Boston92 From United States of America, joined Aug 2006, 3390 posts, RR: 6 Posted (9 years 1 month 3 weeks 5 days 7 hours ago) and read 7277 times:
I am sorry if the title is misleading, but on a recent flight from JFK-PVD on Delta Connection while on the ground, we lost cabin pressure because the baggage people opened the hatch after we were all ready to go. Our ears sure did feel it. Why was there no masks? Do we have to be over 8000 feet for the masks to fall? Why were we even pressurized if we were not over FL 080?
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Shamrock350 From Ireland, joined Mar 2005, 6584 posts, RR: 14
Reply 1, posted (9 years 1 month 3 weeks 5 days 6 hours ago) and read 7248 times:
Aircraft pressurise when the door shuts but I dont think masks drop unless you are at altitude because there is no loss of oxygen.
I could be wrong on that but I do think aircraft pressurise when the door shuts, it's automatic.
RichardPrice From , joined Dec 1969, posts, RR:
Reply 2, posted (9 years 1 month 3 weeks 5 days 6 hours ago) and read 7225 times:
As Shamrock350 alluded to, theres no point in dropping an additional oxygen system if theres no requirement for it - all it would result in is additional cost to the airline to make the systems safe again and delay the aircraft while that was done.
Avt007 From Canada, joined Jul 2000, 2132 posts, RR: 4
Reply 3, posted (9 years 1 month 3 weeks 5 days 6 hours ago) and read 7226 times:
Typically, an aircraft will pressurize to 50 feet or so when the doors are closed, engines running, on the ground, to help the system maintain a nice smooth transition to flight. It's not a sudden change in pressure that drops the mask, it needs to be above a certain cabin altitude, somewhere around 10,000 feet. What type aircraft? If it was a CRJ, the o2 masks fall at 14,000 feet cabin altitude.
Well thats your reason in any pressurized aircraft with overhead masks. Also the crews can elect to drop the masks but would not below 10,000 because the body will be fine with thinner air. And well passengers don't need to have O2 provided to them unless the cabin altitude is 14,000ft or higher. FAA doesn't care about passengers as long as they are a live and sleeping.
Jetlagged From United Kingdom, joined Jan 2005, 2620 posts, RR: 25
Reply 8, posted (9 years 1 month 3 weeks 5 days 3 hours ago) and read 6969 times:
Most modern aircraft will automatically pre-pressurise to 50-100 feet below field elevation on the ground. So if the field is 50 feet above sea level, the cabin altitude will be at around sea level or slightly lower. On some types this doesn't happen until the throttles are advanced for takeoff for just this kind of reason. However, even with the outflow valves fully open, with packs on and doors closed a small pressure differential can exist.
Suddenly releasing even a small cabin differential pressure could be noticeable as your ears are very sensitive. If the pressure difference was released slowly you wouldn't feel it.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
ANITIX87 From United States of America, joined Mar 2005, 3353 posts, RR: 12
Reply 11, posted (9 years 1 month 3 weeks 5 days ago) and read 6897 times:
Quoting RichardPrice (Reply 2): all it would result in is additional cost to the airline to make the systems safe again
What does this consist of? One time we landed in ATH so hard (TWA800, 742) that the masks came out of their housings. What would the crew have had to do? I don't know if the return flight left on time or not, but it was quite a weird landing.
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Quoting Avt007 (Reply 3): If it was a CRJ, the o2 masks fall at 14,000 feet cabin altitude.
As noted, most commercial aircraft only have drop-down masks activate at around 14,000 feet. The decompression announcement starts (if installed) and cabin lights go to to bright (if selected as an option) as well.
"DON MASK, FASTEN SEAT BELT!"
Release your seat-belts and get out! Leave everything!
Kdm From New Zealand, joined Feb 2006, 115 posts, RR: 0
Reply 17, posted (9 years 1 month 3 weeks 4 days 14 hours ago) and read 6759 times:
I have this theory about face masks which it would be nice to know if it rings true.
At 30,000 feet if the plane has a huge problem and takes a sudden dive (like a bit of the fuselage falls off) we have complete loss in cabin pressure I have two choice. 1. take oxygen 2. don't bother.
Theory 1) If the plane depressurises and I need a mask there is a serious problem. I take the mask breath nice chemically produced air, Pilot drops the plane to 10,000 feet. I have now used up my 2 minutes of oxygen but no problem I can now breath. Plane either lands safely so fine, or crashes and a die living and breathing the last 10,000 feet wishing I had passed out.
Theory 2) Plane depressurises, I don't bother taking oxygen. I pass out. either the plane crashes, I don't care as I have passed out or once the plane gets to 10,000 feet I now have enough oxygen to breath so I regain consciousness the pilot has got the plane under control so all is OK.
HAWK21M From India, joined Jan 2001, 31875 posts, RR: 54
Reply 18, posted (9 years 1 month 3 weeks 4 days 14 hours ago) and read 6759 times:
Quoting Boston92 (Thread starter): Do we have to be over 8000 feet for the masks to fall? Why were we even pressurized if we were not over FL 080
Most Aircraft for eg the B737 have an Air - Grd selector sw on the CPC panel that is moved to Flt after all doors are closed to prepressurise the Aircraft.This could be 150-200ft below runway elevation.Hence when the cargo door was opened the Pressure loss was felt.
However for the O2 masks to drop.Cabin Alt needs to reach 14,000ft or manually deployed by crew.
Tristarsteve From Sweden, joined Nov 2005, 4355 posts, RR: 33
Reply 19, posted (9 years 1 month 3 weeks 4 days 14 hours ago) and read 6751 times:
Quoting MarkHKG (Reply 14): Unless the oxygen mask is a chemical oxygen generator system, which requires each individual generator that was fired to be replaced.
When the masks drop down, the chemical generators do not start to produce oxygen until you pull on the mask. If you look you can see a string that goes from the plastic hoses up to the generator. Pulling on the mask pulls the pin out of the generator and starts the generator.
If masks fall down, they need to be repacked. It takes time, and is very fiddly rolling up three or four masks and getting them all nice and neat into a box which is two sizes too small, then closing the door before they fall down again.
Quoting Jetlagged (Reply 15): Of course, but I was think of the case mentioned where the masks deployed in a hard landing, so presumably no oxygen flow occurred (the system would not be armed).
The system is armed, but there would be no flow unless a pax pulled the mask down and put it on.
Quoting Avt007 (Reply 5): Indeed, Alias is right. The Dash has a ceiling of 25,000 feet, and so doesn't require oxygen for the pax
The regulations state that you must be able to descend to 10000ft in a given amount of time. It used to be TWO minutes. At 25000ft you need oxygen if you can't descend fast.
The good old DH Trident 2 had no oxygen system and flew over 30000ft. It could descend fast enough to get down ib time with its air deployable thrust reversers.
ThrottleHold From South Africa, joined Jul 2006, 739 posts, RR: 1
Reply 20, posted (9 years 1 month 3 weeks 4 days 10 hours ago) and read 6706 times:
Quoting Kdm (Reply 17): Theory 2) Plane depressurises, I don't bother taking oxygen. I pass out. either the plane crashes, I don't care as I have passed out or once the plane gets to 10,000 feet I now have enough oxygen to breath so I regain consciousness the pilot has got the plane under control so all is OK.
What if the aircraft is flying over mountainous terrain with an MSA way in excess of 10,000ft? It has to stay up to clear the terrain.
A descent to 10,000ft may take anything up to 8 or 9 mins. Do you really want to risk starving your brain of oxygen for this length of time?
All the crew has to do is write it in the logbook, and walk away. Maintenance (as usual) has to clean up their mess.
Quoting MarkHKG (Reply 14): The decompression announcement starts (if installed) and cabin lights go to to bright (if selected as an option) as well.
I've also seen IFE and inseat power systems tied into this as well. Both are shut off in case of mask deployment.
Quoting Tristarsteve (Reply 19): very fiddly rolling up three or four masks and getting them all nice and neat into a box which is two sizes too small, then closing the door before they fall down again.
I once opened a mask panel to get at something behind it. When the masks were stowed, the string mentioned earlier had wrapped it self around the door, and as soon as I opened it, SNAP, and the O2 starts to flow. I had to wait over an hour for the generator to cool enough to remove. What a PITA.
MarkHKG From United States of America, joined Dec 2005, 960 posts, RR: 1
Reply 22, posted (9 years 1 month 3 weeks 4 days 9 hours ago) and read 6679 times:
Quoting Kdm (Reply 17): If the plane depressurises and I need a mask there is a serious problem.
There are many cases where the masks drop due to a decompression, and it turns out it was NOT a serious problem with the airframe/aircraft itself. (Just wrong configuration settings that are rapidly corrected.) It's not like in the movies where the masks drop right before the plane crashes.
Release your seat-belts and get out! Leave everything!