"carl mciver" wrote in message
nk.net...
"gfulton" wrote in message
...
|
| "carl mciver" wrote in message
| nk.net...
SNIP
| The cabin pressurization system on the 737 is supplied from the engine
| compressor bleeds, as you well know. I'm having a hard time envisioning
any
| scenario wherein a leak in the cabin air con. system could feed oxygen
| deficient air into the cabin. An engine fire could likely contaminate
the
| bleed supply, but that apparently didn't happen here. A malfunction in
the
| high stage precooler maybe, causing it to supply overheated air and
light
| off ducting somewhere. But there's plenty of warning when that happens,
and
| it's taken care of automatically and shut off by the duct overheat
system.
| They wouldn't have been using high stage air at altitude anyhow. A
recirc.
| fan overheat, but that would stink so bad that the crew would shut if
off
| immediately. I can't see any way oxygen defiicient air could be fed to
the
| cabin. The flt. and voice recorder playbacks should be interesting. I
| also think you're a little quick to throw out "idiot" with respect to
the
| people who maintain these things for a living. I've been doing it for
35
| yrs., and the level of incompetency you're describing is very seldom
seen.
| The men I work with are dedicated to the craft and take it very
seriously.
| Our families ride on these things.
|
| Garrett Fulton

I always say it takes at least two hazards to create an accident. Not
that by themselves the hazard would be considered intolerable, but life it
what happens while you're making other plans (John Lennon) and that's why
we
here in the US are so paranoid about the safety issue. Pilots all the
time
fly with systems inoperable (forgot the term) but the airlines define what
is degree of risk tolerable or not, and US airlines are more strict than
most. If you have three redundant systems and one is down, then the
airplane is usually deemed okay to fly. Should the two remaining systems
be
powered from the same power source, you lose the source, and the crew
isn't
aware of it, then you have a serious hazard. Aviation designers plan for
every possible scenario, but life is best at proving that you can't design
for all of them (Flight 800 being a great example, and they're _still_
working on a viable solution!) The sloppier the airline, the more those
hazards creep up on you.
I've heard stories about folks who've flown Aeroflot birds in
"premodern" times and they were scared ****less the whole way. Not only
were they poorly built planes, but poorly maintained as well. Many
countries have second rate aviation authorities, if at all, and
maintenance
to meet requirements (i.e. little to none.) I doubt that the Greek birds
have the poor controls as many, especially South American airlines, but
there's a whole slew of things we in the states take for granted that are
pure luxuries elsewhere. Digitized and maintenance records are the norm
here in the states, while many airlines get by with books not much better
than some truckers (no insult to truckers, but you know what I mean!)
What any of us has to say here in this forum don't mean nuthin' but
speculation until the investigation comes back, and even then there are
politics involved. That EgyptAir 767 (I think I built that one) that
augered itself into the water unofficially was the copilot committing
suicide, but you won't see that since politicians got ahold of the report.
As far as the pack system (the air conditioners are called packs) there
are lots of things that can happen that we wouldn't think of and can't
always be sensored, but I'm no expert on them either, so what I offer here
could be in error. Bleed air is usually fresh air that is taken after the
compressor (then it's pretty hot but fresh air) and that air is used to
drive a turbine. The other side of the turbine takes the fresh outside
air
and compresses it, cools (with more outside air) it to remove the humidity
(that's why it's so dry in planes) and circulates it about the airplane,
while maintaining a pressurized cabin. When at altitude, the packs
recirculate most of the air with a smaller amount of fresh air added,
depending on the setting assigned from the flight deck. If the packs just
recirculate inside air without getting any fresh into the system, then
eventually carbon dioxide poisoning will slowly occur and everyone passes
out, which is my personal scenario based on no useful information. There
are no sensors for excessive CO2. The cabin system also uses bleed air
directly for cargo heating, and to increase the temperature of the inside
air if needed, but I don't know engines well enough to know if an engine
problem would put bad air (excessive CO or CO2) into the bleed air ducts.


Yeah, I was around an old 4 engine turboprop Tupolev something at a place I
worked overseas. The Russians didn't seem to build airplanes with a lot of
finesse, in my opinion. Wasn't a flush head rivet on the thing. Had to
lose several hundred horsepower to drag and the African carrier didn't
maintain it worth a damn. It's a small thing, but the air cycle machines
in the packs never pull in outside air. Air from the ram air doors flows
across the the air to air heat exhangers to cool the engine bleed air before
it enters the air cycle machine, and then again between the compressor and
turbine of the A.C.M. But every molecule of air in the cabin at altitude
has passed through the engine's compressors. The recirc. system was added
years ago as a fuel saving measure. I keep thinking that maybe something
in the aft. baggage bin, (pressurized with cabin air for the dogs), was
releasing some kind of agent. We've been puzzling over this thing at work.
Of course, if it was a terrorist thing, those wailing ****heads would have
long since claimed responsibility.

Garrett Fulton