March 2000 Issue

O2 Rules Ignored

Risks of high-altitude flight brushed off by many pilots who should know better

The article on the Payne Stewart accident [Critical Moments, January] was a well-written discussion of the hazards of flying corporate airplanes at high altitude. I would like to add two points.

When I first joined the airlines, I had not had the benefit of military training. My airline refused to allow their pilots to take altitude chamber “rides” unless they were in the National Guard or Reserves. Like most pilots who have not been exposed to the effects of hypoxia, I didn’t believe the training movies. It wasn’t until I left the airline and had to take the training that I became a believer.

Second, I think the rule requiring one pilot to wear a mask above FL350 or when the other pilot leaves his or her seat is the most widely ignored rule in aviation. This rule is simply ignored – to the great detriment of safe flight. Two chamber refreshers ago, I asked to use a quick-donning mask during the simulated rapid decompression. I was surprised to note the difficulty in getting a good seal quickly. I feel that at altitudes above 35,000 feet, it would be likely that both pilots would become incapacitated. Obviously, it is premature to speculate on the cause of this specific mishap. Nevertheless, I agree with John Lowery that the rule needs to be rethought.

-Richard L Newman
San Marcos, Texas


Lear Flight’s Mysteries Run Deep
I just finished reading the article entitled “Pressure Drop.” I’m not rated in the Lear and found the description and shortcomings of the Lear interesting. Actually, a Lear pilot had told me about the inadequate oxygen quantity problem just a couple days before. Yours was a great discussion; it’s sure not a “fighter-pilot-proof” oxygen system.

However, I had problems with the times of useful consciousness you used in the article, and the assumption that the aircraft was lost due to a rapid decompression. I think everyone could agree that the crew was unconscious between the time they were cleared to FL390 and before reaching FL390, as they never selected altitude hold on the autopilot.

I have undergone altitude chamber training every three years for the past 28 years, but I couldn’t remember having such short times of useful consciousness as you described, or having ever been told about crew members losing consciousness immediately during a rapid decompression.

Also, I attended the Air Forces Flight Safety and Accident Investigation course and remembered different numbers than you related in the article.

The Aeromedical Handbook for Aircrew by D. G. Dobie gives the Time of Useful Consciousness as 45 seconds to 1 minute 15 seconds at 30,000 feet, dropping to 18 to 30 seconds at 40,000 feet. Of course, these are average values, which can vary considerably according to the degree of skill that is involved in the particular task in question.

In difficult circumstances, calling for complex decision making, the effective times of useful consciousness may be reduced. Based on these numbers, in the event of a rapid decompression, the crew would have had at least 30 seconds (at 35,000 feet) to react to a rapid decompression.

Your description of the Lear’s dive capability is 181.8 feet per second. Had they wasted 10 seconds before starting the dive, they still would have descended 3,600 feet in 20 seconds. They could reach 30,000 feet in 27 seconds. At 30,000 feet their TUC (Time of Useful Consciousness) is 45 seconds; they would have gained 15 seconds of TUC. In another 15 seconds they could descend 2,700 feet to 27,300, where TUC is 1 minute, and at 25,000 they have gained an additional minute of TUC. At 21,000 feet they can remain conscious 5 minutes.

While a rapid decompression may reduce these times, I would suggest that a very well-trained pilot of an aircraft suffering an explosive rapid decompression would be motivated to descend at rates greater than those recommended regardless of risk of damage to the airframe, increasing TUC at an even greater rate.

Given this discussion, the only things we know for sure are: (1) The crew was unconscious between 29,000 feet (Cleared to 390) and 39,000 feet. (2) The aircraft was depressurized, based on chase aircraft observation and the CVR. (3) Supplemental oxygen wasn’t available or wasn’t used. It seems to me that the problem could have been slow and incidious. By the time they received a warning of having a cabin pressure above 10,000 feet, they could have been beyond being able to react to it.

Rapid decompression? I’m not so sure.

-Ron Moore
Murfreesboro, Tenn.

Different sources give different times of useful consciousness. We’ve seen estimates of as long at 1½ minutes at 30,000 feet and 30 seconds at 40,000 feet. Speed of ascent also has an impact on the time of useful consciousness. Giving the NTSB time to do its job may provide some answers, because this accident certainly raises its share of questions.


Which Way Is Up?
There is an error in your story “Pressure Drop.”

On Page 6 you note that a pilot suffering CNS symptoms after a sudden decompression was put into a hyperbaric chamber where the pressure was “lowered to below sea level” in order to force nitrogen from his bloodstream back into the tissues. The pressure would not have been lowered by the chamber, but increased.

-Brian Peck
Via e-mail

Guilty as charged. We could have said the effective altitude was lowered or the pressure was increased. We did neither.


Pitch Trim Solves ASI Error Problem
Your article on airspeed indicator failure [Instrument Check, January] brought out many excellent points. I’m sure most pilots don’t think it will happen to them. However, I’ve encountered it twice, once from pitot icing when I had a broken electrical connection, and once from an invasion by insects. The first instance could have been prevented by a more thorough preflight.

In my military flight training during WWII, the lower portion of the ASI was blacked out and we learned to land the PT19 by pitch attitude, control feel and luck. The PT19 had no trim control, which brings up the fact that the trim indicator is, in itself, an airspeed indicator. If the flap configuration is not changed the airplane will always try to fly at the airspeed for which the trim is set. A mark can be placed alongside the trim indicator showing the trim setting for hands off flight at the proper final approach speed for a no flap landing. By using power only (very little elevator input) it is quite easy to land without an ASI. I recommend that pilots mark the proper spot alongside the trim control, cover the ASI and practice a few no flap takeoffs and landings on reasonably long runways.

-Bll Kane
Alameda, Calif.


Help for Handhelds
Mr. Roberts is correct to point out that handheld transceivers are not very effective inside the cockpit [Unicom, January].

However, there is an alternative to an externally mounted antenna, which will be of interest to the majority of us who do not own our own airplanes.

I have gotten good results by mounting the transceiver’s “rubber duck” antenna on the inside surface of a window using an extension cable which has a suction cup mount. The antenna should be placed in the window nearest the station you are calling, and should be oriented vertically for communications use, or horizontally for VOR reception.

The one I like is the Valor Enterprises model BNCSC, which is available from Ham Radio Outlet ( or Amateur Electronic Supply ( If your handheld’s antenna is not attached via a BNC connector, then an adapter will be needed.

I also consider a headset adapter to be a necessity, because otherwise you would have to keep the radio constantly held up to your ear, to avoid missing a call. This will probably be available from your radio’s manufacturer.

Of course, the first order of business must always be to fly the airplane. Only when time permits should one begin trying the handheld.

-Richard Palm
Mountain View, Calif.


VFR/IFR Debate Continues
“VFR vs. IFR” from R.L. Billings [Unicom, November] brought to mind the personal controversy I have resolved with myself over the last couple of years. While IFR is certainly a big step up, why does everyone seem to automatically equate it with safer, more competent pilots? I made a decision to be a safer, more competent pilot as a VFR pilot. This decision involves making sure that you fly with an instructor regularly with specific objectives, including instrument piloting skills.

It also includes being as rigorous in your prep and flying as you would if you were flying into hard IFR. At the end of the day, a pilot’s competence is relative to his or her training and experience, not a piece of paper from the FAA. I know several marginal (but legal) IFR pilots. They are not better pilots than I am. But, in fact, were they fools (which they are not), they could legally go out there and try to fly hard IFR.

My problem with being just IFR legal (as opposed to a regular IFR pilot) is that it may promote risk-taking. When you allow yourself to get a case of “get there-itis”, you’re going to push the edge in IMC. Think about this: Why get and maintain your IFR if you don’t need it?

If you can afford to wait until VMC, why be IFR? Many of my IFR friends spend most of their time trying to keep current and safe, not flying IMC because they need to. If you can’t afford to wait until VMC, maybe you should re-assess why you want to be IFR and what you expect to fly into.

I think the IFR ticket makes many pilots think they have more experience than they really have, and that it’s OK to go as long as there is anybody flying. The smart VFR pilot has no such illusions. Not only that, if you got an IFR rating because you think you “need” one (not because you are a professional), doesn’t that automatically say that you’re already infected with “get there-itis”? How long is it going to be before you feel you have to push it through some big time IMC? I have never been to Flight Service and heard “IFR not recommended” in the weather briefing.

The other thing I have heard about IFR pilots, and would be interested in your opinion, is that they often become “autopilot junkies.” I attended Bonanza training at Flight Safety, and our instructor told us the first thing they do with high time private IFR pilots in the simulator is to suddenly tell them the autopilot is unavailable. Apparently, many are so used to punching the “Go To” button on modern autopilots that they are unable to handle the situation. Of course, this could also be the case with a VFR pilot, but it seems much less likely. Anyway, when I hear that some pilot has “5,000 hours,” I now wonder what the quality of those hours might be.

-B.J. Barbata
Kailua, Hawaii

A smart pilot, whether instrument-rated or not, works hard to develop the skills to fly the airplane as competently as possible and the judgment to know when conditions are too severe for those skills or that airplane.

Any generalization you make about “VFR pilots” and “IFR pilots” is strictly a mental exercise. Personally, we prefer filing IFR on cross-country flights because it allows flying at the airplane’s most efficient altitudes even though it’s often populated by a broken layer of cumulous clouds. It also means search and rescue might come more quickly should something untoward happen.

We also like the convenience of automatically being cleared into busy airspace and having traffic called out. Get-there-itis infects pilots of all certificates and ratings. The important thing to develop is the judgment to know when you can’t make it, IFR or not.

As for your question about autopilots, we have noted the tendency for pilots of more capable planes to be autopilot junkies, but don’t conclude that it’s a result of an instrument rating. Those who frequently make long cross-country flights are more likely to have instrument ratings and high-performance airplanes.

A good autopilot simply gives an easier ride than a less-sophisticated one.

Having said that, it’s also true that our personal preference is for hand-flying except in those cases where the autopilot reduces what would otherwise be a significant workload, such as when an approach clearance is changed at the last minute or when it’s time to put mustard on the in-flight sandwiches. The autopilot is a tool. Like any tool it can be used inappropriately.