How Pilots Handle Aircraft Decompression
Pilots work quickly to keep passengers safe when explosive decompression occurs.
Just when I think I’ve run out of ideas for this column, an incident like the April 1, 2011, Southwest Airlines explosive decompression happens, and I’m presented with great material to share with readers. Explosive decompressions take place rarely but are incredibly frightening for everyone on board an aircraft.
Current FAA training standards require all pilots who fly commercial airliners to complete annual rapid-decompression training in flight simulators. While these simulations cannot entirely replicate atmospheric conditions, we are exposed to all the same flight conditions and sounds. As you can imagine, a rapid decompression can be nerve-wracking and confusing. Even so, such events may be handled successfully when pilots remain calm and remember their basic aviation training rules: Aviate, navigate and communicate.
Join me in the cockpit as I present a decompression scenario that may be similar to the Southwest incident. I hope to give you a glimpse of what the pilots faced as they prepared the aircraft for an emergency descent.
Most often, the first indication that something is wrong is the cabin altitude warning horn blasting in the cockpit. Concurrently, the pilots experience abdominal pain and the feeling of having the wind knocked out of us, because trapped gas expands with the loss of cabin pressure. Our first move is to don our oxygen masks, check the regulator to 100 percent oxygen and establish communication with the copilot. Depending on the altitude of the aircraft and the fitness level of the pilots when the decompression occurs, the UTC, or useful time of consciousness, can be as little as 5 to 10 seconds.
Once the oxygen masks are in place, it is difficult to exhale as oxygen is forced into our lungs through automatic pressure breathing. So we reach for the response checklist and begin the steps to safely descend the aircraft to a lower altitude where the crew and passengers can breathe without supplemental oxygen.
The next step on the checklist is an immediate call to Air Traffic Control (ATC) explaining our situation and declaring an emergency, followed by changing the transponder code (squawk) to 7700: the universal signal to ATC that we are experiencing an emergency. Squawking the code allows expedited handling in descents and vectors for the incident aircraft as we continue to the nearest suitable airport.
Pilots must handle all three of the steps required to end this scenario almost simultaneously. We are aviating (flying the airplane), navigating (descending to our divert, or alternative landing point) and communicating (talking to ATC and to each other). A breakdown in any of these three tasks could be catastrophic. When navigating, we need to know the precise height of the flyover terrain—we don’t always have the luxury of being able to see the ground. What if the decompression happens while we’re flying over 15,000-foot mountain peaks at night? A descent directly to 10,000 feet would be disastrous.
Next up on the checklist: The pilot who’s not flying makes a call to the flight attendants to discern the condition of the cabin and inquire about any injuries. From the cockpit, we don’t know the cause of the decompression or the extent of damage to the aircraft. If we’re lucky enough to see the size and location of the hole in the fuselage, we’ll know more about the severity of our emergency. These details give pilots a good sense of the structural integrity of the airframe and if further damage may be a concern. We don’t want to subject the damaged aircraft to any additional stresses (air load) as we start a high-speed emergency descent.
Without a pressurized cabin, our target level of altitude would be 10,000 feet because that is the highest altitude where we avoid significant oxygen deprivation of the passengers and crew. Those little masks that drop down from above can create chemically generated oxygen for only 10 to 20 minutes, so we must descend quickly to a lower altitude. Ten thousand feet keeps the aircraft high enough to manage the fuel burn. At low altitudes, fuel burn can leave long overwater flights (such as Los Angeles to Sydney) critically short of fuel, even during a divert to a known alternate field.
Once the aircraft has descended to 10,000 feet, the passengers and crew can remove their masks and breathe the ambient air as we make our final descent into the divert airfield. If the structural integrity of the aircraft has been assessed as sound, we’ll make a normal approach and landing. The airport will most likely have dispatched emergency vehicles in anticipation of our arrival. A crew will be standing by to assist with medical emergencies or to extinguish any fires that may occur.
From this point, the aircraft will be sequestered in an unused part of the airport, where inspectors will go over the area of the fuselage looking for the cause of the structural failure.
Did you know?
Current FAA rules prohibit commercial airline pilots from growing beards or goatees. (Mustaches are allowed.) They interfere with the oxygen mask by potentially preventing a tight seal over the nose and mouth.
Ask the Pilot:
Are there guidelines for pilots exiting the cockpit during flight? Besides using the lavatory, are there other reasons for them to come out?
We are required not to leave the cockpit for any reason other than physiological needs. Different airlines have their own procedures for accessing the cockpit in flight, but most of that information is proprietary. Other than going to the lavatory, there really isn’t a need for the pilots to be out of the cockpit. Every time a pilot wants to exit the cockpit, a flight attendant has to block the cockpit door. In an effort not to inconvenience flight attendants, pilots have begun making fewer trips to the lavatories. Unfortunately, this means they often don’t drink enough water and may become chronically dehydrated; in addition, that has led to a marked increase in kidney stones suffered by pilots.
Chris Cooke has been a pilot with a major domestic carrier for almost 20 years and currently flies long-haul routes on the 747-400. He began his career with the U.S. Marine Corps, received Navy flight training and was a Top Gun graduate. In 2011 he will log more than 300,000 miles, all in a window seat.
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