A switch on a plane caused all passengers and pilots to fall into a coma, killing 121 people.

Two fighter jets were sent up to check what was happening to Helios Flight 522 .

"Helios 522, is anyone there?"

Desperate questions echoed over the cockpit radar over Greece on August 14, 2005. This was an air disaster unlike any other. The Boeing 737, packed with passengers, circled the sky on autopilot for more than an hour. The plane had no one at the controls, the captain was gone, the co-pilot was slumped over, and all the passengers were asleep.

What happened on Helios Airlines flight 522?

"Ghost Flight"

Helios Flight 522, a Greek airline , was flying with 115 passengers from Cyprus to Prague Airport in the Czech Republic. The plane departed smoothly at 9:07 a.m., just a few minutes late.

The captain and co-pilot were both experienced pilots. The flight attendant crew consisted of four members, including the engaged couple Andreas Prodromou and Haris Charalambous.

Andreas had just completed his pilot training in the UK, and planned to change his career to match his dream, then marry his girlfriend Haris. Unfortunately, both of these dreams did not come true.

The pilot couple on flight Helios 522. (Photo: Simpleflying).

A few minutes into the flight, the warning siren began to sound. This was a signal for the crew to lower altitude, but the captain ignored it, mistaking it for an error warning. In the minutes that followed, the captain's interactions with air traffic control became increasingly sparse.

At 9:20 a.m., as the plane approached 100,000 feet, no further communication was received from Flight 522. The Boeing circled the coast of Athens on autopilot. Air traffic controllers tried to contact the plane for 70 minutes, but no one responded. The theory was that Flight 522 was being controlled by terrorists.

The Athens Rescue Coordination Center sent two fighter jets to check on the Boeing as it circled in the sky. (Illustration photo: Wikimedia Common).

At 11 o'clock, the Athens rescue coordination center decided to make a daring intervention. Two Greek Air Force fighter jets were scrambled and flew up to check the Boeing's condition. From the windows, the fighter pilots saw a very strange sight.

All the passengers of Flight 522 were asleep, the captain was gone and the co-pilot was lying motionless on the dashboard. But there was one conscious man still walking in the passenger cabin, he went straight to the cockpit and sat in the captain's seat. He was flight attendant Andreas Prodromou , the only conscious person on the flight.

Passed out on the plane

Later investigations showed that at the time the plane lost contact with the air traffic control station, all passengers and pilots were unconscious due to lack of oxygen in the cockpit . The reason Andreas Prodromou was still conscious was because he regularly practiced diving, so his lung capacity was larger than normal people, and he also understood how to use the oxygen supplies on the plane.

Andreas Prodromou entered the cockpit with an emergency access code and tried to wake the pilots but was unable to do so. Andreas had a license to fly small planes but flying a Boeing 737 was too much for him. It is believed that he tried his best to steer the plane away from cities so as not to cause too many casualties.

The Boeing crashed into a hill near Athens, Andreas Prodromou tried to steer the plane away from residential areas. (Photo: FAA).

In the final minutes, the plane was running low on fuel and the left engine had stopped working. The flight attendant repeatedly sent a Mayday distress signal to the radar, but unfortunately he chose the wrong frequency.

Andreas looked out the cockpit window at the two fighter jets. He gestured downward. The right engine had caught fire, and the plane was out of fuel. The Boeing 737 had crashed into a hill near Athens. All 115 passengers and six crew members were killed. It is believed that the passengers were alive, just unconscious at the time of the crash.

The cause of the accident was determined to be that during maintenance of the aircraft, the ground engineer adjusted the knob to manual pressurization mode and forgot to select automatic pressurization mode as usual.

The ground engineer selected manual pressurization mode (MANUAL) instead of automatic pressurization (AUTO). (Illustration photo: FAA)

When boarding the plane, the pilot did not realize this. He accidentally ignored the error alarm, causing the plane to not be pressurized during the flight. Pressurization is an important system , if the plane is not pressurized, the air inside will be very thin, not enough oxygen, so everyone will fall into a coma . It seems that the passengers were not even informed to use oxygen masks in time.

The disaster of "ghost flight" 522 was determined to be due to errors in a series of stages from maintenance , pilots to air traffic control when the air traffic manager was absent, only the staff on duty that day. Helios Airways faced many lawsuits and declared bankruptcy in 2006, just 1 year after the accident.

This is a big lesson for airlines in ensuring compliance with the principle of flight safety responsibility to avoid disasters like the story of Helios Airways.