It was pretty obvious from soon after the BA038 accident at Heathrow 18 months ago that the investigation was going to be long and difficult. But I think what’s become even more obvious is that the whole question of fuel-icing is a lurking beast that is not easily going to go away.
The UK AAIB and NTSB (because of the Delta Air Lines incident that may or may not be linked) have already recommended that EASA and the FAA conduct a much wider investigation of fuel-icing.
Before returning to London after the Paris Airshow this week I was lucky enough to be invited to visit a place where they know a great deal about this sort of thing, and also know what they don’t know. What’s interesting is that they think that understanding the issue better is going to be tough.
It’s one of those technical facilities that’s little-known inthe industry except in those specialised circles where it’s extremelywell-known. Here it is – looks nice doesn’t it? And it is.
Theword “fumer” is preceded by the words “defense de”, mainly because thisis the fuel icing rig – pretty much the only one of its kind.
And they do things like this:
I got to speak to Dr Franck Hervy, whose business card carries the splendidly straightforward job title: Expert Givrage. (That’s icing expert, apologies if you know anyway). Franck very pointedly declines to discuss whatever he may or may not know about the BA038 investigation, but this is a man who lives, breathes and eats icing (well, you know what I mean.) And he has interesting views about fuel icing – primarily that we don’t really understand it, and that it is going to be very difficult to do so.
The working hypothesis the last time the AAIB talked about it was that ice had formed in the fuel lines, then broken away and effectively overwhelmed the fuel-oil heat exchanger, consequently clogging it.
Franck suggests that there are two big difficulties: first we don’t know the size of the water droplets or ice crystals in the fuel, and second, that the mechanism that causes the ice to stick to the pipes may be a form of electrostatic attraction, which is extremely difficult – and dangerous – to investigate. The size of water droplets (which are spherical) in these circumstances is normally measured by laser, but crystals are not spherical, and the refractive index of the fuel/ice mixture through which the laser is passing is also itself hard to measure.
This is significant, because water droplet size controls the super-cooling mechanism that results in ice crystal formation.
The upshot is that the critical conditions in which this icing phenomenon takes place are going to be very difficult to determine, and therefore difficult to address. Franck’s view is that some serious university research is called for – but he’s not aware of an institution with the appropriate expertise.
And, taking the larger view, it really does matter. Because it seems that aircraft operating in and out of hot and humid areas in particular are always going to be at risk of having water in the fuel. So BA038 (and the Delta Air Lines incident being investigated) are not likely to be the end of the tale.
Good luck to the AAIB say I.