Quote:
Originally Posted by ShipDaSherb
Have you ever forgotten to put the passenger cabin A/C on or accidentally left the "fasten seatbelt" sign on for a long time?
Leaving the seat belt sign on is extremely common but everyone ignores it anyway. It's really just a CYA switch for the pilots. If someone is up during turbulence and gets hurt they have less of a case if they were ignoring the seat belt sign. Still, in today's litigious world they will still probably get a settlement from the airline.
The A/C is a different story. Air conditioning and pressurization are run from the same system, so if you forget one, you've forgotten the other. Obviously, forgetting to pressurize can be embarrassing as the masks will fall when the cabin altitude reaches about 14,000'.
Both are run off of high pressure bleed air from the engine, which is very hot as it enters the system. It is cooled through expansion, providing the A/C. The sheer volume of bleed air provides the pressurization. Airplanes leak like sieves; they are not airtight by any means. They stay pressurized because we pump in more air than escapes.
I had a flight many years ago where we neglected to complete the "After Start" checklist, which includes putting the Packs on-line (the term Pack originated, I believe, with the acronym PAC which stood for Pressurization & Air Conditioning system). It was my place to do this checklist, but I was being rushed by the Captain to call for taxi clearance as we were very near the departure runway and he wanted to get into line ahead of a few other airplanes. It's a mistake when we both make it.
It was my takeoff and when I called for the "After Takeoff" checklist, the Captain neglected to actually check the Packs, which was on the checklist. His bad.
We were cleared to 24,000 and as we climbed through 10,000 we got an amber light and an aural alert, as well as a message saying CABIN ALTITUDE. I looked up at the overhead panel and saw the cabin climbing along with the plane. I alerted the Captain and we both recognized that the Packs were off. Recycling didn't do the trick so he pulled out the QRH (Quick Reference Handbook -- used for abnormal and emergency situations).
The airplane was climbing like a scalded ape and by the time I told the controller we needed lower, the cabin had zoomed through 14,000 and the masks dropped in back. First and only time I've had this happen. Naturally the passengers were concerned, though it was never life threatening. We descended to 10,000 (no O2 needed there) and finally got the system on line. We ended up diverting to change planes and continue to our destination. I was kind of surprised that all the passengers got on the 2nd plane. We didn't do a lot to imbue them with confidence in their flight crew.
Last edited by W0X0F; 06-18-2014 at 12:20 PM.