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JOHN
J. NANCE
ABCNEWS.COM
CHAT
TRANSCRIPTS
Pilots Were Unconscious
Aviation Analyst John J. Nance on Payne Stewart Crash
 October
25, 1999 -
Two F-16s followed the jet looking for signs of distress,
and federal officials said it appeared to be flying on autopilot
before the crash.
ABCNEWS aviation analyst John J. Nance discussed the crash
in an online chat.
Moderator at 3:29pm ET
Aviation analyst John J. Nance now joins us.
from [130.64.48.77], at 3:29pm ET
What happened? How did the plane depressurize? How long
does that take?
John J. Nance at 3:30pm ET
What is the most likely probability here is that this aircraft,
which has a very small cabin compared to a commercial jetliner,
lost cabin pressure some time during the climb out of Orlando.
When this sort of thing happens (which is very rare) above
30,000 feet, the time of useful consciousness begins to
get very short for everybody on board.
What I mean by this, is the period of time you have after
a rapid depressurization to get your mask on and oxygen
flowing before your mind becomes so muddled and fuzzy from
lack of oxygen (which we call hypoxia) that you can no longer
help yourself. The time of useful consciousness at 25,000
feet is a fairly sedate 20 to 25 minutes. But the time of
useful consciousness at 39,000 feet is 6 to 12 seconds.
The fact that this aircraft continued climbing right through
their assigned altitude on up to almost 45,000 feet, without
any call from the pilots, indicated to me that this crisis
occurred some place before 39,000 but most probably above
30,000. Whatever happened, it happened very rapidly because
there was no time for the crew to request an emergency descent,
which would be the first and most important action for a
pilot after putting on your oxygen mask.
The entire flight path of the airplane, from Tallahassee
to the ultimate crash site in South Dakota, is consistent
with an airplane being flown only by the autopilot until
running out of fuel. Another inescapable fact is that without
oxygen at 45,000 feet, death would have probably occurred
within an hour.
from [209.30.126.36], at 3:37pm ET
Are we to assume from the news so far that this plane flew
for 4 hours, 3.5 hrs on auto-pilot? That would be an incredible
bit of flying.
John J. Nance at 3:39pm ET
Actually, this is perfectly normal for an airplane to continue
to do what it's programmed to do until the electrical power
fails, which is the result of the engines running out of
fuel. In fact, most modern jets, both business and commercial,
are routinely flown on autopilot from shortly after takeoff
to and through the landing sequence (many airliners can
land themselves after the human pilot programs them).
from [198.173.1.253], at 3:39pm ET
Why did the plane then top out at 45,000 feet? If everyone
were unconscious, wouldn't it keep ascending?
John J. Nance at 3:42pm ET
Good question, Jay. In fact, an airplane cannot physically
climb above what we call its ceiling, a point at which to
go any higher would result in a stall. It is a function
of the power available from the engines and the particular
design of the wings of that airplane plus the overall weight
that determines where that ceiling is. In this case, it
would make sense that the autopilot had been told to climb
and was still attempting to climb, but the aircraft simply
reached its maximum altitude and stayed there during the
rest of the flight sequence.
from [207.168.26.2], at 3:42pm ET
What are the some of the major causes of such a rapid depressurization?
John J. Nance at 3:44pm ET
On an airplane like a Learjet, rapid depressurization can
happen from a number of causes: a door seal could blow out
suddenly; a window could blow out (an extremely rare occurrence);
a duct running from the engines to the cabin pressurization
system could rupture; or, the air conditioning-pressurization
system could suddenly fail.
Because of the obvious sudden incapacitation of the people
aboard in this instance, it is more likely that what happened
here involved a duct, a seal or a window failing suddenly
and catastrophically.
from [128.215.10.10], at 3:45pm ET
Wouldn't they have had instruments to warn them of depressurization?
If so, wouldn't one out of five individuals have time to
put on a mask?
John J. Nance at 3:47pm ET
There is no doubt whatsoever in a small cabin when you've
had a rapid depressurization because your ears will tell
you, the automatic pressurization sensing system will drop
the passenger masks above 10,000 feet, there will be a warning
horn and light in the cockpit and the cabin altitude needle
will have shot up to what we call the ambient altitude (the
altitude at which the airplane is currently flying).
The problem is not recognition of the depressurization,
the problem is the reaction. Only the pilot and copilot
have pressure-breathing equipment that enable them to stay
fully functional at higher altitudes like 39,000 feet. The
passengers' oxygen masks will help, but they will not keep
the passengers conscious until the airplane descends below
28,000 feet. Consequently, the emergency response in all
high altitude aircraft to a rapid depressurization is: oxygen
mask on, 100% flow, and then emergency descent. Since we
had no emergency descent here, it tells me that something
was impairing the pilot's ability to get their masks on
in time. You may ask why one of the passengers in the back
could not have intervened to put the mask on a pilot. The
reason is that if the pilots have passed out, so have the
passengers.
from [206.71.99.198], at 3:51pm ET
Isn't there some kind of requirement for the air crew to
be on oxygen on a flight by a chartered aircraft?
John J. Nance at 3:55pm ET
In a commercial airliner, FAA rules require one pilot of
the two to actually be using oxygen if his or her partner
is out of the seat above 35,000 feet. Other than that, commercial
airliners are required to have the oxygen mask immediately
available, which means turned on and hanging next to each
pilot in a way that would allow the pilot to sweep on the
mask within 2 to 3 seconds. This is the standard methodology
for business jets, whether they are flown under what we
call 'Part 135 on-demand air taxi' or whether it's under
what we call 'Part 91 in a fractional ownership situation,'
which may have been the case here.
from [137.227.112.2], at 3:55pm ET
What risk would an uncontrolled aircraft like this pose
to other air traffic?
John J. Nance at 3:58pm ET
Fortunately, the altitude at which this airplane was proceeding
with no one aboard conscious was high enough (44,500 feet)
to essentially be clear of most air traffic over the United
States. However, the one thing that you can count on is
that anything above 18,000 feet is under positive control
by air traffic controllers. That means that no aircraft
are flying at or above that altitude without being constantly
in contact with an FAA air route traffic control center.
That, in turn, means that through this whole scenario, air
traffic control had the ability constantly to keep other
airplanes clear of the flight path of this Learjet, regardless
of what altitude it might have been using.
I can imagine, certainly, a much different situation if
the aircraft had been flying blinding at a low altitude
through a congested area like Atlanta or Chicago. The challenge
for air traffic control and the possibility of a small airplane
not in contact with air traffic control would be correspondingly
greater.
from [208.140.33.201], at 4:01pm ET
It's a terrible tragedy...however it is lucky that no one
on the ground was injured. What (if any) response would
the military jets had made if the plane were heading out
of control into a metropolitan area? Would they purposely
down an aircraft to try to avoid casualties on the ground?
John J. Nance at 4:02pm ET
There is no set procedure for the Airforce or Navy to scramble
an armed fighter for the purpose of keeping an aircraft
like this away from a population center, simply because
it's an unprecedented occurrence. In fact, as long as there
was no immediate and clear flight path in to a major city,
even with an armed fighter sitting off the wing of the Learjet,
I cannot imagine anyone in the chain of command short of
the president issuing such an order.
However, any fighter pilot who saw an impending disaster
and who had the munitions on board, would be faced with
a very difficult decision. Though that would be an individual
act on the spur of the moment, I doubt any of us would hesitate
if we were certain a major loss of life would otherwise
occur.
from [199.95.153.2], at 4:04pm ET
Does this type of aircraft have a "black box"
John J. Nance at 4:05pm ET
Unfortunately, the number of passengers that a Learjet of
this kind can carry is below the FAA's threshold for requiring
a flight data recorder or a cockpit voice recorder. Could
the owner have put one on board? Yes, but it's unlikely
and not normally done.
from [216.145.24.8], at 4:06pm ET
What model Lear was this? Have there been past occurrences
of rapid depressurization due to bad seals or hatches on
this particular model?
John J. Nance at 4:08pm ET
My understanding, which is preliminary, is that this was
a Lear 35 -- a modern, updated version of the original Lear,
which first came out in the 1960s. All models of this airplane
over the years have really been superlative, pace-setting,
high performance business jets that have amassed a very
good safety record. Is the Learjet prone to rapid depressurizations
for reasons of seals, doors, and windows? No, not any more
than any other highly pressurized small cabin jet. The Lear's
overall safety record has suffered only because of its high
performance nature -- it is not the easiest of small jets
to fly and over the years some accidents have resulted from
lack of pilot proficiency.
from [12.18.117.130], at 4:09pm ET
Is this an unprecedented occurrence or do you know of any
other times something like this has happened? Do you foresee
any policy or procedural changes as a result of this tragedy?
John J. Nance at 4:12pm ET
I have never been one to be spring loaded to anticipate
a rule-based solution for most accidents, although sometimes
-- as with the universal need for enhanced ground proximity
warning systems -- an entire class of accident could be
eliminated by a simple new requirement. In this case, it
is not only too early, but I also see no earmarks yet of
anything that call to mind a previously suggested and rejected
rule or requirement that might have helped. Please keep
in mind that while we're discussing incapacitation based
on cabin pressure loss, there are indeed other possibilities,
such as carbon monoxide or even some bizarre occurrence
in the cabin.
To answer the first part of your question, I am singularly
unaware of any similar occurrence in civil aviation over
the past 3 or 4 decades, from whatever cause. There have
been numerous military incidents over the years involving
hypoxia, usually from a pressure regulator left in the off
position or oxygen masks in fighters not connected properly.
But neither in commercial aviation nor in private aviation
do I recall anything approaching this tragedy, especially
if it involves cabin depressurization and hypoxia.
from [32.97.136.235], at 4:15pm ET
Is it normal that no attempt was made to do anything other
than watch the plane run out of fuel and crash once it was
determined that there was no activity onboard?
John J. Nance at 4:18pm ET
Unfortunately, there was nothing that the pilots in those
F16 chase planes could have done. An aircraft in flight
simply can't be boarded, nor can its flight path be influenced
by another airplane without direct physical and extremely
dangerous contact between the aircraft (such as using the
wing or nose of a plane to try to raise the other aircraft's
wing and begin a turn). The frustration level among those
fighter pilots who responded was terribly high, as it has
been for me as an airline pilot when I heard the rare, unfolding
drama of some airmen in trouble on the radio without being
able to "fix" it just by voice instructions. Here, there
was no conscious mind left to talk to on the Lear.
from [152.5.136.141], at 4:21pm ET
The FAA and the NTSB refuse to speculate on the causes of
accidents such as this. Why do you feel so comfortable doing
so?
John J. Nance at 4:26pm ET
First of all, it's the job of the NTSB to never prejudge
an accident and it's their duty to say nothing about the
cause until all the facts are in. The FAA, though not saddled
with the investigatory responsibility, has both a fiduciary
obligation and a natural reticence to talk about possible
causes until the NTSB has ruled. I am an interface as an
analyst with a responsibility to use my knowledge and long
involvement in aviation to carefully interpret the available
facts at any given point to satisfy the voracious curiosity
of the public and, representing the public, the media.
Somebody has to do this, and if no one from a profession
such as mine will provide this service, the media is left
to flop around with no guidance and no expertise and will
inevitably get it wrong. So it's not that I feel comfortable,
because what my job is to give you the best interpretation
possible. And, if you listen closely, you'll always hear
me talking ad nauseum that we are "guessing at this stage,"
"it's not conclusive but this is what we know" and "this
is only one of several possibilities" and many other caveats
to warn you that these are only a preliminary analysis.
Moderator at 4:28pm ET
Thanks for joining us today John. Any final thoughts on
this tragedy?
John J. Nance at 4:31pm ET
The only thing I think we should focus on is that, while
we've made flying airliners at high altitude a routine,
never-think-about-it occurrence, humans were never meant
to live or work above 30,000 feet, and it's an environment
very unforgiving and potentially lethal to human life because
of the lack of oxygen and pressure. Next time you sit down
on an airline seat and elect not to pay attention to the
flight attendant with a strange yellow cup in hand, think
about the realities of those altitudes. Would you really
know what to do in a rapid depressurization scenario? Next
time, pay a little closer attention.
Moderator at 3:29pm ET
Thanks again. And thank you all for your questions and comments.
Sorry we only had time to respond to a few of them.
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