Helios Airways Flight 522

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Map of Helios Airways Flight 522
Map of Helios Airways Flight 522

Helios Airways Flight 522 (HCY 522 or ZU522) was a Helios Airways Boeing 737-31S flight that crashed on August 14, 2005 at 12:04 EEST into a mountain north of Marathon and Varnavas, Greece. Rescue teams located wreckage near the community of Grammatiko 40 kilometres (25 miles) from Athens. All 121 people on board were killed—the highest death toll for an aviation accident in 2005 until the West Caribbean Airways Flight 708 in Venezuela just two days later.


Flight and crash

Crash area of the flight in red
Crash area of the flight in red

The flight, which left Larnaca, Cyprus at 09:07 local time, was en route to Athens, and was scheduled to continue to Prague. After the flight failed to contact air traffic control upon entering Greek air space, two F-16 fighter aircraft from the Hellenic Air Force 111th Combat Wing were scrambled from Nea Anchialos Air Base to establish visual contact. They noted that the aircraft appeared to be on autopilot. In accord with the rules for handling "renegade" aircraft incidents (where the aircraft is not under the pilots' control), one fighter approached to within 300 feet (100 m) of the ill-fated aircraft [1]. The fighter pilot saw that the first officer was slumped motionless on the controls, and that the captain was not in the cockpit. Oxygen masks were seen dangling in the cabin.

Somewhat later, the F-16 pilots saw someone enter the cockpit and sit at the controls, soon to be joined by another person where the first officer had been sitting, both seemingly trying to regain control of the aircraft. Within minutes one engine, then the other ran out of fuel and the aircraft crashed into a hill, scattering wreckage and bodies and bursting into flame.[2]

The aircraft was carrying 115 passengers and a crew of 6. The passengers included 67 due to disembark at Athens, with the remainder continuing to Prague. The bodies of 118 individuals have been recovered [3]. The passenger list included 93 adults and 22 people under the age of 18. Cypriot nationals comprised 103 of the passengers (mostly of Greek descent and some of Armenian) and Greek nationals comprised the remaining 12[4].


Helios Airways aircraft 5B-DBY at London Luton Airport in 2004.
Helios Airways aircraft 5B-DBY at London Luton Airport in 2004.

The aircraft involved in this incident was first flown on December 29, 1997 and had been operated by dba until it was leased by Helios Airways on April 16, 2004 and nicknamed "Olympia", with registration 5B-DBY. Aside from the downed aircraft, the Helios fleet consists of two leased Boeing 737-800s and an Airbus A319-111 delivered May 14, 2005.

With 121 dead, this was 2005's worst aircraft crash to date (although it was exceeded only two days later by the West Caribbean Airways Flight 708 crash, which killed 160) and was the second accident of the year that caused more than 100 fatalities, the first being Kam Air Flight 904 with 104 deaths. It is the 69th crash of a Boeing 737 (the most numerous passenger aircraft in the world) since it was brought into service in 1968.

Photo of the place where the Boeing crashed you can see here: [5] It is taken some minutes after the crash.

Decompression hypothesis

The leading explanation for the accident is that cabin pressure was lost, disabling the crew.

On December 16, 2004, during a flight from Warsaw the ill-fated aircraft had suffered a loss of cabin pressure and three passengers were rushed to hospital upon arrival in Larnaca. The mother of the first officer killed in the crash of Flight 522 claimed that her son had repeatedly complained to Helios about the aircraft getting cold.[6] Passengers have also reported problems with air conditioning on Helios flights.

The emergency oxygen supply in the passenger cabin of commercial aircraft is fed by chemical generators that provide enough oxygen, through breathing masks, to sustain consciousness for about 15 minutes, normally sufficient for a rapid descent to 10,000 feet (3,000 m), where most people can function, albeit uncomfortably, in the ambient atmospheric pressure. Supplemental oxygen for the flight deck comes from a dedicated tank of gas.

If decompression is rapid ("explosive") at a cruising altitude of 34,000 feet (10,000 m), air rushes painfully out of a person's lungs and middle ear chamber, temperature drops to about −50 °C, a confusing, thick fog fills the cabin, and the windows eventually become misted or frosted. Unable to "hold their breath," passengers can maintain useful consciousness and fumble for their masks for only 5–30 seconds under such conditions. A flight attendant may be more adept at donning a mask. However, at 34,000 feet (10,000 m) altitude even a tight-fitting mask fed by 100% oxygen can supply at best only 90% of sea-level partial pressure of oxygen until the aircraft reaches a lower altitude, just enough for most healthy non-smokers to maintain full mental acuity.

A gradual decompression may not be noticed by the flight crew until their mental function has been substantially compromised by hypoxia to a point where they fail to respond properly to automatic warning signals. Breathing pure oxygen can quickly restore full consciousness if hypoxia has not been too severe for too long. However, on the flight deck of a Boeing 737 oxygen masks can be difficult to reach, and it may not be immediately obvious if the valve for the oxygen tank is in the closed position [7]. Access to the flight deck requires entering a code via a key pad, then waiting for up to 30 seconds until the flight crew authorizes access or the time lock disengages. Under conditions of surprise and high work load, a crew member may perform inefficiently and "grey out" before having accomplished effective action.


Suspicions that the aircraft had been hijacked were swiftly ruled out by Greece's foreign ministry. Initial claims that the aircraft was shot down by the fighter jets are refuted by eyewitnesses and the government.

Loss of cabin pressure and consequent pilot unconsciousness is the leading theory explaining the accident. This would account for why oxygen masks were released. Weighing against this is the fact that the pilots should have been able to descend the aircraft to a safe altitude after donning oxygen masks if they interpreted the alarm signal properly and acted before their minds were too impaired by hypoxia.

The flight data recorder and cockpit voice recorder were sent to a special center in Paris for analysis.

Authorities served a search warrant on Helios Airways headquarters in Larnaca, Cyprus and seized "documents or any other evidence which might be useful in the investigation of the possibility of penal offences."[8]

Most of the bodies recovered were burned beyond visual identification by the fierce fires that raged for hours in the dry brush and grass covering the crash site. However, it was determined that a body found in the cockpit area was that of a female flight attendant [9], suggesting that she was indeed trying to prevent a crash. DNA testing revealed that the blood on the aircraft controls was that of flight attendant Andreas Prodromou, a qualified private pilot, suggesting he was the other person the F-16 pilots saw in the pilot's seat. Autopsies on the crash victims showed that all were alive and maintained cardiac and respiratory function upon impact, but it could not be determined whether they were conscious at the time.

During the 2 months before the crash the aircraft's air conditioning system required repair 5 times.[10] On the morning of the crash, after the aircraft arrived at Larnaca on a flight from the United Kingdom, the cabin crew complained about a distinctly abnormal noise coming from its rear door. Inspection by Helios engineers disclosed no problem and the aircraft was allowed to take off without any repairs.[11] In retrospect, the noise is consistent with faulty sealing of the door that would allow gradual decompression of cabin air as the aircraft gained altitude, resulting in initially subtle but increasing cognitive dysfunction among the flight crew and delay in recognizing the danger until it was too late.


News media widely reported that shortly before the crash a passenger sent a SMS transmission indicating that one of the flight crew had become blue in the face, or roughly translated as "The pilot is dead. Farewell, my cousin, here we're frozen." [12]. Police later arrested Nektarios-Sotirios Voutas, a 32 year-old private employee from Thessaloniki, who admitted that he had made up the story and given several interviews in order to get attention [13]. Voutas was tried by a court of first instance on August 17, 2005 and received a suspended 6-month imprisonment sentence under a 42-month probation term.

The hoax was significant because it seemed to contradict accepted knowledge of cabin-pressure emergencies, especially when combined with other early and erroneous reports.


All times EEST (UTC + 3h because Greece and Cyprus were on daylight saving time)

  • 09:00 Scheduled departure time.
  • 09:07 Aircraft takes off from Larnaca airport.
  • 09:11 Pilots report "air conditioning" problem.
  • 09:15 The aircraft's flight data recorder registers an alarm at 14,000 feet (4,300 m).
  • 09:16 Flight's last contact with Nicosia air traffic control; the aircraft is flying at 22,000 feet (6,700 m).
  • 09:24 Aircraft in cruise at 34,000 feet (10,400 m), probably on autopilot.
  • 09:37 Flight enters Athens Flight Information Region, but fails to establish contact.
  • 10:07 Flight fails to respond to call from Athens Air traffic control (ATC).
  • 10:20 Lanarka ATC reassures Athens ATC that a "problem with air conditioning" was reported earlier.
  • 10:24 Hellenic Armed Forces (HAF) alerted to possible renegade aircraft.
  • 10:45 Scheduled arrival time in Athens.
  • 10:47 Hellenic Armed Forces (HAF) reassured that the aircraft's technical problem seems to have been solved.
  • 10:55 The HAF Joint Chief of Staff, Admiral Panagiotis Chinofotis orders military aircraft to establish visual contact with the airliner.
  • 11:05 Two F-16 fighters take off from Nea Anchialos, Greece.
  • 11:20 F-16s see the airliner over the Aegean island of Kea.
  • 11:25 Fighter pilots see co-pilot slumped unconscious on the aircraft's instrument panel, oxygen masks deployed, but notes no indications of terrorism.
  • 11:41 Fighter pilots note individuals in cockpit presumably trying to regain control of aircraft.
  • 11:50 The left engine stops operating, probably due to lack of fuel.
  • 12:00 The right engine stops operating.
  • 12:05 Aircraft crashes near Grammatiko.
  • 13:10 Scheduled arrival time in Prague.

Further Development

  • The flight Larnaca–Athens–Prague has been renumbered to ZU604/5.
  • The service between Larnaca and Prague has been announced by the company to be discontinued since August 26, 2005.
  • The company announced successfull safety checks of their Boeing fleet August 29, 2005, and put them back to service.

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