Ask the Pilot

The safe landing of the damaged Qantas 747 was no miracle. Plus: If a plane loses pressure, will your eyes pop out?

Published August 1, 2008 10:18AM (EDT)

Back on July 25, this column included a brief item about the safety record of Qantas, the kangaroo-tailed national airline of Australia. That same day, as fate would have it, a Qantas 747 en route from Hong Kong to Melbourne suffered an in-flight decompression, forcing the crew to make an emergency landing in the Philippines. A large hole was discovered in the forward lower fuselage, purportedly caused by a burst oxygen tank.

Although none of the 365 passengers or crew was injured, the incident made news all around the world, with photos of the "car-size hole" amply featured in full, above-the-fold color. Observers were incredulous. "How did the 747 remain in one piece?" Was it not a "miracle" that such a badly damaged aircraft managed to land safely?

In point of fact, no.

When it comes to aviation, media overreaction to minor events is nothing new. While not on a par with, say, the over-the-top coverage surrounding the emergency landing of a JetBlue Airbus three years ago, or the nonsense spawned by "citizen journalist" Jeremy Hermanns in December 2005, the Qantas mishap received its fair share of hype.

Let's begin with that "car-size hole" -- as several commentators put it. The area in question is just forward of the starboard wing, at the front end of a center fuselage fairing. The total area of damage may indeed be the size of a car, but much of it appears to be superficial -- the outer skin panels are torn away, revealing the structure and plumbing beneath. The actual puncture of the pressurized cabin, blown out by the oxygen bottle, is substantially smaller.

As most readers probably understand, airplanes are pressurized to compensate for thinner air at higher altitudes. Pressurization squeezes the air back together, increasing the amount of oxygen so that occupants can breathe normally. Introduce a large enough hole in that sealed vessel, and the pressure can no longer be maintained.

Decompressions can be mild or dangerous -- gradual, rapid or explosive -- depending on the size of the breach, the location at which it occurs, the speed at which it propagates and the level of pressurization (i.e., the airplane's altitude). Those caused by a bomb, for example, run a high risk of destroying the plane, as seen in the terrorist attacks against Pan Am 103 and many others. The initial blast may be small, but resultant forces can rip the plane to pieces in a matter of a few seconds. Damage to crucial systems is another factor. Debris can be flung into engines or smashed against control surfaces. In 1974, the blowout of a lower-deck cargo door on board a Turkish Airlines DC-10 caused the cabin floor to collapse, severing control cables and rendering the plane unflyable. (It went down near Paris, killing 346 people -- the fourth-deadliest accident in aviation history.)

But those are worst-case scenarios. Not even a bomb or other major failures will necessarily result in a crash. Consider the TWA 727 that withstood an onboard explosion in 1986, or the United jumbo jet that survived loss of a cargo door and a large section of fuselage after takeoff from Honolulu in 1989. Several passengers were killed, but hundreds survived. Or, in the most incredible example of all, who can forget Aloha Airlines Flight 243, the
Boeing 737 that lost an entire section of its cabin -- ceiling, sidewalls and all, right down to the floor -- yet managed to land safely, with the death of only one person.

Any fuselage rupture is serious. But serious does not mean imminent disaster. The Qantas jet remained structurally intact, while its crucial systems and flight controls were not adversely affected. This was hardly the near catastrophe implied by much of the coverage.

The crew members faced a rapid decompression, to which they responded, as would be expected, by initiating an emergency descent. This is standard procedure following any uncontained loss of cabin pressure. The pilots first don their oxygen masks, then run through a series of five or six steps to establish a rapid descent. The plane will lose altitude at several thousand feet per minute. The idea is to reach a safely breathable level -- 10,000 feet, typically -- as quickly as possible. Troubleshooting begins after you get there. Oxygen masks in the cabin will have deployed automatically -- or, if need be, the crew will release them with a switch.

I can understand that many passengers would be upset and frightened. There they are, cruising along, when suddenly there's a loud noise, the cabin depressurizes, the masks drop, there's dust and debris spinning around, and the plane begins to plummet. But that plummet is a textbook maneuver.

A pilot is likely to spend an entire career without ever seeing a real emergency descent, but it's something that's rehearsed all the time in simulator training. To passengers, the speed and angle will seem radical, but they are well within the plane's capabilities and nothing hazardous.

Over mountainous terrain, incidentally, crews will preprogram detailed diversion paths for use should a decompression occur at any point where an immediate descent to 10,000 feet is impossible. A safe altitude must always be reachable before supplemental oxygen runs out. If that guarantee cannot be met, you cannot proceed over that area of high terrain. This makes certain parts of the Himalayas, for example, no-fly zones for most commercial aircraft.

Reports are that numerous drop-down masks on the Qantas jet were found to be inoperative. This is possibly because the oxygen bottle supplying them was the one that burst. (There were 13 separate bottles in that area, only one of which exploded, according to a preliminary investigation.) It's true that without supplemental oxygen, unconsciousness can strike in seconds during a very rapid or explosive decompression, but the critical factor is getting the plane to a lower altitude. Provided this is accomplished quickly, death or injury is highly unlikely, and the flight attendants have portable oxygen units with which to assist passengers whose personal masks aren't working. (In the aforementioned United accident over Hawaii, the flight-deck oxygen lines had been severed, leaving the pilots without a backup source. Fortunately the incident occurred at a low-enough altitude where breathing wasn't a problem.)

One reason for hysteria in these types of scenarios is a widespread misunderstanding of what, exactly, pressurization is for and what happens if it goes away. The masks come dangling out of their holsters, and people get frantic. There's this notion of pressurization as a sort of physiological hell, like being at the bottom of the ocean in a deep-sea diving bell. Nothing illustrates this better than the time I was asked, "If a plane loses pressure, will my eyes pop out?"

Be advised that pressurizing a plane does not keep your eyes in. All it does is replicate the levels of oxygen near sea level. As discussed above, losing that pressure can indeed be hazardous. But in the vast majority of cases it's not, and provided a descent is initiated quickly, there's little to worry about.

Meanwhile, will this event reflect badly on Qantas, an airline that prides itself on safety and reliability? Probably not. We'll wait for the official findings, of course, but here, by all accounts, was a well-trained crew reacting professionally to an in-flight emergency. Nearly 400 people landed safely, without so much as a single serious injury.

Only three days later came another Qantas drama. Flight 692, a Boeing 737 headed to Adelaide, Australia, returned to Melbourne for a precautionary landing. The culprit was a landing-gear door that failed to latch properly after takeoff. The landing-gear bays are unpressurized, so the door had no effect on pressurization. Or much else, really -- all in all, this was about as minor a problem as you could hope to have. Nevertheless, the malfunction touched off "chaos" aboard the jet, and received a flurry of media attention afterward.

What is it with planes and doors? Aircraft exits are the subject of a great deal of misinformation and misunderstanding, and it seems that a week can't go by without hearing the latest story about a passenger who went cuckoo and tried to yank one open, only to be tackled and restrained by those around him, who thought they were on the verge of being ejected into the troposphere.

While the news never fails to report these events, it seldom if ever mentions the most important fact: You cannot -- repeat, cannot -- open the doors or emergency hatches of an airplane in flight. Yes, I know, this was covered in a prior column, but there have been at least two cases of door-induced hysteria in the past several days, and it bears repeating.

The doors can't be opened for the simple reason that cabin pressure won't allow it. Think of an aircraft door as a drain plug, fixed in place by the interior pressure. Almost all aircraft exits open inward. Some retract upward into the ceiling; others swing outward; but they all open inward first, and not even the most musclebound human can overcome the force holding them shut. At a typical cruising altitude, up to eight pounds of pressure are pushing against every square inch of interior fuselage. That's over 1,100 pounds against each square foot of door. Even at low altitudes, where cabin pressure levels are lower, a meager two-pounds-per-square-inch differential is still more than anyone can displace -- even after six cups of coffee and the frustration that comes with sitting behind a shrieking baby.

So while I wouldn't recommend it, unless you enjoy being pummeled, beaten and choke-held by scared passengers who don't know better, a person could, conceivably, sit there during flight, tugging on the handle to his or her heart's content. The door is not going to open (though you might get a red light flashing in the cockpit, causing me to spill my Coke Zero). You would need a hydraulic jack, and the Transportation Security Administration doesn't allow those.

By Patrick Smith

Patrick Smith is an airline pilot.

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