A-320 One Pack U/S

[sharpshooter41]

I fly a 320 from the 1000 (MSN) series. The MMEL however, does not mention any altitude restriction in case of One Pack U/S operations.

On the other hand I have seen that there is an altitude restriction of 37,000 in case of Airbus 319 from the 3000 (MSN) series.

Is it possible that there is no altitude restriction in case of One Pack Operations for the 320 OR is there a typo mistake here.

[Airmann]

You've come across an interesting point, here's what my MEL says, it includes A320s/321s/319s (new and old)

All A320 & A321:

With Speedbrakes available: No ALT restrictions
Without Speedbrakes: 31,500ft.

319s

With Speedbrakes available: ALT restricted to 37,000ft.
Without Speedbrakes: 31,500ft.

Probably has to do with regulations.
With speedbrakes available, the A320s and A321s can achieve a high enough rate of descent that in the event of the loss of the remaining PACK the aircraft can reach a safe altitude quickly enough from max ceiling (39,800) not to necessitate a limitation on the alt. The A319, due to it being lighter, cannot achieve the required rate of descent and needs to be limited to 37,000ft, even with spoilers available.

Without Speedbrakes all aircraft are limited to 31,500ft.

This is my guess.

[sharpshooter41]

Thanks for the prompt response.

However, because the Max speed is the same for all (319/320/321), the ROD may not be all that different.

Also, the Cabin length of a 321 is much longer than a 319. If anything the time available for keeping the cabin pressure within acceptable limits in case of 319 should be substantially more than a 321. So if a 319 is restricted to 37,000 the limit for 320/321 should be substantially lower.

[OPEN DES]

Hi!
My 2p

The full speedbrake deflection of the A319 is about as effective as the half-one on the A320 and A321 hence the longer time needed to get down.

Then about cabin leakage rates:
There is no significant difference between the three. The A319/A320 should do no worse than 900 ft/min and the A321 no worse than 850 ft/min.

Rgds

[Airmann]

Here's your answer:

From PER-DES-EMG

A descent from FL370 to 1500ft for:

A320
@65t = 6.2 minutes

A321:

@55:5.8min
@75t: 7.3min
(interpolate @65t: 6.55min)

A319:
@65t: 7.3min

----

Times from FL370 to FL100 using the same charts at 65t (interpolating for A321)

A321: 4.5minutes
A320: 4.2 minutes
A319: 5.35minutes

In all cases above this is with speedbrakes extended flown at Mmo/Vmo

----

Max Spoiler Deflection, Clean config, Manual Flight:

A321: 25 degrees
A320: 40 degrees (spoilers 3 & 4)
------20 degrees (spoiler 2)
A319: 25 degrees (spoilers 3 & 4)
------17.5 degrees (spoiler2)

[sharpshooter41]

Thank you very much.

However I am still surprised that cabin length / cabin volume does not figure in this situation.


What you have written about the spoiler deflection is for Manual Flight. For flight with Auto Pilot engaged the difference between 319 and 320 is small.

320 Spoiler 3 & 4 25 deg

Spoiler 2 12.5 deg


319 Spoiler 3 & 4 25 deg

Spoiler 2 17.5 deg

[safelife]

All well and reasonable but then again Airbus doesn't require the autopilot to be switched off in an A320 for an emergency descent.
And with the autopilot on the max. Spoiler deflection is the same as on the A319.

?

[Airmann]

Ya you're right about the spoilers. I edited my post and added those numbers in as an afterthought. But the bottom line is that the 320/321 are much quicker to descend than the 319.
As for the exact aerodynamic reason why, I'll leave that to the experts. I don't have a clue. But I guess we can rule out both weight and spoiler deflection as the figures I posted are for the same weight and it looks like spoiler deflection is the same for all aircraft with AP on.
The other thing that came to mind was the fuselage drag, but looking at the numbers the 320 descends quicker than the 321.

[IFixPlanes]

We had the same question regarding this limitation forwarded to Airbus
Airbus explains it nearly like Airmann "guess" at answer #2.