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Landing Emergency, Is Plane Already Depressurized  
User currently offlinetransaeroyyz From Canada, joined Dec 2010, 150 posts, RR: 0
Posted (3 years 7 months 2 hours ago) and read 3624 times:

In a quick Landing Emergency, the plane is on the ground, at what point can u open the exits, how do u when when the plane is depressurized, is there a visual cue besides the flight attendants instruction to open, seconds count...

5 replies: All unread, jump to last
 
User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 1, posted (3 years 7 months 1 hour ago) and read 3605 times:

Quoting transaeroyyz (Thread starter):


In a quick Landing Emergency, the plane is on the ground, at what point can u open the exits, how do u when when the plane is depressurized, is there a visual cue besides the flight attendants instruction to open, seconds count...

In most planes the cabin outflow valve will go fully open (ie depressurize) once the landing gear hits the ground (a "squat" switch on the gear sends the signal to the pressure controller which then adjusts the outflow valve). The pressurization system should also ensure the cabin will be at field level upon landing, preventing a pressure bump. This is a very broad explanation though, each plane has it's own quirks. In most modern planes pressurization is automatic requiring little to no direct input from the crew.

[Edited 2011-04-05 13:05:00]

User currently offlinetransaeroyyz From Canada, joined Dec 2010, 150 posts, RR: 0
Reply 2, posted (3 years 6 months 4 weeks 1 day 22 hours ago) and read 3542 times:

Quoting Fly2HMO (Reply 1):
once the landing gear hits the ground (a "squat" switch on the gear sends the signal to the pressure controller


that's awesome. but how about i throw a belley landing scenario at ya..


User currently onlinefr8mech From United States of America, joined Sep 2005, 5520 posts, RR: 14
Reply 3, posted (3 years 6 months 4 weeks 1 day 21 hours ago) and read 3497 times:

Quoting transaeroyyz (Reply 2):
that's awesome. but how about i throw a belley landing scenario at ya..

Then the fuselage ruptures and you don't have an issue.

The cabin pressuriazation system prevents the aircraft from landing while pressurized. If the system is operating in manual, I'm sure that there is a step in the procedure to dump the cabin, by fully opening the outflow valve, prior to landing.



When seconds count...the police are minutes away.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (3 years 6 months 4 weeks 1 day 16 hours ago) and read 3429 times:

Quoting transaeroyyz (Thread starter):
In a quick Landing Emergency, the plane is on the ground, at what point can u open the exits

By the time you can get to them, they should be ready to open.

Quoting transaeroyyz (Thread starter):
how do u when when the plane is depressurized

If you can't open the door, the plane is pressurized.

Quoting transaeroyyz (Thread starter):
is there a visual cue besides the flight attendants instruction to open, seconds count...

No, nor is any needed. The pressurization controller will have the pressure equalized before touchdown and the outflow valves will go full open on touchdown anyway. And, on some designs, starting to actuate the door handle will open relieve valves.

Quoting transaeroyyz (Reply 2):
that's awesome. but how about i throw a belley landing scenario at ya..

The pressurization controller would have already equalized the cabin prior to landing, so even if the gear function doesn't work there shouldn't be any pressure.

Tom.


User currently offlineMarkhkg From United States of America, joined Dec 2005, 960 posts, RR: 2
Reply 5, posted (3 years 6 months 4 weeks 1 day 16 hours ago) and read 3414 times:

Quoting fr8mech (Reply 3):
I'm sure that there is a step in the procedure to dump the cabin, by fully opening the outflow valve, prior to landing.

Just to point out there have been a few incidents where a cabin remained pressurized once on the ground and flight attendants attempted to open the door (in one case for an evacuation). One aircraft that was studied in particular was the A300. The doors in the studied situations were unable to be opened (as Airbus doors do not have pressure vent gates on their doors, unlike other aircrafts) initially, but later burst open. Flight attendants have been killed in these types of accidents.

(See http://www3.ntsb.gov/recs/letters/2002/A02_20_23.pdf )

Quoting fr8mech (Reply 3):
Then the fuselage ruptures and you don't have an issue.

Also, Airport Rescue and Fire (ARFF) are actually taught to puncture/make forcible entry into the fusulage/window in case the aircraft remains pressurized and they can't get the doors open in a serious emergency so as to remove the differential. This is, of course, a last ditch step.

Quoting tdscanuck (Reply 4):
If you can't open the door, the plane is pressurized.

Currently manufactered Airbus doors are equipped with a red pressurization warning light on the inside of the cabin. The light illuminates if both engines are off, the door is disarmed but the cabin differential pressure is above 2.5 Hpa. This warning light can be seen from the exterior of the aircraft through the door's window.



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