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 :}

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:

JT

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

G

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

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?

guiones
 

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

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

(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_repos...38_Hypoxia.pdf

Hope this helps clear things up.

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

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!

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

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