Posted by Kayleigh DeMace on January 18, 2017

Buckle up readers. This one is creepy and quite sad.

Imagine sitting comfortably in your seat during takeoff, everything seems to be going well, then the oxygen masks drop. You're up high, but the plane is still ascending. No word from the cockpit.

Imagine the absolute confusion and terror.

Those on the ground thought it might be a possible hijacking. But what really happened?

Helios Airways Flight 522 Takes Off

On a warm summer day in 2005, Flight 522 took off from Larnaca, Cyprus to Athens, Greece for a flight a little over one hour long. There were 115 passengers on board and a crew of 6.

In the cockpit, the pilot, Hans-Jürgen Merten, and copilot became confused not long after takeoff. They were unable to figure out why the takeoff configuration alarm went off and the equipment cooling warning lights went on.

Unaware that the oxygen masks fell in the cabin, they radioed the Helios operations center and spoke with a ground engineer-the same one who had performed the pressurization leak check.

Pilot: "The ventilation cooling fan lights are off."

Engineer: "Can you confirm that the pressurization panel is set to AUTO?"

Pilot: "Where are my equipment cooling circuit breakers?"

This was the last transition from Flight 522. The plane continued to fly and two F-16s were sent to investigate. They found that the captain was not in the cockpit and the co-pilot was slumped over in his seat and unresponsive. No passengers seem to signify they saw the jets.

Then, the jet pilots spotted movement in the cockpit. No words were exchanged, but the person did see the jets. Not long after, the plane crashed in the hills of Grammatiko, 25 miles from Athens.

The crash of Flight 522 was the 69^th crash of a Boeing 737 since they were released in 1968. There were 121 fatalities, making this tragedy the deadliest in Greece's aviation history and the fourth deadliest crash of Boeing 737-300s.

After the crash, the investigation began to determine the cause. At first, they couldn't find the cockpit voice recorder. Questions were left unanswered for some time, until a few key pieces of the plane were uncovered from the wreckage, including the cockpit voice recorder and a control panel.

The official ruling? Lack of cabin pressure and oxygen rendered Flight 522 a ghost plane.

Asphyxiation

Officially, this is what is believed to have happened. The cabin was not pressurized before takeoff, likely due to issues the plane experienced earlier. Therefore, those aboard the plane passed out due to a lack of oxygen in the cabin.

The crew who flew the same plane earlier that morning reported a frozen door seal and noises coming from the aft service door on the plane's right side. The door was fully inspected and followed by a pressurization leak check. However, after performing the leak check in the manual setting, the settings were never set back to -AUTO.-

When the flight took off, the cabin was never properly pressurized and the aft valve was likely partially open. When the alarm went off, it was actually the cabin altitude warning horn, which the crew had mistaken for the take-off configuration warning. The two alarms sounded similar.

The man who jet pilots spotted in the cabin was a flight attendant who was able to remain conscious by using a portable supply of oxygen. He likely attempted to save the plane, but without success. When the crew and passengers passed out due to lack of oxygen, it is believed that the plane continued to climb in altitude and fly on autopilot until both jets shut off once the plane ran out of fuel.

Another Possible Cause?

Do you believe in ghosts? Some believe this might have been a haunted aircraft. Some think that the alarms went off because of spiritual interference, not unlike what happened in Supernatural's Phantom Traveler.