Boston92
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Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 5:45 am

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
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 5:55 am

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
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 6:01 am

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
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 6:02 am

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.

[Edited 2007-04-04 23:05:11]
 
Alias1024
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 6:04 am

Dash 8s don't have oxygen masks for passengers. I'm guessing that is what you were on since that is what is shown when I search JFK-PVD on delta.com.
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avt007
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 6:06 am

Indeed, Alias is right. The Dash has a ceiling of 25,000 feet, and so doesn't require oxygen for the pax.
 
SkyexRamper
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 6:12 am

Quoting Boston92 (Thread starter):
while on the ground

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.  Wink Big grin
Good Luck to all Skyway Pilots! It's been great working with you!
 
Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 7:37 am

Quoting Alias1024 (Reply 4):
Dash 8s don't have oxygen masks for passengers.

Well that explains everything. But I doubt we were pressurized to 50 feet because I dont think I would have felt it that much. Plus, JFK is somewhere around 50 feet in elevation, right?
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Jetlagged
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 9:06 am

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.
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Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 9:30 am

Quoting Jetlagged (Reply 8):

All right thanks. BTW, did somebody steal somebody elses signature or is just a very rare coincidence?????
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Jetlagged
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 9:55 am

Quoting Boston92 (Reply 9):
BTW, did somebody steal somebody elses signature or is just a very rare coincidence?????

Coincidence, I hope  Smile
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ANITIX87
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 12:25 pm

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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Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 12:49 pm

Quoting ANITIX87 (Reply 11):

It is like when airbags deploy on your car, if they do, you need to take it tnto the mechanic, you can not just 'put it back in'.
"Why does a slight tax increase cost you $200 and a substantial tax cut save you 30 cents?"
 
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Jetlagged
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 1:13 pm

Quoting Boston92 (Reply 12):
It is like when airbags deploy on your car, if they do, you need to take it tnto the mechanic, you can not just 'put it back in'.

Not quite the same. Airbags aren't reusable and must be replaced whereas oxygen masks simply need to be restowed. Time consuming nevertheless, especially on something the size of a 747-200.
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Markhkg
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 2:48 pm

Quoting Jetlagged (Reply 13):
whereas oxygen masks simply need to be restowed.

Unless the oxygen mask is a chemical oxygen generator system, which requires each individual generator that was fired to be replaced.

Quoting Boston92 (Thread starter):
Do we have to be over 8000 feet for the masks to fall?



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!"  Smile
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Jetlagged
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 9:47 pm

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

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 glass isn't half empty, or half full, it's twice as big as it needs to be.
 
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Starlionblue
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 10:15 pm

Quoting Jetlagged (Reply 13):
Airbags aren't reusable and must be replaced whereas oxygen masks simply need to be restowed.

You mean I could be wearing a used mask? Not that it isn't better than passing out, but eeeeww.  Wink

[Edited 2007-04-05 15:16:36]
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kdm
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 10:30 pm

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.

I prefer option 2. Have I got this wrong.
 
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HAWK21M
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 10:34 pm

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.

regds
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Tristarsteve
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RE: Loss Of Cabin Pressure, Why No Masks?

Thu Apr 05, 2007 10:48 pm

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.
 
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ThrottleHold
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 2:14 am

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?

Best choice is to don the mask.
 
avt007
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 2:36 am

Quoting ANITIX87 (Reply 11):
What would the crew have had to do?

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
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 3:13 am

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.
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Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 6:45 am

Quoting ThrottleHold (Reply 20):
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?

There is only a supply for 2 min of air, and when the plane loses oxygen, I doubt the pilot will perform a normal 2000 fpm descent to FL140. It will be a most UNcomfortable rapid descent down.
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Markhkg
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 6:56 am

Quoting Boston92 (Reply 23):
There is only a supply for 2 min of air,

Passenger oxygen systems typically produce oxygen for 10-15 minutes.
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ThrottleHold
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 7:23 am

Quoting Boston92 (Reply 23):
There is only a supply for 2 min of air

A chemical generator will supply 15-20 mins of O2, depending on the type fitted.

Quoting Boston92 (Reply 23):
I doubt the pilot will perform a normal 2000 fpm descent to FL140.

On the Airbus, an emrgency descent is performed at thrust idle and speed brakes deployed. With the autopilot engaged, only 1/2 speed brake deployment is available. In the event of serious structural damage, the speed may be limited to well below Vmo/Mmo resulting in a slower descent rate. It can take many minutes to descend from FL410 to FL100.
 
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Jetlagged
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 8:17 am

Quoting Tristarsteve (Reply 19):
The system is armed, but there would be no flow unless a pax pulled the mask down and put it on.

In a bottled O2 type system, as on the 747-200, pulling the mask will not release oxygen unless the main oxygen valves have been opened, either automatically by high cabin altitude or by the crew manually operating the system. So if the masks drop down in a heavy landing no flow will occur. When I said the system was not armed, perhaps I should have said activated?
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andz
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RE: Loss Of Cabin Pressure, Why No Masks?

Fri Apr 06, 2007 2:11 pm

Quoting Starlionblue (Reply 16):
You mean I could be wearing a used mask?

I'd like to see the scientific odds on the same aircraft having more than one depressurisation requiring passenger oxygen.
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Starlionblue
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RE: Loss Of Cabin Pressure, Why No Masks?

Sat Apr 07, 2007 1:54 am

Quoting Andz (Reply 27):
Quoting Starlionblue (Reply 16):
You mean I could be wearing a used mask?

I'd like to see the scientific odds on the same aircraft having more than one depressurisation requiring passenger oxygen.

Hehe. Very good point. Besides, if the choice is cooties or dying, I'll take the cooties.  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
EMBQA
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RE: Loss Of Cabin Pressure, Why No Masks?

Sat Apr 07, 2007 3:51 am

Quoting Alias1024 (Reply 4):
Dash 8s don't have oxygen masks for passengers

Not true..!! It depends on the interior configuration. Most if not all of Mesa's Dash-8's have drop masks which are supplied by a bottle, not chem generators. Freedom's are some of the oldest Dash-8 out there, and do not have masks.

[Edited 2007-04-06 20:53:06]
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Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Sat Apr 07, 2007 6:29 am

Quoting EMBQA (Reply 29):
Freedom's are some of the oldest Dash-8 out there, and do not have masks.

Damn, I am having a blank, what do they call the emergency exits? It is an old war term. It'll come to be later. I keep coming back to Storkie Exits, but damn, that is not it.
"Why does a slight tax increase cost you $200 and a substantial tax cut save you 30 cents?"
 
474218
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RE: Loss Of Cabin Pressure, Why No Masks?

Sat Apr 07, 2007 7:26 am

Quoting Boston92 (Thread starter):
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?

The cabin was not pressurized, if it had the cargo door could not have been opened. Aircraft doors are forced against their stops and seals when they are pressurized, this prevents them from being opened if there is even a small amount differential pressure between the of cabin and outside pressure. While air is being pumped into the cabin (and cargo compartments) whenever the engines are running, when the aircraft is still on the ground the outflow valve (or valves) would have been open, allowing that pressure to escape.
 
avt007
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RE: Loss Of Cabin Pressure, Why No Masks?

Sat Apr 07, 2007 8:20 am

If it was indeed a Dash, you are correct, the outlfow valves should have been open, I don't think they close until the power levers are above a certain angle. Again, if it was a Dash, the baggage door is a plug type, fitting from the inside out, and I'm pretty sure you couldn't open it if pressurized. But you can open a Dash main cabin door if there is 0.5-1.0 psi differrential. You just have to pull hard enough on the lever. But it opens outward, making it much easier.
As for the start of this post, it couldn't have coincidental with the door opening, and the crew turning the bleeds on, who knows?
 
Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Sat Apr 07, 2007 9:12 am

It was a Dash, and because of my window seat, I could see the baggage handlers say the number "4" to our captain, meaning four more bags. They re openede the hatch and our ears sure did feel it. I don't know how the hell they did it, but they did.
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HAWK21M
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RE: Loss Of Cabin Pressure, Why No Masks?

Sat Apr 07, 2007 3:01 pm

Quoting Boston92 (Reply 33):
They re openede the hatch and our ears sure did feel it. I don't know how the hell they did it, but they did.

Considering the cabin pressure while on ground.Opening the door would not take effort.Was the Anticoll lights on at that time.
regds
MEL
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474218
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RE: Loss Of Cabin Pressure, Why No Masks?

Sun Apr 08, 2007 2:52 am

Quoting Avt007 (Reply 32):
But you can open a Dash main cabin door if there is 0.5-1.0 psi differrential.

If the Dash main cabin door is 2' X 5' (I presume it is actually larger) there would be between 600 lbs and 1200 lbs pushing the door against the stops, a lot of pressure to over come.
 
avt007
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RE: Loss Of Cabin Pressure, Why No Masks?

Sun Apr 08, 2007 3:55 am

I was doing a pressurization run outside the hangar when a guy came out with the logbook and opened the door. It has a lever outside the aircraft which slides the door upwards to clear the latches. It can be done! There was no damage to the door or our ears. He did say it was hard to pull the handle.
 
Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Sun Apr 08, 2007 4:38 am

Quoting Avt007 (Reply 36):
There was no damage to the door or our ears.

I never said there was "damage" to our ears, or that it hurt, I just said you could feel it. More like a discomfort.
"Why does a slight tax increase cost you $200 and a substantial tax cut save you 30 cents?"
 
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HAWK21M
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RE: Loss Of Cabin Pressure, Why No Masks?

Sun Apr 08, 2007 11:10 am

Quoting Avt007 (Reply 36):

I was doing a pressurization run outside the hangar when a guy came out with the logbook and opened the door

Wasn't the Anticolls on during the Pressurisation Check.
regds
MEL
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avt007
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RE: Loss Of Cabin Pressure, Why No Masks?

Sun Apr 08, 2007 12:03 pm

Yes the red lights were on, but here is a classic case of night shifts screwing you up, and why I don't like pressurization runs near other people. The fellow with the logbook came in front of the a/c and waved the book at us. My partner in the left seat waved him in to the a/c, and a split second later, realized his mistake. I leapt out of the cockpit for the door handle, but didn't make it in time. We were all tired, and had we done the run in a remote location, this kind of mistake likely wouldn't have happened.
 
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HAWK21M
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RE: Loss Of Cabin Pressure, Why No Masks?

Sun Apr 08, 2007 5:45 pm

Quoting Avt007 (Reply 39):
We were all tired, and had we done the run in a remote location, this kind of mistake likely wouldn't have happened.

Fatigue Induced error  Smile
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VHXLR8
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RE: Loss Of Cabin Pressure, Why No Masks?

Mon Apr 09, 2007 12:18 am

Quoting Boston92 (Reply 23):
There is only a supply for 2 min of air

As already mentioned, not true.

Quoting MarkHKG (Reply 24):
Passenger oxygen systems typically produce oxygen for 10-15 minutes.



Quoting ThrottleHold (Reply 25):
A chemical generator will supply 15-20 mins of O2, depending on the type fitted.

Absolutely!! A couple of examples; 737/767 have 12 minutes; A330s have 15 mintues; 767s can also have a high terrain configuration which takes them up to 22 minutes.

The above are all chemically generated systems; so once the flow starts, it continues until it runs out.

For stored gaseous systems (namely 747s), O2 is only supplied to the masks that are in use, and can be shut off if not needed. For this reason, there is no actual time on supply, as it all depends on pax numbers, and length of necessity.
 
Markhkg
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RE: Loss Of Cabin Pressure, Why No Masks?

Mon Apr 09, 2007 5:51 am

Quoting VHXLR8 (Reply 41):
For stored gaseous systems (namely 747s), O2 is only supplied to the masks that are in use, and can be shut off if not needed.

I watched an old TWA training video for the older variant of the 747, and when the masks drop, the decompression announcement starts, in perfect British accented English, "There is no cause for alarm, but due to a decompression..." So prim and proper -- Cracks me up!
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Alias1024
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RE: Loss Of Cabin Pressure, Why No Masks?

Mon Apr 09, 2007 8:13 am

Quoting Boston92 (Reply 30):
Damn, I am having a blank, what do they call the emergency exits? It is an old war term. It'll come to be later. I keep coming back to Storkie Exits, but damn, that is not it.

I think you are looking for sortie. It is just French for exit. Freedom picked up Dash 8s that uesd to fly in Canada, hence the English and French.
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Boston92
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RE: Loss Of Cabin Pressure, Why No Masks?

Tue Apr 10, 2007 12:48 pm

Quoting Alias1024 (Reply 43):

I just had my return trip this morning and I noticed that. My friend who was with me said it was an old war term, but this morning he just noticed it was french.
"Why does a slight tax increase cost you $200 and a substantial tax cut save you 30 cents?"
 
VHXLR8
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RE: Loss Of Cabin Pressure, Why No Masks?

Tue Apr 10, 2007 2:23 pm

Quoting MarkHKG (Reply 42):
I watched an old TWA training video for the older variant of the 747, and when the masks drop, the decompression announcement starts, in perfect British accented English, "There is no cause for alarm, but due to a decompression..." So prim and proper -- Cracks me up!

"There is no cause for alarm, but please put on your oxygen maks, or else you may die within the next few minutes. Also, our duty free sales will be closing shortly. Thank you"  Silly
 
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Jetlagged
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RE: Loss Of Cabin Pressure, Why No Masks?

Tue Apr 10, 2007 8:36 pm

Quoting Boston92 (Reply 44):
My friend who was with me said it was an old war term

The word sortie is still used in the military to mean a raid. You are leaving your base to do this, hence sortie. It's from the French verb sortir (to leave). Maybe the term originated in the Middle Ages when castles were the thing to have and everyone important spoke French.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
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Starlionblue
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RE: Loss Of Cabin Pressure, Why No Masks?

Tue Apr 10, 2007 10:52 pm

Quoting Jetlagged (Reply 46):
Maybe the term originated in the Middle Ages when castles were the thing to have and everyone important spoke French.

I don't want to talk to you no more, you empty headed animal food trough wiper. I fart in your general direction. Your mother was a hamster and your father smelt of elderberries.


You don't frighten us, English pig dogs. Go and boil your bottoms, you sons of a silly person. I blow my nose at you, so-called "Arthur King," you and all your silly English K-nig-hts.


[Edited 2007-04-10 15:54:02]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Jetlagged
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RE: Loss Of Cabin Pressure, Why No Masks?

Tue Apr 10, 2007 11:09 pm

 rotfl   rotfl   rotfl 
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
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RE: Loss Of Cabin Pressure, Why No Masks?

Wed Apr 11, 2007 9:48 am

What sort of chemicals do they use in the O2 generators? If I'm remembering my chemistry right, the two possibilities that come to mind are potassium chlorate or potassium superoxide.
Hydrogen is an odorless, colorless gas which, given enough time, turns into people.

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