Sources: Crew's Inability To Understand Cockpit Warnings Or Speak A Common Language May Have Spelled Flight's End

The cockpit crew aboard a doomed Helios Airways 737-300 was confused by alarms and failed to recognize that the plane was losing cabin pressure -- they succumbed to the lack of oxygen and eventually lost consciousness. The aircraft crashed near Athens, Greece, August 14th, killing all 121 people on board.

That's the story from unnamed sources close to the investigation into the Helios disaster, as told to a reporter from the International Herald Tribune.

The problem was further compounded, according to those sources, by the cockpit crew's apparent inability to communicate. The pilot was German, the copilot a Greek Cypriot and neither spoke good enough English to communicate effectively in the international language of aviation.

Eventually, the sources tell the Herald Tribune, one engine quit because it ran out of fuel. The assymetric thrust caused the autopilot to disengage and the aircraft plunged to the ground.

A Confusing Cacophony Of Warning Horns

The information cited by the paper's sources was gleaned from a new-generation flight data recorder, along with records of a maintenance check done the night before the aircraft went down. But critically, investigators have reportedly finding a pressurization valve and an air outflow valve in the wreckage -- both set improperly. A pressurization control knob was turned to the wrong setting during the previous night's maintenance, according to the Herald Tribune sources. The cockpit crew didn't catch the mistake during their preflight inspection.

When they heard an alarm in the cockpit as they crossed 10,000 feet, the paper reports both pilots assumed it was an improper take-off configuration warning. Although the same horn is used for both improper take-off configuration and to warn the crew that the aircraft isn't being properly pressurized, the improper configuration alert sounds only when the aircraft is on the ground, those sources said.

When the aircraft passed through 14,000 feet, oxygen masks dropped down in both the cockpit and the cabin. A master caution light illuminated and, simultaneously, an alert sounded indicating improper cooling in the avionics bay.

The cockpit confusion grew as the aircraft climbed on autopilot. While both pilots could speak enough English to satisfy ATC requirements, neither apparently possessed the language skills to sort out the growing technical issues that would eventually lead to their deaths, according to the report.

Why wasn't the pilot in his seat at the time of the crash? The Herald Tribune reports he had gone to the back of the flight deck to pull the circuit breaker for the avionics bay environmental warning on the advice of ground crew members with whom the pilots were talking on the radio. As the plane continued to climb, the pilot passed out on the flight deck. The copilot collapsed in his seat.

The 737 continued on autopilot to Athens, where it entered a programmed holding pattern, shadowed by a pair of Greek F-16 fighters trying to figure out why the Helios flight was proceeding NORDO. Eventually, one engine quit because of fuel exhaustion and the final chain of events was set in motion, according to the Herald Tribune's sources.

Boeing Rewrites The Book

Boeing, the plane's manufacturer, has already promised to revise its manuals for the 737 to strengthen admonitions to crew members: Know what warning is sounding and why. In a notice to customers, Boeing pointed out that the improper take-off configuration warning will only sound while the plane is on the ground.

"Confusion between the cabin altitude warning horn and the takeoff configuration warning horn can be resolved if the crew remembers that the takeoff configuration warning horn is only armed when the airplane is on the ground," the notice said. "If this horn is activated in flight, it indicates that the cabin altitude has reached 10,000 feet."

FMI: www.boeing.com, www.flyhelios.com