British Airways Emergency Descent

[Hardworker]

Dual Bleed Failure

So why did the airbus have a dual bleed failure, anyone know what the fault was?

[blueloo]

Your 12 minute or 22 minute limit for O2 chemical generator, is merely a function of what the airline has installed. Usually if a/c operates over areas of higher terrain, with a longer diversion time at a higher altitude they will require O2 generators with a higher capacity.

[cheesycol]

HD - I recall them saying they had dropped out of CAS and had a FIS from Scottish, it was about that point London Mil took over.

[Sick Squid]

Some of you might be wondering where your little epics have gone. Some of you might be a little annoyed.

Tough. What I've just deleted is the perfect example of where this site has been going wrong in the past, pandering to attention-whores and those whose knowledge of aviation is gleaned from inside their left nostril.

We'd rather you all had the spats elsewhere and left the speculation on this site for those who actually have an idea of what they are talking about. So don't waste your time or ours by wielding your handbags in such an oh-so cutting and acerbic manner, it'll just get deleted and the thread kept on topic. Without you.

Keep doing it, and the "without you" part becomes relevant sitewide.

Enough. Keep this on topic, any further off topic posts will be deleted. This site has an editorial policy in place now, and we will stick to it.

Squid
Moderator

[slip and turn]

Well I for one am no longer annoyed. Nicely edited Sick Squid , seriously, and sincere apologies for the bits of mine that inflamed some contributors to complete distraction.

May I just ask Oktas8 about this barotrauma thing?

JAA recommended max cabin altitude fpm in a normal descent is actually 300fpm right?

... and JAA recommended max cabin altitude fpm climbing is 500fpm because human ear design/anatomy simply copes much better going up than going down?

Many European lo-co routes achieve landing in just 20 mins from top of descent and when they do, and when I have had just the slightest cold (I have not had a serious one for years) I have had to be very careful consciously managing repressurisation inside my ears.

My science -trained brain tells me that something like 500fpm cabin altitude descent rate could easily cause me loss of control of repressurising my inner ears if I had the slightest cold. One of my kids suffers from hay fever and occasional mild asthma. Having had seriously tearful problems (I am talking of an intelligent comunicative teenager here who also understands some of the science) we still routinely use pain killers as a precaution for loco descents, and I'd say 1 in 4 still causes actual serious discomfort.

I have seen figures that suggest that as many as 1 in 7 UK schoolkids are asthma sufferers who use inhalers (for those who might not be sure if asthma and ear problems might be linked, asthma sufferers generally exhibit inflamed mucous membranes I think both in bronchial tubes restricting breathing, and in Eustachians which is where the pressure equalisation problems occur of course).

My main question is where do these 500fpm, 1500fpm, 2000fpm "no real problem" cabin altitude descent rates come from? (if they are cabin altitude descent rates?). Who has decided they are ok?

Rates like that sound definitely painful to a significant proportion of the population to me. And from time to time in the PPRuNe medical section you see pilots with habitual normal descent inner ear problems too ...

Obviously explosive decompression up high more or less instantly sends cabin altitude to actual altitude?

So at say 38000, with 12 minutes of O2, if decompression was explosive, pilot must get down to around 14000 where most pax can breath unaided before pilot can level off?

So that is indeed 2000fpm. Very painful to me I am sure, especially on a slight cold day.

Consequences just sound a bit too easily dismissed to me ... a good argument for more than 12 minutes down the back?

Also does anyone know typically how long it would take for the cabin altitude in an Airbus like this to reach a halfway house at say 24000 if for some reason bleed air totally failed around 10000, warnings failed and aircraft reached cruise height?

[Swedish Steve]

So why did the airbus have a dual bleed failure, anyone know what the fault was?

Both bleed thermostats had failed independently.
Both replaced and all OK. No connection found. Just one of those coincidencies.

[LeftHeadingNorth]

If you lose your cabin pressure you don't really consider the ROD. It's simply get down as fast as possible regardless if you have 4 hours of oxygen for the pax in the back. Sure a few ears will pop but that is a minor issue considering the situation.

[threemiles]

So at say 38000, with 12 minutes of O2, if decompression was explosive, pilot must get down to around 14000 where most pax can breath unaided before pilot can level off?

So that is indeed 2000fpm. Very painful to me I am sure, especially on a slight cold day.

When decompression is really explosive fpm will be much higher than 2000!

[Pax Vobiscum]

S&T - I sympathise with your ear problems (from which Mrs PV also suffers), but bear in mind that the pressure differential per 1000 ft decreases with increasing altitude (see The Engineering ToolBox). So a rate of descent of 2000fpm at 38000 is, in terms of rate of pressure increase, roughly equivalent to 800fpm at 10000.

FWIW (and I fully realise that I don't get a vote), in the unlikely event that I ever experience explosive decompression, I'd quite like the professionals at the front to get me back down to a breathable altitude as soon as possible (consistent with safety) and let any discomfort issues go hang. Thanks in advance

[PEI_3721]

IIRC the manufacturer’s production tests on an regional jet required >6 min cabin leak rate from an 8000ft cabin to 14000ft cabin at FL300; the test was conducted with both packs off.

Explosive decompressions to ambient are extremely rare. Even with the loss of a window, the packs will provide significant airflow and with the outflow valves closed, a reasonable cabin rate could be maintained (aircraft type dependent). The crew will have time to assess the situation and plan their descent if required.
For a real explosive decompression then there may be concerns other than passenger comfort to consider. If the damage is judged severe then aircraft speed or maneuver might be the critical parameters and all timings ‘go out of the window’.

I recall that a significant proportion of cabin HI ALt alerts are due to crew switching error during the climb (Pack switching or APU to Engine Air), thus following a warning a quick check of the system is always a good idea.

[llondel]

Quite apart from the ear discomfort of a rapid descent, what about suffering the bends? If there's been a rapid decompression then you've just exposed everyone to a similar problem to divers. Getting back to a reasonable pressure quickly is going to minimise any issues with unwanted bubbles in the tissues.

[Oktas8]

in response to slip & turn

Umm. There are some excellent posts after your post S&T where you asked me to further explain myself. Perhaps you have already had a satisfactory answer?

In my post, I was not specifically referring to the JAR 300fpm guide. It would keep just about everyone not only safe but also comfortable. A good thing to aim for in "normal" descents.

So if you are in a lo-co descent which takes only twenty minutes, you will go from a cabin altitude of about 8000' to sea level at a rate of about 400fpm. As I and Pax Vobiscum have explained perhaps not very well, this would be fine at altitude but a little uncomfortable for some when the aircraft gets down near sea level.

So where did my 500fpm figure come from? Experience in unpressurised aircraft. Sorry, but usually we have to descend at that rate to fly standard airways and instrument approach profiles. If a passenger is showing discomfort, I'll do my best to shallow the descent or even level off for a while.

Where did my 2000fpm (corresponding with about 5500fpm at airline cruising level) come from? Plucked it out of thin air as what is just bearable (I didn't say comfortable) for a healthy person in my experience. If you have a cold, there will be serious pain and perhaps barotrauma - but this is a very rare and potentially very hazardous situation. As others have said better than I can, it's deemed "acceptable" as an emergency procedure where normal health & safety rules go out the window. With all the air, if you'll excuse the pun...

I did not mean to imply either that airliners do actually descend at this rate - it depends on the emergency - or that it would be in any way acceptable in "normal" ops.

Obviously explosive decompression up high more or less instantly sends cabin altitude to actual altitude?

Yes. But this is extremely rare, and is often associated with structural failure. The golfer's situation was unusual because a bizjet contains very little volume of air in comparison to an airliner, so a leak will result in less time for pressurised air to leak out.

So at say 38000, with 12 minutes of O2, if decompression was explosive, pilot must get down to around 14000 where most pax can breath unaided before pilot can level off? So that is indeed 2000fpm. Very painful to me I am sure, especially on a slight cold day.

No. Even if pax comfort was relevant in this emergency (which it isn't), 2000fpm at altitude is the pressure equivalent of about 650fpm at sea level, increasing to about 1500fpm equivalent as the aircraft approaches 14000'. So saying 2000fpm, while technically true, makes it sound worse than it actually is. I don't minimise the discomfort for most pax, and even perhaps injury-causing pain to a proportion of passengers.

Quite apart from the ear discomfort of a rapid descent, what about suffering the bends?

Not such a problem as you might think. The pressure change from aviation depressurisation is no more than the pressure change from surfacing quickly through 5m of water. I suppose there's a chance of the bends, but it's not likely.

My sincere apologies for the size of this huge post, and I hope it was slightly interesting without being too far off thread.
Cheers, O8

[Diver_Dave]

Llondel

Mods: I am not in anyway an aviation professional. If inappropriate please delete.

Llondel,

As I know nothing about the dynamics of an explosive decompression I'll
avoid the aircraft side of this, however as a diver (instructor and mixed
gas decompression diver) I may be able to shead some light on the DCS issue.

DCS (the bends in one of it's forms) is caused by the rapid dissolution of dissolved nitrogen (Normally) from the blood).

On gassing is really only starts from a dive perspective at 10M (Near
enough 1ata).

You'll have to forgive the terminology issues but I'm assuming that
you are talking about the difference between the cabin altitude and
the real altitude at whichever altitude the Cabin decompression happens.

In this case yes the blood would have dissolved gassed, however,
the serious problems happen at >1ata diference and increase (not quite
exponentially).

So to answer.

Above sea level (1ata) (I know I know it's not strictly accurate) the dissolved nitrogen content isn't
really a limiting factor. And certainly isn't
going to lead to a DCS.

From our point of view the more serious is residual gas loading that's
fine at sea level but off gasses at altitude leading to a hit. This is something we teach.
NO DIVING 24hrs before flying. (Physiologically 12-18hrs is PROBABLY enough)
but Bends don't read tables. ***

Hope this helps a bit

DaveA

*** Not wishing to hijack the thread, this is a serious issue and
talking to a Captain positioning a few years ago was told that flights back from
theRed Sea were looking at where Decompression chambers were available
for diversion planning. If this is the case MY SPORT seriously needs to take a look at itself.

[Suzeman]

Here is a report on the incident from UK Airport News

Suzeman

29.06.08

A British Airways plane was in danger of being shot down when it dived towards a foreign warship in an emergency, the People reports.

The Airbus A319 had to make a rapid descent when it lost cabin pressure. However, officers on the Dutch ship off the coast of Scotland ordered battle stations as their anti-attack radar picked up a mystery aircraft hurtling towards them at 400 mph.
The newspaper reports that the more than 100 passengers on board pulling on oxygen masks on Flight 784 from Heathrow to Stockholm had no idea they were plunging into range of the vessel's guns. However, 'disaster was averted when the Dutch radioed a warning for the pilot to identify his aircraft.' The BA captain replied instantly and diverted back to Heathrow where he landed safely.

An aviation source told The People: ‘The BA pilot had to descend immediately to avoid those on board suffering oxygen starvation. It was chance that it took the aircraft towards the ship. Nobody is to blame - quite the opposite. The Dutch officers and BA flight crew followed procedures to the letter - there should be pats on the back all round.'

A BA spokesman confirmed the flight returned ‘with minor pressurisation problems’ but refused to confirm the incident with the warship.

[slip and turn]

Many thanks for the comprehensive response Oktas8. I hadn't considered what I suppose is essentially a reverse exponential of ambient pressure against altitude. Thanks PV for the link to the tables.

As for discussion of likelihood of 'the bends', I guess that's just another argument for getting down quickly. I know PADI have long taught the no dive in 24 hours before flight rule, so I can see how the uncontrolled decompression from a hole or leak or other failure coupled with the residual gas load in a diver's bloodstream that Diver_Dave mentions might cause 'off gas'.

I do wonder how many divers take serious note of the rule however. I am fairly sure I caught the tail end of some reality tv show in UK recently where contestants were diving and flying same day (flying after diving).

Repressurising via a rapid descent is the first part of a correct solution I imagine?

But back to the incident in hand then, Steve said:

Both bleed thermostats had failed independently.
Both replaced and all OK. No connection found. Just one of those coincidencies.

Failed independently and simultaneously? Surely not? Or can they be destroyed by some common mishandling action? Any idea of time difference between one failure and the next?

[PEI_3721]

Many of the posts overlook the point that with a pressurisation failure at altitude, the cabin climbs; the rate might be quite slow (excluding the rare event of rapid and total loss of pressure). As the aircraft descends the cabin rate of climb would be a dynamic mix of aircraft descent rate, any residual air system input, and cabin leak rate. The cabin will not start descending until the cabin and aircraft altitudes match, and then the rate is not necessarily the same as the aircraft.
High climb rates are generally of less concern to passengers than high descent rates.
Look at the cabin altitude instruments when there is a warning.

[Rainboe]

Some of you might be wondering where your little epics have gone. Some of you might be a little annoyed.

Tough. What I've just deleted is the perfect example of where this site has been going wrong in the past, pandering to attention-whores and those whose knowledge of aviation is gleaned from inside their left nostril.

We'd rather you all had the spats elsewhere and left the speculation on this site for those who actually have an idea of what they are talking about. So don't waste your time or ours by wielding your handbags in such an oh-so cutting and acerbic manner, it'll just get deleted and the thread kept on topic. Without you.

Keep doing it, and the "without you" part becomes relevant sitewide.

Enough. Keep this on topic, any further off topic posts will be deleted. This site has an editorial policy in place now, and we will stick to it.

Squid
Moderator

So what's the topic? This is Rumours and News and the topic is a very minor British Airways incident. If this is going to be a discussion about medical/physical issues of depressurisation to pander to an 'attention whore', may I suggest the Moderator moves this to either Technical or Medical. we have been told <Enough. Keep this on topic, any further off topic posts will be deleted.> The topic is a BA depressuristion, not scraping up everything everybody knows about the theory of the subject! How about Moderating then?

[L337]

I agree fully with Rainboe. This section is Rumours and News. The thread has been moderated into a thread more relevant to Spotters corner.

[Rainboe]

As this topic has now apparently changed to 'An Idiot's Guide to General Pressurisation Theory', I think the following statement needs examination:

As the aircraft descends the cabin rate of climb would be a dynamic mix of aircraft descent rate, any residual air system input, and cabin leak rate. The cabin will not start descending until the cabin and aircraft altitudes match, and then the rate is not necessarily the same as the aircraft.

If you have lost pressurisation input, then the cabin and A/C altitudes will match on the way down. If a leak is small and the pressurisation input is maintained, then hopefully the cabin will descend ahead of the A/C without matching, so it is not automatically correct- only true if you have a large leak, and then the descent rates will match.

But I am uncomfortable with this being discussed under the title it has. I take it the 'British Airways' part of the title is long since redundant? For marks for an obscure and bizarre Moderation effort?- 4/10

[RAT 5]

I've always been uncomfortable with the concept of hurtling down ASAP to 10,000'. I paraglide at 12,000' and ski at that altitude as well. Somehow this magic threshold has become a do or die finishing line to a vertical race.
I remember an Air Europe B757 coming out of Bangor UK bound a few years ago. He had a depressurisation problem, hurtled earthwards as per SOP's, down to < 10,000'. It was reported that a considerable number of pax had burst ear drums. I've never had one, but know those who've had. It is extremely painful and can render you 'incapacitated'. What if that happened to one or both pilots? A not so bad situation has become much worse.
Lack of O2 is not a problem due to onboard systems and routes chosen to obey the rules.

Why is it not SOP to reduce ROD, say 2000fpm, once below 15,000' so as to be something more manageable for the majority of ears. I for one will do so should the event occur. Once below 18,000' you ain't gonna die due to lack of puff.

It is curious that in most real events something is learnt and procedures modified with the experience gained. In this scenario it does not appear to have been the case.