Aviation experts are baffled by the fact that no distress signal was transmitted by the Germanwings plane that crashed in the French Alps on Tuesday.

Two experienced pilots told Times of Malta the time it took for the Airbus A320 to descend from its cruising altitude should have given the cockpit crew ample time to communicate with air traffic control.

Mark Micallef Eynaud, former chief of flight operations at Air Malta, said initial indications were that the aircraft was “a flying machine” not an-out-of control metal structure.

“The time taken to descend, about eight minutes, would indicate that the aircraft was in a controlled descent, which was steeper than would be normal on arrival at an airport but not as rapid as an aircraft out of control,” he said.

It was a view shared by Joe Farrugia, head of operations at Medavia, an aviation company. Mr Farrugia is also a former Air Malta chief pilot for Airbus aircraft.

He said pilots were trained to communicate immediately with air traffic control should anything go wrong. “It does raise suspicion that no distress call was made despite the ample time available to the pilots.”

Dropping at about 4,000 feet per minute, although considered a fast descent, was not out of this world, Capt. Farrugia said.

There is no way that a conscious crew would inadvertently descend through some 30,000 feet without being aware

“Eight minutes is a very long time and I would find it very strange that the pilot would not have sent a distress call, which only takes a few seconds,” he said.

The cause of the crash is not yet known but the cockpit voice recorder has been recovered from the crash site.

The aircraft crashed in a mountainous region in southern France on its way to Dusseldorf from Barcelona. All 150 people on board died.

Capt. Micallef Eynaud said the absence of an emergency distress message suggested there was no in-flight catastrophic failure of the aircraft structure. “There is no way that a conscious crew would inadvertently descend through some 30,000 feet without being aware. If they were unaware, the crew had no indication of the descent on the flight deck, were unconscious or chose to ignore the warnings.”

He said if systems were functioning normally and the aircraft entered a descent not initiated by the pilots, a sequence of warnings would have followed.

Instruments would have given crew the initial warning that the aircraft was not at the set height. Air traffic control would have also received warnings of the height change and communicate with the pilots to determine why this was so.

Warnings would be audible and unmistakable as the aircraft approached the ground, Capt. Micallef Eynaud said, adding pilots were trained to react in “a determined and aggressive manner” when this happened.

This leaves open the question as to what might have happened in the cockpit of the A320.

Capt. Micallef Eynaud said one possibility was that the pilots became unconscious due to pressurisation failure leading to a lack of oxygen.

Such a failure could result from a structural problem, in which case, the effects would be rapid and very noticeable in the aircraft, he noted.

Pressurisation failure could also result from a technical problem that leads to a slow but steady reduction in oxygen levels.

“However, in both cases warnings occur as the ambient height passes 10,000 feet and at 14,000 feet when further unmistakeable warnings occur and the oxygen masks are automatically deployed for the passengers,” Capt. Micallef Eynaud said.

Another possibility was the contamination of the air on board the plane that would have affected badly both crew and passengers. However, this would, in all probability, have led to the aircraft to continue flying at 38,000 feet (its cruising altitude) until it ran out of fuel.

“If the pilots suspected problems with air quality and started a descent they would immediately use the oxygen mask available and breathe pure oxygen from a separate source. This should prevent them losing consciousness.”

He said speculation about the effects of icing on sensors leading to incorrect indications to the pilots had been floated, especially after recent accidents. However, he added, a pilot aware of such a problem was well trained to cope with it and this should not lead to the loss of an aircraft.

Capt. Micallef Eynaud cautioned against rash judgements at this juncture noting that much depended on what accident investigators found at the crash site.

His sentiments were echoed by Capt. Farrugia, who pointed out that there could be information known to investigators that would not have been disseminated publicly yet.

What investigators will look for

Accident investigators will try and establish the sequence of events that led to the crash through an examination of the flight data and cockpit voice recorders.

This would give an indication of what the crew were aware of and what they did, according to Mark Micallef Eynaud, an experienced pilot.

The site investigation would also determine the angle and speed of impact as investigators will look for evidence of any failure from the wreckage.

Capt. Micallef Eynaud said that important information would be gleaned from the accident site and the debris, which would determine whether the engine was operating or not and if it was at a high or low power setting.

But investigators will also examine human factors, including the training, the state of mind and health of the crew.

“The investigators will also look for evidence of external influences and would want to know if the pilots were in their seats on impact, whether there were other people on the flight deck and if so who,” Capt. Micallef Eynaud said.

Did plane’s multiple safety features fail?

The A320 that crashed in France may have been 24 years old but it still had multiple safety features. Kurt Sansone speaks to John Baptist Camilleri, an aviation engineer.

John Baptist Camilleri finds it “curious” how the crew of the A320 that crashed in France failed to send out a distress signal.

The president of the Association of Airline Engineers believes it is still too early to speculate on what could have happened but adds that nothing could be ruled out.

Mr Camilleri says the Airbus A320 is a very safe aircraft and, in the unlikely eventuality that it experienced a sudden loss of power in its two engines, other safety features would have kicked in.

The eight-minute time window mentioned would have given the crew ample time to start the auxiliary power unit, he says. “This unit can be up and running in about 90 seconds and will provide sufficient power to allow the crew to communicate with air traffic controllers and attempt to restart the engines provided the airplane had enough fuel.”

Mr Camilleri points out that even if the auxiliary power unit failed, the A320 has an air turbine that auto-deploys if both engines fail. The turbine will turn through the natural air flowing against the plane, generating electricity.

He says the turbine will generate enough electrical power to operate the basic instruments and navigation equipment. “This includes a hydraulic pump that would supply enough power to allow the crew to operate limited flight controls and glide the aircraft.”

If all systems failed, the crew would still have had the possibility of using at least one battery-powered VHF radio to communicate with ground control.

“As things stand it seems either none of these safety measures worked or else they functioned but, somehow, the pilots were incapacitated and unable to control the aircraft,” he says.

Insisting it is too early to establish the cause of the crash, Mr Camilleri says the pilots could have been subjected to rapid decompression which prevented them from using the onboard supply of oxygen to be able to take control of the situation.