The mystery of Flight 522

In August 2005, Helios Airways Flight 522 took off from Larnaca, Cyprus, to fly to Athens. Although radio contact was lost minutes after departure, the Boeing 737 nevertheless flew along its flight plan route for 2 hours to Athens where it began to circle at 34,000 feet. Alarmed at the prospect of a 9/11 scenario, the Greek Air Force launched a fighter jet to intercept the airliner.

The fighter pilot came alongside and saw that the captain's seat was empty and that the co-pilot appeared slumped over the controls. Soon after, the 737 began to descend and a few minutes later crashed with the loss of all 121 on board.

It didn't take the investigators long to work out that the aircraft's pressurisation system had failed and that, as it had climbed out of Larnaca, the pilots had succumbed to oxygen starvation. The autopilot had nevertheless guided the aircraft along its programmed route to Athens. But lacking a human instruction to descend to the airport, the autopilot put the plane into the holding pattern where it circled until it ran out of fuel.

As the investigation developed two further key facts emerged: (1) the plane's pressurisation system had been tested immediately prior to the fatal flight but the engineer had failed to reset the system to "Auto" meaning that it did not automatically activate on the fatal flight; (2) a low pressure warning horn sounded in the cockpit of Flight 522 as it climbed out of Larnaca but the pilots didn't recognise the warning for what it was because it was the same sound as an alert to a situation much more familiar but which can only happen on the ground: the pilots believed they were dealing with a rogue warning but their attempts to troubleshoot were barking up the wrong tree and they succumbed to hypoxia before they realised their error.

So who was to blame? The engineer for failing to reset the pressurization switch to "Auto"? Boeing for designing the 737 with a pressurisation warning which could be mistaken for something else? Or the pilots for misdiagnosing the problem?

I was fairly certain the blame lay with the pilots until I fell into a similar trap last night involving a piece of equipment almost as complex to operate as a Boeing 737-300, namely a Hoover HNF6127-37S front loading washine machine.

Carol comes through yesterday evening and reports that the washing machine wasn't going on to its spin cycle. The last time the w/m didn't do what it was supposed to, I pulled out the filter and found a coin in it, the removal of which caused the machine to start working perfectly again. This time, I opened the filter and pulled out two coins and found a third jammed in the hose. I spent about 15 minutes before I managed to dislodge it with a pair of pliers as ingeniously suggested by Carol. But although that rendered us a total of €1.25 better off, it did not place us back in possession of a working washing machine.

Around about the elapsed time that would have seen us passing out from hypoxia had we been the crew of an unpressurised 737 climbing to cruising altitude on autopilot, the kitchen voice recorder at 5 Rua da Assomada picks up First Officer Duncan saying "Do you think the coins might be a red herring?". Captain King replies "Dunno, possibly, I can't think what else to try ..." And a few minutes later the voice of the F/O is heard saying "Oh look - the spin speed dial is at zero! I must have accidentally nudged it out of place when I was cleaning it yesterday ..." Problem solved.

 As can be seen, the Hoover HNF6127's control panel (with spin speed dial outlined) makes a 737's pressurisation control panel look the very model of simplicity by comparison (all you have to do is set it to "AUTO")

So whose fault was the machine machine incident, albeit happily resolved without so much as a lost sock? Carol's for accidentally setting the spin speed to zero? Hoover's for designing something as daft as a spin speed of zero (WTF?) Or mine for barking up the wrong tree of the coins in the filter and not scanning the instrument panel to look for another more obvious solution? Not so simple to answer, is it?

Pilots, operators and manufacturers of commercial airliners and lawyers representing the aforementioned please take note.