All I Need is the Air that I Breathe

6 Nov 09 4 Comments

Sylvia in the SaratogaOne question I didn’t deal with in my Frequently Asked Questions was whether the Saratoga has oxygen. The plane does have an oxygen tank and you can plug masks in on the ceiling to take it in directly. We’ve never used the supplemental oxygen other than to test to make sure it’s really there. The plane is not pressurised and we very rarely fly high enough that it is an issue.

What is the issue? Hypoxia: oxygen deficiency. The altitude at which pilots can be affected varies based on a number of issues including health, age and training.

Hypoxia (medical) – Wikipedia, the free encyclopedia

Symptoms of generalized hypoxia depend on its severity and acceleration of onset. In the case of altitude sickness, where hypoxia develops gradually, the symptoms include headaches, fatigue, shortness of breath, a feeling of euphoria and nausea.

F16 pilot wearing maskThe onset of hypoxia is often masked by the euphoria – you have a general sense of well-being and can be apathetic to the fact that something has gone wrong. You will feel confused and disoriented. Your time of useful consciousness is limited – the time in which you remain capable of making sensible decisions and correcting the issue.

A recent and well-known hypoxia incident was the crash of Helios Flight 522, in which the flight crew were incapacitated due to hypoxia. The plane flew into a holding pattern over Athen’s International Airport and after the sixth loop, two Hellenic Air Force F16s flew to intercept. One of the F16 pilots was able to see into the cockpit: the Captain’s seat was vacant and someone was slumped over the controls in the First Officer’s seat.

You can read the full details on the Final Accident Report (in English). There were, as always, a series of factors that led to the final crisis and the detailed analysis makes for interesting, albeit chilling, reading.

However, hypoxia is not just an issue for high-level jets. As a part of my UK PPL, I was told to start considering hypoxia symptoms whenever I flew over 8,000 feet and to actively be monitoring the risk at all times over 10,000 feet. The FAA has a specific regulations for flights over 12,500 feet. The flight crew must have supplemental oxygen available and use it when the flight is at a cabin altitude pressure of 12,500 to 14,000 feet for more than 30 minutes. Above 14,000 feet the flight crew must use supplemental oxygen for the entire duration of the flight at that altitude.

The passengers aren’t required to have their own oxygen supply until the cabin pressure altitude is above 15,000 feet as they hopefully are not making critical decisions. Personally, I’d ask for my fair share on any flight over 12,000.

A tragic VFR case in 2003 involved a PA-28 flying over the Rockies. You can read the full accident report from the NTSB – again a number of issues came into play. The pilot was delayed due to bad weather and changed her planned routing to avoid further weather. She requested an altitude of 15,500 feet. The PA-28 was unpressurised and did not carry supplementary oxygen. Radar data indicates that the pilot flew above 12,500 feet for 2 hours, 17 minutes, above 14,000 feet for 1 hour, 49 minutes, and at approximately 16,000 feet for an estimated 45 minutes.

While flying above 14,000 feet, from 18:42 to 20:31, the pilot received numerous heading corrections from ARTCC, some of them by as much as 70 degrees. On one occasion, the pilot reported that she was over Montrose, Colorado, and the ARTCC informed her that she was over Telluride, Colorado. The pilot responded with “roger that, I appreciate it, can’t see a darn thing out here.” The radio communication between the pilot and ARTCC became increasing difficult and erratic. Many other aircraft assisted in relaying information between the two.

The radar data showed that she began to descend rapidly (1,077 feet per minute) and five minutes later made a mayday call – possibly the result of the increased air pressure as she returned to below 10,000 feet. She had come to her senses too late.

At 20:35, the pilot transmitted the following: “Denver radio, mayday, mayday, I’ve got myself in (unintelligible).” At 20:37, a Federal Express flight 1290, flying in the area, said “yeah, we just picked up a strong Emergency Locator Transmitter (ELT) signal on 121.5, it’s gone now.” The ELT signal was not received again. On the morning of January 25, 2003, at approximately 09:30, a rancher observed a column of smoke on his land. Upon investigation, he discovered the downed airplane.

Fuel ConsumptionHer flight plan was never viable. She shouldn’t have been at that altitude without supplementary oxygen but also she’d planned a 4-hour flight based on having 8-hours of fuel in the plane. In all actuality, with the most efficient fuel burn, the flight required 5 hours and 25 minutes – in an aircraft with 5 hours maximum endurance.

In addition, she had a strong headwind. She lost total engine power due to fuel starvation and she was not in a mental state even to realise the issue until the plane was rushing towards the ground.

Gradual hypoxia is insidious as it is difficult to realise that there is an issue, clearly she flew for hours without ever realising that she was beginning to suffer from oxygen deprivation. However, at least there is a chance of noticing. A sudden change of air pressure resulting in reduced oxygen has much more dramatic effects, even at levels where we’d be able to survive a short amount of time under other circumstances.

The AOPA article Luck Saves the Day, describes an instance of sudden onset of hypoxia, miraculously with no fatalities.

The pilot and two passengers were in a Cessna 421B, a pressurized cabin-class twin. They were warned of isolated, severe thunderstorms in the area but it seemed trivial to route around them. However, the pilot relied on the radar and spotted a gap, 15-20 miles wide, that would allow direct route that was “clear on the scope”. Clouds were visible ahead but due to the position of the sun, they appeared white.

The pilot very quickly found himself in a hailstorm, which can be masked on radar, painting “a far more benign picture than what is actually in front of the aircraft”.

Then, a piece of ice the size of a golf ball broke the windshield.

LandingThe only possible procedure at this point is to use supplementary oxygen immediately (presuming you have it) and descend. The time of useful consciousness at 19,000 feet is severely limited. The sudden onset due to the broken windshield is much more severe than generalised hypoxia.

The pilot was still reacting to the windshield, ducking into his seat and the passenger (a VFR pilot) took control to attempt to keep the wings level. And then their time was up.

The passenger stated that he “never felt dizzy or lightheaded.” Nevertheless, the 421 crash-landed in a field with all occupants unconscious. The passenger in the backseat did not remember the crash. “When I came around, all was quiet.”

You can read the full article on AOPA Online.

May we all be so lucky on the day the flight goes wrong…


4 Comments

  • That’s pretty shocking, isn’t it?

    I use a pulse oxymeter on flights over about 8,000 feet. I regularly cruise at FL100 or FL120 in the Cirrus but putting the oxygen masks on is a huge pain so I monitor my O2 levels and avoid it if I can.

    I did an experiment recently on one flight where I got all my PAX to test their blood o2. Scores varied between 78% and 96% with no obvious explanation for the variation (i.e. no smokers or people with colds). This makes me think that there’s no general o2 level that works for everyone and that we probably need to understand our own personal reaction to hypoxia and when it sets in. But how?

    On another quick point, I think you probably need to consider supplemental oxygen above 5,000 feet or so at night because hypoxia can reduce night vision even at relatively low levels.

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