why single pack limit flight level
 

according to mel when single pack only operate limit fl to 350 for b777 and 310 for a300-600. some said that to prevent smoke come to cabin in case of cargo fire but my opinion is cause of not enough air to maintain cabin altitude in high flight level.:confused:

Single pack on a twin is enough to provide cabin pressure. The reason you are limited to FL250 is because of the possibility of the remaining pack failing. At FL 390 you would have no air, emergency decent, Oxygen deployed, major event. At FL250 you just mosey on down to FL 100 and there is no drama.
QED.

nope!

It's pounds of air per pax per minute.

One has to wonder...with questions like these, what the heck are the new guys taught in ground school?
Very little, it seems, and this is positively not good enough.

Perhaps he is asking why the MEL will allow flight with a pack inoperative at a lower level but questions why there is no descent mentioned in QRH checklists with inflight pack loss on some types?

I think you will find it is all about the odds game. At dispatch, if you only have one pack, you plan at a lower level because you are departing under a MEL with reduced redundancy. You may have to load extra fuel. If you are already up there at FL 370 with two packs, and one fails, you can carry on at normal cruise levels. The reasoning is probably because a) the odds of a second pack failure on the same flight is remote and b) you may not want to compromise your fuel reserves by descending to FL250.
The way I rationalise this thinking is that we are not required in certification to assume that simultaneous with an engine failure on takeoff the gear won't retract, or the other engine will fail a few minutes later. However, if you are doing a gear-down ferry, you do have to consider one other failure (an engine) in your performance calculations, because you are planning a flight at a reduced level of redundancy.

Well done, Mach E Avelli, spot on.

Exactly. :ok:

We had a similar thing some years back with a 767 operating throughout Asia, we had no pneumatics from one engine and were waiting on spares, operated okay under an MEL with reduced altitude etc until we were to do a Hanoi to Moscow direct flight and we were grounded.

We could NOT operate that flight as there was a large part of the flight around Afghanistan where the minimum safe altitude was something like 14,000 feet (from memory), and had we lost the other engine or its pneumatics we could not have descended low enough (with NO press/aircon) and did not carry enough (pax) oxygen to stay at altitude.

Airsupport,

You can have a depressurisation even with two packs operating. Where I am it's a requirement to have a depressurisation strategy and a proven escape route any time flying over areas with MORAs above 10 000'. Being on one pack or two shouldn't make any difference, should it?

Using that logic we could never have operated that route, nor could any other similar aircraft, unless we had installed a heap more oxygen.

It was only a problem on one flight where we were down to only one pneumatic source, this is where the odds come in to it.

That was the only cancellation we had on that run, and the ONLY other delay was due to guess what???

One toilet system U/S.

That was similar actually, we would not depart either end with only one toilet system working for a 12-13 hour flight, but if one went U/S during the flight, well................ :uhoh:

Not all twins can maintain cabin pressure at cruise altitude with one pack. The MD80 definitely can't. If you lose a pack in an MD80, you are required to descend to FL250 in order to maintain the cabin. This happened to me once while at FL330, and the cabin altitude began climbing around 300-400 fpm immediately. We descended to FL250, but that was not even enough. The cabin still was climbing. We then descended to FL230, and found that we could hold the cabin fine at that altitude.

Twins such as the 757, 767, 777, etc can hold the cabin just fine at max cruise altitude for one reason.... ETOPS. That way the loss of one pack won't force a descent while in the middle of the ocean... you can keep on flying at your planned cruise altitude. But if dispatched with a pack inoperative, you'll have to limit flight to a lower cruise altitude, although it is still much higher on those airplanes (FL350 for a 757).

So you're saying you operated a service in which,in the event of a depressurisation,you could not have descended below FL 140 before the Pax O2 ran out? Under what regulator?

I can assure you this would be illegal under many jurisdictions. We have certified escape routes to allow us to get the Pax down before the O2 runs out on every sector where the terran is high, including the Himalayas.

Australian.

Nuff said!!

20.4 and 20.6 -

Supplemental oxygen for passengers
8.8 A pressurised aircraft that is to be operated above Flight Level 250 must carry an amount of supplemental oxygen that is sufficient:
(a) to provide:
(i) 10% of the passengers with oxygen during all periods when the cabin altitude is above 10 000 feet and up to and including Flight Level 140; and
(ii) each passenger with oxygen during all periods when the cabin pressure altitude exceeds Flight Level 140; or

(b) to provide each passenger with a 10 minute supply of oxygen;
whichever amount is the greater.

We complied with that every trip EXCEPT the trip we didn't go, BECAUSE WE COULDN'T GUARANTEE THAT FOR THAT TRIP. :ugh:

Airsupport,

I'm not trying to pick an argument or put you down. I AM saying that different jurisdictions have different interpretations and standards.

Under JAR or the UAE GCAA (Which is JAR complient) you must be able to supply passengers with oxygen for the entire time above 140 in the event of a depressurisation, no matter how unlikely that depressurisation is.

You stated that you could not fly a paricular route on one pack because of the increased likelyhood of a depressurisation. I simply telling you that under some sets of rules it makes no difference how many packs are operating.

You then state-Does this mean you CAN guarentee not to have a depressurisation if you have two packs operating? What about if you have a windoow or door blow out, or an outflow valve failure? Under the rules I fly under, you must be able to cope with a depressurisation at all times.

I do NOT know, or care less, what jurisdictions you operate under.

I have for some 40 years operated Worldwide with ONLY Australian registered Aircraft under Australian regs.

Also I did NOT ever say we could not operate a flight because we only had one pack?

IF you are going to start arguments or put people down at least learn to read first. :rolleyes:

Gee...Terribly sorry- in a thread regarding single pack operations I mistook what you said- you had one Bleed rather than one pack, How dare I!!

You still seem to imply that a servicible aeroplane is a guarentee that you will not depressurise, could you explain why?

Still, you know better. YOU'VE worked under one whole set of regs for 40 years. I only flew in Aus for just under twenty, so I'm obviously wrong.

Mind you, in the eight or so operating under OS regs, the holes in the Aussie system become rather glaring.

Now, with an attitude lke that, I wonder which Australian Airline you work for.....

.. oh dear .. let's holster the handbags and talk in a relaxed fashion as if over a cleansing ale .. ?