Pressure drop in Boeing 737: ghost flight Helios 522: 121 people flew unconscious to their deaths

The crash of a private Cessna Citation plane over the Baltic Sea off the Latvian port of Ventspils is a mystery to investigators.

Pressure drop in Boeing 737: ghost flight Helios 522: 121 people flew unconscious to their deaths

The crash of a private Cessna Citation plane over the Baltic Sea off the Latvian port of Ventspils is a mystery to investigators. The machine was on its way from Jerez de la Frontera in southern Spain to Cologne on Sunday, but did not land. Contact between the ground stations and the crew had already broken off. Therefore, fighter jets from France, Germany, Denmark and Sweden had come out to pursue the plane until it lost altitude due to lack of fuel and fell into the sea.

Experts suspect that there was a pressure drop in the cabin of the plane, after which the occupants fell unconscious. In such an incident, oxygen masks are actually used, which are available to both the cockpit crew and the passengers.

Normally, the crew tries to navigate the aircraft to a low altitude by requesting air traffic control, because at a jet's cruising altitude of around 11,000 meters there is no chance of survival due to the lack of oxygen.

The private jet case is reminiscent of one of the worst plane crashes in Europe a few years ago. On August 14, 2005, a Boeing 737-300 of Cyprus' Helios Airways took off from Larnaca, and the crew of six was supposed to carry 115 vacationers back to Prague via Athens.

But shortly after take-off from Cyprus, the German flight captain Hans-Jürgen Merten, a former Interflug pilot, radioed a problem with the cooling system. Later, the radio contact with the machine breaks off completely. F-16 fighter jets from the Greek Air Force then take off because the government fears a possible hijacking or an act of terrorism. The Boeing turns holding patterns near Athens.

One of the F-16 pilots can see that the cockpit seat is vacant and the co-pilot has collapsed over the control column. One after the other, both engines failed, and a short time later the passenger plane crashed into mountainous terrain about 30 kilometers north-west of Athens Airport.

None of the 121 people on board survived the crash. Many of them may have been unconscious before the impact due to hypoxia, the lack of oxygen in the blood caused by the drop in pressure in the cabin. If the blood is not sufficiently supplied with oxygen through respiration, there is a clouding of consciousness, then fainting and even death.

During the investigation of the aircraft accident, it turned out that a rotary switch for the cabin pressure control was not set to "automatic" but to "manual". The crew had not noticed this when working through the checklists before take-off. In addition, they did not correctly recognize important acoustic warnings in the cockpit. The Greek Ministry of Transport also criticized the lack of oversight by the Cyprus aviation security authority.

In the weeks before, there had already been several problems with the aircraft's air conditioning system. On the evening before the accident flight, a pressure test of the cabin was carried out on the basis of a tip from the pilots during maintenance. The pressure test simulated the conditions that prevail during a flight. But he remained unconvinced.

For this test, the switch had been switched to "manual" by the technicians and then not reset to "automatic", which nobody noticed the following day.

Also read:

- Crossing courses - the Überlingen air disaster with 71 dead on July 1, 2002

- When Uwe Barschel narrowly escaped death

- 148 dead near Königs Wusterhausen: crash of the Interflug Ilyushin Il-62 50 years ago

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