Helios Airlines Tragedy Clues Emerge

Boy, this sounds really awful (BRAMP! BRAMP! BRAMP!):

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.

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. ... 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.

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?"

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.

...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.

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 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.

...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.