Cabin pressure problems

[Helo]

A quick question for you all, resulting from my wife's BA flight from Zurich to Gatwick yesterday evening. Apparently there was a problem pressurising the cabin, or retaining the pressure, such that the aircraft flew back at 8,000ft.

Was just wondering if anyone can explain:

1) Is this common?
2) What might be the cause?
3) Is the fuel burn rate much greater at that level, and if so, doesn't that eat into safety margins? Would continuing such a flight be a problem if it was long-haul because of burn rate?
4) Does flying at 8,000 feet put you into weather i.e. is the flight generally more uncomfortable?
5) Why were all the fizzy drinks apparently spraying everywhere when opened by the cabin crew during the inflight service - doesn't seem to tie up with what I presumed was a lower than normal air pressure in the aircraft?
6) Does such a flight cause ATC particular headaches, or is it straightforward to cope with?

Thanks for any input that you can give.

Helo

[The Greaser]

I think it is highly unlikely that enough fuel would have been on board to allow flight at 8000' unless the aircraft was tankering fuel.
As for the fizzy drinks, the cabin is normally pressurized to around 8000' so it should have been no different to any other flight.

[Helo]

Thanks for the reply. I've checked again with my wife and 1) there was definitely some pressurisation problems, as the captain apologised after take-off for any uncomfort people might have experienced with equalising pressure, etc, and 2) the flight definitely went over Paris at 8,000ft because again, an announcement was made stating the height and pointing out the great views that you don't normally get from higher up.

I guess the fizzy drinks had probably just been shaken about, and perhaps the flight ended up descending down to 8k, although that said, it apparently flew much lower than normal for the duration (although I appreciate it's impossible for passengers to estimate).

Anyone else - any thoughts on the other questions about possible causes, implications, etc?

Thanks

[Wannabe Flyboy]

I'm not an expert here but from what I know...

1) Is this common?
No.

2) What might be the cause?
Broken/clogged valves inlets or another physical fault in the aircaft. Or something completly different!

3) Is the fuel burn rate much greater at that level, and if so, doesn't that eat into safety margins? Would continuing such a flight be a problem if it was long-haul because of burn rate?
Correct - the fuel use will me much higher. Jets swallow fuel like mad a low level. Did you fly all the way at 8,000' or did you start off high? If it was a known problem before departure then the extra fuel would've been uploaded.

4) Does flying at 8,000 feet put you into weather i.e. is the flight generally more uncomfortable?
It depends where the weather is but there are more likely to be large, unfriendly clouds at that level so there is more chance of turbulence, yes.

5) Why were all the fizzy drinks apparently spraying everywhere when opened by the cabin crew during the inflight service - doesn't seem to tie up with what I presumed was a lower than normal air pressure in the aircraft?
737 cabins normally pressure to 7000-8000 feet at higher levels so that wouldn't be a problem in theory. Pass on this one.

6) Does such a flight cause ATC particular headaches, or is it straightforward to cope with?
One for the ATC forum I reckon. It depends what else is at 8000' at the time.

[ExSimGuy]

30 years ago it was quite common - a lot of the operational turbo-props then didn't have (working?) pressurisation!

Not only did it increase the fuel-burn (not so much as with jets, which are designed to operate at 30,00 feet of more), but the actual land-speed was a lot lower so a one-hour flight (on a presurised a/c) would be 90 minutes on the same route with the same a/c without pressurisation - and I think the difference then was only about 12,000 feet against 8,000. (there's way more drag at 8K than up higher where the air is thinner)

But at least you didn't need oxygen if you had to bail out ;)

[GwynM]

Are you sure it wasn't 8,000m (about 26,250 ft):O

[OZcabincrew]

I don't know about airlines over that way, but down here if an aircraft had cabin pressurisation problems just after take off, enough so that the Captain had to make a PA apologising for any discomfort caused, then more than likely the aircraft would turn around and go back to where it just took off from so that engineering could go over it.

Oz

[ExSimGuy]

Don't know the SOPs, but logically (?) it might be better to carry on a short ZRH-LGW sectorand accept the extra fuel burn and half an hour flying time (you'd probably lose the fuel and time anyway if you had to dump it before returning) - especially if the airline was LGW-based, and you'd have your own guys on-hand when you got there.

Returning would mean time to fix the a/c at ZRH, maybe another half hour, maybe much longer.

[OZcabincrew]

down here, the airline i work for has a policy of "safety before schedule". so in the end if the Captain has made a PA apologising for it being uncomfortable, it comes down to the safety and well being of the passengers and crew, so therefore i would be pretty certain they would turn back. They would offload the pax, load them onto different flights if the aircraft was going to take time to fix it, do it and then use it for a later flight. That is what i would expect they would do, i may be wrong though.

Oz

[BOAC]

Helo - as 'the greaser' has said, it is MOST unlikely that the 'fault' (if any) developed after take-off from ZRH since there would then be no way there would be enough fuel for the trip at "8,000ft". It was not usual in BA to tanker fuel ZRH-LGW.

If indeed the reported facts are correct, it is a more likely explanation that the a/c was dispatched to fly back to base unpressurised due to some problem or other, which could not be fixed in ZRH, in which case it would have to remain below 10,000ft, and appropriate fuel loaded.

Among likely problems could be a bleed-air leak - necessitating no bleed air from the engines, a 'leak' - such as a door seal which had failed, a failed open outflow valve or perhaps a faulty pressurisation controller. A single aircon pack failure would allow flight up to 25,000ft, so that would not fit.

[Helo]

As always, a great forum - thanks for the replies.

[Jet II]

it comes down to the safety and well being of the passengers and crew, so therefore i would be pretty certain they would turn back.

what makes you think that it is any less safe to fly back unpressurised? - Pressurisation is only a 'comfort' issue, the aircraft will fly perfectly safely with no packs operating.

[Jordan D]

Question: Mexico City is at 10000ft (as are some other South American cities) - does this mean planes depressurise on arrival?

Jordan

[Wannabe Flyboy]

The pressure inside the cabin has to equal the pressure outside the cabin, and when on the ground this is most easily done by just dumping the pressure and everything will equal out.

[Bealzebub]

Jordan,

Mexico city is 7,341 ! Not 10,000

La paz Bolivia is 13,355 ft but that is the exception.

There are a couple of other airports in peru over 10,000 ft elevation such as :
Andahuaylas ; Cuzco ; Jauja ; Jaliaca and Punta Ventilla.

Potosi in Bolivia is also on the list. Obviously these are not major destinations and the only airports of reasonable length that I can locate.

[Jordan D]

My bad - seems that basic point of Geography A-Level failed me. Ok, take La Paz then .....

Jordan