The Tragic Story of Helios 522

On August 14, 2005, a passenger aircraft, Helios 522 took off from Larnaca, Cyprus heading to Athens, Greece, expecting a normal hour-and-a-half journey. Onboard were 121 people: 115 passengers, four cabin crew members, and two experienced pilots. However, the plane landed in history as the deadliest plane crash in the history of Greece, due to an overlooked flight setting and a host of unfortunate coincidences.

The Flight Begins

A mere 25 minutes after takeoff, when the plane reached an altitude of 34,000 feet, instead of contacting Athens air traffic control, the plane began rotating in an unresponsive holding pattern. No response came from the cockpit, triggering alert procedures which sent two F-16 fighter jets to make a visual inspection. These fighter jets reported zero external damage to the plane, but gave a chilling description of the state of the passengers and the cockpit. Passengers were motionless with oxygen masks on, the captain's seat was empty, and the first officer was frozen in a forward-leaning position.

Meanwhile, the onlookers saw an unknown individual enter the cockpit, put on the captain's headphones, and start operating the controls. Despite efforts by the F-16 to guide a landing through hand signals, the Helios 522 sadly crashed, resulting in the death of all on-board.

To unravel the what, why, and how behind this tragic event, we're going to time travel to 8 hours prior to the flight's departure.

Eight Hours Prior

Eight hours before Helios 522's tragic flight, the plane had just arrived from London. Upon landing, the ground team received reports from the cabin crew of an issue with the right service door seal. Cabin door seals are key components of maintaining cabin air pressure. Alan Irwin, a 44-year-old ground engineer, inspected the door and conducted a cabin pressurization leak check to ensure no air was leaking through.

The Forgotten Manual: Showcasing Human Dependence on Auto

Here's where the first misstep occurred. For the leak check, Irwin had switched the pressurization system from auto to manual mode. After the check, in an unfortunate oversight, he forgot to switch it back to auto mode, a setting crucial during takeoff. This left the system stuck in the manual setting. Despite having the responsibility of ensuring the auto setting of the pressurization system in their pre-flight procedure checklist, both the highly experienced pilots also overlooked this critical detail.

The reason behind such an oversight by trained and experienced pilots was attributed to expectation bias, which is essentially seeing what one expects to see and not the reality. With the pressurization mode normally left untouched and on auto, the pilots didn't suspect it to be in any other mode. Further, the inconspicuous green light indicating manual mode rather than a more alarming red infringed the perception that everything was normal. Multiple assessments failed to catch this manual setting, signaling a failing in both humans and the system's design.

14,000 Feet: When Confusion Began Leading to Disaster

Five minutes post-takeoff, at an altitude of 12,000 feet, confusion ensued in the cockpit. A warning sound started beeping, which resembled the on-ground take-off configuration warning. However, this was not an actual take-off warning, but rather the cabin altitude warning, signaling low cabin air pressure. The mix-up occurred due to the unpleasant coincidence of both warnings having near identical sounds. With the cabin pressure decreasing, passenger oxygen masks were automatically released at 14,000 feet. But, due to concurrent warnings, including an equipment cooling off warning, the pilots overlooked this critical signal.

At this point, a lack of oxygen, also known as hypoxic hypoxia, started affecting the crew members. Hypoxia impaired the pilots' cognitive capabilities, resulting in further confusion, and eventually, loss of consciousness. However, since the plane was on autopilot, it continued on their planned route. The oxygen supply depleting and eventually running out caused all passengers to lose consciousness due to hypoxia.

The Holding Pattern Leads to Hope

Now cruising on autopilot, Helios 522 reached the holding pattern above Athens International Airport. At this point, fighter jets arrived to assess the situation. Shortly thereafter, a spark of hope appeared when a man was spotted entering the cockpit. This individual turned out to be a flight attendant, Andreas Prodromou, who managed to stay conscious using an emergency portable oxygen supply. Though not qualified to fly a Boeing 737, Prodromou was a commercial pilot. He tried controlling the plane, but it was only a matter of time before the plane's fuel ran out. Unable to land safely, Prodromou guided the plane to crash in a mountainous area away from any urban settlements, avoiding further casualties.

Lessons Learnt: Improvements Post-Accident

In the aftermath of this tragedy, several amendments and improvements were made in pilot training and flight checklist procedures. Mobile checklists were simplified and the warning systems of the aircraft were improved. This tragic event led to a step forward in safety regulations to prevent such accidents from reoccurring.

Walking away with the understanding that a small misstep can snowball into catastrophic outcomes, the tragic story of Helios 522 leaves us with a profound thought of checking and reassessing every small detail in high-stakes scenarios like aviation.