logged Cabin Pressurisation system: very slow cabin altitude rate (all versions up to 1.07)

[kevinh]

Cabin altitude should change at a rate that equal to the cabin vertical speed. It is far slower than that and so cabin altitude is usually well behind the commanded cabin altitude. This has been a problem since initial release of the A350.

In a steady managed climb the Cabin VSI shows 400 ft/min, which is a reasonable value. However the indicated cabin altitude only climbs at 100 ft/min, 25% of the rate it should be. This means that as you get close to cruise altitude the cabin altitude is far too low and cabin differential pressure is in the amber or red range, which should never happen under normal conditions.

On my last flight, as I reached cruise level (FL390) the cabin altitude was still only 3,340 ft (6,000ft being the commanded cabin altitude), cabin diff press was 10.2 psi and it took over 24 minutes for the cabin altitude to finally reach 6,000 ft.

During descent, with cabin vertical speed stabilised at the commanded rate of -250 ft/min, the cabin altitude rate was -75 ft/min. Thats 30% of the value it should be.

Kev

 

Edited April 8 by kevinh

[richboy2307]

Thanks, reported.

[kevinh]

On 4/8/2025 at 6:15 PM, richboy2307 said:

Thanks, reported.

@richboy2307 I see the latest A350 version has a much improved ECS pressure controller, but the cabin is still a bit slower than it should be climbing and descending. The cabin altitude is always behind the target value. It works well enough during climb but the simulated cabin had to resort to a sudden 2000 ft/min rate of descent to catch up with the aircraft before touchdown. That would have made some ears pop. If you don't have ECAM pressurisation page selected you probably won't notice this but I did as I was checking to see if it worked properly now. 

Kevin

[richboy2307]

Hi @kevinh

Thanks for your report.

If you can, please provide the OFP (PDF) for your route where you noticed this so I can share with the team for reproduction/fix testing.

Thanks!