Contrails From United States of America, joined Oct 2000, 1845 posts, RR: 0 Posted (10 years 7 months 1 week 5 days 11 hours ago) and read 2765 times:
The first leg of my trip to HNL had a surprise ending on April 9 on AA 1379, en route from DCA to DFW, when, in this order, the air conditioning went off, the plane went into a steep dive, the oxygen masks came down, and the head flight attendant ordered pax to don our oxygen masks.
The flight was almost over. I had estimated we were getting close to Texarkana, which is where flights usually start descending for DFW. The pax remained calm, in fact I thought the oxygen masks coming down was the result of someone pushing the wrong button. We continued on to DFW and arrived a bit early, due I'm sure to expedited clearing by ATC.
This was a first for me, and I won't mind if it's the last. AA gave pax 5,000 miles for the "unsettling event", which was nice of them. I was never concerned for my safety, but I was concerned about catching my flight to HNL at DFW.
Were any other A'netters on this flight? Are there any AA folks out there who know the whole story? Has anyone else been through such an incident? I suspect the Captain was just excercising an abundance of caution, which I certainly understand. It didn't seem to me that we actually depressurized, but then having never been through this I'm not exactly an expert.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 7 months 1 week 5 days 10 hours ago) and read 2682 times:
Though the aircraft may not have experienced an explosive decompression or even a rapid one, the flight crew felt it necessary to deploy the masks and order their use. This is probably because, for whatever reason, the flight crew could no longer maintain the cabin pressurization. This is most likely a result of a failed outflow valve, though many other variables could be involved, including, but not limited to:
- dual pack failure
- pnuematic system failure
- multiple electrical failures
What kind of aircraft? Usually the weak point is the outflow valve, since most aircraft only have 1, though they redundant control paths.
AA737-823 From United States of America, joined Mar 2000, 6215 posts, RR: 10
Reply 5, posted (10 years 7 months 1 week 5 days 3 hours ago) and read 2335 times:
IF the outflow valve had failed open, the air conditioning most certainly would not have been turned off. All air OUT + no air IN = decompression.
IF the outflow valve had failed closed, the passenger would have noticed it. No air OUT + some air IN = increased pressure sensation, until the safety dump valve (which is generally set pretty high, over 8.4 psi on the 767) opens.
Therefore, I doubt that it was an outflow valve failure. I suspect it was a pack problem, But dual pack failures would seem to be virtually impossible. Perhaps it was a controller failure. But then, there are two of those as well.
In any case, this story is odd, and must be an example of several things going wrong at the same time. THANKFULLY, there was not an explosive decompression, or even a rapid one, as those have a tendency to burst everyone's eardrums.
In any event, Contrails, the oxygen masks being 'accidentally' deployed is not likely. The system is automatic, with the controller releasing the mask compartment latches when cabin altitude exceeds 14000 feet (that's 767 info- MD-80 should be about the same). There is a manual deployment switch, for the flight crew to operate, but it is a guarded switch and cannot be "bumped" accidentally.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 6, posted (10 years 7 months 1 week 4 days 21 hours ago) and read 2159 times:
You make the assumption, as most do, that a valve has to fail open or closed. A valve can fail in any position in between open and closed. I do find it strange that the pack system was shutdown, but I wasn't there. They may have already had one on MEL when the second one failed.
Quote: AT CRUISE- 34,000 LOST ALL PRESSURIZATION. BOTH PACKS WENT TO ZERO FLOW. STARTED DESCENT PERFORMED PROCEDURES BUT NO HELP. HAD TO DROP O2 MASKS IN BACK. PACKS BEGAN TO WORK AGAIN BETWEEN 8000-6000 FEET. FLOW ON METERS LOOKED LIKE THIS: UNTIL CABIN PRESSURIZED DOWN TO AROUND 4000 THEN THE LEFT FLOW BEGAN TO BACK OFF TO MATCH ON THE RIGHT SIDE. (NOTE:WEATHER WAS CLEAR-NO CLOUDS)
Maint. electronic logbook shows lots of troubleshooting, replacing multiple sensors in all sorts of places in the A/C systems of this acft during the following few days [far too many to list here].
*NO CARRIER* -- A Naval Aviator's worst nightmare!