why single pack limit flight level

[Hanuman]

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:

[rubik101]

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.

[FE Hoppy]

nope!

It's pounds of air per pax per minute.

[411A]

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.

[Mr.Buzzy]

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?

[Mach E Avelli]

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.

[411A]

Well done, Mach E Avelli, spot on.

[airsupport]

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.

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.

[Wizofoz]

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?

[airsupport]

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:

[TWApilot]

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).

[Wizofoz]

Using that logic we could never have operated that route, nor could any other similar aircraft,

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.

[airsupport]

Australian.

[Wizofoz]

Nuff said!!

[Bula]

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.

[airsupport]

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

[Wizofoz]

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-EXCEPT the trip we didn't go, BECAUSE WE COULDN'T GUARANTEE THAT FOR THAT TRIP.

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.

[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.

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:

[Wizofoz]

we had no pneumatics from one engine

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.....

[john_tullamarine]

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

[Wizofoz]

Just what I was going for, John. How about it Airsupport? Can you agree to some analysis and comment on your posts with out the emotive stuff?

[FE Hoppy]

AMC 25.831(a)
Ventilation
The supply of fresh air in the event of the loss of one source, should not be less than 0.18 kg/min (0·4 lb/min) per person for any period exceeding five minutes. However, reductions below this flow rate may be accepted provided that the compartment environment can be maintained at a level which is not
hazardous to the occupant.

from CS 25

[airsupport]

Just what I was going for, John. How about it Airsupport? Can you agree to some analysis and comment on your posts with out the emotive stuff?

Well apart from the fact that YOU brought the emotions into it, you seem to have a problem with Australia and Australian Regulations, so please take it out on the Australian Regulator and NOT me. :ok:

[Wizofoz]

No prob AS, so can you discuss a point you brought up? You said you couldn't fly a particular route with a bleed problem because of the high MSA and increased chance of a depressurisation. I simply tried to bring up the idea that there is ALWAYS a risk of depressurisation and that most operators are required to have strategies to deal with them.

Is it the case that in your operation (and if it is it isn't your fault!) you can operate over terrain where you would not be able to guarentee getting the pax down to FL140 before running out of O2 in a depressurisation situation?

[Wizofoz]

Airsupport,

I've given you quite some time to reply, but you seem to have left the building. You seem to take any attempt to Analise the rules you fly under, as you interpret them by your statements, as some type of personal attack. Not the case. You made a statement, and subsequently seemed to try and defend it, that peaked my interest. I was simply asking you to definitively state what I thought you were implying, while pointing out it was different (and IMHO not as safe) as operational rules from other regulators.

To summaries- You said you could not operate a particular route single bleed because of the increased risk of depressurisation, and the inability to guarantee oxygen supply to the pax whilst over terrain that would preclude a descent below 14000'. I pointed out that most operations require that guarantee even when all systems are operating.

I would simply like a confirmation that, under Aussie regulations, it is considered a guarantee that you will not depressurise if you have a fully-functioning bleed/aircon system, and that you therefore do not need to be able to descend below 14000' before the pax O2 runs out if you should.

[airsupport]

As I told you before, please refer your questions to CASA, I don't make the rules. :ugh::ugh::ugh:

[Bolty McBolt]

Thread drift?

On other CASA registered aircraft that fly over Afghanistan etc there are very strict rules and limits regarding the amount of pax O2 available before departing Asia (BKK, SIN, HKG).
On the 744 the PAX oxygen must be full as the 744 has bottled pax oxy but the 767 has chemical oxygen generators good for 35mins.

Question? Are there chemical oxygen generator available for the 767 with greater capacity than 35mins, if so how long would they need to last to get you out of worst case scenario in Afghan airspace mentioned in this thread?
Greater than 14,000 etc


NB I know of other Chemical oxy generators fitted to other aircraft good for up to 45mins but each assy are larger in installation. e.g as fitted to some A330-200

[Wizofoz]

So, Australia DOES have rules regarding LSALT and oxygen availability, as per most other regulators.

So why would having one bleed source change route capability WRT Pax Oxy requirements?

[Wizofoz]

As I was saying:-

QANTAS flight plunged 20,000 feet after a door "popped" mid-flight, passengers are reporting.

The plane has just made an emergency landing in the Philippines following reports that a door "popped", causing depressurisation, during a flight between London and Melbourne.

Qantas is refusing to confirm the incident, but passengers who have called Herald Sun Online say oxygen masks dropped from the ceiling during the incident.


Others said the plane suddenly plunged from 30,000 feet to 10,000 feet.

Luci of Melbourne told NEWS.com.au that her father, who was on the flight, said "there was a large hole in the fuselage where the landing covers are located".

"(My father said) everybody is fine and they have disembarked in Manilla where they're awaiting another plane," Luci said.

"He also said that the staff were very calm and that the emergency procedures went very smoothly."

One passenger reported the pilot did 'an amazing job' of controlling the craft.

Flight QF 30 was due to arrive in Melbourne around 10pm tonight.

It was one hour from Hong Kong when the incident occured.

The plane is now on the tarmac at Manila airport with all passengers - the majority of them Australians - on board.

Good job by the crew but it makes my point-

Airsupport, I think you were in error saying that a bleed problem meant you couldn't fly a particular route because of depess- Pax O2 issues. Aircraft have to be able to cope with a loss of pressurisation no matter how many bleed systems they have operating.

[dkz]

320-232 Mel - you can DISPATCH with one pack inop and have NO LIMITATION on the Flight Level (only if the speedbrakes work), if no speedbrake - limit FL 315 in one pack.

In flight, pack failure - no limitation.

http://img244.imageshack.us/img244/4115/melir3.jpg

[Centaurus]

what the heck are the new guys taught in ground school?

The CBT programmes merely teach "need to know" as against "nice to know". The alternative is to go back to desk bound engineers using chalk and talk and a whiteboard. Fine, if said engineers are first class lecturers who can bolster student's interest but too many had no idea of class-room teaching technique and bored their audience silly.

Decades back, the lectures on a Viscount course I attended as a pilot went for six bloody weeks and that included two full 8 hour days on the autopilot alone which had about six knobs to twiddle. While CBT is sufficient to pass a type rating it is up to the student to research further if he desires. The internet is marvellous for those keen enough to research stuff.

[md-100]

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.

Was that a MD81?? Because i can guarantee that a well sealed MD80 keep the cabin ok with just 1 pack. It happened to me and I didnt even notice, beacuse mad dog doesnt warn you the pack shut off