HHHramp From United States of America, joined Sep 2001, 89 posts, RR: 0 Posted (11 years 12 months 3 days 22 hours ago) and read 2183 times:
At school today, one of my classmates was giving a demo of the ECS (AC and pressurization). While a group of us was in the aft cargo bin of a 727-100 going over the pressure relief valves. A question came up when he gave the pressure ranges for the cabin. He said, and these are rough numbers, the overflow valve allows for a maximum positive pressure of 8 or 9'ish PSID (with the cabin able to stand up to 12 PSID). He also said that the maximum negative pressure allowed was 1 PSID.
My question to him and the instructor that remains unanswered is:
How do you develop negative pressure differential?
This may seem dumb to some people here but, I could not see how it would be done.
B747skipper From , joined Dec 1969, posts, RR:
Reply 5, posted (11 years 12 months 2 days 15 hours ago) and read 2030 times:
Negative relief ??? ...
Well - that happens in real life, with stupid F/Es when there were some...
As an example, cabin is 7500 feet high, aircraft descends from FL370, but our friend "forgot" to reset pressurization to landing field elevation...
Result is, painfull ears when the aircraft descends through 7,500 feet... then continues to descend at 1,000 fpm... insults of passengers... ooops !!!
Another type of problem... not negative relief...
There is the other type of idiots, such as landing in Denver, elevation 5300 feet, but our superior F/E resets cabin to sea level (as a habit, right?) -
When the airplane touches down... ear drums get cleared, in seconds...
With PanAm we used to say "Eaaaarrrrrwax and taaaaampax" for such cases.
Aviation has humour (some at least)