Helios Airways Flight 522



Helios Airways Flight 522 was a flight from Larnaca, Cyprus to Prague, Czech Republic with a stopover to Athens, Greece. It crashed on 14 August 2005, following loss of pressure that incapacitated the crew, killing all 121 passengers and crew on board. The aircraft was left to fly on autopilot until it ran out of fuel and crashed near Grammatiko, Greece. It was the deadliest aviation accident in Greek history.

Background
The captain of the flight was Hans-Jürgen Merten, a 59-year-old German contract pilot hired by Helios for holiday flights, who had been flying for 35 years (previously for Interflug before 1990) and had accrued a total of 16,900 flight hours, including 5,500 hours on the Boeing 737. The first officer was Pampos Charalambous, a 51-year-old Cypriot pilot who had flown exclusively for Helios for the past five years. He has 7,549 flight hours throughout his career, with 3,991 of them on the Boeing 737.

Accident
That morning, the aircraft arrived from London and the previous flight crew had reported a frozen door seal and abnormal noises coming from the right aft service door. They requested a full inspection of the door. The inspection was carried out by a ground engineer who then performed a pressurization leak check. In order to carry out this check without requiring the aircraft's engines, the pressurisation system was set to "manual". However, the engineer failed to reset it to "auto" after completing the checking.

After the aircraft was returned into service, the flight crew overlooked the pressurisation system state on three separate occasions: during the pre-flight procedure, the after-start check, and the after take-off check. During these checks, the flight crew failed to notice the incorrect setting. The aircraft took off at 9:07 with the pressurisation system still set to "manual", and the aft outflow valve partially open.

As the aircraft climbed, the pressure inside the cabin slowly decreased. As they passed 12,040 feet (3,670 m), the cabin altitude warning horn sounded. The warning was supposed to have prompted the crew to stop climbing, but the crew mistook it for a take-off configuration warning, which signals that the aircraft is not ready for take-off, and can only sound on the ground. The alert sound is similar for both warnings.

In the next few minutes, several warning lights on the overhead panel in the cockpit illuminated. The equipment cooling warning lights came on to indicate low airflow through the cooling fans (a result of the decreased air density), accompanied by the master caution light. The passenger oxygen light illuminated when, at an altitude of approximately 18,000 feet (5,500 m), the oxygen masks in the passenger cabin deployed.

Shortly after the cabin altitude warning sounded, the captain radioed the Helios operations centre and reported "the take-off configuration warning on" and "cooling equipment normal and alternate off line". He then spoke to the ground engineer and repeatedly stated that the "cooling ventilation fan lights were off". The engineer (the one who had conducted the pressurization leak check) asked "Can you confirm that the pressurization panel is set to AUTO?" The captain, who was already starting to feel the initial symptoms of hypoxia, disregarded the question and instead asked in reply, "Where are my equipment cooling circuit breakers?". This was the last communication with the aircraft.

The aircraft continued to climb until it leveled off at FL340, approximately 34,000 feet (10,000 m). Between 09:30 and 09:40, Nicosia ATC repeatedly attempted to contact the aircraft, without success. At 09:37, the aircraft passed from Cyprus flight information region (FIR) into Athens FIR, without making contact with Athens ATC. Nineteen attempts to contact the aircraft between 10:12 and 10:50 also met with no response, and at 10:40 the aircraft entered the holding pattern for Athens Airport, at the KEA VHF omnidirectional range, still at FL340. For the next 70 minutes, the aircraft remained in the holding pattern.

Two F-16 fighter aircraft from the Hellenic Air Force 111th Combat Wing were scrambled from Nea Anchialos Air Base to find the aircraft. They found the passenger jet at 11:24 and observed that the first officer was slumped motionless at the controls and the captain's seat was empty. They also reported that oxygen masks were dangling in the passenger cabin.

At 11:49, flight attendant Andreas Prodromou entered the cockpit and sat down in the captain's seat, having remained conscious by using a portable oxygen supply. Prodromou only had been able to enter now due to the door having a code. He held a UK Commercial Pilot Licence, but was not qualified to fly the Boeing 737; crash investigators concluded that Prodromou's experience was insufficient for him to be able to gain control of the aircraft under the circumstances. Prodromou waved at the F-16s very briefly, but almost as soon as he entered the cockpit, the left engine failed due to loss of fuel. The plane left the holding pattern and started to descend. Ten minutes after the loss of power from the left engine, the right engine also failed, and just before 12:04 the aircraft crashed into hills near Grammatiko, 40 km (25 mi; 22 nmi) from Athens, killing all 121 passengers and crew on board.