Helios Airways Flight 522 was a Boeing 737-31S flight that crashed on 14 August 2005 at 12:04 p.m. Eastern European Summer Time (EEST) into a mountain north of Marathon and Varnavas, Greece, also 19 miles north of Athens' Eleftherios Venizelos Airport. 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.
The day before the fatal flight the technicians had tested the Pressurization Mode Selector (PMS) switch which permits pilots to control cabin altitude (pressure) but then left the switch on MANUAL. The normal position should have been AUTOMATIC so that the pressurization system adapts as the aircraft climbs.
The pressurization system works through the aircraft air-conditioning system by drawing in air from the front of the jet engines, the airflow being provided by the jet fans. The pilots should have normally checked the PMS switch setting during their pre-flight procedure but unfortunately they did not.
The next day Helios 522 took off at 9.07 a.m. local time on its route from Larnaca, Cyprus to Prague, Czech Republic with a stop at Athens. As the aircraft climbed over the Mediterranean, the cabin alert horn sounded. This is an avionics high temperature warning indicating that the systems were overheating. The pilots were confused as to what was causing the overheating. The aircraft continued to climb and the air pressure and oxygen levels in the cabin became dangerously low.
At 14,000 feet, oxygen masks were automatically deployed and the master caution light flashed in the cockpit. The flight crew had made contact with Helios maintenance engineers on the ground to ask them what should be done and they were told to remove the alarm circuit breaker to silence the horn. The captain left his seat to deal with this and probably became unconscious during his search. A short time after, the co-pilot also became unconscious.
The aircraft continued to climb until its flight management computer knew it had reached cruising height. The computer then took the plane into Athens airspace and entered a holding pattern. The pilot, a German, and the co-pilot, a Cypriot, suffered hypoxia due to lack of oxygen. During the onset of hypoxia, thinking becomes very illogical. Tests on the effects of hypoxia in a pressure chamber show that the subject finds it difficult to answer simple questions and mathematical questions, such as addition or subtraction of numbers after some time in a low oxygen environment.
As there was no response coming from the airplane, at 10.55 a.m. the Greek air force sent two F-16 fighter jets to intercept the plane. At 11.20 a.m. they caught up with the airliner at 34,000 feet over the Aegean Island of Kea and peered inside the cockpit. The F-16 pilots saw the co-pilot slumped over the controls but could not see the captain, and oxygen masks were dangling inside. “When a pilot has no communication with the control tower, the procedure dictates that other planes must accompany and help the plane land. Unfortunately it appeared that the pilot was already dead, as was possibly everyone else on the plane,” Cyprus Transport Minister Haris Thrasou said.
The jets then flew by a second time and they saw two people in the cockpit possibly trying to take control of the plane. At that time it was unclear if they were crew members or passengers.
Helios Flight 522 was circling over Athens with everyone unconscious or dead with the exception of 2 crew members, who later also perished.
After investigations it is believed that a steward, Andreas Prodromou, who had just begun flying lessons, attempted to take control of the plane. DNA testing revealed that the blood on the aircraft controls was that of the flight attendant Prodromou. The other was a female flight attendant. All the flight attendants would have donned their oxygen masks and loss consciousness due to lack of oxygen. The two people seen in the cockpit were wearing oxygen masks connected to portable oxygen tanks, which was why they were still alive. At 30,000 feet it isn’t possible to stay conscious for long, maybe 15 to 30 seconds.
Having been in the air for three hours, Helios Flight 522 ran out of fuel. The engines shut off and the plane crashed into a mountain north of Athens, killing everyone onboard.
Helios 522 crashes into a mountain after running out of fuel.
Since the September 11, 2001 attacks on the World Trade Centers, in order to prevent terrorists from entering the cockpit and taking over the aircraft, the cockpit door has an electronic combination lock. Therefore it is believed that the 2 crew who were using portable oxygen tanks were unable to enter the cockpit because of this combination lock. It is not sure how they did finally get into the cockpit. One theory is that as the plane ran out of fuel and the engines cut out, the lock lost power and the cockpit door could be opened. However, it was then too late.
There is an outflow valve at the rear of the Boeing 737 which can be opened or closed. In the closed position, cabin pressure is maintained. In the open position, air leaks out and the cabin is depressurized. This was the case with Helios 522.
The control of this outflow valve is via 2 electrical wires running in close proximity, perhaps in the same conduit. The second wire is a backup. Airplanes have backup systems, such as 3 hydraulic systems to manipulate the control surfaces for pitch, roll and yaw during flight. If one hydraulic system should fail, there are a further 2 for backup. It is very unlikely that all 3 systems should fail at the same time.
It is believed that Boeing may have made a design error with the 737 by placing these two wires in close proximity. If one should short-circuit or catch on fire, it will affect the backup wire, rendering the system inoperable.
A pressurization control incident with a Boeing 737-436 G-DOCE in May 2003 presented wrong indications to the pilots and the PMS was finally switched to manual position like that found in the Helios 522 wreckage.
The outflow valve main and backup wires were in close proximity possibly due to cost cutting.
According the Helios 522 final report, in a previous pressurization incident with the Helios accident aircraft: “The Captain stated that there might have been a problem with the outflow valve.” The Air Accident and Incident Investigation Board (AAIB) of Cyprus was not able to reach a conclusive decision as to the causes of this previous incident, but indicated as one of two possibilities: “An electrical malfunction caused the opening of the outflow valve.”
The day before the fatal flight the technicians had tested the Pressurization Mode Selector (PMS) switch which permits pilots to control cabin altitude (pressure) but then left the switch on MANUAL. The normal position should have been AUTOMATIC so that the pressurization system adapts as the aircraft climbs.
The pressurization system works through the aircraft air-conditioning system by drawing in air from the front of the jet engines, the airflow being provided by the jet fans. The pilots should have normally checked the PMS switch setting during their pre-flight procedure but unfortunately they did not.
The next day Helios 522 took off at 9.07 a.m. local time on its route from Larnaca, Cyprus to Prague, Czech Republic with a stop at Athens. As the aircraft climbed over the Mediterranean, the cabin alert horn sounded. This is an avionics high temperature warning indicating that the systems were overheating. The pilots were confused as to what was causing the overheating. The aircraft continued to climb and the air pressure and oxygen levels in the cabin became dangerously low.
At 14,000 feet, oxygen masks were automatically deployed and the master caution light flashed in the cockpit. The flight crew had made contact with Helios maintenance engineers on the ground to ask them what should be done and they were told to remove the alarm circuit breaker to silence the horn. The captain left his seat to deal with this and probably became unconscious during his search. A short time after, the co-pilot also became unconscious.
The aircraft continued to climb until its flight management computer knew it had reached cruising height. The computer then took the plane into Athens airspace and entered a holding pattern. The pilot, a German, and the co-pilot, a Cypriot, suffered hypoxia due to lack of oxygen. During the onset of hypoxia, thinking becomes very illogical. Tests on the effects of hypoxia in a pressure chamber show that the subject finds it difficult to answer simple questions and mathematical questions, such as addition or subtraction of numbers after some time in a low oxygen environment.
As there was no response coming from the airplane, at 10.55 a.m. the Greek air force sent two F-16 fighter jets to intercept the plane. At 11.20 a.m. they caught up with the airliner at 34,000 feet over the Aegean Island of Kea and peered inside the cockpit. The F-16 pilots saw the co-pilot slumped over the controls but could not see the captain, and oxygen masks were dangling inside. “When a pilot has no communication with the control tower, the procedure dictates that other planes must accompany and help the plane land. Unfortunately it appeared that the pilot was already dead, as was possibly everyone else on the plane,” Cyprus Transport Minister Haris Thrasou said.
The jets then flew by a second time and they saw two people in the cockpit possibly trying to take control of the plane. At that time it was unclear if they were crew members or passengers.
Helios Flight 522 was circling over Athens with everyone unconscious or dead with the exception of 2 crew members, who later also perished.After investigations it is believed that a steward, Andreas Prodromou, who had just begun flying lessons, attempted to take control of the plane. DNA testing revealed that the blood on the aircraft controls was that of the flight attendant Prodromou. The other was a female flight attendant. All the flight attendants would have donned their oxygen masks and loss consciousness due to lack of oxygen. The two people seen in the cockpit were wearing oxygen masks connected to portable oxygen tanks, which was why they were still alive. At 30,000 feet it isn’t possible to stay conscious for long, maybe 15 to 30 seconds.
Having been in the air for three hours, Helios Flight 522 ran out of fuel. The engines shut off and the plane crashed into a mountain north of Athens, killing everyone onboard.
Helios 522 crashes into a mountain after running out of fuel.Since the September 11, 2001 attacks on the World Trade Centers, in order to prevent terrorists from entering the cockpit and taking over the aircraft, the cockpit door has an electronic combination lock. Therefore it is believed that the 2 crew who were using portable oxygen tanks were unable to enter the cockpit because of this combination lock. It is not sure how they did finally get into the cockpit. One theory is that as the plane ran out of fuel and the engines cut out, the lock lost power and the cockpit door could be opened. However, it was then too late.
There is an outflow valve at the rear of the Boeing 737 which can be opened or closed. In the closed position, cabin pressure is maintained. In the open position, air leaks out and the cabin is depressurized. This was the case with Helios 522.
The control of this outflow valve is via 2 electrical wires running in close proximity, perhaps in the same conduit. The second wire is a backup. Airplanes have backup systems, such as 3 hydraulic systems to manipulate the control surfaces for pitch, roll and yaw during flight. If one hydraulic system should fail, there are a further 2 for backup. It is very unlikely that all 3 systems should fail at the same time.
It is believed that Boeing may have made a design error with the 737 by placing these two wires in close proximity. If one should short-circuit or catch on fire, it will affect the backup wire, rendering the system inoperable.
A pressurization control incident with a Boeing 737-436 G-DOCE in May 2003 presented wrong indications to the pilots and the PMS was finally switched to manual position like that found in the Helios 522 wreckage.
The outflow valve main and backup wires were in close proximity possibly due to cost cutting.According the Helios 522 final report, in a previous pressurization incident with the Helios accident aircraft: “The Captain stated that there might have been a problem with the outflow valve.” The Air Accident and Incident Investigation Board (AAIB) of Cyprus was not able to reach a conclusive decision as to the causes of this previous incident, but indicated as one of two possibilities: “An electrical malfunction caused the opening of the outflow valve.”
2 comments:
Amazing how they work these things out after the crash. Pity the steward couldn't have got control of the plane earlier.
True, it's really sad. The NTSB (National Transportation Safety Board) spends months or years pulling airplane parts from the ocean floor and then re-assembling all these little parts together until it looks like the plane before the crash to try to work out what caused the crash. They must be some of the most brilliant minds on the planet.
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