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How Good Are Door Seals?  
User currently offlineALbyDAL From United States of America, joined Aug 2006, 22 posts, RR: 0
Posted (7 years 11 months 1 week 3 hours ago) and read 3204 times:

I've always wondered how well an aircraft door actually seals off the cabin. I know that with most doors opening inwards, the pressurization of the plane actually makes the seal stronger. I was in an exit row of an AA MD-80 yesterday and noticed that when I pulled back on the rubber trim around the exit door a little bit I could hear a noticeable hissing sound. The trim then snapped back in place very quickly when I let go of it, as if there was very strong suction behind it. Stuff like this makes me wonder!

17 replies: All unread, jump to last
 
User currently offlineAirfoilsguy From , joined Dec 1969, posts, RR:
Reply 1, posted (7 years 11 months 1 week 2 hours ago) and read 3193 times:

Quoting ALbyDAL (Thread starter):
when I pulled back on the rubber trim around the exit door a little bit



Quoting ALbyDAL (Thread starter):
Stuff like this makes me wonder!

People who screw with aircraft doors while in flight make me wounder. Lucky nobody saw you.


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 2, posted (7 years 11 months 1 week 2 hours ago) and read 3176 times:

The seal you pulled was not the main door seal.That is more Outboard.The seal you touched is a flappertype used to reduce noise.
regds
MEL



Think of the brighter side!
User currently offlineALbyDAL From United States of America, joined Aug 2006, 22 posts, RR: 0
Reply 3, posted (7 years 11 months 1 week 1 hour ago) and read 3152 times:

Quoting Airfoilsguy (Reply 1):
Quoting ALbyDAL (Thread starter):
when I pulled back on the rubber trim around the exit door a little bit

As mentioned... it was part of the trim on the interior panel, NOT the actual door seal. Roughly akin to me fidgeting with a window shade.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17003 posts, RR: 67
Reply 4, posted (7 years 11 months 1 week ago) and read 3124 times:

Quoting Airfoilsguy (Reply 1):
People who screw with aircraft doors while in flight make me wounder. Lucky nobody saw you.

There is very little you can do to a typical airliner door at cruise altitude which would be dangerous to the aircraft. Otherwise they'd secure it somehow.


As for door seals, they are not perfect. You will get leakage of heat and air. Still, they are a good compromise of weight/complexity vs tightness. Think of it this way: even if a whole window popped out, the pressurization system could easily compensate. So a slightly leaking door seal is no biggie.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineOnetogo From United States of America, joined Feb 2006, 314 posts, RR: 0
Reply 5, posted (7 years 11 months 6 days 23 hours ago) and read 3114 times:

Quoting Starlionblue (Reply 4):
Think of it this way: even if a whole window popped out, the pressurization system could easily compensate.

Is that right?


User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 6, posted (7 years 11 months 6 days 23 hours ago) and read 3110 times:

Quoting Starlionblue (Reply 4):
Think of it this way: even if a whole window popped out, the pressurization system could easily compensate. So a slightly leaking door seal is no biggie.

Not exactly. A door seal leaking, yes, but a missing window is too big of "leak:" the aircraft would rapidly depressurize. Besides condensation elimination, why do you think there is a plastic shield in front of the window?


User currently offlineDavid L From United Kingdom, joined May 1999, 9524 posts, RR: 42
Reply 7, posted (7 years 11 months 6 days 23 hours ago) and read 3099 times:

Quoting Starlionblue (Reply 4):
even if a whole window popped out, the pressurization system could easily compensate.

While the aircraft made an emergency descent to 10,000 ft or so.  Smile


User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 8, posted (7 years 11 months 6 days 22 hours ago) and read 3077 times:

The noise or whistling that may occur from any leak in a cabin door is normally more of an issue than the small amount of air that leaks past, as the aircraft's pressurization system can more than compensate for that.

Keep in mind that the outflow valve(s) are always open to some degree, creating a controlled leak, so as to exhaust stale air and make room for fresh air. Air even goes down the sink drains, as they are open to to outside, through the drain masts.  Wink

Chris



Don't blame me, I don't work here...
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17003 posts, RR: 67
Reply 9, posted (7 years 11 months 6 days 22 hours ago) and read 3072 times:

Quoting N231YE (Reply 6):
A door seal leaking, yes, but a missing window is too big of "leak:" the aircraft would rapidly depressurize.

As David L is saying, the pressurization system can compensate fast enough for the plane to reach a safe altitude.

As N8076U is saying, the outflow valve(s) are making a controlled leak the whole time. Close those and there's room for quite a big unexpected leak.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBjones From United States of America, joined Feb 2002, 123 posts, RR: 0
Reply 10, posted (7 years 11 months 6 days 21 hours ago) and read 3058 times:

A hole the size of a window would most definately result in a rapid decompression, at least on the aircraft size I am most familiar with (narrowbody jets). Perhaps in something the size of a 747 it would result in a slower decompression but I tend to think not much slower. The incidents I have heard of where a rapid D occurred have in most cases been the result of fairly small (significantly less than 1 sq ft) holes.

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17003 posts, RR: 67
Reply 11, posted (7 years 11 months 6 days 21 hours ago) and read 3056 times:

I guess I stand corrected. But isn't the point of the pressurization system to keep the plane pressurized enough to reach a safe altitude in a reasonable time in case it springs a leak?


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 12, posted (7 years 11 months 6 days 20 hours ago) and read 3027 times:

On the L-1011 a 5 square inch leak in the passenger or cargo door seals (cumulative over all the doors) would lead to an additional 68 pound fuel burn per hour, or $11,750 per year, in 1977 dollars. Door seals are very important.

User currently offlineBjones From United States of America, joined Feb 2002, 123 posts, RR: 0
Reply 13, posted (7 years 11 months 6 days 20 hours ago) and read 3019 times:

No a pressurization system is to provide a safe and comfortable environment for humans at an altitude that is efficient for the aircraft and above most weather that would affect the flight. The oxygen masks are what are there to keep the passengers and crew safe and alive long enough to descend to a safe altitude for breathing without supplemental oxygen.

User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 14, posted (7 years 11 months 6 days 14 hours ago) and read 2950 times:

Quoting Starlionblue (Reply 4):
Think of it this way: even if a whole window popped out, the pressurization system could easily compensate

Not if you consider Both the Outer & Middle pane popping out.
regds
MEL



Think of the brighter side!
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 15, posted (7 years 11 months 6 days 6 hours ago) and read 2877 times:

Quoting Starlionblue (Reply 11):
I guess I stand corrected. But isn't the point of the pressurization system to keep the plane pressurized enough to reach a safe altitude in a reasonable time in case it springs a leak?

The pressurization system is a means of comfort to sustain life on board the aircraft, without any masks or suits. But should the system fail, that is why oxygen masks are provided above each seat, and usually, the pilots have about 12 minutes (depending on the aircraft) to bring it down to a safer altitude.


User currently offlineDavid L From United Kingdom, joined May 1999, 9524 posts, RR: 42
Reply 16, posted (7 years 11 months 6 days 2 hours ago) and read 2845 times:

Quoting Bjones (Reply 10):
A hole the size of a window would most definately result in a rapid decompression

Of course, but...

Quoting Bjones (Reply 13):
No a pressurization system is to provide a safe and comfortable environment for humans at an altitude that is efficient for the aircraft and above most weather that would affect the flight. The oxygen masks are what are there to keep the passengers and crew safe and alive long enough to descend to a safe altitude for breathing without supplemental oxygen.



Quoting Bjones (Reply 10):
Perhaps in something the size of a 747 it would result in a slower decompression but I tend to think not much slower



I was under the impression that airliners had to be certified to "manage" a pressure loss caused by a window blowing out (possibly two) long enough for the crew and passengers to don their masks. Not at normal pressure levels, obviously, but also not at zero pressure differential. Otherwise, why would Concorde's windows have been so much smaller?


User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 17, posted (7 years 11 months 6 days ago) and read 2826 times:

Quoting David L (Reply 16):
Otherwise, why would Concorde's windows have been so much smaller?

Concordes windows were indeed smaller so as to allow the pressurisation system to handle multiple blowouts and maintain a 'breathable' (not necesarily a comfortable) level while the aircraft descended from operational altitude, without requiring deployment of masks.


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