A320...Single Pack Inop...(Dispatch Vs Inflight)

[kuwait340]

Hello...

if you have a single pack inop while you are on the ground...the MEL restrict the max cruising altitude to 31500 feet.

but if you are inflight with both packs opearating..and then you have a single pack inop...the ECAM will not mention that the max altitude is 31500 feet...even the FCOM3 3.02.21 p.1 AIR PACK 1(2) FAULT says" Affected pack....off" ...so if you cruising at more than 31500feet ...do you have to descend or maintain your level.

in my opinion....the restriction applies on the ground only, to take into account the pressurization of the aircraft(not as effective as both packs on)...while inflight the aircraft is pressurized...and you don't have to descend.

any ideas...

thanks

[Essential Buzz]

You are correct - the 31500' limit is a dispatch requirement only. In flight you are permitted to maintain (or climb to) your planned level - pressurisation permitting!

The procedure is the same on Boeing aircraft, albeit with a different MEL altitude restriction.

[SIDSTAR]

Kuwait340

That's correct. Most aircraft are the same. Dispatching with one pack inop usually means that the single pack cannnot pressurise the cabin to more than the restricted altitude (with a reasonable buffer built in) whereas if the pack fails in flight while the cabin is already pressurised to the required level, a single pack can keep it at that level.

However, I have flown with Captains who wanted to descend to a lower level when operating single-pack , so that they would be nearer to FL100 in the event of that pack failing in flight. In one case I had to point out to a Captain that he could certainly do that but we wouldn't then have the fuel to continue to destination.

[Starbear]

The differences between MEL and QRH (or ECAM) procedures is actually more fundamental than that and is based like many things in aviation on probabilities and failure analysis at design/certifcation stage.

A failure of any component inflight is just that: a single failure and multiple failures are generally not considered unless specifically stated in the drills.

But when dispatching with the same single component already unserviceable the MEL procedures must (and do) consider a further failure of another component in that system inflight and that is why the pack/altitude restriction is there for dispatch and not inflight.

A single pack should always be able to pressurise the a/c in all phases of flight, the certification would have covered that or an additional restriction would apply.

There are numerous examples of this philosophy but one of the best for demonstration purposes is provided by comparing MEL and QRH procedures for say, a pair of flight spoilers and quoting Boeing only here (B757 specifically) but expect Airbus to be similar:

Eicas "SPOILERS" message (advisory)
QRH: one or more spoiler pairs are inoperative: Roll rate inflight may be reduced: Speedbrake effectiveness may be reduced inflight and during landing. (my italics but note, no restrictions at all)

MEL:
Flight Spoilers:

Number Fitted:10
Number required for dispatch: 8

One symmetrical pair may be inoperative in the down position provided:
(a) Ground spoilers operate
normally, and
(b) Flight Manual performance is
adjusted as follows:
1) Gross weight shall not
exceed 98,436 kgs
(217,000 lbs),
2) Flaps 1 operation is
prohibited,
3) Antiskid inoperative
departure is prohibited,
4) Field length limited
weight is reduced by
1450 kgs (3,200 lbs),
5) Minimum runway length
is 6,000 feet,
6) Altitude does not exceed
FL 300,
7) Airspeed does not exceed
270 kts. or .70 Mach,
whichever is lower,
8) Required landing field
length for flaps 25 or 30
is increased by 450 feet,
9) Autoland operation is
prohibited, and
10) Autospoiler operation is
prohibited for landing
and Flight Manual
decrements are applied.

The differences are huge beacause the MEL must consider a further pair of spoilers failing inflight and so ability to stop in RTO case; descend in depressurisation case; reduce speed from MMO or VMO etc. etc.

[kuwait340]

Excellent guys....thanks for sharing the info's.

[Dream Land]

Not really about "on ground", your MEL is for reference only after dispatch, when that is varies with airline, your MEL should specify when you are technically "dispatched", some airlines consider when the aircraft first moves under it's own power, others consider after takeoff.

[john_tullamarine]

Not really about "on ground", your MEL is for reference only after dispatch

you're missing the point, I suspect. Starbear's first few sentences are on the mark....

(a) if it breaks before you go, then you either get it fixed or invoke the MEL if the CFU idea appeals on the day, considering all operational circumstances .. ie, the philosophy is that the captain has the final say as to whether the MEL will/will not be invoked

(b) if it breaks after you are on the way, then

(i) you do the best you can, considering that
(ii) the MEL gives you a lot of good guts guidance in the decision making process as it considers a lot of things in which the average line pilot doesn't have any significant background
(iii) it follows that one can, indeed, go back and get it fixed after despatch if the captain considers it warranted to do so ...

Looking at the original question, the answer is straightforward .. despatch with multiple units leaves you with a back up in the event of one breaking .. despatch with one gives you the one shot only .. all a risk management and consequences consideration as embodied in the design standards and certification interpretation ...

[Dream Land]

you're missing the point, I suspect. Starbear's first few sentences are on the mark.... The mark that you are missing is that just because an aircraft is on the ground may or may not impact the flight with a restriction. If you haven't been to several airlines like myself, you'd know that point of dispatch is the difference, just trying to point that out.

[Meek]

Further to the above, you may not be able to get it fixed at outstation. Hence if at base, check with Engineers to avoid AOG at outstation.

[OPEN DES]

I think I remember that the max altitude with one Pack per the MEL is 37000ft provided the spoilers are operative. And 31500 with no restriction on speedbrakes.