Cabin leak rates / decompression

[RMC]

Anyone have any information on cabin leak rates in the event of a double pack failure (either flight test cabin altitude rise or ground test maintenance manual pressure drop). In previous threads I have seen cabin altitude rise of between 300 and 2,000 FPM for different types. Apart from door seals, electrical wiring bungs, system Non return valves and flying control cable seals (non FBW) where else would the aircraft leak air?

[Corrosion]

Fuselage belly drains, drain masts, some fuselage seams can leak littlebit, windscreens from seals, bad repairs with cherry max rivets if rivet center pin is missing.
How depressing is to find badly leaking aircraft on ground leak rate test... leaks from everywhere.

[vapilot2004]

Moveable cockpit windows, pitot-static feed throughs come to mind theoretically to add to your list, and practically, the lower fuselage water drains are known leakers and the landing gear wheel wells are common sources of structural air leakage.

[piratepete]

If you fly up to , say 40,000 feet, turn off both packs, even in a brand new aircraft, typically the outflow valve will drive shut.If you try to open the OV for some reason it cannot be opened usually due to a heavy duty spring resisting this action (failsafe).In one exercise I found that the air leaked out very very slowly (new A/C) and it can take up to 30 minutes before the cabin altitude would reach above 10,000 feet.FWIW

[OPEN DES]

A320 out of the factory will have a leakage rate of around 500ft/min, with two packs off. Approximately double that for in-service (older) aircraft.
Leakage rate will be increased significantly in smoke configuration, i.e. blower and extract in OVRD. Around 1800-2000 ft/min for a new a/c.

[RMC]

Thanks. One last question to those who have depressurised how cold did it get in the cabin....will it go down closer to initial cruise altitude temperature (especially with adiabatic cooling) or somewhere between cruise altitude temperature and the 10,000' temperature?
Just tried it in the sim at 36,000' and Boeing predicted 1,900 feet per minute rate of climb. Obviously it will vary with altitude / differential pressure / aircraft type /age and build quality. Pirate Pete what aircraft type took 30 minutes to loose pressure.

[aerobat77]

well, i see nobody of you talks actual experience because anybody of you misses the most important: without any bleed air source the door sealings will not be inflated anymore resulting in significant pressure loss inside the cabin . this is not a question how old the aircraft is.

regards

[Exup]

Only aircraft I have worked on that had inflatable door seals was Gulfstream, I'm sure there are probably more out there but not to many, especially commercial pax/cargo types.

[Corrosion]

Originally Posted by Exup

Only aircraft I have worked on that had inflatable door seals was Gulfstream, I'm sure there are probably more out there but not to many, especially commercial pax/cargo types.

Think "aerobat77" meant normal door seals which usually have air passages to allow pressurized cabin air enter into seal, just to make them expand nicely against frame. Offcourse there is some types which have own pressure feed for seal, canīt remember how is it reacting if bleed air source is lost. Immediately if source is lost or just by slow leak. (Jetstream 41)

[Highway1]

The acceptable leak rate for 737 is 100 secs from 4 PSID down to 2.5 PSID cabin pressure - on older airframes it can get difficult to achieve that.

[Gauges and Dials]

Originally Posted by Corrosion

Fuselage belly drains, drain masts, some fuselage seams can leak littlebit, windscreens from seals, bad repairs with cherry max rivets if rivet center pin is missing.
How depressing is to find badly leaking aircraft on ground leak rate test... leaks from everywhere.

Older mechanics say they miss the bad old days when passengers smoked a lot of cigarettes -- leaks were easy to find; just look for the trail of nasty brown goo.

[Bergerie1]

747-100 series UK CAA Certificate of Airworthiness Air Test pressurisation leak rate test, para 7.2.6. At 30,000ft, I quote:-

'With normal cabin diff. put GALLEY/LAV FAN ON and switch all A/C packs to OFF. Record leak rate over 1 minute; 750' maximum. Restore normal pressurisation.

[Gauges and Dials]

Originally Posted by Bergerie1

747-100 series UK CAA Certificate of Airworthiness Air Test pressurisation leak rate test, para 7.2.6. At 30,000ft, I quote:-

'With normal cabin diff. put GALLEY/LAV FAN ON and switch all A/C packs to OFF. Record leak rate over 1 minute; 750' maximum. Restore normal pressurisation.

Diff Eq time.

Let's say leak rate is linearly proportionate to the difference between cabin and outside altitude. And let's say at 30000 feet with normal cabin pressure, the cabin climbs at 750 feet per minute.

And let's say the evil genius who set up this word problem (We'll stipulate that he is Mr. Roberts, my calc teacher, may his kind soul rest in peace) has also told you that all O2 systems have failed.

What rate of descent do you need to achieve to prevent the cabin from ever getting above, say, 12,000 feet.

No fair using simulation. This has to have a closed form solution.