Ask the pilot

Death in the skies: A fatal misreading of an alarm led to the Helios 522 tragedy.



Patrick Smith
September 17, 2005 1:34AM (UTC)

"There is, to this point, no convincing evidence that any of the crashes were the result of negligence, be it shoddy maintenance, substandard training, or anything else." That was me, a week ago, reacting to the attempts of some to demonize small airlines after the spate of recent accidents in Canada, Europe, Asia and South America. It was never my contention that the involved companies -- heretofore unknowns like Helios Airways, TANS, Mandala and West Caribbean -- would be absolved of all wrongdoing, but jumping to conclusions was and remains a bad idea, as does the negative stereotyping of certain types of airlines.

Disclaimer filed, things aren't looking good for the Cyprus-based Helios, whose 737 went down near Athens, killing everyone on board, after apparent pressurization trouble. Reports emerging from Greece portray the unfolding of a grim cockpit comedy, the captain and first officer confused by the sound of a pressure alarm while struggling to communicate. The German captain and Cypriot first officer -- the latter described in some articles as "young" and "inexperienced," which may or may not be meaningful -- did not share a common language and had difficulty understanding one another in English. Both allegedly passed out before the significance of the alarm could be determined. The cause of the initial pressure malfunction, say anonymous sources, was a control knob faultily installed by maintenance staff during the previous evening's inspection.

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Although definitive conclusions won't be reached for many weeks, these latest reports are as close to a post-crash smoking gun as we can hope, or hope not, to see. (Cheers to International Herald Tribune correspondent Don Phillips, by the way, for his accurate, distortion-free story.)

With respect to the communication conflict between pilots, it's natural to suspect a training problem -- a young carrier with insufficient means to recruit or adequately train linguistically compatible crew members. English is the default and official language of worldwide civil aviation, shared -- in varying degrees of eloquence -- by pilots and air traffic controllers in all but the remotest corners of China and Russia. (Yes thats rudely Americentric of us. What do you want, Latin? Esperanto? Besides, though we didn't invent the airline -- for that see the Dutch and Colombians --- we did invent the plane.) Weakness in fluency is sometimes a problem between controllers and pilots -- several years ago, the near collision of two 747s at Chicago's O'Hare was blamed partly on confusion over taxi instructions, American controllers barking critical orders to Chinese and Korean crews -- but rarely do you hear of dangerous misunderstandings between pilots themselves.

Not until transcripts are released can we judge for certain if and to what extent a language barrier affected the outcome of Helios flight 522, and what this might reveal about the training culture at the tiny Cypriot carrier -- potential lessons that similar airlines can ignore at their own peril. It's important to realize that some of the industry's leading names hire pilots from a wide array of cultures and nationalities. The melting pot cockpits of Singapore Airlines and Emirates, to pick two, showcase any number of linguistic backgrounds. The difference, maybe, isn't about which tongue the pilots use but about how they use it. Singapore and Emirates crews endure weeks of training with experienced instructors in world-class facilities on state-of-the-art equipment. Above and beyond a candidate's grasp of English, is the overall qualification regimen at Helios sufficiently rigorous? Does the carrier send its crews to an outside school, as many do? If so, to where and using what sort of syllabus? And so on. Many young and small companies can boast of every facet of their training. As for Helios, from the sound of things we have to wonder.

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A pressurization knob left out of place by a mechanic, while clearly negligent (apply above questions to maintenance personnel), should not entail a fatal catastrophe. From what we know, the misinstalled knob led to a faulty (perhaps even nil) rate of pressurization, in turn triggering an aural cockpit warning as the cabin reached the equivalent of 10,000 feet. Nothing deadly just yet; there was still plenty of time to troubleshoot and possibly rectify the entire problem.

Unfortunately, the pilots misinterpreted the alarm, believing it to be an errant sounding of the takeoff configuration horn. On the 737-300, both systems share the identical claxon, with a critical caveat: On the ground, the noise means wrongly deployed flaps or slats; in the air, it means the cabin altitude has exceeded 10,000 feet. (Either way, the alarm serves as something of a last resort, with the presumption that crews will have, nine times in 10, noticed and corrected things beforehand.)

Boeing, maker of the 737, acknowledges the potential for confusion, but the use of duplicate alarms is not unheard of, and crews are trained to know, or certainly to seek, the difference. With a token bit of 737 experience myself, I have to chuckle morbidly when reading of the Helios pilots' reaction. I vividly recall a simulator session not so long ago, during which our instructor had programmed a gradual depressurization of the cabin, setting off that very same alarm during cruise flight. All was quiet and uneventful until BRAMP, BRAMP, BRAMP, the speaker screamed. The captain and I sat there for a moment staring at each other. "Why the hell is the takeoff horn going off?"

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It wasn't, of course, and after a few moments of scanning the instrument panels, including the pressurization controls, we found the actual culprit. (Wrongly aligned knob or not, separate indicators display the existing level of cabin pressure at all times.) During previous exercises involving a rapid or sudden decompression it was common to hear, and properly interpret, the same horn. Without the accompanying cues, however (a simulated explosion or other violent breach), the sound was confusing. A leaky outflow valve, a balky door seal -- any of several malfunctions can bring about a slow, insidious decompression. Usually they are detected and addressed before the blaring has a chance to start. But, as I experienced firsthand, not always.

Rule 2B in flying: If something is giving you what appears to be screwy information, apply some screwy thinking. If the takeoff configuration horn is sounding when you're at 30,000 feet, stop for a minute. Maybe it isn't the takeoff configuration horn. Snoop around and see. Do not, on the other hand, assume you know what's happening and begin to dig for a circuit breaker in order to silence the warning. That's what the Helios pilots attempted to do after consulting with their maintenance department via radio. While the captain was up looking for the right breaker to quell the noise, his unpressurized jet continuing to climb, he succumbed to hypoxia and passed out. Already impaired, the first officer lost consciousness soon thereafter. On automatic pilot, the plane ascended to 34,000 feet and kept going all the way to Athens, a way point along its route from Larnaca, Cyprus, to a planned destination of Prague, Czech Republic. Over Athens it entered a preprogrammed holding pattern until eventually running out of fuel.

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In addition to a level of incredulity over the egregious and ultimately fatal misinterpretation of the aural alerting system, we're left with a litany of obvious questions: Why were the pilots not able to spot the improperly installed controller knob during their preflight checks? Why did they not catch the lack of increasing pressure during initial climb -- whether on the instrument indicators or simply by feeling it in their ears and sinuses? Why did they fail to draw a connection between deployment of the main cabin oxygen masks, an indication of which was made clear by a cockpit annunciator, and the ongoing siren? Why didn't the maintenance staff, in contact with the pilots over the air, offer a clue as to what might be happening? And when the ceiling masks came popping from their holsters, why didn't the flight attendants summon the pilots' attention, further hinting at the fact that something considerably more dire than a disobedient takeoff alarm was unfolding?

The language issue is bound to be the most oft-cited factor in this accident. The notion of two pilots unable to talk to each other is sensational and, on the face of it, blatantly absurd. But while I see a communication failure for sure, there's considerably more to go with it. The crux of this accident isn't about a failure to understand English, it's about why two qualified 737 pilots, regardless of what languages they spoke or didn't speak, were incapable of deciphering the cause of a yelping cockpit alarm, and why nobody was able to help them.

Is something rotten at Helios Airways? If so, remember that this airline's profile is the exception and not the rule. And if you find it inappropriate, even boring, that I'd devote this space to the details of a six-weeks-old crash that occurred half a world away, bear in mind that the lessons already being sifted from the wreckage will have broad applications worldwide, to the eventual benefit of everyone who flies. (For simulator instructors, sadists that they are, and indeed should be, there are few greater joys than getting hold of the templates of earlier disasters, with which to confound and terrorize unsuspecting trainees. While it's too late for those on Helios 522, you can expect that warning horn to get plenty of play in 737 curricula around the globe.)

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Consider also the series of breakdowns, from the tangible mistake of a misrigged instrument to the subsequent garble of procedure and protocol. None of these things, independently, was enough to kill. Eventually, as the miscues compounded, the bottom fell out. We've seen this pattern before, and one hopes we'll learn from it. The air safety chain, unlike other metaphorical chains, is designed to be safer than its weakest link. Steeped in redundancy and oversight, we rely on technology to catch human error, while somewhat paradoxically we depend on our own intelligence and seat-of-the-pants skills should all that fancy wiring let us down. This time, we discover that rare failure on both sides of the equation.

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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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