The crash of the Germanwings flight in the Alps on Tuesday has focused attention on the safety record of the French aviation company Airbus, which manufactured the A320 plane.
Experts have pointed out similarities between the crash that killed 150 people and another incident involving an Airbus flight last November.
On that occasion, data from malfunctioning sensors triggered a sudden plunge by an Airbus plane shortly after it had taken off from Bilbao, in northern Spain.
The A320 plane, operated by German airline Lufthansa, unexpectedly lost height after its automated systems misinterpreted data. In that case, the plane had been flying on autopilot when the pilot noticed one of the displays was “increasing unusually rapidly”, according to the German Federal Bureau of Aircraft Accident Investigation.
The display was reporting the plane’s “angle of attack” information, which concerns the alignment of the wing line and flight path. But the sensors were giving incorrect data. That faulty data triggered the activation of the aircraft’s ‘Alpha Protection’ system, which usually prevents stalling and the effects of wind shear.
When this was combined with other technical information, the plane responded by automatically ordering “a nose-down pitch rate”, which meant that in effect it went into a dive. “The nose of the airplane dropped further and the copilot counteracted this movement with the sidestick,” noted the report. “The copilot stated the airplane did not respond as expected and continued to descend.”
For at least 45 seconds, the pilot battled to stop the plane from dropping any further, as it plunged about 1200m. Only when the controlling sidestick was pushed as far back as possible were the plane’s systems overridden to allow it to fly horizontally again. It subsequently emerged that some of the plane’s sensors had frozen shortly after take-off and only defrosted as the plane came into Munich to land.
At the time, Airbus issued an “operational engineering bulletin”, which is a rapid-response temporary notice sent out by the manufacturer to the users of an aircraft. On December 14 2014, the European Aviation Safety Agency also sent out an emergency directive for overriding the “undue activation of Alpha Protection” for Airbus planes. The directive warned pilots to switch off sensors if they malfunction.
Some aviation experts believe that as plane operation systems have become more sophisticated, pilots have become increasingly dependant on them.
This can lead to serious difficulties if the systems develop a fault, as was the case with a 2009 Air France crash. In that case, an Airbus A330 crashed after leaving Brazil for an overnight flight to France. Frozen sensors led pilots to misinterpret the situation and crash the plane into the Atlantic. All 228 people on board were killed.
In October 2005, a British Airways Airbus A319 had a “major electrical failure” as it was leaving Heathrow on its way to Budapest. “This resulted in the loss or degradation of a number of important aircraft systems,” noted the subsequent Air Accidents Investigation Branch report.
Radio lost power
According to the report the pilot tried to transmit a mayday call to air traffic control but it was not received because the radio had also lost power. In this case, the pilots were able to reboot the systems and the plane continued its journey.
Airbus is responsible for manufacturing some of the most popular aircraft in the world, which log millions of incident-free hours in the air every year. It has delivered about 6 200 short-haul and medium-haul jets in the A320 group.
The Germanwings plane that crashed this week had been delivered to Lufthansa in 1991, three years after the first A320 entered service. The plane was transferred to Germanwings, and had flown about 58 300 flight hours in about 46 700 flights in the past 24 years. – © Guardian News & Media 2015