Captjetblast From Argentina, joined Aug 2001, 281 posts, RR: 0 Posted (10 years 11 months 2 weeks 2 days 15 hours ago) and read 2242 times:
I've heard that cockpit air is completely refreshed every 3-5 minutes, and new air comes from the (first?) compression stage from the engines. That's the reason for the air conditioner system always working, the compressed air becomes too hot.
There's an active thread today covering the emergency landing of a Continental B757 in N.C. "due to smoke in the cockpit due to engine problem".
So if we have smoke in on engine then we'll have smoke in the breathable air?
Apathoid From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 11 months 2 weeks 2 days 15 hours ago) and read 2212 times:
Not always...it depends on the problem with the engine. Typically, engine induced smoke in the cabin is the result of an oil leak on the compressor bearing that allows engine oil into the bleed air system. This is a very rare occurence, but it does happen. Most other engine problems will not result in smoke being brought in through the environmental air systems. Aircraft that use ACM's or Air Cycle Machines for the cooling of cabin air can also get smoke in the cabin from a failure of the ACM. Usually, its the same as a compressor bearing leak. Lubricating oil gets on the wrong side of the seal and you have smoke in the cabin.
FredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 2, posted (10 years 11 months 2 weeks 2 days 15 hours ago) and read 2212 times:
Which stage the air con bleed air comes from can vary a bit, but early in the compressor is typical.
However, bear in mind that in the compressor section very little has been done to the air. Most engine fires will be later in the engine cycle. Thus, no smoke in the air. The things I can imagine which might put smoke in the air con bleed air is a failed bearing in the front part of the compressor, things going wrong in nacelle or inlet wane heating and external factors.
I've heard of it happening but can't remember when.... can anyone come up with more ways to get smoke in the air bled from the compressor?
Apathoid, that appears to have been post #848 for both of us, and nearly at the same time too. Quite a coincidence!
[Edited 2004-01-15 20:41:38]
I thought I was doing good trying to avoid those airport hotels... and look at me now.
Avioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 3, posted (10 years 11 months 2 weeks 2 days 15 hours ago) and read 2217 times:
The only way to get smoke from the engine is to have smoke forward of the bleed pickoff point.
In the CFM-56-7 the air is from the 5th stage at settings above idle and 9th stage when the engine is at idle. There is the possibility of smoke coming off one of a couple of bearings or it may come from flying through a smoke stream like a volcanic plume (or going into EWR can be pretty disgusting on occasion).
Most of the problems I've had to chase down were caused by the APU or ACM and were initially reported as "Dirty Socks Odor in the cabin" (that's what engine oil smells like when it's heated without burning). If someone didn't find the source of the smell early on, you could bet it would become obvious when the bearing with the bad seal let go.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533