An investigation has begun into the unexplained crash of Flight 4U9525, of budget airline Germanwings, which crashed into the Alps in southeastern France en route from Barcelona to Dusseldorf with the loss of all 150 passengers and crew.

The aircraft descended from cruising height of 38,000ft to around 6,000ft in eight minutes before air traffic control lost contact just before 11am. According to witnesses who saw the aircraft descend, there was no sign of smoke or in-flight explosion, and weather at the time was good. The black box flight recorder has been found, and will reveal more in time.

Such incidents are actually quite rare in statistical terms. Flight 4U9525 appears to have involved a major malfunction of some kind as the aircraft was cruising, while the majority of accidents occur during take-off or landing. In fact most air accidents that involve fatalities also result in a large proportion of the passengers surviving because they occur nearer the ground, a fact that is not generally appreciated but sadly also not the case here.

The aircraft: Airbus A320

The aircraft, an Airbus A320, is a model that is in great demand from all parts of the world, and its reputation for safety and reliability is unequalled. It is one of a smaller, single-aisled family that comprise the A318, A319, A320 and A321, and has been in production since the late 1980s, and sales of the updated models show little sign of decline.

The A320 family has an accident rate of 0.14 fatal crashes per million departures, which is considered excellent. The total number of accident fatalities is below 1,500, which good considering its two decade service history and that more than 6,000 are in daily use.

There have been some memorable A320 accidents; in June 1988 an Air France airliner crash landed in high trees while performing a fly-by-wire landing at the Mulhouse air display in France. Three of the 136 passengers on board died, and airliners are no longer permitted to perform at airshows with passengers on board.

In January 2009, in a remarkable piece of airmanship a US Airways A320 taking off from La Guardia in New York had a double engine failure from birdstrikes and subsequently glided to a perfect ditching in the River Hudson. Of the 155 people on board there was only a single serious injury.

In this case it’s been reported that the particular aircraft involved was 24 years old, with the aircraft having previously been in service with German national airline Lufthansa before being transferred to Germanwings, a Lufthansa subsidiary. While this may surprise some, there’s little doubt that its full service records will show it was airworthy before its final departure, and that all necessary servicing had been completed in the years since manufacture. European airspace and flights are heavily audited by the European Aviation Safety Agency and are considered very safe. Lufthansa operates 100 A320s, Germanwings 60.

The A320 family were among the first so-called “fly-by-wire” airliners, a great innovation when they first flew. In simple terms, the cables and pulleys connecting the moveable flight control surfaces (elevators, rudder and ailerons) to the pilots' controls are replaced by electronic connections. These permit lighter pressure, swifter response, and better handling than previous manual systems, and do away with the image of “wrestling with the stick”. It’s now accepted that fly-by-wire technology, once the preserve of military aircraft, are perfectly safe for commercial use.

In-flight emergency

With regard to airborne emergencies it goes without saying that there are procedures for all eventualities, and that these are practised by aircrews on a very regular basis. In all cases, teaching on the impact of human factors dictates that one pilot physically flies the aircraft while another attempts to isolate or solve the problem using checklist procedures, and will advise the cabin crew and the air traffic authorities that an emergency exists.

So it’s puzzling to investigators that Flight 4U9525 issued no “mayday” distress call, as confirmed by France’s aviation authority despite earlier contradictory reports. This is unusual: if the situation was so catastrophic that it led to an immediate and rapid descent, for whatever reason, then possibly the aircraft or its communications systems had become disabled in some way. If it was cabin depressurisation that caused such a descent, each pilot has about 15 minutes of independent oxygen supply (the passengers have no more than 12 minutes' worth).

It’s tragic that even at the low altitude of around 6,000ft that the aircraft was unable to avoid colliding into the lower slopes of the Alps, and that all on board perished. What remains certain is that the air accident investigators will piece together Flight 4U9525’s final moments to assemble a true picture of what happened in the run up to the crash in an effort to prevent its re-occurrence. Sad though these events are, commercial air travel remains the safest form of travel in the 21st century, and is likely to remain so.

This article was originally published on The Conversation.