JumboJim747 From Australia, joined Oct 2004, 2464 posts, RR: 44 Posted (9 years 4 months 5 days 20 hours ago) and read 3901 times:
Why do the pilots pressurize the aircraft on the ground.?
Wouldn't it be too early to do so as they would have a fair amount of time to do it while airborne.
Im thinking maybe it would be a bad idea for the aircraft as it sometimes needs to go back to the gate for different reasons and then it has to be un presureized again.
Why not just do it while say at climb.
Jetlagged From United Kingdom, joined Jan 2005, 2565 posts, RR: 25
Reply 1, posted (9 years 4 months 5 days 17 hours ago) and read 3844 times:
It's done automatically as soon as throttles are advanced to takeoff power on most modern airliners, not a pilot action.
All this does is pre-pressurise the cabin to about 200 feet below aircraft altitude so dumping this for an immediate landing is not a problem.
In the case of an aborted takeoff, the cabin would automatically depressurise on closing the throttles.
Pre-pressurising puts the outflow valves in a controlling mid position, rather than fully open. This helps smooth out cabin pressure bumps which might occur on rotation. It also means the crew can't forget to start pressurising the aircraft during the climb
On older, three crew aircraft such as the 747-200 it was usual to take off unpressurised, with the packs being switched on one at a time during initial climb. A two man crew would not necessarily have the time to carry out this procedure properly.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
HAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 2, posted (9 years 4 months 5 days 17 hours ago) and read 3847 times:
In ref to Pressurisation in case of Chapter 21.On the B737 pre pressurisation is carried out to prevent a pressure bump inside the cabin when the Aircraft gets Airborne.Its a matter of a flick of a switch & is not a lengthy process.
If "Presurisation" refers to the Chapter 29,Hydraulic system,then its to check for leaks & any warning lts.
SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 3, posted (9 years 4 months 5 days 16 hours ago) and read 3823 times:
It is not pressurized to the full allowable differential, but just to maybe 200 feet below field elevation - a fraction of a pound per square inch.
In addition to the benefits above, relating to the outflow valve, consider this: A small amount of pressure will seat the plug-type doors and windows fully. Also, a slightly pressurized fuselage tube is stronger than an unpressurized one. Open an aluminum beer can some time. As soon as you break the pressure seal the sides become really flexible. Metal is the same thickness as before, the difference is a very small amount of internal pressure, or simply, resistance to compression.
Happiness is not seeing another trite Ste. Maarten photo all week long.
TheGreatChecko From United States of America, joined Mar 2004, 1130 posts, RR: 2
Reply 4, posted (9 years 4 months 5 days 15 hours ago) and read 3802 times:
When I fly the King Air, we pressurize it for the above reasons, but also because it provides for a slightly quieter cabin due to the better gap seal. It provides for a slightly more comfortable cabin for the passengers and thats what its all about!
"A pilot's plane she is. She will love you if you deserve it, and try to kill you if you don't...She is the Mighty Q400"
2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 14, posted (9 years 4 months 2 days 17 hours ago) and read 3121 times:
AIRLINERS.NET CREW DATABASE EDITOR
Quoting XFSUgimpLB41X (Reply 13): On the CRJ, if we begin a descent before we reach 6000 feet the airplane automatically thinks that we are returning to the field and sets cabin elevation for where we just departed from.
What constitutes a descent to activate this? If, for example, you have to level off at 5000 feet for traffic, and during your level-off you sink 30 or 40 feet, does that set cabin elevation to the departure airfield?