The aircraft continued to climb until it leveled off at F元40, 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 F元40. It remained in the holding pattern, under control of the auto-pilot, for the next 70 minutes. Shortly after the cabin altitude warning sounded, the captain radioed the Helios operations center 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 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. 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. In the next few minutes, several warning lights on the overhead panel in the cockpit illuminated. The alert sound is identical for both warnings. 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. During these checks, no one on the flight deck noticed the incorrect setting. The aircraft took off with the pressurization system still set to "manual," and the aft outflow valve partially open.Īs the aircraft climbed, the pressure inside the cabin gradually decreased. 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.Īfter 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. They requested a full inspection of the door. The inspection was carried out by a ground engineer, who then performed a pressurization leak check. 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. It was the deadliest aviation accident in Greek history. 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. 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.
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