Single Pack Ops A320

[YankeeGolf]

A320/321

Problem:

Dispatch with One Pack u/s - Some sections of the MEL specify limit of FL325 and some sections DO NOT specify an Altitude limit.

Why and what is the logic behind this?

ANOTHER un-related problem:
Dispatch with ALL systems on plane working:
flying along in cruise at FL380 and one pack fault, and cannot be recovered, pressurisation is holding, any regulation, limitation that neccesitates a decent to a lower level?

thanks:8

[bflyer]

hi

The only consideration that i am aware of is for flight spoilers...if they are operative and pressurization is holding, then it should be ok
If on the other hand the aircraft is dispatched with them inop..the aircraft in our manuals is limited to F315..tht is the level you can desend from without flight spoilers to F100 within the time frame for oxygen available in the event where you loose the other pack and aircraft pressurization is completely lost

[Down Three Greens]

A colleague of mine asked the same question to Airbus

When an aircraft is dispatched with one pack inoperative, Airbus takes into account a failure in flight of the remaining pack and a descent to FL100.

The FL limitation provided in the MMEL ensures that:

The cabin altitude will never be above 15,000 ft during the descent, and
The oxygen masks will not drop during the descent.

Hence the FL limit.

Hope this helps

[YankeeGolf]

Yes, FL315, I stand corrected. Thanks!

What about losing a pack while cruising at FL390, pressurisation is holding normal, any documentation from airbus that warrants a decend to FL315 and below?

Many thanks to fellow bus drivers around the globe

[mcdhu]

Surely not. If the pack fails in flight, run the ECAM procedure; the MEL limitations discussed above do not apply since the aircraft is already in flight.

Cheers
mcdhu

[Down Three Greens]

No documentation from Airbus that requires descent. It's an MMEL (... and thus MEL) restriction only.

[YankeeGolf]

Noted, Thank you all!:ok:

[john_tullamarine]

Important to keep in mind what the MEL is all about .. and that is to permit the intentional despatch with bits and pieces U/S.

It is the intentional aspect that drives the philosophy. With intent it is appropriate to address the basic certification requirements .. eg, for packs, why did we have two for the original certification ? If we launch with one U/S, then what do we need to do in the way of restriction to achieve a similar risk environment to normal operations ? and the M(M)EL words follow on from the answer to that question.

the MEL limitations discussed above do not apply since the aircraft is already in flight.

That's fine .. but it is a wise pilot who reviews the MEL after the situation has settled down .. the words provide a few more bits of the puzzle for his/her flight conduct decision processes.

[YankeeGolf]

So what you are saying is that it is Prudent and Good airmanship/common sense to CONSIDER a descend to a lower level after one pack fault in cruise at lets say FL390 even if the pressurasation is holding.

It is not a requirement nor a limit as airplane is already inflight, correct?

:rolleyes:

[john_tullamarine]

That's the way I would look at it ... do I have adequate fuel to tolerate continuing at a lower level ? If so, I would weigh up the fuel cost against the (probably low) risk of having a serious depressurisation at normal cruise level in the event that the other pack lets go ...

[guiones]

You guys are not making much sense!

If you have and explosive decompression, no matter how many packs you have operating; you can get down from 390 within the oxygen generator time, whatever the option of minutes your airline chose.

The MEL limitation is ONLY for dispatch, it does NOT apply in flight. The reason it is limited by MEL is the ability to pressurize the A/C in climb and just a preventive measure at that. If you are at FL390 and turn off a pack, nothing happens; if you turn off both pack you would get a cabin altitude rate of climb of about 650 to 800 FPM; I have seen it even on 10 and 12 year old A320's. If at that time you make a good decision and a timely EMERG DESCENT, most likely you will get to 14,000 (or 16,000 with HIGH ALT PB) before even the masks drop.

DTG: Your colleague is either making it up or asked the wrong department at Airbus, and BTW masks drop normally at 14,000 not 15,000 unless you have selected the optional HIGH ALT PB then they drop at 16,000. If he is with an Airbus operator in management, tell him to pm me and I'll give him the Dept where he should send this questions.

G

[YankeeGolf]

guiones,

Can u share with us which department in airbus we can contact concerning this problem?

Many thanks

[mcdhu]

I would have thought that JT's post no 10 above makes absolute sense.

The final part of any decision making model GRADE, DODAR etc is to continuously review/evaluate the outcome which includes asking the question ''what if the next one fails?''.

True, an (emergency) descent from FL390 should sort it out but it will probably be ugly; an emergency descent from FL 310 will be less so.

But there are many more factors to consider - but at least we should consider them.

Must go flying

Cheers all,
mcdhu

[Touch'n'oops]

YankeeGolf

With regard to your question about whether you should descend from FL390 with a pack that's failed while you were up there.

My answer would be no. AS LONG AS pressurisation holds.

Think of a aircraft like a leaky balloon. It takes a lot of puffing to inflate it, but once the balloon is filled it takes a lot less puffing to keep it inflated.

[guiones]

YG:

If you have a Technical Management position for an Airbus Operator, you should have access to the Airbus World site; thats the best way to go. There are also adresses directly to the technical deptarments in Toulouse for every system, this is also only for Airlines that operate Airbus; certainly not for curious people on a forum. If you have any questions, feel free to pm me.

mcdhu:

An EMERG DESC from 390 and 310 should be exacly the same, the ONLY difference should be about 2 minutes to get to the desired altitude, noting ugly. Worst case scenario is that the the mask will drop, nothing else.

G

[john_tullamarine]

Worst case scenario is that the the mask will drop, nothing else.

I would also suggest consideration of what-ifs and how high the cabin might peak during any descent .. considering that we are looking at typical populations in the cabin and all the potential medical complications which might attend a cabin pressure excursion ?

If you don't have a reasonable option and need to stay high .. fine. If you have options, then consider what your responses might be during court time when you are called to account for your decision making processes by counsel for a passenger who suffers injury and then sues ...

[guiones]

JT:

We are talking Airbus procedures not lawyers. If every time you fly you are worried about lawyers, stay home.

The chance of a dual pack failure is rare, and Airbus sees it that way.

Would be intresting what other procedures or recomendations from the manufacturer you do not follow to please lawyers.

My answer is: I followed manufacturer procedure and recomendations.

If the passengers can't handle a dual pack failure, imagine what an explosive decompression would do to them. If you read my previous post, the A320 series with both paks off get a cabin rate of climb of about 650 to 800 FPM, hardly dramatic.

G

[john_tullamarine]

Normally I would not respond but the liability topic is relevant and very important .. not to mention very poorly considered and understood by the average professional going about his business ...

We are talking Airbus procedure not lawyers.

At the enquiry, we ARE talking lawyers. Every time you make a decision, give advice, etc., as a competent professional .. your call can be brought to account in court.

If every time you fly you are worried about lawyers, stay home.

Not only every time I might fly .. but every time I put my engineering or management hat on as well. This is the reality of the modern world, liability, and responsibility. Not so much a case of being worried as being aware and prudent.

The chance of a dual pack failure is rare, and Airbus sees it that way.

Of course a dual failure is not an everyday event - I think we all accept that .... but your view is that the Commander ought not consider the circumstances of the particular flight and merely follow the QRH or equivalent in the nature of an automaton ?

My answer is: I followed manufacturer procedure and recomendations.

.. and that will provide you with some protection. However, I think that you need to read some court/BOI/etc. transcripts .. might cause you to raise your eyebrows a little, I suspect. Your view is idealistic but, in practice, not the way the real world works after the event ..

[guiones]

JT

I do not let lawyers or enquirys dictate the way I operate an airplane; I do that better than them.

I follow procedures and recomendations developed by the manufacturer after extensive testing and with the knowlege of the people that developed the systems. If there is a procedure I do not agree with, I ask Airbus.

You are putting words in my mouth by saying "but your view is that the Commander ought not consider the circumstances of the particular flight and merely follow the QRH or equivalent in the nature of an automaton?"
The PIC has the ultimate authority of decision making; never sugested to take that away; but procedures were developed with more knowlege than you, I or any single person might have, I follow them. The A320 series is complex enough to start second guessing the way it is recomended by Airbus that we fly it.

Where do you stop with your thinking, what other recomendations do you change, what other areas and what parameters do you allow yourself to protect yourself from liability? The lawyers will always find a way to find you at fault; example: "why did you descent when the experts at the manufacturer and you documents onboard say you do not need to, maybe if you stayed at 390 like Airbus recomended you would have stayed out of the clear air turbulence that hurt your typical 90 year old great grandma that was walking with her cane to the restroom? Do you think you know better than the experts at Airbus?"

We can not let aviation ignorant lawyers dictate the way we operate the A/C; that is what make us different.

And BTW, I don't need to read about lawyers and accidents or incidents; I have testified about procedures at several and have been involved in many accident investigations(currently involved in one). One of the big reasons I take what Airbus writes very seriously.

Happy landings.

G

[john_tullamarine]

I guess that we shall remain in gentle disagreement on some points, then ...

[NSEU]

Think of a aircraft like a leaky balloon. It takes a lot of puffing to inflate it, but once the balloon is filled it takes a lot less puffing to keep it inflated.

Doesn't an aircraft depressurise as it climbs? At sea level, the aircraft cabin is at sea level. At cruise level, the aircraft cabin is at several thousand feet :}

[Ministry_Cork]

NSEU - CABIN ALTITUDE—Cabin pressure in terms of equivalent altitude above sea level. the oxygen

[YankeeGolf]

guiones

Could u share with us the contact from airbus that you were referring to?

As the old saying goes: "It is NOT who is correct, it is What is correct"

Merci.:ok:

[guiones]

JT

Agree to disagree, thank you for your insight; it helps me with another angle alltogether.

G

[guiones]

YG

Unless you have access, it will not do you much good; it is airbusworld.com There is a link for questions that goes directly to the STL Dept in Toulouse. Ask your company's management to give you access or ask the questions for you. Feel free to pm me if I can help.

If you need name and number for Airbus contacts, pm me; if you are a current Airbus pilot you can have them.

Airbus has a very good Customer Technical Support System set up; each operator has an RCSM (Resident Customer Support Manager) locally in your base who answers to the CSD (Customer Service Director) who is ussualy in Toulouse. They have full access to the STL Department where your procedures and FCOMS come from and to Flight Test. There are also Technical representatives assigned to every operator.

Check with management, the resources are there.

G

[NSEU]

NSEU - CABIN ALTITUDE—Cabin pressure in terms of equivalent altitude above sea level. the oxygen

Ministry_Cork, sorry, I don't understand your point.

Cabin pressure is less at altitude than it is at sea level (or excessive differential would literally blow up the aircraft at higher altitudes). If the pressure in the cabin at sea level is 14.7 psi (or more) at takeoff and the cabin pressure at 40,000ft is, say, 11 psi (7000' cabin alt), did the cabin pressure decrease (de-pressurise) or increase?

[Down Three Greens]

Please be assured that the Airbus customer service route to which you refer in yesterdays post was followed to the letter.

Cheers :ok:

DTG

P.S Check your PM's

[Down Three Greens]

I think we may be confusing issues here. It is correct that the O2 masks with drop at 14,000ft but I think the MMEL limitation is based around certification requirements. The 14,000ft and 15,000ft discrepancy may be linked to the following regulations.

A good reference would be

FAR Part 25 Sec. 25.841 effective as of 07/05/1996 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/FED94F31539484AB852566720051AA5D?OpenDocument)

(1) If certification for operation above 25,000 feet is requested, the airplane must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of 15,000 feet after any probable failure condition in the pressurization system.

Other possible link

FAR 135 Oxygen Requirements
Occupants: 135.157(a,b)

Pressurized aircraft

If the cabin pressure ever exceeds 10,000 ft msl, the requirements for unpressurized aircraft apply.

To prepare for a possible pressurization loss:

Highest Altitude O2 reserve
> 25,000 ft msl (at any time) 10 min supply for each occupant
> 15,000 ft msl and descent cannot be made to 15,000 ft msl in four minutes - 1 hour supply for each occupant
> 15,000 ft msl but the aircraft is always at an altitude where descent to 15,000 can be made in 4 minutes - 30 min supply for each occupant

An Airbus FAST article

http://www.airbus.com/store/mm_repository/pdf/att00007996/media_object_file_FAST38_Hypoxia.pdf

Hope this helps clear things up.

[guiones]

DTG

First of all the source for your previous post regarding your collegue is the correct one and you are a true gentleman, thank you for your pm.

I take back my critisism of your colleagues source, I still do not agree with the statement, but we will research it.

I am aware of the certification requirements for pressurization, but the limiting factor is not DUAL PACK FAILURE (you would only get a cabin rate of climb of about 650 to 800FPM); the limiting factor is explosive decompression.

Lets say you are at FL390, both packs fail, you need to descent to 14,000' (descent 25,000') you can descend at an average of 4,000 FPM (not very steep) it will take you a little over 6 minutes. Lets say the cabin for some reason was at max alt 8,000 and will climb at a max of 800 FPM (6,000 to 14,000) it woul take 7.5 minutes. All conservative numbers

If the certification was based on single pack operation at FL310, there would be a procedure or ECAM when one pack fails to limit the ceiling to 310.

BTW, FAA Part 135 is Air Taxi, this would not apply for certification, more so for operation under Part 135.

G

[Down Three Greens]

Thanks for your PM Guiones. Much appreciated.

Appreciate the feedback on the FAR's too. As an EU-OPS operator, I would guess FAR 25 still applies. i.e. Transport Category Aircraft

FAR Part 25 Sec. 25.841 effective as of 07/05/1996

(1) If certification for operation above 25,000 feet is requested, the airplane must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of 15,000 feet after any probable failure condition in the pressurization system.

I would suggest the MEL 'ethos' that Airbus may be using is the probability of SINGLE pack failure.

....ignoring OEB 149 of course.....The probability of two pack failure events when your have two servicable packs (i.e. one fails followed by the other) is much smaller and hence the MEL limitation applies on single pack ops with SINGLE failure case. A DUAL PACK FAILURE is double failure ( Probability of Pack One Failure x Probability of Pack Two Failure) and thus is not a probable failure condition.

As far as the rates of descent go. The Airbus maximum acceptable leakage on flight test is 850 fpm but I can only guess that they use some form of modelling to define their emergency descent profile.

Thanks for the discussion! :ok: We'll get there in the end!

[Down Three Greens]

Another wording of FAR 25

3. In high altitude mode and for operation over 25 000 ft, the warning altitude setting is such that corrective actions can be taken in time to insure that cabin pressure altitude can not exceed 15,000 ft "in the event of any reasonably probable failure" of the Pressurization System.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgELOS.nsf/0/eb3fc2b4897f9c05862574a3005cdf07/$FILE/TC0030IB-T-%20SE-13.pdf

[h3dxb]

Gentlemens, U speak here about 2 different things:
Point 1 is: Mel dispatch with 1 pack inop, downgraded to FL315 for Pax comfort and sufficent aircirculation
point 2 is: MEL does NOT apply in flight, as per FCOM and MEL preamble, U have to follow ECAM and/or QRH , unfortanly I don't have the A320 docs in front of me, don't nail me here I refer to A330.

In case of 2 Bleed faults, perf. emerg. descent to FL220 and let start APU for Bleed recovery.

The other case, that U loose the second pack, don't forget U have the Emerg. Ram Air Inlet left. According to AMM the use is limited for ALT<10.000ft and Delta P 1.006PSI due to the fact the air is going direct in the LP air distribution unit, but at least U have some fresh air for yr PAX.
The CPC goes in a Mode where the Outflowvalve will alsmost completly close, and a Delta P (DP) from 8 PSI sounds big , but the bleeed leackage from the fuselage is not so high like mentioned, so the volume of AIR with a DP of 8 PSI is enorm, enough time to get reduced by a almost closed OFV for descending on a safe ALT.

Hope this info helps a little bit, pls don't nail me on the A320, the last little bird I saw a yr ago.

rgds