What Caused The Crash Of Helios Airways Flight 522?
Basically, both the pilots have to check the controls one by one, according to a checklist, and ensure that they are on the correct settings. But even after this checklist, the pilots do not switch
the pressurization system from auto to manual. At 6:07 am, the flight takes off and after takeoff, the pilots have to execute an after-takeoff checklist, and the very first item on this checklist was to check the pressurization system. But surprisingly even this time it is left in manual mode. But how can so highly experienced pilots make such a big mistake?
Even after checking three times, why didn’t they succeed in bringing such an important switch in the correct position? The answer to this, is human psychology. According to the investigators, the pilots that day became victims of "the expectation bias."
Having expectation bias a person sees or hears that he usefully expects to see or hear, while the reality is something else so, generally no one used to disturb the pressurization mode And it used to always stay on auto mode. That's why the minds of the pilots had strongly expected the pressurization to surely be on auto.
So strongly, that even after checking the knob thrice, assumed that it was on auto itself. Investigators also found, when pressurization was in manual mode, it was indicated by a green light, and a green light generally does not indicate an incorrect setting. In place of green light, had there been a red light to indicate manual mode, the pilots might have realized something was wrong.
Apart from this, the investigators found that the design of the checklist was also very complicated. In that the pressurization system setting was clubbed with various other settings. And clubbing multiple settings together increases the chances of missing a setting or two.
Finally, it was also found that it was mentioned in the training records of the first officer that during training, he did not follow the SOPs properly. While executing the checklist, used to make mistakes. Used to overreact on non-normal situations and used to lose confidence. And for these reasons, even after checking thrice, the pilots did not change the pressurization from manual to auto. But this was a story just until takeoff.
Even after this, the pilots had opportunities to rectify their mistake. But they didn't do that. 5 minutes after takeoff, the plane reaches an altitude of 12,000 feet and just then the takeoff configuration warning sound of the plane starts beeping. Both pilots get confused because the takeoff configuration warning occurs when the plane is on the ground and not ready for takeoff.
Actually, it was not a takeoff configuration warning at all, but was a cabin altitude warning. Due to the pressurization system being on manual, the plane's air pressure was constantly decreasing, and the cabin altitude warning occurs
when the air pressure is low for the plane's altitude. Coincidentally, takeoff configuration and cabin altitude, both these warning sounds, sounded absolutely identical. And that's why the pilots got confused. After 2 minutes the pilot comes in contact with the ground engineer. And tells him about the takeoff configuration warning.
During this time, the plane being on auto pilot, also keeps moving forward, and its altitude also keeps increasing. On reaching an altitude of 14,000 feet, due to the low air pressure, the oxygen masks of passengers get released.
And the indication of release of oxygen mask is also received by the pilots in the cockpit. But at the same time, due to the low air pressure, the equipment cooling systems of the plane also stop working. Because due to low air pressure, they do not get enough air to cool the equipment. The pilots also get equipment cooling off warning.
Due to the combination of these two warnings, pilots unfortunately only pay attention to the equipment cooling off warning. Had the pilots at this time, seen the indication of the passenger oxygen mask released, they would have understood that the cabin air pressure has gone down.
And when there is a problem of low air pressure, the pilots have to immediately apply the portable oxygen mask they have, so they can remain conscious and control the plane and reduce its height. But they do not use the oxygen mask, because the pilots never get to know that the air pressure is getting low.
Instead, they think that the whole problem is of equipment cooling. The captain feels the equipment is overheating due to overflow of current That's why the captain asks the ground engineer about the location of the plane’s circuit breakers, so that he can use them to reduce the overflow of electricity and prevent the equipment from overheating.
The ground engineer tells him that the circuit breakers are behind the captain's seat, after that contact with the pilot is lost. The captain rises from the seat to retrieve the circuit breakers and faints from hypoxia.
Similarly, the first officer also becomes unconscious. Later, during the investigation, the ground engineer tells that while talking to the captain, his words were not making much sense. He looked quite confused. Investigators believe that this may have happened because my that time the captain already would have started having symptoms of hypoxia.
Well in the meantime, the plane, set on autopilot, while going up in height reaches an altitude of 34,000 feet. And continues on towards Athens. Within 12 minutes, the oxygen cylinders of the passengers also start emptying, and one after the other, all the passengers faint. Well during this time the plane set on auto pilot reaches a height of 34,000 feet, levels and moves towards Athens.
About an hour after all this, the plane reaches above Athens International Airport and begins to circle in a holding pattern. Two fighter jets come and report the situation of the plane and shortly after, a man is seen entering the cockpit. That person is none other than the flight attendant, Andreas Prodromou, who using the emergency portable oxygen supply available on the flight, remains conscious until entering the cockpit.
Andreas held a UK commercial pilot's license, but was not qualified to fly Boeing's Helios 522. Still, he tries to control the plane, but the plane's fuel runs out. He signals to the pilot of the F-16 that the plane is going down.
Shortly after which the plane starts descending rapidly. Andreas is unable to land the plane safely, but he manages to crash the plane away from the urban area of Athens into a mountainous area. So, this was the tragic story of Helios 522.
Due to the wrong positioning of a small switch and several unfortunate coincidences that followed, this plane crashed. 121 people lost their lives and it became the deadliest plane crash in the history of Greece.
After this accident, many steps were taken in Boeing and the aviation industry. Pilot training was improved. The plane's warning systems were improved and the pre-flight and after takeoff checklists were simplified.
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