How One (Wrong) Switch Crashed Helios 522?

PLAN CRASHED DUE TO THE WRONG PUSH OF A BUTTON

On August 14, 2005, at 6:07 am,

a passenger aircraft, Helios 522 takes off from the city of Larnaca, Cyprus. This aircraft is going to the city of Athens, in Greece. Which is going to take about 1-1/2 hours. It has total of 121 people on board, In which there are 115 passengers, four cabin crews, and two pilots. About 25 minutes after takeoff, at 6:23 This aircraft reaches an altitude of 34,000 feet And is flying on its decided path. A about 1-1/2 hours after takeoff, at 7:37, the plane approaches at Athens International Airport and starts rotating in the holding pattern.

The holding pattern is an oval path, in which any plane awaiting permission to land, has to keep circling. Athene ATC contacts Helios 522 several times and tries to grant the landing permission, but they don't get any response and the plane keeps rotating in a holding pattern without any contact. 

An alert is issued after 15 minutes and two F-16 fighter jets of the Hellenic Air Force are sent to check the air craft. The two approach the F-16 aircraft and report some startling things. They report negative external damage to the plane. But the captain's seat is empty and the first officer is leaning forward and not moving at all.

Apart from this, no passenger is reacting on seeing the F-16 jets. Many passengers are sitting with oxygen masks on but they too are absolutely motionless. Shortly thereafter, the F-16's pilot sees a man without any oxygen mask entering the cockpit and takes the captain's seat. He puts on the headphones and is seen using the controls placed on the front. The F-16 pilot asks the person to land through hand gestures, 

In response to which, the person sitting in the captain's seat points down with his hand and shortly after, the Helios 522 aircraft starts falling rapidly and crashes. This accident takes the lives of all 121 people aboard the plane and leaves behind some profound questions. After all, what happened in those 1-1/2 hours after takeoff that none of the passengers and the first officer were absolutely motionless?

Why was the captain's seat empty, who was the man who entered the cockpit, and what was he doing there? To know the answers to these questions, we have to go back 8 hours. At 1:25 in the morning, the same Helios 522 aircraft lands in Cyprus after flying 2-1/2 hours from London. The crew of this flight observes some problem in the plane.

They report to the team of ground engineers that the plane's right service door seal was getting freezed and the door was also making noise during the flight. It is very important for all the doors in a plane to close properly, otherwise, the air pressure of the cabin may leak. But what is this cabin air pressure?

To understand this accident deeply, we have to first understand the cabin air pressure. You must have seen photos that many mountaineers, when climb thousands of feet high mountains, such as Mount Everest, they need oxygen mask for survival.

This is because, at that height, the air pressure is very low. Air is made of three components. Oxygen, nitrogen and argon. In which the share or concentration of oxygen is 21%. But as our altitude or height increases, The concentration of oxygen in the air starts decreasing. Meaning oxygen molecules keep decreasing.

Due to which, even after breathing normally, we get less oxygen than before. On the summit of Mount Everest at 29,000 feet high, the air pressure is three times less, causing the risk of hypoxia. In hypoxia, the human body parts are not able to function properly and the person becomes unconscious and eventually can even face death. And that's why mountaineers need oxygen masks and oxygen tanks. But most commercial aircrafts fly way above Mount Everest at an altitude of 37,000 feet.

Even then, the passengers sitting in the aircraft are able to breathe easily without any oxygen mask. But how? Due to cabin air pressurization. The engines of the plane draw the air from the front, compress it, and throw it back rapidly, due to which the plane moves forward and some compressed air made from these same engines is pumped inside the plane, so that the air pressure inside the plane be maintained. Cabin pressure is controlled by an outflow valve. 

When the air pressure is more than needed, the outflow valve is opened, so that the air pressure can decrease and vice versa and this exactly is cabin air pressurization system, which ensures that there is enough air inside the plane for the crew and passengers to breathe.

Now coming back to the story. A 44-year-old ground engineer, Alan Irwin, gets the responsibility of inspecting Helios 522's door. He does do a visual inspection of the door and then does a cabin pressurization leak check to see if air pressure is leaking through the door.

At this time the plane was on the ground and the engines of the plane were off. So, without using the engines, the ground engineer uses the auxiliary power unit, i.e. APU, to pressurize the plane. APU provides energy to any plane when the engines of the plane are shut. Also, for this test, the ground engineer switches the pressurization system from auto to manual mode.

In the whole test, the ground engineer does not see any problem in the plane or the door and he clears the plane for the next flight. But he forgets one thing. According to rules, the ground engineer has to put the pressurization system back in auto mode. Actually, at the time of a plane’s takeoff it is very important for the pressurization system to be in auto mode so that according to its altitude the plane can automatically maintain the cabin's air pressure. 

But the ground engineer mistakenly leaves it in manual mode, but this was not the only mistake. Rather, this was only the beginning of the mistakes. Around 5:00 p.m. the four cabin crew and two pilots of the Helios 522 hold a pre-flight meeting and then board the plane to set it up.

The captain of this flight was 58-year-old Hans-Jurgen Merten. Who had total experience of 35 years and 16,900 flight hours. And the first officer was 51-year-old Pampos Charalambous, who had an experience of about 17 years and 7500 flight hours.

To prepare the plane for takeoff, both the pilots have to perform some duties, Which is called a pre-flight procedure. During this pre-flight procedure, the first officer had a duty to insure that the pressurization mode was on auto, but the first officer leaves it in manual mode. After the pre-flight procedure, pre-flight checklist has to be executed. 

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