In the history of aviation, few incidents are as haunting as the story of Helios Flight 522. On August 14, 2005, what began as a routine flight from Larnaca, Cyprus, to Athens, Greece, unfolded into a tragic and bizarre disaster.
This article delves into the mysterious “ghost flight,” examining the Helios airline, the aircraft, the accident, the subsequent investigation, and the safety changes implemented as a result of this tragic event.
Helios Flight 522 accident
Introduction to Helios Airways
Founded in 1988, Helios Airways was a budget Cypriot airline that operated regular and charter flights connecting Cyprus to various European and African locations. The airline was based at Larnaca International Airport in Larnaca.
The Aircraft: Boeing 737-31S
The aircraft involved in the accident was a Boeing 737-300 that took its first flight on December 29, 1997. It was subsequently leased to Helios Airways on April 16, 2004, and given the nickname ‘Olympia‘. In addition to this Boeing 737-300, Helios Airways’ fleet consisted of two leased Boeing 737-800s and an Airbus A319-100.
Passengers and crew on Helios Flight 522
The Helios Flight 522 was carrying a total of 115 passengers and 6 crew members. The passengers were all citizens of Cyprus and Greece.
Captain Hans-Jürgen Merten was a 58-year-old German contract pilot employed by Helios only for holiday flights. He had 35 years of flying experience and accumulated a total of 16,900 flight hours throughout his career, including 5,500 hours on the Boeing 737.
The first officer, Pampos Charalambous, was a 51-year-old Cypriot pilot who had been working with Helios for the past five years. He had accumulated 7,549 flight hours when Flight 522 took place.
What happened on August 14, 2005?
The flight
Helios Airways was scheduled to depart from Larnaca at 09:00 local time and was bound for Prague, Czech Republic, with a stopover in Athens, Greece.
Prior to Flight 522, flight crew had noted a frozen door seal and unusual sounds from the right back service door. Following an inspection by a ground engineer, a pressurization leak check was conducted. To perform the check without the need for the aircraft’s engines, the pressurization system was set to ‘manual’. Regrettably, the engineer forgot to switch it back to ‘auto’ upon completing the test. This would become hugely significant.
The plane was put back into service, but the current flight crew failed to notice the incorrect pressurization system setting on three separate occasions: before the flight, after-start checklist, and after take-off. Surprisingly, nobody in the cockpit detected the wrong setting either. At 09:07, the aircraft took off with the pressurization system still set to ‘manual’ and the back door outflow valve partially open.
As the plane ascended, the cabin pressure started to decrease and upon reaching an altitude of 12,040 feet, the cabin altitude warning horn went off. The crew mistook this warning for a take-off configuration alert, which indicates that the aircraft isn’t prepared for take-off and only activates whilst on the ground. Unfortunately, both warnings sounded identical, and in this instance, a chain of calamitous events then began to unfold.
The equipment cooling warning lights also indicated low airflow, and the passenger oxygen masks deployed at around 18,000 feet.
The captain contacted the Helios operations center and explained the problem. The same ground engineer who has previously dealt with the pressurization leak asked if the pressurization panel was set to ‘auto’. Unfortunately, it was already too late. The captain was suffering badly from hypoxia due to the loss of pressure.
The plane climbed until it reached an altitude of around 34,000 feet before leveling off. During the time between 10:12 and 10:50, there were nineteen unsuccessful attempts to establish contact with the aircraft. At 10:40, the plane entered the holding pattern for Athens Airport, where it remained for the next 70 minutes, being controlled by the autopilot.
Interception and communication attempts
At 11:05, the Greek military sent two F-16 fighter jets to make visual contact with the ‘ghost flight’ (the name given to a situation where an aircraft, while airborne, experiences an accident that incapacitates both the crew and passengers). The fighter jets successfully intercepted the plane at 11:24 and noticed that the first officer was motionless at the controls, while the captain’s seat was empty. Also, they saw oxygen masks hanging down within the passenger cabin.
The events that followed were increasingly dramatic. At 11:49, Andreas Prodromou, a flight attendant, was seen occupying the captain’s seat, utilizing a portable oxygen supply to remain conscious. Despite lacking qualification to fly the Boeing 737, Prodromou briefly acknowledged the F-16s before the left engine flamed out due to fuel exhaustion, prompting the aircraft to initiate a descent. Remarkably, Prodromou skillfully steered the plane away from Athens towards a rural area, preventing any ground casualties.
The crash
The right engine flamed out 10 minutes after its counterpart and the aircraft crashed down at 12:03 into the hilly terrain near Grammatiko village, 20 miles northwest of the Athens International Airport. 121 souls were lost. Tragically, it was later determined that crash victims would still have been alive at the time of the crash.
Helios Flight 522 investigation
Flight data recorder and cockpit voice recorder
Andreas Prodromou was a trained pilot, but not trained to fly a Boeing 737. The cockpit voice recorder (CVR) revealed that he made a call of “MAYDAY, MAYDAY, MAYDAY, THIS IS HELIOS FLIGHT 522 ATHENS”. Unfortunately, it was never received, as the radio was still tuned to Larnaca rather than Athens.
The main factors that led to this crash were identified as a failure by the pilots to spot that the pressurization system was set to ‘manual’, failure by the crew to identify associated problems, and other warnings that led to hypoxia.
Previous pressurization problems
In the lead-up to the crash, the airplane’s environmental control system had undergone maintenance or checks on seven separate occasions. Additionally, passengers on other Helios Airways flights had documented issues with the air conditioning.
Criminal proceedings and legal implications
Relatives of the crash victims filed a suit against the Cypriot government for negligence leading to this disaster. There was also a lawsuit filed against Boeing for using an identical alarm to identify different types of issues.
Helios flights were terminated on November 7, 2006, as the company’s financial assets were frozen by the Cypriot government following the decline of its reputation after the Helios Airways Flight 522 tragedy.
On December 23, 2008, Helios Airways and four of its officials in Cyprus were charged with 119 counts of manslaughter, as well as causing death by recklessness and negligence.
Safety changes implemented
Subsequent National Transportation Safety Board (NTSB) recommendations were aimed at improving crew training in regard to recognizing warnings associated with pressurization problems and configuring the air conditioning/pressurization system correctly before the takeoff. Also, they sought to improve maintenance procedures.
Additional cockpit warning lights were fitted as crucial safety features to help differentiate between take-off configuration and pressurization issues in Boeing 737 aircraft models from −100 to −500.
Similar incidents to Helios Flight 522
1999 South Dakota, USA Learjet 35 crash
On October 25, 1999, a Learjet 35 carrying six people crashed in Edmunds County, South Dakota, after flying uncontrolled for four hours and covering a distance of 1,500 miles. This occurred due to everyone onboard being incapacitated by hypoxia resulting from an unspecified depressurization. The aircraft had departed from Orlando, Florida, and had been bound for Dallas, Texas.
2000 Burketown, Australia Beechcraft Super King Air 200
On September 4, 2000, a Beech Super King Air turboprop with eight people on board took off from Perth, Western Australia, bound for Leonora. Initially, communication with the aircraft was fine. However, the pilot’s speech gradually deteriorated, eventually leading to him apparently losing consciousness. The aircraft flew for about five hours before running out of fuel and crashing. This tragic incident was also widely referred to as a ‘ghost flight’. The specific cause of depressurization remains unknown.