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Emergency descents


Be prepared for the unexpected and comply with mandates.

By Don Witt
ATP. Learjet series, Airbus A320,
Boeing 737, Boeing 757/767

Training will help us detect our unique physiological responses to an insidious loss of cabin pressure. It is critical to a successful response to rapid decompression.

There are 2 likely reasons for emergency descents – fire and/or decompression. In the case of decompression, it may occur quickly, and it can be either rapid or explosive.

Examples of the latter that came from structural failure are Aloha Airlines Flight 243 (Boeing 737 with a popped top) and United Airlines Flight 811 (Boeing 747 that experienced a cargo door failure over the Pacific).

When structural failure happens, procedures in the Aircraft Flight Manual (AFM) may need to be modified. The crew of United Airlines Flight 811, for example, elected to keep the landing gear retracted for their emergency descent, because they were not sure whether or not they could make it back to Hawaii with the added drag after losing 2 of their 4 engines.

In a rapid or explosive decompression, the prime directive is getting the oxygen masks on immediately. Seems simple in a simulator, but in a real event it is much more difficult, and it gets more complicated by sudden loss of visibility due to condensation, objects swirling around in the cockpit, and physical  pain.

Sudden decompression at today’s cruise altitudes will very likely result in pain in some parts of the body, and the crew must be prepared to fight through the pain and get that mask on quickly. FAA’s AC 25-20, Pressurization, Ventilation and Oxygen Systems Assessment for Subsonic Flight including High Altitude Operation, states that the period of useful consciousness at a cabin/cockpit altitude of 40,000 ft is only a few seconds, and we get slow and dazed even before we pass out.

Because of this, FAR 135.89 (b)(3) states that above FL350 one pilot must wear his mask. Part 91 requires this above FL410. These are the most frequently violated rules of the FARs. You may be a pilot who does not comply, believing you can mitigate the risk you take by keeping the mask on your lap.

But this is a tactical mistake, because an explosive decompression will probably mean a loss of vision in a condensation cloud while your mask flies off your lap to parts unknown. It is best to leave your mask where you know where it is. A more comfortable solution to this may be to carry a third “cruise” mask.

FAA’s CAMI offers training courses for pilots and flight crews to be better prepared to deal with potentially fatal inflight events, such as loss of cabin pressure, hypoxia, and decompression sickness.

The value of training

Training in an altitude chamber is very advantageous. FAA’s Civil Aerospace Medical Institute (CAMI) in Oklahoma City OK can provide such courses. Other sources include Arizona State University in Mesa AZ, and ETC’s Falcon Hypobaric Chamber in Southampton PA.

However, the degree of decompression demonstrated in these hypobaric chamber training sessions is kept quite a bit less than that which could be encountered in an actual aircraft. This is  specifically to avoid experiencing the degree of pain and physical damage that might be encountered in a real-world decompression at high altitude.

FAA’s Portable Reduced Oxygen Training Enclosure (PROTE) travels the country and allows training in one’s own personal responses to hypoxia without any of the potential pain of pressure changes.

Executing the descent

Many jet AFMs recommend that emergency descents begin by rolling the aircraft into a bank. FAA’s Airplane Flying Handbook recommends a bank of 30º to 45º. And the new Airman Certification Standards (ACS) says exactly the same in the Task section – Emergency Descent. The business jet in which I currently instruct does not recommend a bank to help get the nose down because of a history of fatal overspeed accidents in this fleet.

If we happen to be flying on an airway, then, once a descent is stabilized, it is a very good idea to turn left or right off that airway, regardless of control considerations. The incredible accuracy of today’s GPS navigation means that if we should meet another aircraft on that same airway, we are not so likely to pass to one side or the other of it as we were decades ago.

Remember the mid-air collision in Brazilian airspace in 2006 of an Embraer Legacy and a Boeing 737? They were victims of technical inaccuracy. Of course, this is not a factor if we are proceeding direct somewhere. One heading is as good as another.

The agency’s PROTE is a mobile solution that can accommodate 5 trainees to practice procedures when faced with events leading to hypoxia at altitudes of up to 25,000 ft.

Once the descent is established, how critical is it that we descend as quickly as possible? (Right on the red line or the gear limit speed all the way?) For many of us, a glance over the shoulder or call to the rear could confirm passenger condition.

(Although the Aloha Airlines Flight 243 crew never knew anything  about the cabin crew or passengers until they were on the ground. Communication was impossible in that nightmare scenario.)

AC 25-20 reads, “Exposure to cabin altitudes in excess of 25,000 ft for more than 2 minutes without supplemental oxygen could, in some cases, cause permanent physiological (brain) damage.” So, your best efforts to descend quickly may indeed be appropriate.

And you should squawk 7700 as soon as possible, even if you have already told a controller of your emergency descent. Other controllers may not yet know, particularly in the low-altitude sectors of the facility.

And with regard to communication, trying out the microphone in the oxygen mask from time to time is also a good idea. Does it work? If we have been complying with 135.89 (b)(3) or 91.211(b)(ii) all along, we would already know.

If one must switch from COMM1 to INTERPHONE in order to transmit to ATC or to your crew mate, it can get pretty confusing as to who we just spoke to. It may be best to just stay on COMM1 and transmit out anything you have to say to your crew mate. He hears you in the speaker side tone. Who cares who else hears you?


Once we are down to lower altitudes, where do we go? Everyone may report that they are feeling fine, but decompression sickness (DCS) may show up some hours later as evolved gas problems, bends, chokes, or neurological issues, such as seizures. Seizures happened many years ago in flight to a USAF T-39 Sabreliner copilot after an explosive decompression at cruise altitude and the ensuing emergency descent.

VisionSafe’s Emergency Vision Assurance System, together with smoke goggles, allows a pilot to see instruments and to see out through the windscreen in the worst smoke-in-the-cockpit conditions.

How is DCS treated if it occurs? It may require a hyperbaric medicine chamber. I recently called 3 different Air Route Traffic Control Center (ARTCC) managers to ask if their controllers knew where hyperbaric chambers were located in their areas of responsibility. In each case, the surprising answer was “No, we don’t know.”

But interested pilots may download a listing of certified hyperbaric medicine chamber locations from the Undersea & Hyperbaric Medical Society (UHMS) online, and keep it on an iPad. It would be unfortunate to land somewhere after an emergency descent and then have to load a passenger (or yourself) on a medevac flight to another city where such a chamber is located.

In the chaos of an emergency descent, did we note the final altitude of the cabin? Certainly, after an explosive or rapid decompression to a very high cabin altitude, we should attempt to get everyone to go straight to a medical facility upon deplaning.

We cannot force them, but we should do our best. Picture a passenger alone in his hotel room coming down with delayed onset neurological DCS symptoms unknown to anyone else.

Insidious decompression

Slow decompression is a different sort of hazard. The Payne Stewart Learjet accident and the Helios Airways Flight 522 crash are 2 examples. Training in a chamber or PROTE would help us detect insidious decompression if cockpit warning systems fail.

Is our crew mate acting or sounding a little strange? Maybe he or she is our “canary in a coal mine.” Not everyone proceeds down the hypoxia route the same way. General Dynamics F-16 Fighting Falcon pilots escorting the Helios Airways Boeing 737 saw a flight attendant in the cockpit who was apparently attempting to fly the airliner when everyone else was unconscious. Sadly, he was unsuccessful.

If you fly regularly with flight attendants or with medical personnel, have you ever discussed with them what to do if both pilots appear incapacitated? They should at least know where your masks are and how to put them on your face. If the cab-in masks dropped and these folks looked to the cockpit only to see you both slumped at the controls, would they simply despair until they too succumbed? I have never heard of such training, but I do not see why it would not be a good idea.


Airlines which fly to Central and South American destinations publish special “Decompression Routes” that crews need to follow in emergency descents to avoid terrain. Once down to a physiologically safe altitude, how do we proceed to destination through complex high terrain such as that of the Andes? These “Decompression Routes” spell that out.

For business jet operators who don’t have all the benefits when pre-planning, equipping their aircraft with Enhanced Ground Proximity Warning System (EGPWS) or Terrain Avoidance and Warning System (TAWS) with an appropriate and accurate database and a good display is a necessity since, after leveling off, the crew’s problems may have only just begun if there is higher terrain between them and where they need to land.


Fire inside the aircraft that cannot be extinguished quickly may be a pilot’s worst nightmare. The crew must multitask to the Nth degree. The attempt to put out the fire is primo, but so is the absolute quickest descent to land and evacuate. Can we delay one to complete the other?

An emergency descent to get on the ground in a burning airplane may require procedures “out of the box.” This is an area where experimentation in a simulator can be eye-opening. Would you expect that a business jet could descend from FL410 to be stopped on a runway and evacuated in less than 4 minutes? It can be done in one jet I am familiar with, but only if there is a workable runway within about 25 miles distance.

If we can’t get the fire out and we are far over water, ditching could be the only option. Or if we are far from a lighted runway at night, such as on some routes from our southern border to TLC (Toluca, Mexico City, Mexico), we may be out of survivable options.

Some operators carry fire containment bags and accompanying fireproof gloves, but moving a Lithium-ion (Li-ion) battery-powered portable electronic device (PED) and sealing it in such a bag may not be a good option. But the best procedure is not intuitive. FAA has produced videos on fighting Li-ion fires in aircraft. The recommended course of action is dousing the fire repetitively with water, but never submerging it in water or ice, or trying to seal it in a container wherein temperature may build rapidly.

Smoke may make aircraft control impossible, and only a crew with full face masks and EVAS systems could survive. The best response to an inflight cockpit/cabin fire requires the best equipment and the best training.

Don Witt was a USAF F-4 pilot and holds a DFC. He is a retired United Boeing 767 and Airbus A320 captain and former safety manager for a large corporate flight department. He is presently a Learjet instructor and has been a long-time aerobatic instructor.