Total pack failure
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As one who did a spell of production test work, this was one of the "boxes" that was required to be ticked. At max diff all bleeds would be selected to off and the increase in cabin alt (decrease in pressure) would be measured over time. It was not in any way an "ear popping" experience.
Regarding the emergency bleed air fitted to older types, and maybe to some still current, it is indeed unregulated, and of the warm kind. Many schools teach that it is extremely hot, and tell tales of pax emerging from the cabin after landing wearing nothing but boxer shorts. Having relied on it once in an old straight wing Citation, I can vouch for the fact that such stories are exaggerated. The cabin gets warm - perhaps a bit too warm, but unfortunately for me at least, the three females in the rear did not feel compelled to stip down to their underwear!
Regarding the emergency bleed air fitted to older types, and maybe to some still current, it is indeed unregulated, and of the warm kind. Many schools teach that it is extremely hot, and tell tales of pax emerging from the cabin after landing wearing nothing but boxer shorts. Having relied on it once in an old straight wing Citation, I can vouch for the fact that such stories are exaggerated. The cabin gets warm - perhaps a bit too warm, but unfortunately for me at least, the three females in the rear did not feel compelled to stip down to their underwear!
As I understand it, in the FL510 test, a valve simulating the aircraft cabin window is fitted to the emergency exit. At 510, it is opened suddenly to simulate loss of a window at maximum certified altitude. I heard, when opened, the pilots looked at each other and said something like, "is this IT?" Less than 600 fpm cabin rate. An amazing amount of air is pumped into a fuselage to overcome a window failure. Explosive decompression, by definition, is more than a a failure of a normal component, say outflow valve failing open, more like a main cabin door coming off! I know, shutoff a pack at FL450 in a GLEX and you might get a momentary 100 fpm spike as the valves adjust to change in flow
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Having experienced it myself, we did have a passenger strip down, and became so uncomfortable he lay on the floor. He had a load of chocolate goods that were packaged and on a seat, that he was taking to the destination for Christmas presents. They were all melted.
On another occasion, we didn't go to emergency pressurization, but we did have a duct separation at the back of the cabin. It resulted in bubbled and burned cabin trim and parts of the interior that were hot enough I burned my hand when feeling for the heat. I had been summoned by a passenger who felt it was too hot; the passenger was right.
When I experienced a depressurization due to a door seal failure, the resulting noise was loud enough that neither I, nor my F/O, were able to hear ATC.
I experienced emergency pressurization one night during a cargo run, shortly after takeoff from a mountain airport. It was loud, and hot.
Each of those events occurred in different types of aircraft.
On another occasion, we didn't go to emergency pressurization, but we did have a duct separation at the back of the cabin. It resulted in bubbled and burned cabin trim and parts of the interior that were hot enough I burned my hand when feeling for the heat. I had been summoned by a passenger who felt it was too hot; the passenger was right.
When I experienced a depressurization due to a door seal failure, the resulting noise was loud enough that neither I, nor my F/O, were able to hear ATC.
I experienced emergency pressurization one night during a cargo run, shortly after takeoff from a mountain airport. It was loud, and hot.
Each of those events occurred in different types of aircraft.
Join Date: Aug 2008
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pressurization where higher is lower.
Brian,
In level flight at cruise with a complete pack(s) failure the cabin pressure differential will fall, not rise, as higher pressure inside the cabin will leak overboard into the lower ambient pressure outside the jet. With the cabin pressure leaking overboard and the differential pressure in the cabin decreasing, the cabin altitude will ascend, rise, and get further away from sea level pressure until there is no differential between the pressure inside the jet and the pressure in the surrounding atmosphere.
The temperature outside the jet at normal jet cruising altitudes is 55 degrees Celsius below zero (-55C) plus or minus a few degrees. Without a means to heat the cabin the temperature will rapidly cool.
At sea level, where your altitude is low you have higher ambient pressure. As you go up in altitude, go higher in the atmosphere the ambient pressure drops, it is lower. It is an inverse relationship: higher altitude yields lower pressure, lower altitude higher pressure.
In level flight at cruise with a complete pack(s) failure the cabin pressure differential will fall, not rise, as higher pressure inside the cabin will leak overboard into the lower ambient pressure outside the jet. With the cabin pressure leaking overboard and the differential pressure in the cabin decreasing, the cabin altitude will ascend, rise, and get further away from sea level pressure until there is no differential between the pressure inside the jet and the pressure in the surrounding atmosphere.
The temperature outside the jet at normal jet cruising altitudes is 55 degrees Celsius below zero (-55C) plus or minus a few degrees. Without a means to heat the cabin the temperature will rapidly cool.
At sea level, where your altitude is low you have higher ambient pressure. As you go up in altitude, go higher in the atmosphere the ambient pressure drops, it is lower. It is an inverse relationship: higher altitude yields lower pressure, lower altitude higher pressure.
