European transport commissioner Antonio Tajani and several French politicians have seen fit to pronounce on aviation safety in the wake of the Yemenia Airbus A310 accident in a way that reflects a distressing degree of nationalistic prejudice.

Without any knowledge of what caused the Yemenia accident, they have clearly pre-judged the carrier as not being up to standard.

A little more than month ago an Air France Airbus A330 tragically went missing over the Atlantic; in August 2005 an Air France A340 was completely destroyed in a landing at Toronto Pearson airport; and in 2000 the airline lost a Concorde and everybody on board. What would the European Commission and France think of politicians from other countries who drew conclusions about Air France and the DGAC (French aviation authority) from these accidents, especially if the comments were made public before any facts about the events had been established?

Suddenly Tajani is calling for European air safety standards to be enforced worldwide. The media's response to his statements has been to report him as calling for a worldwide airline blacklist, an idea that seems to appeal to editors.  But what exactly is a global blacklist? What would its purpose be? And who would organise it, under which law, and on what authority?

The EU does not have the power to enforce its rules or standards outside Europe, and it never will have. The International Civil Aviation Organisation already has the task of policing global standards. Any influence the EU wants to wield can be exercised through ICAO.

Europe already exercises the right to stop airlines that do not meet ICAO standards from entering EU airspace but, having examined Yemenia, it had chosen not to do that. Incidentally, the airlines that the EU bans are on its global blacklist of all foreign carriers that may not use EU airspace: surely that qualifies as a global blacklist? Or do we need another? 

When the Yemenia accident happened, although no facts whatsoever had been established about it, suddenly it was open season for the most unpleasant kind of political posturing. Another thing that the politicians pushed out - and the editors lapped up - was the story that Yemenia had mounted a conspiracy to transfer French and Cormori passengers from the gleaming A330 used on the Paris-Sanaa leg of the journey to a rusty A310 for the fatal Sanaa-Moroni flight. The fact that it is normal practice operate a big aeroplane on a trunk route and a smaller type on a minor route like the one from Yemenia's hub to the Cormoros Islands was apparent missed by politicians and journalists.  

Of course, where France is concerned, this attitude dates back to the Flash Airlines accident in January 2004. The now-defunct Egyptian charter carrier's 737-300, packed with French holidaymakers, was lost climbing out of Sharm el-Sheikh. It was discovered that Switzerland had banned Flash, and France itself had had its doubts about the airline but had not banned it. So political and media hell broke loose at the time.

French politicians now seem to feel they must be seen to be doing something, but their actions consist only of inelegant attempts to cover their own backsides.

They sound almost as bad as Brazilian politicians in the wake of the Gol collision and the TAM Congonhas overrun, who fired off salvoes of blame in all directions to distract attention from the fact that they had underfunded the aviation infrastructure in the country they governed. It was high farce.

And these people are the guardians of our regulatory systems and our safety? Don't make me laugh.

The following statements apply to all accidents involving all airlines flying all types of aircraft, whether people in them were hurt or not:

1. If the accident involves a big Western-built jet airliner with lots of people on it, it will either be an Airbus or a Boeing, because they are the only Western aircraft manufacturers left on the planet that make big jet aeroplanes.

2. Accidents do not happen because the aeroplane is an Airbus or a Boeing (or an Embraer or a Tupolev), they happen because of a combination of circumstances that often involves natural phenomena like bad weather or darkness (or both), sometimes involves a technical problem, and almost always involves human mistakes or frailties (plural).

3. The humans who made the mistakes will either have made errors of commission or omission (or both), and the errors can become contributory factors or directly causal - usually the former. The list of people (not exhaustive) who might have made a contributory mistake includes:  aircraft and aero-engine manufacturers: airframe, engine and avionics maintenance engineers; airline operations personnel; airport handling agents; cargo or baggage  managers; air traffic controllers; or pilots.

4. The part played by the corporate or departmental managers whose employees made the front-line errors or omissions might prove to be critical in an accident if the mistakes were the result of inadequate employee selection, training, supervision, or management communication (two-way).

5. Pilots are "the system's goalkeepers". Their main job may be to aviate, navigate and communicate, but they also have to deal with the results of any failure at any point in the organisation upstream of them (see item 3). If the system bangs enough fast balls at them, they will eventually let a goal through, and the media will call it pilot error.

6. Prof James Reason (who invented the "Swiss cheese" model of organisational safety management) was right. Humans will inevitably make some mistakes, so to imagine you can prevent them completely is delusional. The optimum answer is to build a system that is error-tolerant, with multiple layers of defences that will identify and correct a mistake before it combines with other circumstances to become dangerous. That applies to both companies and to aircraft design. Pilots are the last line of defence against errors in either.

7. It is not at all rare for the cause of an airline accident to remain a mystery for a long time, especially if human factors are involved, which they usually are.

8. Accident investigators tend to establish lots of individual facts very quickly because it is easy to see what the result was, but the cause is usually not evident.

9. The flight data recorder and cockpit voice recorder ("black boxes") are both very important to gaining a full understanding of precisely what happened and why it did. But if most of the wreckage, including critical parts like the flight deck, the engines and the control surfaces, is recovered, a great deal can be deduced without them.

If Paul-Louis Arslanian, the BEA's chief investigator in charge of the AF447 probe, says he does not have any answers yet, how can the rest of the world be so sure of its many theories?

Arslanian has more direct access to information than any of us has, and an international team of the best analysts available. But you can tell by his demeanour that he doesn't have answers yet. Not of the causal variety, anyway.

Like the rest of us who want to understand what happened, I'm certain he has fears about what he might find but, as he reminded journalists firmly at a press conference today (17 June), it is his job at all times to deal only in established facts. He is clearly very tired of the out-of-control speculation about AF447 which, he says, only serves to create "confusion".

I believe that the reason Arslanian called the press conference today, despite not having any more technical information to impart since the last time he spoke about a week ago, was because it was an opportunity he could not afford to ignore. The global media was gathered for the Paris Air Show on the doorstep of the BEA's Le Bourget headquarters, so he thought he would do his best to paint a picture of the task his team faces, and to describe in detail the nature of the search for evidence. 

The search so far, and the plans for the next few weeks of the search, will shortly be revealed on Flightglobal. They are impressive, multinational, and a testimony to the industry's determination to do what it takes to ensure that mystery is dispelled.

AF447 is like other accidents in many respects. It's absolutely normal not to have a clue, for months, about what was likely to have caused a recent accident, even if it took place at a major international airport. Only a little less than three weeks have passed since AF447's loss, but because of where it took place, nothing truly meaningful has been recovered yet. 

What has made this accident feel somehow different is the fact that we have been tantalised by the ACARS data. That is a first. We are not used to it. The trouble is the ACARS data is incomplete, generating questions but providing no answers. It only supplies symptoms and doesn't identify the disease. As a result, the field of plausible possibilities remains almost endless.

The interrupted ACARS data provides no evidence of why and how the aircraft got from a high cruising altitude to contact with the sea. It provides us with no aircraft structural data, and absolutely no information about what the crew saw, felt, thought, said and did.

Nature abhors a vacuum. Information vacuums are just as unpopular. Intelligent people will not be able to resist rehearsing "what if" scenarios, and there's nothing intrinsically wrong with that - unless the people doing it forget that they are just guessing.

This group has just disembarked after a 27 May A380 flight from Airbus' Toulouse base.

The flight was mounted to demonstrate two really clever and seriously useful avionic advances that Airbus is just about to see certificated. One will make airborne collision a little less likely, the other will prevent runway overruns. Overruns are the most common type of aircraft accident, and one of the most expensive.

The team in the picture (above) consists of some technical journalists - including me (on the far left) - and numerous Airbus engineers and test pilots all of whom have played their part in bringing these development programmes to fruition.

The skipper on this flight - he's the 6th person from the left wearing the blue tie - was experimental test pilot Claude Lelaie.

Lelaie

 During the flight we carried out a number of full-stop landings to demonstrate the aircraft's brake-to-vacate (BTV) system, but also to show off an amazing extrapolation of the BTV's inherent capabilities which - for me - was the day's showstopper: it was ROW/ROP - the runway overrun warning and protection system.

And, finally, we witnessed  - in action - a new way of making TCAS resolution advisories (RA) more manageable for pilots. More of that later. 

BTV allows the pilot to pre-set the runway exit at which he wishes to turn off, so the aircraft's braking system arranges smooth reduction of runway speed down to 10kt with 50m to go to the exit - unless the pilot wants to intervene because it's a fast-exit taxiway and he doesn't need to exit that slowly. 

This may sound a like the ultimate in unnecessary optional extras, but it would be incredibly useful, especially in poor visibility, for minimising runway occupancy time.

How does the aircraft's braking system know where the exit is? GPS, of course.

Now, imagine you're flying your A380 and you are on short final approach to runway 32L at Toulouse. I'm sitting in the back watching your performance on these two displays (below) on a rack of monitor instruments. At the moment you're doing nicely:

The right image shows split shots from two video cameras, one beneath the belly and another on the fin. In the former, the nose-gear is obscuring the runway threshold.

The left image, absolutely contemporaneous with the video, shows the aircraft's position relative to the runway (the magenta aircraft symbol). Sorry I didn't get a video of this because if I had you would be seeing the two images - the real world and the runway plan - moving in synch. 

Here's a picture of the same scene taken from the flight deck, but from a little further out:

...and here's me (below, left) keeping an eye on you from the back (I can see all the flight deck activity - you're on video):

Now let's have a look at ROW/ROP and what it will do for you. Here's the control that will enable you to tell the aircraft what you want the brakes to do:

If you want BTV, you select it. If you just want a normal landing you select the braking action you want.

Now here's a picture that will enable us to identify the essential offerings available:

Just before your top of descent briefing you've called up this image on your navigation display so you can choose the landing you want at Toulouse. You've toggled the cursor (magenta chevrons) onto the threshold of runway 14L and clicked. That has designated the runway, and up comes the magenta crossbar that tells you where your landing roll would come to a full stop if the runway was dry, and a second - further on - if it was wet. That's ROW/ROP working for you. If the runway was too short the crossbars would be in the overrun.

If you had selected BTV for the brakes, you would get the same display, but having designated the runway, you would have then to move the cursor over the image of the exit you want, and click to designate that.

Smart, eh? But it's also easy to use.

The Southwest pilots who overran at Midway on a snowy night would have given a lot for something like this.

But it gets better.

When ROW/ROP gives you those stopping point designators for your top of descent briefing, it assumes you will fly a standard profile at standard reference speeds, crossing the threshold at 50ft and putting the beast down in the touchdown zone. But it still works if you don't do any of those.

If you are high and fast on approach, ROW/ROP knows, and the stopping point designators move away from you down the runway. If you then carry out an extended flare as well, they may move beyond the runway end and, if they do, you will get two warnings: one scripted on the primary flight display saying "runway too short", and a recorded voice saying the same words.

What I tell you now is not strictly relevant, but I was struck by it just the same: the voice that tells you "Runway too short" (or alternatively "If wet, runway too short), is highly compelling because it's different: it's not one of those dead-pan, mid-tone, American-accented voices. It's a male voice, but pitched-up, and with an exquisitely English English accent. Your invisible guardian sounds as if he is looking over your shoulder and is genuinely worried about what he sees.

It would make anyone go-around.

But if you elect not to go around, when you touch down the system gives you absolutely maximum braking for the conditions.

Anyway, ROW/ROP is fantastic, and the same capabilities and logic that generated it could be used to create a take-off performance monitoring system, something lots of people have tried to do before and failed. My guess is that Airbus will go there, but they are certainly not admitting it.

Now let's look at the TCAS (traffic alert and collision avoidance system) improvements. Project leader for the programme, Paule Botargues (below), is explaining the system to us before the flight:

Botargues

Botargues and her team haven't tampered with TCAS itself, they have just integrated TCAS with the autopilot and the flight director. It's easy for me to say, blithely, that the team had merely to integrate these functions, but the task is actually very complex because it entails so many systems, inputs and so much software.

Remember that, at present, if the crew receives a TCAS RA, they disconnect the autopilot and fly the vertical RA trajectory manually.

Now the result of Airbus' work is that, if the autopilot is engaged when an RA is generated, unless the pilot disengages it the autopilot will fly the RA trajectory precisely as demanded. If the pilot is flying manually at the time, he does not have to transfer his attention to the TCAS RA indicator and fly according to that, he just follows the flight director in the normal way and thus performs a perfect RA trajectory.

To test and demonstrate the system, the  the team has rigged up a system that generates virtual conflicting traffic on the TCAS display, causing it to provide the usual sequence of visual traffic proximity awareness, followed by a traffic advisory and finally a resolution advisory. This picture I took in flight is not very good, but on the nav display you can see the yellow aircraft symbol (our A380) and the red "conflicting aircraft" just ahead of it that has generated a "climb" RA. 

Studies show that pilot reaction to RA is frequently slow, but when the action finally comes it is almost always an over-reaction, occasionally dramatically so, resulting in altitude deviations that are hazardous in their own right.

The TCAS RA indicator (see on the right of the image below) is not easy to fly accurately, especially when the pilot is psychologically aware that failure to follow it may result in a terminal collision:

So this new system, which Airbus calls AP/FD TCAS mode, makes sublime sense.

Just before I sign off I'll share a little anecdote about this demo flight.

One of the technical journalists that had come along to test-fly the new systems was a recently retired Delta Air Lines Boeing 777 pilot called Earl Arrowood who had never flown a fly-by-wire Airbus of any kind in his 30,000h career. And like the three other journalist/pilots there that day who were taking turns in the left hand seat, this hoary old Georgian aviator was given no simulator time to prepare for the experience, but blithely carried out several approaches, full-stop landings and take-offs.

You want to know what he thought about flying this giant, sidestick-controlled Airbus after a lifetime of McDonnell Douglas and Boeing? I asked him afterwards - although I didn't really need to because he was so enthusiastic about it. He told me he loved it, and it took him "less than a minute" for him to forget he was flying a sidestick.

Air France has just admitted that it cannot hold out hope any longer of re-establishing contact with flight AF447. By now, the company says, this Airbus A330-200 from Rio de Janeiro to Paris would have run out of fuel if it were still airborne.

At present, information is very sparse. According to the airline, the last report from the aircraft provided evidence of an electrical short circuit that occurred shortly after encountering turbulence, and possibly a lightning strike. Aircraft are designed to be able to survive lightning strikes. They have to be, because they occur often, usually causing minor damage but, very rarely, serious damage to electrical or control systems.

Modern aircraft are so reliable and have so many backups for every system that a single electrical fault, or even the loss of an entire circuit, would be easily dealt with if that were all that had occurred. If the fault has been correctly interpreted as a short-circuit, that raises the spectre of an electrically-caused fire, and fire is always serious in an aircraft. But at this point there is no access to evidence of that type.

An event like this is the kind the aviation world hoped it would not see again, because it involves a world class carrier flying the latest generation of airliner, and it occurred en route, not during take-off or landing in difficult weather. It's a chilling reminder that nothing is impossible, however unthinkable.

For anyone who doubts that a certain type of electrical fault could start a fire that could bring an aeroplane down, whether the fault was initiated by a lightning strike or something else (this example was something else), look at the Canadian Transportation Safety Board's report on the Swissair 111 Boeing MD-11 accident at Peggy's Cove, Halifax on 2 September 1998.

What makes manufacturers who are considering a new aircraft choose fly-by-wire or traditional control systems, sidestick or control yoke? Of course, for a big-jet it's no contest any longer: it'll be FBW, but there will still be a wrangle over the pilot's cockpit control.

Most planned new business jets and some of the latest regional airliners are now rolling off the production lines with FBW flight control systems, so it is clear that the concept of having the pilots' manual control inputs vetted and - under certain circumstances - modified by a flight control computer system is not considered an issue.

But Bombardier is not going to use FBW for its all-composite Learjet 85 that will see service in 2013. Why? More of that later.

When the debate comes down to sidestick versus control yoke in a FBW aircraft, it is difficult to see whether the manufacturer choice is a matter of conviction, or a decision to maintain an aircraft family link to make cross-crew qualification easier, or - finally - a matter of culture.

My cultural theory suggests the manufacturer's choice of a control yoke on a fly-by-wire aircraft is driven by the knowledge that their core pilot market has a traditional idea of the way flightdecks should look and feel.

Is that preference for tradition unique to aviation? Of course not. This affinity for "retro" design is analogous to the preferences of those US truckers and bikers who continue to buy (respectively) new Mack Rawhide trucks and Harley Davidsons despite - or probably because of - their old fashioned design. There's no question but that they have their own kind of beauty, and they sound - and feel - good.

And in the ads for its chronometer watches, does Breitling display an F-16 or the like? No, it goes for an air-race-modded Mustang to signify beauty combined with speed and power, despite the fact that the F-16's not only a looker, but it could out-turn - let alone out-run - a P-51, even when the latter has been fitted with a mighty Rolls-Royce Gryphon piston engine with contra-rotating props. 

Anything to back up that theory? Yes, actually, but because marketing statements can be couched in terminology that is intended to be all things to all men, it is difficult to know exactly what to make of Bombardier's comments to Flight about the projected Learjet 85. On that programme, Flight recently reported: "Bombardier had considered moving to fly-by-wire design and side-stick controller for the Learjet 85, but prompted by customer input, selected a traditional control yoke and control cables, although brake-by-wire will be included." Bombardier's Ralph Acs, vice-president for the Learjet 85 programme, explained: "If you're a Learjet owner, you really like the rock-and-roll ride."

Interesting, since Bombardier has decided to take the sidestick/FBW route with its CSeries regional jet that will go live the same year.

Get the Paris air show issue of the magazine to read more on the "digital versus delightful" debate. 

This is about a comment that was appended recently to my blog "The toxic subject that won't die".

It doesn't matter, it seems, whether the gas turbine powers a ship or an aeroplane. It can, as Troy Moeller says, "blow atomised synthetic lube oil all over you". And then you lose your job and your health.

Here is his account:

"Having worked on board a Perry Class Frigate and an Arleigh Burke Class Destroyer as a Gas Turbine Systems Tech Mechanical USN the stark truth is that we entered the Engine Enclosures on a regular basis.

USS Oliver Hazard Perry

USS Arleigh Burke

"That is with the Combustor Sump blowing the atomized synthetic lube oil all over us and unfortunately in us. I was diagnosed with "Adult Onset Asthma" just a few months after reporting to the Fleet. The downward spiral of my pulmonary health took years to realize and even longer for VA pension compensation. I realized a long time ago who the culprit was but what do I do? While grateful for the pension it doesn't begin to recompensate me for lost wages or harm done me. I also would like the Navy to address the fact that thousands of GSM's are still in harm's way."

If you have suffered like this, get in touch with us and, as Troy requests in his comment, with him also.

Finally, to demonstrate just how touchy the airline industry is seen by its employees to be over the matter of contaminated cabin air, I have just taken the names of the cabin crew out of our story about two reported fumes incidents that took place in Lufthansa Airbus A340-600s.

Why? ...because one of them contacted me requesting  that I do so, because of the fear that any future application for a job with another airline employer would be turned down. Lufthansa, commendably, has not hassled the reporters, they tell me, but the publicity we gave the event has persuaded at least one of them that the worry about career security is such that it's not worth reporting again.

What a sad reflection on the industry that this should be so.

With its free-of-charge Safety Standdown seminars at Wichitaw and EBACE Geneva, Bombardier takes civil pilots into realms way beyond the "aviate, navigate, communicate" arts of flying they are traditionally exposed to.

You have to go to one to find out what I mean, because you don't know what you don't know until somebody shows you.

But when you've been to the Standdown, especially to the full four-day Wichita session, you walk away taller, with the enthusiasm you once felt about your profession renewed, and a justified belief that you can do your job better.

The training on offer puts you in scenarios that normally only military pilots get to train for - but which are highly relevant to any pilot in any job. As I said before, it makes you realise how narrowly focussed your training has been.

Then the human factors instruction takes you beyond anything anyone else does, providing a degree of self awareness as an aviator that will stand you in good stead when things get tough at any level.

If you have the opportunity to go to the Standdown and you don't take it, you - or your employer - need your head checked.  Quite apart from anything else, it is serious fun for serious aviators.

The Standdown takes pilots beyond the graduate level and into the realms of the Masters. 

Neurotoxic poisons in bleed air is not a new subject on this blog, but the more information we get on it, the more serious looks the aviation industry's studied decision to ignore the dangers associated with contaminated cabin air, or to obfuscate.

To read about the human misery caused by cabin air contamination in airliners, go to The toxic subject that won't die, and also, to read the personal testimony of suffering pilots and cabin crew, visit our AirSpace forum.

Meanwhile aviation journalist Tim van Beveren has conducted an interview with toxicologist Prof Dietrich Henschler of Wuertzburg University, Germany, who has been one of the world's leading experts in workplace contamination since the 1950s. Then he was doing research on the precise group of chemicals that are often pumped into aircraft cabins when engine oil seals become faulty - tri-cresyl phosphates (TCP).

Such industry studies as are being done are looking for one particular variant,  tri-ortho-cresyl phosphate (TOCP) when in fact, Henschler reveals, other variants are present and are far more harmful. 

In his interview, Henschler reveals that TCP is much more dangerous than widely realised when it has been broken down into isomers, which is what happens when aircraft engine oils are heated and vapourised: 

Tim van Beveren:  Is it a major concern to you as a toxicologist that aircrews and passengers are being exposed to TCP, including MOCP (mono-ortho-cresyl phosphate) and DOCP (di-ortho-cresyl phosphate) at higher levels than TOCP in the aircraft cabin?

Prof. Dr. Henschler: As long as the mixture, which is almost a technical product, contains ortho-cresyl in whatever concentration, it is a matter of concern. So therefore [all efforts] should be made to lower the concentration of ortho-cresyl as far as possible.

Tim van Beveren:  Is is acceptable for the aviation industry to focus on the TOCP content of the TCP only?

Prof. Dr. Henschler: No, this is completely misleading because this underestimates the real toxic potency of the mixture of the product.

Tim van Beveren:  Given that TCP in jet oils contains a variety of isomers of TCP including MOCP and DOCP, is it acceptable for those monitoring for TCP to state levels are acceptable as they are below government-set exposure standards?

Prof. Dr. Henschler: To my information there is a lack of threshold limit values with TCP. One has been elaborated by the American Governmental Hygienists group who establish occupational exposure standards. They call it tri-ortho-cresyl phosphate and the value is 0.1 mg / m³. I think this has been elaborated on a very vague basis of data. The publication they are referring to comes from two Englishmen who have been paralysed during World War II, and there have been two or three air analyses performed there. This is trivial data to establish an official occupational standard. To my information no other country has established such a value up to now.

Tim van Beveren:  You were heading the MAK commission (Maximale Arbeitsplatz Konzentration = maximum workspace concentration - this German government commission established/s the limit values for toxic substances in the working environment) in Germany, so how did you deal with this standard of exposure limits?

Prof. Dr. Henschler: I was always against establishing an exposure standard in view of the lack of relevant data we have at hand.

Tim van Beveren:  Would it be more appropriate to look at the mixture of contaminants in the jet oils rather than to the individual chemicals?

Prof. Dr. Henschler: You have to look at the mixtures because they are very complicated, they are varying in the content of the individual compounds and they are changed in the course of being heated up on metal surfaces, so that decomposition products will result. So you always have to look at what in the exposure air. And my recommendation is to establish competent analytical procedures to look at what is that exposure.

Tim van Beveren:  Is it possible with today's existing technology?

Prof. Dr. Henschler: It certainly is. It's a matter of what you invest in, in such methodology. Modern analytical techniques are so sensitive, so reliable, so competent.

Tim van Beveren:  So it's just a matter of money?

Prof. Dr. Henschler: Maybe, yes

Tim van Beveren:  Have you ever discussed your findings with oil manufacturers, governments or the military?

Prof. Dr. Henschler: Oil manufacturers, at least in our country are familiar with what I've published. My only contact with military people has been in Morocco. France had been the protecting country for Morocco and the French government asked me in 1959 when this epidemic occurred in Morocco, to be helpful in identifying the active agent and what could be done. So we had a sample at hand, analysed this and came to an evaluation what type of phosphate was active there.

Tim van Beveren:  What initiated your research into TCP back in 1956?

Prof. Dr. Henschler: Interesting question. After World War II the economic miracle in Germany ended up with an explosive increase in goods transportation by railway and they needed a paint which is resistant to UV irradiation and to meteorological influences, and this company who tried to develop such a product as an additive to lacquers asked me to have a look at what they had at hand at present with tricresyl phosphate with low content of ortho-cresyl. So this was the very beginning of the whole thing, and much to my surprise the mono-ortho esters were by far the most toxic components of the mixture of ten isomers.

Tim van Beveren:  Would you say that breathing synthetic jet engine oils containing organophosphates such as TCP are likely to be harmful?

Prof. Dr. Henschler: These are harmful compounds.

Tim van Beveren:  Why?

Prof. Dr. Henschler: Because they exert a toxic activity which we are well aware of, which is very nicely explainable how the mechanism of action is with these simple compounds. So, in view of the severity of the clinical symptoms and the ensuing fate of the patients involved, I would say it's a dangerous material - it should be avoided as far as possible.

Tim van Beveren:  When you started your research, what for you were the most interesting or maybe surprising findings?

Prof. Dr. Henschler: The extremely high toxicity of the mono-ortho ethers, which went completely against expectation. If you had at hand the three symmetric ethers tri-ortho, tri-meta, tri-para, you would have expected that with a lowering of the ortho-cresyl content of the mixture that toxicity will go down. But the contrary is right - it goes up. This was the most interesting and surprising finding I had.

Tim van Beveren:  And is this common knowledge since?

Prof. Dr. Henschler: Hopefully, yes. Some people know, others do not, I don't know the reason why. Sometimes chemistry is a little bit complicated, and thinking into molecular structures is, to some people an awful business, and though they resist a little bit in going deeper into the matter.

Tim van Beveren:  Would you think that proper scientific studies of the phenomena we're facing here, of contaminated cabin air should be done, and can it be achieved with today's technology?

Prof. Dr. Henschler: They should be done on a large scale where you monitor with analytical techniques what is the outlet, what comes into contact with the individuals at exposure, and what is the composition of these complex mixtures. And this in relation to the complaints brought forward by the cabin personnel and the passengers on a large epidemiological basis.

Tim van Beveren: So if TCPs shouldn't be in the engine oil, there should be other substances which are available?

Prof. Dr. Henschler: Less toxic or non-toxic ones! Better alternatives, yes.

Certainly TCP is a very toxic compound, but not the only one. There is another candidate for being eliminated, beta-naphthylamine which is a proven human carcinogen of high potency. The others I don't know of.

Tim van Beveren: What makes these chemicals so dangerous to the human being?

Prof. Dr. Henschler: Cancer is one of the irreversible phenomena in medicine. If cancer comes into consideration, the evaluation changes from non-irreversible. Cancer in humans is in some way inevitable, the efficiency of treatments is still a little low.

Tim van Beveren: So given the fact that some claim that TOCP is the most toxic but there is MOCP and DOCP as well in the oil, what would you say as a toxicologist about just focusing on the TOCP?

Prof. Dr. Henschler: This is a crude underestimation of the toxic potential. If you focus on TOCP, tri-ortho-cresyl phosphate which has the lowest toxicity of all isomers containing ortho-cresyl. So, we have to focus on the di- and particularly the mono-ortho ethers. For regulatory purposes I would recommend to say an amount of TCP as a whole containing ortho-cresyl to a certain extent. This is a clear-cut definition.

Tim van Beveren: Would you say that there are differences between inhaling TCP and ingesting TCP?

Prof. Dr. Henschler: Principally not, because what is active is not the compound itself but a metabolite which has to be taken up either through the digestive tract or the skin or the pulmonary tract, to be transported to the blood and from there to the liver where it is enzymatically converted to the highly reactive intermediate. So it doesn't matter through which entry the compound gets access to the circulation.

Tim van Beveren: Would you inhale heated engine oil?

Prof. Dr. Henschler: Me? No, never! I was very much surprised to read these reports that people get exposed to these compounds.

Tim van Beveren: You did research back 50 years ago. You initiated research, you found that there is a high toxicity. What does it tell you now 50 years later? It seems that people do not draw the right conclusions?

Prof. Dr. Henschler: It tells me that they haven't picked up the recommendations of careful toxicologists. I have always recommended to keep emission exposures as low as possible and look for better alternatives, so it was much of a surprise to me to be informed of those types of incidents.