O2 and Cypriot airliner crash

wrote

In accounts of the crash of the Cypriot airliner in Greece,

My thoughts on yesterday's accident.

The way the regulations require that it be done.

First........During the preflight, someone ensures that the emergency
oxygen bottles in the lower cargo holds have their valves opened and are
ready for use.

Second...During the cockpit preflight, each pilot tests his oxygen mask
for proper operation and for pressure delivery of oxygen.

Then.......With the engines running and before takeoff, the air
conditioning and pressurization system is turned on (pack valves opened)
and the cruising altitude set in the controller by a crewmember and
verified by the checklist.

The system then functions normally, maintaining a cabin pressure of about
8,000 feet until starting descent.

However if something goes wrong and the cabin altitude rises
uncontrollably............

First.......At 10,000'cabin altitude, A VERY loud warning sounds to alert
the crew. If at cruise altitude, this MANDATES first, immediate donning
of the pilot's oxygen mask followed immediately by an emergency descent
to 14,000'.

Second.. At 13,000' cabin altitude, the outflow valves automatically
close in an attempt to maintain cabin pressure if the system has been
properly turned-on before takeoff. If the system was not properly
turned-on before takeoff, the warning should have occurred during climb.

Third.....At 14,000' cabin altitude, the passenger oxygen masks
automatically drop.

All of these systems are independent. News reports indicate that the
passenger O2 masks did deploy. If so....

Did the warning sound? If it did why was there no emergency descent?
Why was pressure not maintained when the outflow valves closed? Perhaps
the pack valves were not opened before takeoff? Had the pilots O2 bottle
been replaced and the valve not opened or checked during preflight?

Looks like a lot of human error to me. Just speculating.

Bob

Most passenger O2 systems use chemically generated O2.
There are no bottles to check. There are cabin walk around bottles
and the flight deck is bottled O2, but passengers are not. Remember
the Valujet crash. The initiating event was a cargo bay/cabin fire casued
by
improperly shipped O2 generators igniting in flight.

"pbc76049" wrote
Most passenger O2 systems use chemically generated O2.
There are no bottles to check.

Depends on the age of the B-737. Boeing used pax bottles
for a long time. But this is immaterial to the discussion
of why the pilots did not have O2.

Bob Moore
ATP B-707 B-727
PanAm (retired)

"pbc76049" wrote in message
...
Most passenger O2 systems use chemically generated O2.
There are no bottles to check. There are cabin walk around bottles
and the flight deck is bottled O2, but passengers are not. Remember
the Valujet crash. The initiating event was a cargo bay/cabin fire casued
by
improperly shipped O2 generators igniting in flight.


Even if the passengers have chemically generated O2, the pilots have O2 from
a bottle. Pilots are required (and most do) check their O2 before take-off.
The chemically generated O2 units cannot be turned off once in use and then
must be replaced. Therefore pilot positions have bottled O2.

Duane

"Bob Moore" wrote in message

My thoughts on yesterday's accident.

My thoughts were tending in the same direction, Bob. Speculation on the
availability of O2, or the system integrity, is fine, but the first and most
obvious question to me was as to why the airplane was still at altitude.
Job 1, superceding all others, is to get the craft to breathable air. What
was going on? All it takes is one body in the cockpit to initiate the
descent.

JG

wrote:

In accounts of the crash of the Cypriot airliner in Greece, all I've
read say that loss of cabin pressure could not, by itself, incapacitate
the pilot. Yet, I was once told by an ATP that at 40k feet (admittedly
this plane was at 35k) O2 supply by itself will not suffice to keep you
conscious and that the drop down masks only give a false sense of
security.

The O2 masks are intended to keep you conscious during the descent to an
altitude where they are unnecessary, as is the O2 supply for the cockpit
crew. There is not enough O2 system capacity to cruise for a long period of
time.

When minimum enroute altitudes over high terrain are coupled with O2 time
limits there are routes in the lower 48 which are not legally flyable by
commercial airliners with certain MEL restrictions, though these details are
not always clearly emphasized in information available to the pilot.


Jack

p.s. speculation about the cause of a specific accident without the benefit
of the results of the investigation is a fools' game.

wrote:
In accounts of the crash of the Cypriot airliner in Greece, all I've
read say that loss of cabin pressure could not, by itself, incapacitate
the pilot. Yet, I was once told by an ATP that at 40k feet (admittedly
this plane was at 35k) O2 supply by itself will not suffice to keep you
conscious and that the drop down masks only give a false sense of
security. He said that the ambient pressure is so low that even 100% O2
does not provide enough to keep you conscious without a pressure
breathing mask. If he's right, that could explain the crash, especially
given that all it would take is 20 seconds of distraction (i.e., not
donning the mask) to knock out the pilot as indicated in the table
below. On the other hand, I checked and a standard atmosphere at 35k
feet is 7.0 in of Hg, which is more than the partial pressure of O2 at
sea level (6 in = 20% of 30 inches), which would seem to contradict the
info given by the ATP. Any thoughts or corrections to my reasoning?


Tlme of useful
consciousness
Altitude (ft) without oxygen

40,000 15 seconds
35.000 20 seconds
30,000 30 seconds
28,000 1 minute
26,000 2 minutes
24,000 3 minutes
22,000 6 minutes
20,000 10 minutes
15.000 Indefinite


Sure pp is 6" at sea level, but at 35 k ft (using your numbers) the pp
O2 is 20% of 7" or 1.4" Hg. At that pressure only about 50% of the
hemoglobin in your blood is saturated, and it hangs on to that O2 pretty
strongly, so it's not available for use by your brain (or anywhere else).

Shawn

On Mon, 15 Aug 2005 04:21:32 UTC, wrote:

: Yet, I was once told by an ATP that at 40k feet (admittedly
: this plane was at 35k) O2 supply by itself will not suffice to keep you
: conscious...

Oxygen is only part of it. The breathing reflex is triggered by the
carbon dioxide partial pressure in your lungs: when atmospheric
pressure falls below that you never get the trigger and your lungs
just stop working. This is a Bad Thing.


Ian


--

CO2 is generated by cellular respiration. This is essentially
independent of oxygen, as a matter of fact, anaerobic respiration can
occur in the absense of adequate oxygen, but it is VERY inefficient, and
makes LOTS of waste products.

Arterial CO2 concentration, having left the lungs, is around 35-45 torr
(mmHg). In mixed venous blood, returning to the lungs, it is around 50
torr/mmhg or so.

At sea level, atmospheric CO2 is in the high 20's/low 30's mmhg. The
body's buffer system in a healthy individual will RAPIDLY move the CO2
level back towards normal if it vary's too much from those values. So,
even at altitude, your venous blood gas values are pretty much normal
after one pass around the body. You hold your breath, and this blood
with "venous" levels of CO2 will make a second pass, and when it hits
the chemo and baro receptors in in your carotid (artery) bodies you will
start getting that URGE to breath.

All of this is independent of how oxygen is handled by the blood. Each
gas's function in the body is more or less independent of each other.
Even though your body uses oxygen to make CO2 as a waste product, your
body will continue to make CO2 for a short time without adequate oxygen.
As an example: the burn in your muscles after a sprint - lactic acid
generated along with CO2 when the oxygen requirement of the muscles
outstrips the oxygen supply.

To say "the lungs stop working" is at best, technically inaccurate. You
are just too hypoxic to make the muscles responsible for gas exchange to
work properly.

Dave

wrote:

Any thoughts or corrections to my reasoning?

The ATP is correct. While people do vary greatly, and some people have been able
to perform adequately without oxygen at 20,000' or more, most people can't go
much higher than 10,000' without suffering some ill effects. Because of this,
the FAA requires that a pilot use oxygen if they spend over 30 minutes above
12,500'.

In general, people can use a cranula or similar device to provide oxygen up to
about 20,000' (the FAA limits use of these to 18,000'). These simply bleed
oxygen into the air you breathe. Above that, you need a low-pressure mask. These
ensure that all you are breathing is oxygen and are good up to about 25,000'.
Above that, you need a pressure mask. Those increase the pressure of the oxygen
and work well up to about 35,000'. Above that, you need a pressure suit or a
pressurized aircraft.

The emergency drop-down masks for airline passengers are low-pressure. They
won't keep you conscious at 35,000', but they may keep you alive.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.