Helios Airways Flight 552, a Boeing 737, crashed on the 14th of August 2005 near Athens, leaving no survivors behind. This tragedy occurred after the aircraft failed to pressurize the cabin, causing the crew and passengers to pass out due to a lack of oxygen. As a result, the plane continued to fly on autopilot for more than two hours until it ran out of fuel and crashed. Ultimately, this accident, known as the “Ghost Flight”, became a major case in aviation safety and led to increased security procedures in the industry.
Hypoxia, the silent killer
After the departure from London Heathrow Airport to Lanarca International Airport, the crew reported a frozen door seal and abnormal noises coming from it. This led them to request a full inspection, focusing especially on the pressurisation system.
During these inspections, the ground engineer set the pressurisation system to manual mode but did not switch it back to automatic, creating the condition for what would follow. Subsequently, during the flight from Lanarca International Airport to Prague Ruzyně International Airport with a stop in Athens International Airport, the crew failed to check a few critical points, one being the setting up of the pressurisation system. Due to the aft outflow valve remaining partially open during ascent, the pressure inside the aircraft decreased dangerously fast.
At 12,040 feet, the first alarm sounded; however, because it resembled the sound of the take-off configuration warning alarm, the crew mistook it and did not respond. In the next few minutes, many alarms sounded, but since the crew was already suffering early signs of hypoxia, their response to them was affected. The captain talked to the ground engineer for a few minutes, but during their conversation, he fell unconscious. Many attempts were made to contact the aircraft, none of which were successful, so the Hellenic Air Force sent two F-16s to establish visual contact. As they arrived at the scene, a horrific discovery was made; no one on board was conscious, and the plane was simply flying on its own.
After a while, the flight attendant Andreas Prodromov entered the cockpit and tried to manage the problem. He got to change the route away from civilisation, but unfortunately, the left engine flamed out, resulting in its crash. The plane was found in the village of Grammatiko; no survivors were found in the wreckage.
Small mistakes, tragic consequences
The investigation revealed a chain of failures that led to the crash. A maintenance oversight left the pressurisation system in manual mode, and the flight crew misinterpreted the cabin’s altitude warning horn as a different alarm. As the aircraft continued to climb, both pilots and passengers were incapacitated by hypoxia. Contributing factors included a design flaw in the warning system, which used the same sound for different alarms, and inadequate crew training to recognise and act upon the loss of cabin pressure.
Aftermath: Changes in the industry
After this accident, the industry took drastic measures and introduced several changes to strengthen safety. The cockpit warning systems were redesigned, so the alarms weren’t remixed, reducing the risk of misinterpretation. Pilot training was updated to recognise the effects of hypoxia and pressurisation failures. Crew resource management was also renewed, with a focus on encouraging checklist discipline and cross-checking to catch errors.
Conclusion
The Helios Airways Flight 552 accident showed how small mistakes and skipping steps can escalate to devastating consequences. Beyond the tragedy, the industry improved in many fields such as crew training, safety culture and warning systems. It stands as a reminder that, in this field, every detail matters and must be taken care of with constant vigilance.