al study does not address the exact reason for the samples examined after the flights. Talk is only about flight personnel "who reported fume/odour during their last flight". Thus, there is neither a clear definition nor information about the conditions under which flight personnel voluntarily submitted to the examination. Thus, everyone could decide at a whim whether they thought they had noticed anything. And if so, what.

  • The regulations CS 25.831 and CS 25.832 prescribed by the EU, in particular the specification CS 25.1309, which requires sensors for the purpose of a) detection and b) warning, are disregarded by all airlines and are not controlled or enforced by the EASA.
    Thus one can basically distinguish - at first linguistically - between "Fume" versus "Smell" event, "Fume and Smell" or "Smoke and Fume" event. In the IATA rules and regulations, for example, the term "Cabin Air Quality Events" is used, whereby smoke, fume, odours can occur alternatively and/or cumulatively. BG Verkehr regularly reduces such events to an exclusive occurrence of "odours". The problematic situations which, according to the officially conceded probability occur with a frequency of 1:2000 flights, are still generally referred to as "fume events" and thus compete in terms of language and facts with the non-hazardous situations of "smells" of various kinds. It would make more sense, as suggested by SCHOLZ 2019, to refer to the serious fume events, where it usually (but not always) smells like "smelly socks" or an intense "acrid smell" can be perceived, as "Cabin Air Contamination Event (CACE)". In this text, "Fume Event" refers to such a "CACE".

  • However, since none of the "fume/odour" incidents that occurred has apparently led to a report being made to the AAIB or the BG Verkehr (in any case, not a single word has been said about this), the only conclusion that can be drawn is that none of the occasions for the voluntary investigation can be a serious fume event or a cabin air contamination event.
    This would require the existence of appropriate sensors, i.e. qualitative and quantifiable information about contamination of the cabin air. Such instruments do exist. However, the airlines and the responsible professional association for transport are not interested. Otherwise, such sensors would have been used long ago. 

This would make it possible to set aside any comments about the significance of such a study, which is regularly traded highly by the BG Verkehr and which - actually - should make statements about the health effects on flight personnel, as  irrelevant.

However, since it represents an important element in the strategy of the statutory accident insurance (GUV) or the responsible Berufsgenossenschaft Verkehr (BG V) to trivialize potential dangers and hazardous substances in order to fend off claims by those affected and rely on ignorance of the complexity of the interrelationships among those affected and/or their lawyers, including the judges, further points of criticism are to be made here.

  • No less important to scientific honesty is the disclosure or transparency of the methodological procedure. It is generally known and communicated by the BGV itself that blood and urine samples must be examined promptly in order to be able to perform meaningful human biomonitoring (HBM). The time span is 24, maximum 48 hours.
    As the Vereinigung Cockpit (VC) has found out through many inquiries, this requirement has apparently not been consistently met. It has been reported that (only individual?) samples were not sent refrigerated. Some were apparently even on the road for several days. Such samples are absolutely worthless.

    SCHINDLER et al do not comment on this aspect with a single word.

    It would have made sense, for example, to carry out monitoring of the cabin air in parallel to the 
    (in parts absolutely unsuccessful) urine tests. This was not done. In the SCHINDLER et al study this is not even a desideratum. There were also no blood tests performed parallel to it. According to the MAK commission, only the blood test is useful when analyzing the ToCP indicator "creatinine".
  • The urine samples examined were taken only once and obviously at a considerably inconsistent time, because it is said that they were collected within 12 hours after exposure. In addition, there is no precise knowledge about the excretion of the tested substances in humans. The authors therefore only mention experiments in rats that excreted 90% of p-TCP in urine within 24 hours. For this reason, too, the results are hardly meaningful; it must be assumed that the actual exposure is far higher than was derived from the results of the one-time samples taken more or less randomly and inconsistently.
  • Further this is general scientific standard: The force of expression of a comparative study stands and falls with the control group which can be compared.
    SCHINDLER et al use a cohort from their historical collection: urine samples, 5 years old, which were collected for other purposes at the time. And this within an age brackett from 11 to 68 years. And, as SCHINDLER et al emphasizes, from a "general population with no known occupational exposure to organophosphates.

    The significance is therefore also reduced to near zero in material terms.

Further details will not be discussed here.

Conflict of interests?

As a final remark, the question remains: Have the authors commented on possible conflicts of interest in connection with their work, as is the general standard?

SCHINDLER et al do not, according to their own statements. We know from sociology and the ethical discussion of medicine that many scientists see themselves as completely independent and neutral in their statements, and do not consider it possible that things could be any different. This seems to be the case with SCHINDLER et al.

The author of the publication, Birgit Karin SCHINDLER, is - as well as all other co-authors –an employee of the IPA Institute, an institution of the German Social Accident Insurance (DGUV), which is organized as an association and supported by the professional associations. Through this central umbrella organization, they bundle their interests and (can) enforce them due to their monopoly position.

The 'review' of the study, which is accompanied by critical comments here, is a commissioned work of that professional association, which is financed by the aviation industry and therefore naturally has no interest in communicating other findings.

Of course there are. For not only the ToCP examined by SCHINDLER et al and the likewise toxic TCP versions (a total of 5 further isomer positions of TCP), which are not further examined here, play a role during Cabin Air Contamination Events, but also many other substances. For example the no less toxic n-hexane, which can enter the cabin air in case of contamination by hydraulic fluids (see for example MACKENZIE-ROSS 2008 and 2016, RENEMANN 2016).

How important the professional associations and/or their IPA institute estimate the SCHINDLER et al study in their strategic measure bundle to be, becomes clear by the fact that with this - technically and organizationally not very complex - investigation and/or publication further co-authors were added:

  • the head of the IPA Competence Centre for Medicine (Prof. Dr. med. Jürgen BÜNGER)
  • and one of his colleagues (Prof. Dr. med. Horst Christoph BRODING),
  • the head of the IPA-Biomonitoring (Dr. Tobias WEISS)
  • and one of his employees (Dipl. Ing. Stephan KOSLITZ)
  • and - last but not least - the head of the IPA Institute himself (Prof. Dr. med. Thomas BRÜNING).


The study SCHINDLER et al 2013:

 Birgit Karin Schindler, Tobias Weiss, Andre Schütze, Stephan Koslitz, Horst Christoph Broding, Jürgen Bünger, Thomas Brüning (2013): Occupational exposure of air crews to tricresyl phosphate isomers and organophosphate flame retardants after fume events, Arch Toxicol  87: 645-648

Critical comments by:

ANDERSON, Judith (2014): Comment on Schindler, BK, Weiss, t; Schütze, A.; et al. „Occupational exposure o fair crews to tricresyl phosphate isomers and organophosphate flame retardants after fume events”, Arch Toxicol (2013) 87: 645-648 – Letter to The Editor

Vereinigung Cockpit (2013): Review and comment on Schindler et al, document written for the use of the scientific based discussion at the IFALPA Meeting in Auckland   

Mündliche und schriftliche Anmerkungen und Diskussionen mit Rainer FRENZEL-BEYME (RFB), Xaver BAUR (XB), Arie ADRIAENSEN (AA)

Studies that focus on other hazardous substances and are mentioned here:

Sarah J. Mackenzie Ross (2008), Cognitive function following exposure to contaminated air on commercial aircraft: a case series of 27 pilots seen for clinical purposes, Journal of Nutritional & Environmental Medicine 17 (2): 111-126

Virginia Harrisson, Sarah J. Mackenzie Ross (2016): An emerging concern: Toxic fumes in airplaine cabins. Cortex, 74: 297-302

Reneman L, Schagen SB, Mulder M, Mutsaerts HJ, Hageman G, de Ruiter MB (2016): Cognitive impairment and associated loss in brain white microstructure in aircrew members exposed to engine oil fumes. Brain Imaging Behav. 10 (2): 437-444


This text was created within the framework of the research project "Risk perception" at the Competence Center Communication (CCOM) of the University of Applied Sciences (HAW) Hamburg: ( as well as and can be accessed directly at

Related documentation on the substance in question, tricresyl phosphate (TCP), is available at (FORTHCOMING !)