HELIOS AIRWAYS FLIGHT 522

Helios Airways Flight 522 was a Helios Airways Boeing 737-300 flight that crashed into a mountain on 14 August 2005 at 12:04 EEST, north of Marathon and Varnavas, Greece. Rescue teams located wreckage near the community of Grammatiko40 km (25 miles) from Athens. All 121 on board were killed.

Background

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

Flight and crash

Hans-Jürgen Merten, who was a German contract pilot hired by Helios for the holiday flights, served as the captain. Pampos Charalambous, a Cypriot who flew for Helios, served as the first officer. 32-year old Louisa Vouteri, a Greek national living in Cyprus who served as a chief purser, replaced a sick colleague.

The flight, which left Larnaca, Cyprus at 09:07 local time, was en route to Athens, and was scheduled to continue to Prague. Before take-off the crew failed to set the pressurisation system to "Auto," which is contrary to standard Boeing procedures. Minutes after take-off the cabin altitude horn activated as a result of pressurization. It was, however, misidentified by the crew as a take-off configuration warning, which signals that the aircraft is not ready for take-off, and can only sound on the ground. The horn can be silenced by the crew with a switch on the overhead panel.

Above 14,000 ft (4,267 m) cabin altitude, the oxygen masks in the cabin automatically deployed. An Oxy ON warning light on the overhead panel in the cabin illuminates when this happens. At this point, the crew contacted the ground engineers. Minutes later a master caution warning light activated, indicating an abnormal situation in a system. This was misinterpreted by the crew as indicating that systems were overheating.

At some point later the captain radioed the engineer on the ground to say that the ventilation fan lights were off. This suggests that the captain was suffering from hypoxia, as the 737-300 has no such lights. The engineer asked the captain to repeat. The captain then said that the equipment cooling lights were off, which again suggested confusion. The engineer said, "This is normal, please confirm the problem." The engineer then asked, "Can you confirm that the pressurization system is set to AUTO?" The captain, however, disregarded the question and instead asked in reply, "Where are my equipment cooling circuit breakers?" The engineer then asked whether the crew could see the circuit breakers, but received no response.

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 accordance with the rules for handling "renegade" aircraft incidents (where the aircraft is not under pilot control), one fighter approached to within 300 ft (91 m), and saw the first officer was slumped motionless at the controls. The pilot could also see that the captain was not upright in the cockpit and that oxygen masks were seen dangling in the passenger cabin.

Later, the F-16 pilots saw the flight attendant Andreas Prodromou enter the cockpit and sit at the controls, seemingly trying to regain control of the aircraft. He eventually noticed the F-16, and signalled him. The pilot pointed forward as if to ask, "Can you carry on flying?" Prodromou responded by shaking his head and pointing downward. The cockpit voice recorder recorded him calling "mayday" multiple times. Within minutes, due to lack of fuel, the engines failed in quick succession and the aircraft began to descend. Prodromou grabbed the yoke and attempted to steer, but the plane continued, hit the ground and exploded. At the time of impact, the passengers and crew were likely unconscious but breathing. None survived.

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 were recovered. The passenger list included 93 adults and 22 people under the age of 18. Cypriot nationals comprised 103 of the passengers and Greek nationals comprised the remaining 12.

The cause of the crash (according to air crash investigations) was that the cabin pressurization control valve was set to manual and was not switched back to auto after post-maintenance pressurisation testing was completed. As a result, the cabin never pressurised during the ascent to 35,000 feet (11,000 m). The flight attendant seen in the cockpit managed to stay conscious by using the spare oxygen bottles provided in the passenger cabin for crew use.

Investigation

Loss of cabin pressure—which, without prompt alleviation, would cause pilot unconsciousness—is the leading theory explaining the accident. This would account for the release of oxygen masks in the passenger cabin. Weighing against this is the fact that the pilots should have been able to don their own fast-acting masks and make an emergency descent to a safe altitude provided that they recognized the pressurization system as the source of the alarm and acted before their minds were too impaired by hypoxia.

The flight data recorder and cockpit voice recorder were sent to 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 criminal offences."

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 male flight attendant and DNA testing revealed that the blood on the aircraft controls was that of flight attendant Andreas Prodromou, a pilot-in-training with approximately 260–270 hours of training completed. Autopsies on the crash victims showed that all were alive at the time of impact, but it could not be determined whether they were conscious as well.

The preliminary investigation reports state that the maintenance performed on the aircraft had left the pressurization control on a 'manual' setting, in which the aircraft would not pressurise automatically on ascending; the pre-takeoff check had not disclosed nor corrected this. As the aircraft passed 10,000 feet (3,000 m), the cabin altitude alert horn sounded. The horn also sounds if the aircraft is not properly set for takeoff, e.g. flaps not set, and thus it was assumed to be a false warning. The aircrew found a lack of a common language and inadequate English a hindrance in solving the problem. The aircrew called maintenance to ask how to disable the horn, and were told where to find the circuit-breaker. The pilot left his seat to see to the circuit breaker and both aircrew lost consciousness shortly afterwards.

The leading explanation for the accident is that the cabin pressurisation did not operate and this condition was not recognised by the crew before they became incapacitated. Decompression would have been fairly gradual as the aircraft climbed under the control of the flight management system. The pressurisation failure warning on this model should operate when the effective altitude of the cabin air reaches 10,000 ft (3,000 m) at which altitude a fit person will have full mental capacity.

The emergency oxygen supply in the passenger cabin of this model of Boeing 737 is provided by chemical generators that provide enough oxygen, through breathing masks, to sustain consciousness for about 12 minutes, normally sufficient for an emergency descent to 10,000 feet (3,000 m), where atmospheric pressure is sufficient to sustain life without supplemental oxygen. Cabin crew have access to portable oxygen sets with considerably longer duration. Emergency oxygen for the flight crew comes from a dedicated tank.

Timeline

Path of Helios Airways Flight 522
Date: 14 August 2005 All times EEST (UTC + 3h), PM in bold
Time	Event
0900	Scheduled departure
0907	Departs Larnaca International Airport
0911	Pilots report air conditioning problem
0912	Cabin Altitude Warning sounds at 12,040 feet (3,670 m)
0920	Last contact with Nicosia ATC; Altitude is 28,900 feet (8,809 m)
0923	Now at 34,000 feet (10,400 m); Probably on autopilot
0937	Enters Athens Flight Information Region
1007	No response to radio calls from Athens ATC.
1020	Athens ATC calls Larnaca ATC; Gets report of air conditioning problem
1024	Hellenic Air Force (HAF) alerted to possible renegade aircraft
1045	Scheduled arrival in Athens
1047	HAF reassured that the problem seemed to have been solved
1055	HAF ordered to intercept by Chief of General Staff, Admiral Panagiotis Chinofotis
1105	Two F-16 fighters depart Nea Anchialos
1124	Located by F-16s over Aegean island of Kea
1132	Fighters see co-pilot slumped over, cabin oxygen deployed, no signs of terrorism
1149	Fighters see an individual in the cockpit, apparently trying to regain control of aircraft
1150	Left (#1) engine stops operating, presumably due to fuel starvation
1154	CVR records two MAYDAY messages
1200	Right (#2) engine stops operating
1204	Aircraft crashes in mountains near Grammatikos, Greece