The Germanwings Airbus crash site consists of acres of parts no larger than a few square feet – the plane apparently flew into a mountainside at full speed so crash analysis will depend almost entirely on the contents of the black box.
Since the black boxes on aircraft are at the heart of any aircraft crash investigation, it is useful to understand just what they are.
We’ll also look at the safety record of the Airbus series of passenger planes.
To begin with, the “black box” (technically the FDR, Flight Data Recorder or the CVR/Cockpit Voice Recorder) is actually international orange, a color intended to be highly visible in almost any conditions. The reason it is called a black box is probably due to an engineering tradition dating back more than a century where designers of complex systems will take standard components and integrate them in the design. Another reason for the black box designation is the fact that early units recorded data on photographic film – therefore the interior of the boxes are dead, flat black.
When the standard component is complex but can be treated as just an input and output signal or fluid or something else, then the engineer will just draw a box to represent where it fits in the design and treat it as a black box – something which he knows will do certain things but he doesn’t know anything about how it works.
The Airbus is a fly-by-wire aircraft as are many newer planes, meaning that there is no direct cable or hydraulic connection between the cockpit and the various control surfaces and engine controls.
That essentially means the airplane is flown by computers and, as anyone with technical knowledge of computer hardware or software knows, computers can sometimes do things no one expected.
The black boxes are usually two separate units but the FDR and CVR can also be built into a single box. The FDR is also sometimes referred to as the ADR or Accident Data Recorder and the unit is able to store more than 15 hours of data.
What aircraft have FDRs and CVRs? Every commercial aircraft, passenger or cargo, have been required to carry them since 1967.
Why do they survive horrific crashes when nothing else does? First, they are built to survive an impact equivalent to 3,400 times the force of gravity.
Second, they are designed to survive temperatures of 1,000 degrees C (1,830 degrees F.)
To put this into perspective, pure lead melts at about 330 degrees C. Copper melts at 1,085 degrees C. Even a Morgan silver dollar will melt at 1,000 degrees C.
The FDR digitally stores an array of flight data such as speed, control settings, etc.
The CVR is simply a very heavily insulated and protected digital recorder. This is what has already been recovered from the Germanwings Flight 9525 which crashed in the Alps yesterday.
Finally the data recorders are generally mounted to the frame of the aircraft in the tail section which is the most survivable location in most crashes.
So, is there any record of computer-related problems in the Airbus? On October 15, 2008 The New Zealand Herald reported the results of a Australian Transport Safety Bureau investigation into an earlier Qantas flight between Singapore and Perth which experienced a sudden descent of 650 feet in a matter of seconds, injuring 70 of the 303 passengers when those not seated with seat belts on were tossed around the cabin.
When flying at angels 37 (37,000 ft.) a sensor failed, causing the autopilot to believe the airplane was about to stall which it attempted to correct by diving (the correct procedure IF it had been going too slow).
A Lufthansa flight from Bilbao to Munich experienced a sudden descent caused by the autopilot at a dangerously rapid rate of 4000 feet per minute. This was caused by icing on two sensors.
The crew was only able to regain control of the aircraft by disconnecting the autopilot unit.
In the CRC “Digital Avionics Handbook” edited by Cary R. Spitzer, Cary Spitzer discusses and illustrates the autopilot and fly-by-wire systems on the Airbus family of planes. Airbus was possibly the first commercial aircraft equipped with an electronic autopilot.
“The Airbus A320 (certified in early 1988) is the first example of a second generation of civil electrical flight control aircraft…”
Some illustrations are viewable at Google Books.
Although the Airbus fleet has an excellent safety record, there are problems with any complex machine and there have been more than 60 reported serious incidents involving the A320 family of aircraft, resulting in nearly 800 fatalities (not including any recent crashes.) – See NTSB
It is important to note that some of these incidents are not actually related to the airplanes, such as drunk pilots, towed aircraft hitting obstacles and being damaged, unavoidable collisions with vehicles sitting on landing strips, etc.
However, some incidents have been due to flying too low, perhaps dropping rapidly under autopilot control.
On the other hand, the famous Sully Sullenberger landing in the Hudson was in an Airbus disabled by bird strike – the aircraft’s quality made it possible for the pilot to land on the water and not breakup on impact.