Remembering Helios Airways flight 522

On the 14th of August 2005 Helios Airways Flight 522, a scheduled international passenger flight from Larnaca Airport (LCA/LCLK) to Prague Havel Airport (PRG/LKPR) with a stopover in Athens-Elefthérios Venizélos International Airport (ATH/LGAV), crashed after ATC lost contact with the pilots operating the flight. It aircraft crashed near Grammatiko, Greece, killing all 121 passengers and crew on board. It is the deadliest aviation accident in Greek history.

An investigation into the accident by Greece's Air Accident Investigation and Aviation Safety Board (AAIASB) concluded that the crew had failed to notice that the cabin pressurization system was set to "manual" during takeoff checks. A ground engineer had (allegedly) set it to "manual" to conduct testing before the flight, but had forgotten to restore it to "auto" afterward. This configuration was subsequently missed by the crew during their pre-flight checks. This caused the plane to gradually depressurize as it climbed, and resulted in everyone on board suffering from critical hypoxia, resulting in a "ghost flight". The negligent nature of the accident led to lawsuits being filed against Helios Airways and Boeing, with the former also being shut down by the Government of Cyprus the following year.

Because the plane's autopilot was programmed for FL340 the aircraft continued to climb until leveling out at that altitude some 19 minutes after takeoff. At 09:37 the 737 entered the Athens FIR but no contact was established with the flight. Over Rodos at about 09:52 the airplane entered the UL995 airway. At 10:21 the airplane passed the KEA VOR, which is located about 28 nm south of the Athens airport. The airplane then passed the Athens Airport and subsequently entered the KEA VOR holding pattern at 10:38. 

All efforts by Greek air traffic controllers to contact the pilots were futile. Around 11:00 two Greek F-16 fighter planes were scrambled from the Néa Anghialos air base. The F-16 pilots reported that they were not able to see the captain, while the first officer seemed to be unconscious and slumped over the controls.

At 11:49, the F-16's reported a person not wearing an oxygen mask entering the cockpit and occupying the captain's seat. The F-16 pilot tried to attract his attention without success. 

At 11:50, the left engine flamed out due to fuel depletion and the aircraft started descending. At 11:54, two Mayday messages were recorded on the CVR.

At 12:00, the right engine also flamed out at an altitude of approximately 7100 feet. The aircraft continued descending rapidly and impacted hilly terrain.

Aircraft Details
Airline: Helios Airways
Code: ZU/HCY
Aircraft: Boeing 737-31S
Registration: 5B-DBY
Serial Number: 29099
Engines: 2 x CFMI CFM56-3C1
First Flew: 29/12/1997
Age: 7.8 Years