Ask the pilot

What's more dangerous, an in-flight decompression, or reading about one? Somebody please pass the pilot some oxygen.


Patrick Smith
August 26, 2005 11:30PM (UTC)

Air disasters, like celebrity deaths and tropical storms, seem to happen in threes. No sooner were the flames doused in Toronto when a Cypriot 737 went down in bizarre fashion on Aug. 14, followed two days later by an MD-80 in Venezuela.

Make that fours. We shouldn't forget the Tunisian turboprop that crashed in the Mediterranean on Aug. 6. News coverage was sparse, but 13 people died after the ATR-72 ditched in choppy seas off the Sicilian coast.

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Such weird statistical bunchings are prone to make us skittish, though it's imperative to bear in mind that a handful of accidents does not, in the context of tens of thousands of daily departures, measurably impact the odds of being in a crash. According to the International Civil Aviation Organization (ICAO), the global accident rate a quarter century ago was three fatal incidents per million flights. By 2004 the rate was one-sixth of that, at 0.5 incidents per million. The recent series of casualties, while unusual, is unlikely to skew the long-term data.

That's the left brain talking. Speeding down the runway, we tend to be at the mercy of that other, less rational hemisphere. Regardless of what the calculator shows, the majority of travelers are never fully at ease when sitting on a plane, and there's nothing like a spate of tragedies to push already squeamish flyers over the edge. Four events in two weeks was enough to prompt the BBC to ask, "Is flying still the safest way to travel?"

The answer, of course, is yes, though voices of reason and reassurance have been few. Amid growing angst, the last thing people need is incendiary misinformation from the news media, and regrettably that's what they're getting. As reviewed in this space on Aug. 12, the accuracy of reports following the Air France debacle were tolerable at best. Then, just as the story began to fade came the terrible crashes in Sicily, Greece and Venezuela. Each of those was a media botchery waiting to happen, their mysterious circumstances taking in the full encyclopedia of aviation's most misunderstood buzzwords -- things like "decompression" and "engine failure."

Enter the usual suspects, from the Associated Press to the network anchors, who this time truly managed to outdo themselves.

The worst of the lot comes from the scorched hillside north of Athens, unintended terminus of Helios Airways flight 522, a tourist charter en route between Larnaca, Cyprus, and the Czech capital of Prague. All 121 passengers and crew were killed when the Boeing 737-300 went down after a possible in-flight decompression.

But what exactly is a decompression, and what are its consequences? As you might expect, those vary greatly, but an Aug. 15 dispatch from the Associated Press, written by correspondent Elana Becatoros and prominently splashed on front pages worldwide, included this explanation from Chris Yates, aviation analyst at Jane's Transport: "If the airplane lost cabin pressure ... effectively everybody would be doomed with a short space of time."

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Having stumbled across this nugget over breakfast, I quietly put my bagel down and wondered if the time hadn't come to give up the fight -- to at last hurl my Macintosh out the window and perhaps stick my head in the oven. (Instead I went and listened to an old Hüsker Dü song, "Crystal," with its line, "Sucked out of the first class window!") Note the ellipsis points, included in the story as shown above. Giving Chris Yates benefit of the doubt, and assuming he's cognizant of the many potential variants of decompression, which we'll get to in a minute, we're forced to assume Becatoros omitted the necessary qualifiers for the sake of punch and pith. In doing so she offers us a snippet of utter nonsense.

Two days later came another outrageous summation, this time courtesy of the AP's Derek Gatopoulos. "Decompression would cause a rapid loss of oxygen on board," Gatopoulos informs us, "giving passengers and crew a few seconds before losing consciousness amid subzero temperatures. Death would be minutes behind."

And there we have it: Becatoros and Gatopoloulos, tied neck and neck for providing two of the most luridly renegade statements I've encountered in all my years of vetting crash accounts.

If you need a primer on what cabin pressurization does in the first place -- something the mainstream media (and certainly Hollywood, whose disaster portrayals invariably include dangling rubber masks and shrieking passengers, no matter how inappropriate) -- has never grasped, try reviewing here. To briefly recap: Up high, the atmosphere is thin and oxygen scarce. This rarefied air is great for fuel economy, but not so great for breathing. Pressurization squeezes the air back together, increasing oxygen density and allowing a plane's occupants to breathe normally.

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What really happens when a plane loses pressurization depends entirely on where, when and how quickly the loss occurs. A rapid high-altitude decompression can indeed be violent, explosive and deadly. But most are gradual and ultimately harmless, like those that occur when a door is not properly sealed or an outflow valve is on the fritz. Such decompressions are not terribly uncommon, and neither are they deadly, or anything close to it, in the vast majority of instances. For that matter, pressure levels are designed to change as a plane climbs and descends; upon landing, a jet will have, yes, decompressed, to field level. To some extent we're wrestling with semantics, but people ought to know that "decompression" is a fairly ambiguous term. The AP's renditions give the erroneous impression that any pressurization anomaly is, by nature, a deadly one.

Becatoros' article goes on to inform us that Boeing 737s are, "like all Boeing planes, equipped with warning systems that alert pilots when decompression is occurring." True, though the system is considerably more sophisticated than she makes it sound. Flight deck instruments show exact readouts of pressurization levels at all times. Past a certain point, should the pilots for whatever reason not be aware of an ongoing malfunction, alarms are triggered. That point is quite conservative -- the equivalent of breathing at 10,000 feet -- allowing more than ample time to troubleshoot and, if need be, descend to a lower height.

What Becatoros and Gatopoloulos are getting at, albeit recklessly, are the effects of a sudden decompression at high altitude. Up at cruising altitude, a cabin is pressurized at or near its maximum differential, with the greatest potential for damage and injury. The worst-case scenario would be a fuselage breach caused by a bomb or catastrophic structural failure. This is a full-blown emergency, leaving pilots and passengers with only moments to deploy their oxygen masks. The time of useful consciousness after a full decompression at 37,000 feet can be less than 10 seconds.

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Yet even this is by no means a nonsurvivable proposition. All flight decks are equipped with at least one backup oxygen supply, and that supply is tested prior to every departure. According to regulations, each pilot must have nearly instantaneous access to his or her mask and be able to withdraw and deploy it with one hand within five seconds. Masked and able to breathe, the crew would next initiate an emergency descent to a safer height. Flight attendants, meanwhile, have their own emergency supply, including portable walk-around units, while passengers, as everyone knows, are furnished with drop-down masks.

So, the question isn't why the Helios 737 depressurized, necessarily, but why the crew didn't -- or couldn't, or chose not to -- make use of its supplemental oxygen. Don't ask me. Based on what's known to this point, the Helios disaster is one of the strangest I've ever encountered. But things being not immediately explainable -- hardly a rarity when it comes to air crashes -- does not grant a license to sensationalize or distort.

Another reported quote, from Helios spokesman Giorgos Dimitriou, is that the jetliner had "no problems and was serviced just last week." Maybe, though he paints a rather dumbed-down portrait of maintenance protocol. Unscheduled repairs might have taken place "last week," and some routine checks are more thorough than others, but aircraft are serviced and inspected, one way or the other, before and after every flight.

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Dimitriou's statement contradicts widespread reports claiming the Helios 737 had a history of pressurization trouble. An accident waiting to happen, the stories seem to insinuate. But is this so? From a pilot's point of view, not really. The reports speak mainly of a door seal problem, the likes of which, while inconvenient, are seldom if ever lethal. If anything, a known pathology only intensifies the mystery of why the crew didn't or couldn't don its masks. At the time of the crash Helios was operating only three aircraft, and pilots assigned to small fleets come to know the quirks and idiosyncrasies, good and bad, of individual ships. Any erratic system would have been carefully monitored en route, and the preflight inspection of emergency equipment accomplished with particular diligence.

One would hope.

All that, and we haven't gotten to Venezuela yet, where on Aug. 16 a Colombian-registered jetliner went down, killing 160 people. The chartered West Caribbean Airlines MD-80, carrying tourists from Panama to the island of Martinique, crashed after reportedly losing power in both engines.

The prospect of dual engine failure has been analyzed in this column before. It's a remote possibility, but on extremely infrequent occasions -- and this appears to have been one of them -- it happens. Whether the MD-80 was victimized by fuel contamination, sabotage, volcanic ash, or separate and spontaneous mechanical failures remains to be seen. What needs to be reiterated in the meantime is that having lost all engines, a jet will not -- repeat not -- "fall," "drop," "plummet," "spin," "plunge," "nose-dive," or otherwise come flailing out of the sky like a pheasant full of buckshot, as was attributed to the doomed MD-80 in any number of news accounts.

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No matter how large or heavy, an airplane is perfectly able to glide. As airline passengers, all of you have been gliding during idle-thrust descents without knowing it. Granted, the failure of both engines brings on a host of ancillary problems, but the basic descent rate and the accompanying sensations would be no different than what you've felt on routine arrivals into Chicago, Denver or Tokyo.

"Investigators believe the plane fell at a rate of 7,000 feet a minute after its engines failed," read an Associated Press story. That's a pretty severe gradient, if it truly happened, but the reporter's implication is that, sans powerplant, the plane commenced to come down like a stone. Obviously something else was going on. Perhaps the crew lost control, or had begun a temporary emergency descent (no power means no pressurization, for one thing), or both. To wit, in steps Col. Francisco Paz of Venezuela's National Civil Aviation Institute. "The plane went out of control and crashed," Paz concludes, barely 24 hours after the accident. Maybe it did, maybe it didn't. And if so, why?

Lastly, to address one smaller but consistently annoying infraction, we follow the datelines to Palermo, Sicily, close to where that Tunisian turboprop ditched in the Mediterranean three Saturdays ago. That the aircraft, a French-built ATR-72, was identified in many headlines as a "jet," when in fact it was a twin-engine turboprop, is the fault of the local papers and not the Associated Press or any correspondent, but within the article was a common oversimplification:

"The pilot was among five people with serious but not life-threatening injuries," wrote Aidan Lewis of the AP. Elsewhere in the piece were two other references to "the pilot."

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All commercial jets and turboprops with 10 or more seats have a minimum of two pilots. The pilot in command, who sits on the left, is the captain. His or her colleague, seated on the right, is the first officer. The latter is referred to in vernacular as the copilot. Both captain and first officer are fully qualified to operate the aircraft in all conditions. When assigned to multiple legs, they typically alternate flying duties, though the captain is officially in charge at all times. On long-haul runs that include auxiliary crews, five or more "pilots" might be present. The term is misleading and unclear. The public is led to believe only one suitably qualified crewmember is aboard, perhaps assisted by an apprentice copilot who can't actually fly. It'd be better to employ the more specific descriptions of captain and first officer. Or, if you must, captain and copilot.

That concludes Ask the Pilot's style guide.

It's a little unfair to blame a hard-working journalist for going with the quotes supplied by a purported expert, but is it proper that an analyst from Jane's Transport be speaking about the technicalities of aircraft pressurization? Should a military colonel be credited with black box summaries before investigators are even on the scene? One story on the Helios tragedy included a quote from a representative of the Regional Airline Association -- an advocacy group for small carriers based in the United States! Why not an engineer from the airplane's manufacturer? Why not a pilot? For what it's worth, yours truly has volunteered his services numerous times to the AP and other organizations, to no avail.

Probably because of articles like this one.

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Do you have questions for Salon's aviation expert? Send them to AskThePilot and look for answers in a future column.


Patrick Smith

Patrick Smith is an airline pilot.

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