SPECULATION over what had caused the Helios plane crash was rife yesterday, as airline experts questioned the failure of the pilots to react promptly to fall of cabin pressure on flight ZU 522.
There is usually adequate time to take action once cabin pressure starts to drop and all planes carry warning systems.
Initial reports suggested that a drop in cabin pressure sparked by problems in the air conditioning system led to the worst aviation disaster in Greek and Cypriot history.
The Digital Cabin Pressure Control System (DCPCS) of a Boeing 737 is pressurised by bleed air, supplied to the packs and controlled by outflow valves, situated on the outside of the aircraft. It is controlled by an automated system that could fail in the event of the air conditioning system breaking down among other things.
In such an event, pilots would immediately descend the aeroplane and take it to an altitude of around 10,000 feet. It is this system that is believed to have failed, causing cabin pressure to drop.
Cyprus Airways Captain Efstathios Liasis told the Cyprus Mail that he believed that other factors could have been involved, given the pilot’s failure to descend the aircraft to an altitude where oxygen levels and temperatures were safe.
Captain Liasis said: “There are two systems controlling cabin pressure and the temperature in a plane. During a normal flight, say at 35,000 feet, if these two systems fail, the pilots know, and are trained, to descend quickly to around 10,000 feet, not just for the oxygen levels but also for the temperature.
“Because as you can imagine temperatures up there could be anything between -40C and -50C. When the plane goes above 15,000 it needs oxygen because the air thins at such an altitude.
“For some strange reason, the pilots did not react when the cabin pressure dropped which leads me to the view that perhaps something else went wrong up there.”
Another person who expressed bewilderment over what had happened was private pilot and Olympic Airways engineer Vasilis Bakounis. He told Greece’s Alpha TV that he couldn’t explain “why the pilots were unconscious in the cockpit”.
The President of the Greek Airline Pilots’ Association, Evangelis Sagos, also posed the same question. “Why did the pilots not descend quickly? It was very strange,” he said.
Sagos added: “Perhaps a small discharge of cabin pressure would have gone unnoticed. But a sudden drop of cabin pressure would cause objects inside the aircraft to fly all around the place and the pilots would obviously notice. They would then have 20 seconds to put their oxygen masks and descend the aircraft. That should be enough time.
He did not subscribe to the view that the air conditioning system had anything to do with the cabin pressure problems. “I find it hard to believe that the cabin pressure is connected to problems in the air conditioning system. They are different kinds of systems.
“At the altitude that they were at with temperatures being around -50C, I don’t believe that anybody would have survived, especially flying around for the 40 minutes that they were reportedly in the air. Everybody would have frozen,” concluded Sagos.
Meanwhile an airline engineer told the Cyprus Mail it was far too early to apportion blame for the disaster. “We cannot speculate as to the cause of the crash at such an early stage. The black box has to be recovered and thorough investigations will have to be carried out to establish the actual cause of the crash. Coming up with different theories at this stage, is not helpful.
“There are many theories being discussed. For example, I have just got off the phone to some colleagues in Greece who suspect that toxic and non-detectable fumes, like carbon monoxide, from the air condition system, may have leaked into the cockpit and caused the pilots to lose consciousness. However, that would not explain any possible cabin pressure drop.”
