F172Driver

Video - Breaking News Videos from CNN.com

So I don't fly jets but with my limited understanding of a jet engine im curious how fumes could get into the cabin? Is this a credible story or just the media tryin to look busy?

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Twin Wasp

The bleed air going to the cabin is tapped off in the compressor section before the burner cans where fuel is added. The air is sometimes named after the stage the air was tapped off at. So you could have second stage air, 8th stage air, 13th stage, etc. There are bearings towards the front end of the engine and in theory some oil could leak into the air supply. Since jet engines don't have that much oil in their system, you're probably talking a few drops added to thousands of gallons of air. I'd like to hear him explain how CO gets into the system since it's a by product of combustion and that happens a ways after the air was bleed off.

I like how they say this has been going on since the 60s but it's "Breaking News."

tomgoodman

13th stage bleed air is extremely hot (enough to cause an engine fire warning if it leaks). Dirt/oil in the lines or valves it passes through could easily lead to smoke and fumes.

F172Driver

Thanks for the insight guys. This kinda sounds like a possibility that it could happen but it would be a rare event and probably a mistake like a broken seal or something getting dripped in an air line. Am I right or does this occur regularly?

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joepilot

Some of the airconditioning ducts were fiberglass, at least on the 727. If the engineer called for too high a temperature an a cold day, you could get a duct overheat, and it smelled quite bad. There was an automatic trip off for duct overheat, and it almost always worked.

Joe

rickair7777

Hot bleed air could actually combust oil or skydrol if it leaked into the compressor upstream of the bleed. The combustion by-products could include toxins (especially skydrol) and probably CO2 and CO. However, the amount of CO would be totally insignificant in the volume of bleed...the real hazard is from exotic chemicals with neuro-toxic properties.

The was an RJ crew back in the early days that ended up on permanent disability back in the 90's after something leaked (skydrol?). IIRC it was comair, but I'm not 100% sure about that.

If I smell anything funny (other than the usuall smell of ass or glycol from the packs) I'm on O2 instantly.

shdw

Wear them all the time, it can make you feel like a fighter pilot!

Phantom Flyer

First of all, one only has to catch some of the stories of the Air France #447 accident to realize that most of the "news outlets" can't get anything straight when it comes to aircraft incidents/accidents. To call the pitot tubes "external speed monitors" (verbatim quote...numerous times) is only a drop in the bucket of inaccurate, sensationalized "reporting". I could not download this story but CNN has reported, on numerous occasions, that the quality of cabin air in commercial aircraft is a cause for concern. Generally, it's nonsense.

Twin Wasp was on the money with his posting. The tap-off for bleed air used by the packs is either 8th or 13th stage bleed air or both, depending on the manufacturer of the engine, and there is almost no chance of a contaminant entering the supply source. The only way I know to get a healthy dose of exhaust air into the cabin is to taxi too close to another aircraft and then exhaust gases can enter the pack intakes and get distributed through the manifolds into the cabin.

As for CNN......well, that's what the remote is for. Turn it OFF.

G'Day Mates

joepilot

The DC-8 was built to avoid most of these problems. It was built with four turbo compressors for cabin pressurization, which used engine bleed air to spin a turbine which spun a compressor to pressurize outside air. These were located in the nose, and gave the DC-8 its characteristic "smile". Cooling was provided by electrically powered Freon airconditioners. When many of the DC-8s were re-engined in the 80s with CFM-56 engines, most were converted to normal airconditioning packs. After the conversion, if you lost electrical power on the ground, the packs failed to on, and you could not move the bleed valves. This meant that you had better shut down the engines quickly or you would have smoke in the cabin, because you also lost the electrical cooling fans. There was at least one ground evac due to this design flaw.

Joe

F172Driver

I figured this could happen but it is unlikely. Gotta love the media "reporting" on things and using wikipedia to fact check it. I thought about offering to be a freelance aviation consultant for the local paper but never did it, maybe I should.

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