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Earlier this year, the Outer House of Scotland’s Court of Session handed down judgment in Gough v Cannons Law Practice [2025] CSOH 28 where the two pursuers sought damages for the loss of a chance to bring novel Aerotoxic Syndrome (“ATS”) claims against their former employers.
The cases were brought by former pilots (the pursuers) against a firm of solicitors (the defender).
As helpfully summarised at [2] of the decision:
Specifically, each pursuer claims to suffer from Aerotoxic Syndrome or “ATS”. This is a controversial diagnosis. The condition is not recognised in the International Classification of Diseases and there are no generally accepted or validated diagnostic criteria for it. Each pursuer maintains that his condition has been caused by exposure to toxic fumes on a daily basis while he was employed as a pilot.
Lord Richardson noted at [90]:
I heard on a number of occasions about the personal injury claims being brought by approximately 220 pilots and cabin crew at the High Court in London on the grounds of ATS. This group of claimants includes 51 claims which were issued by Thompsons in March 2019 involving pilots and cabin crew working for EasyJet, British Airways, Thomas Cook, Jet2 and Virgin Atlantic… The proceedings are being managed collectively and are at a relatively early stage procedurally. Five lead claimants have been identified and the lead defendant is British Airways.
The lead cases have been selected to give a fair spread of facts. They include some cases based on fume events and some based on chronic exposure. At present, the process of disclosure is ongoing. The remaining cases are being held in abeyance. Mr Hayward [of Thompsons Solicitors, acting for the claimants in the group litigation] thought that the trial in the cases would be likely to take place at the end of 2025 or early 2026. He estimated the trial would last 6 weeks.
The pursuers were arguing in Gough that, but for the defender’s negligence, the pursuers would have been part of the ongoing collective proceedings in England.
In the lead up to the forthcoming ATS litigation, this blog article aims to give something of a “sneak preview” of the potential battlegrounds by highlighting the key areas of contention in Gough in relation to the pilots’ underlying claims.
After all, Lord Richardson had the benefit of considering extensive evidence from “9 factual and 12 expert witnesses… The factual witness statements extended over 500 pages; the expert reports over 1,000; and there were more than 25,000 pages of productions” [6].
However, it is important to acknowledge the limitations of this “sneak preview”: the Court of Session’s approach in this loss of a chance case is different to what the High Court will be required to determine in the group litigation.
As set out at [340]:
the role of the court [in Gough] is not to predict the outcome of the ongoing collective proceedings in England but, rather, to value what was lost by the pursuers as a result of the defender’s negligence.
Thus, the Court was not tasked with conducting a “trial within a trial” but rather to value the chances of success of the underlying claims that the pursuers lost, by considering whether the pursuers’ chances of success can be rejected as negligible or speculative (see for example [433]-[434]).
Lord Richardson ultimately decided at [459] that “the pursuers had a real and substantial chance of success in their claims against Thomas Cook” whilst making clear that “in respect of each of the four aspects of the pursuers’ claims focussed on by the defender [the “battlegrounds” addressed below], significant uncertainties remain.”
The Court assessed the pursuers’ chances of success in their claims against Thomas Cook at 40% (which amounted to a loss of £24,762.80 in respect of former pilot Mr Gough and some £1.1m in respect of former pilot Mr Montague-Trenchard).
To determine the merits of the underlying claim, the defender in Gough contended that there were four fundamental issues which the pursuers would be required to address to be successful [294]):
The defender highlighted problems with the pursuers’ claims in relation to each of these issues which, the defender argued, meant that the pursuers’ claim would have been bound to fail and that there was therefore no need to evaluate the lost chance. That argument was ultimately unsuccessful.
To be successful in the underlying claim, the pursuers would have had to prove that their former employer Thomas Cook knew or ought to have known of the risk of injury to which the pursuers were exposed at the time of their employment (1998 to 2005 in Mr Gough’s case and 1998 to 2003 in Mr Montague-Trenchard’s case) [400].
Lord Richardson was not prepared to dismiss the pursuers’ chances of success as being negligible or merely speculative on the issue of foreseeability in light of the evidence he had heard. He accepted that Professor Howard’s generic report provided an evidential basis for the proposition that in 2004 in the UK, it could be said that “The problem of oil contamination of aircraft cockpit and cabin air supplies has been known for some years.” (AAIB Report 1/2004, Conclusions, para 15).”
He went on to say, though, “considerable uncertainties remain” on this issue which factored into his overall assessment of the pursuers’ chances of success [407]. Those uncertainties included both the actual and constructive awareness of Thomas Cook and the resolution of the question as to whether foreseeability of the risk of the injuries arising from fume events at the material time would be deemed to be foreseeability of the “type” of injuries sustained by the pursuers [407] (the pursuers submitting that the type of harm from fume events was of the same kind as that which arose from long-term exposure [238]).
This issue was dealt with comparatively briefly. Lord Richardson decided that the pursuers’ chance of success on the issue of breach of duty could not be dismissed as merely negligible or speculative albeit there was significant uncertainty in relation to this issue also [412]. TLord Richardson considered that the strength of the pursuers’ case on breach was dependent on them being successful in relation to causation. The pursuers’ argument went as follows: given the potentially very significant consequences of ATS, the pursuers had, at the very least, a good starting point on breach of duty as it would be very surprising if nothing could be done to address such a significant risk ([239][412]). On this point, the Court referred to Munkman: Employer’s Liability (17th edition) [quoted here in part]: “…The greater the magnitude of the risk and the greater the gravity of harm should the event occur, the higher is the duty to take precautions, even if these are expensive or difficult to adopt.”
The Court considered, by analogy with McGhee v National Coal Board [1973] 1 WLR 1, that the pursuers could succeed even if the precise mechanism which caused the injury was not known. At [414]:
The identification of the particular substance or substances the exposure to which the pursuers contend caused their condition is not an essential element of their claim against their employers. In my opinion, it would have been possible for the pursuers to succeed in their claims if, for example, they had proved, on the balance of probabilities, that their employment had caused or at least materially contributed to their symptoms without pinning down precisely which chemical or chemicals was responsible. Such a possibility would be consistent with the evidence I heard as to the composition of cabin air containing many different chemical compounds.
Lord Richardson highlighted the difference between proving something in a civil action on a balance of probabilities (legal proof) and the ordinary meaning of “proof” in other contexts, particularly a medical or scientific context. Legal proof is less stringent[415].
The Court had to consider two discrete arguments in relation to causation: (1) whether the problems as to causation were so significant as to mean that the pursuers’ chances of success were negligible and (2) whether ATS was a divisible condition [417].
Issue (1) was a significant battleground: the majority of the evidence that Lord Richardson heard was focussed on the general issue of causation [418].
At [419], Lord Richardson helpfully summarised the pursuers’ case on causation as follows:
The defender highlighted the absence of medical consensus as to any causal relationship between contaminated cabin air and the pursuers’ symptoms.
Lord Richardson went on to consider various criticisms raised in relation to the experts. Whilst he decided that he did not ultimately have to determine whether he preferred the evidence of one expert over another ([433]), Lord Richardson was satisfied that Professor Howard’s evidence “establishes a basis for inferring that the pursuers’ symptoms could have been caused by contaminated air to which they were exposed”. However, he found that Professor Bridge’s evidence raised a series of factors which “give rise to significant doubts in respect of causation”.
Those factors, set out at [435], included:
On divisibility, Lord Richardson concluded that “I do not consider that it follows from the evidence that I have heard that ATS is necessarily a divisible condition” [442]. He considered this issue went to the overall assessment of the pursuers’ prospects of success [444]. In reaching his conclusion on divisibility, he referred toa 2017 article by Professor Howard and his co-authors “The Aetiology of ‘Aerotoxic Syndrome’ – A Toxico-Pathological Viewpoint” which identified three complications in understanding the issue of causation: (i) the complexity of the mixture to which the aircrew are exposed; (ii) the wide variability between individuals’ ability to metabolise and detoxify OP compounds; and (iii) the fact that low-dose repeated exposure can increase the vulnerability of neurons to a subsequent high-dose event.
If the “sneak preview” of Gough is anything to go by, we can expect the battlegrounds in the forthcoming ATS litigation to be hotly contested with extensive technical and expert evidence. It will be interesting to see how the High Court applies longstanding and familiar legal principles, derived from historic industrial disease cases, to an entirely novel area. The forthcoming ATS litigation will have potentially enormous consequences for the airline industry and is keenly awaited.
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