AIR CRASH INVESTIGATION: Ghost Plane | Helios Airways Flight 522

AIR CRASH INVESTIGATION: Ghost Plane | Helios Airways Flight 522 | Incapacitated Pilots | MAYDAY
'Helios Airways Flight 522 was a scheduled passenger flight from Larnaca, Cyprus to Prague, Czech Republic, with a stopover to Athens, Greece, that crashed on 14 August 2005, killing all 121 passengers and crew on board. A loss of cabin pressurization incapacitated the crew, leaving the aircraft flying on autopilot until it ran out of fuel, and crashed near Grammatiko, Greece. It was the deadliest aviation accident in Greek history.
FLIGHT AND CRASH
When the aircraft arrived from London earlier that morning, 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 pressurization system was set to "manual." However, the engineer failed to reset it to "auto" on completion of the test.
After the aircraft was returned into service, the flight crew overlooked the pressurization system state on three occasions: during the pre-flight procedure, the after-start check, and the after take-off check. During these checks, no one on the flight deck noticed the incorrect setting. The aircraft took off at with the pressurization system still set to "manual," and the aft outflow valve partially open.
As the aircraft climbed, the pressure inside the cabin gradually decreased. As it passed through an altitude of 12,040 feet (3,670 m), the cabin altitude warning horn sounded. The warning should have prompted the crew to stop climbing, but it was 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 alert sound is identical for both warnings.
In the next few minutes, several warning lights on the overhead panel in the cockpit illuminated. One or both of 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 automatically 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?" However, the captain, already experiencing the onset of hypoxia's initial symptoms, 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 VOR, still at FL340. It remained in the holding pattern, under control of the auto-pilot, for the next 70 minutes.
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 intercepted 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. His girlfriend, Haris Charalambous, was also seen in the cockpit helping Prodromou try to control the aircraft. Prodromou held a UK Commercial Pilot Licence, but was not qualified to fly the Boeing 737. Prodromou waved at the F-16s very briefly, but almost as soon as he entered the cockpit, the left engine flamed out due to fuel exhaustion, and the plane left the holding pattern and started to descend. Crash investigators concluded that Prodromou's experience was insufficient for him to be able to gain control of the aircraft under the circumstances. However, Prodromou succeeded in banking the plane away from Athens and towards a rural area as the engines flamed out. There were no ground casualties. Ten minutes after the loss of power from the left engine, the right engine also flamed out, 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.
INVESTIGATION
The flight data recorder and cockpit voice recorder were sent to Paris for analysis. The CVR recording enabled investigators to identify Prodromou as the flight attendant who entered the cockpit in order to try to save the plane. He called "Mayday" five times but, because the radio was still tuned to Larnaca—not Athens—he was not heard by ATC. His voice was recognized by colleagues who listened to the CVR recording.
Many of the bodies recovered were burned beyond recognition by the post-impact fire. 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 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 for humans to sustain consciousness without supplemental oxygen. Cabin crew have access to portable oxygen sets with considerably longer duration.
The Hellenic Air Accident Investigation and Aviation Safety Board (AAIASB) listed the direct causal chain of events that led to the accident as:
-non-recognition by the pilots that the pressurization system was set to "manual",
-non-identification by the crew of the true nature of the problem,
-incapacitation of the crew due to hypoxia,
-eventual fuel starvation,
-impact with the ground.
Previous Pressurization Problems
On 16 December 2004, during an earlier flight from Warsaw, the same aircraft experienced a rapid loss of cabin pressure, and the crew made an emergency descent. The cabin crew reported to the captain that there had been a bang from the aft service door, and that there was a hand-sized hole in the door's seal. The Air Accident and Incident Investigation Board (AAIIB) of Cyprus could not conclusively determine the causes of the incident, but indicated two possibilities: an electrical malfunction causing the opening of the outflow valve, or the inadvertent opening of the aft service door.
The mother of the first officer killed in this crash claimed that her son had repeatedly complained to Helios about the aircraft getting cold. Passengers also reported problems with air conditioning on Helios flights. During the 10 weeks before the crash, the aircraft's environmental control system was repaired or inspected seven times.
A 2003 flight of a Boeing 737 between Marseilles and London Gatwick showed that a cabin-wide pressurization fault could be recognized by the flight crew. A problem was first noticed when the crew began to feel some discomfort in their ears. This was shortly followed by the cabin altitude warning horn, which indicated that the cabin altitude had exceeded 10,000 feet (3,000 m), and this was seen to continue to climb on the cockpit gauge. At the same time, the primary AUTO mode of the pressure control failed, followed shortly by the secondary STBY mode. The crew selected the first manual pressure control mode, but were unable to control the cabin altitude. An emergency descent and subsequent diversion to Lyon was carried out. The failure of the pressurization control system was traced to burnt electrical wiring in the area aft of the aft cargo hold. The wiring loom had been damaged by abrasion with either a p-clip or "zip" strap that, over time, exposed the conductors, leading to short circuits and subsequent burning of the wires. There was no other damage. The wiring for all the modes of operation of the rear outflow valve, in addition to other services, run through this loom.'
Source: Wikipedia
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