It's not a direct cause because it does not guarantee the loss of the plane. Rather, it's an indirect cause because it puts the plane at risk unless the crew does exactly the right things.
Here's a recent example, described here on rec.aviation.piloting, dated 25 June, in which the crew responded correctly:
Well, I'm sure you have all heard of the Air France accident. I fly the
same plane, the A330.
Yesterday while coming up from Hong Kong to Tokyo, a 1700nm 4hr.
flight, we experienced the same problems Air France had while flying
thru bad weather.
I have a link to the failures that occurred on AF 447. My list is almost
the same.
http://www.eurocockpit.com/images/acars447.php
The problem I suspect is the pitot tubes ice over and you loose
your airspeed indication along with the auto pilot, auto throttles and
rudder limit protection. The rudder limit protection keeps you from over
stressing the rudder at high speed.
Synopsis;
Tuesday 23, 2009 10am enroute HKG to NRT. Entering Nara Japan airspace.
FL390 mostly clear with occasional isolated areas of rain, clouds
tops about FL410.
Outside air temperature was -50C TAT -21C (your not supposed to get
liquid water at these temps). We did.
As we were following other aircraft along our route. We approached
a large area of rain below us. Tilting the weather radar down we could
see the heavy rain below, displayed in red. At our altitude the radar
indicated green or light precipitation, most likely ice crystals we
thought.
Entering the cloud tops we experienced just light to moderate
turbulence. (The winds were around 30kts at altitude.) After about 15
sec. we encountered moderate rain. We thought it odd to have rain
streaming up the windshield at this altitude and the sound of the plane
getting pelted like an aluminum garage door. It got very warm and humid
in the cockpit all of a sudden.
Five seconds later the Captains, First Officers, and standby airspeed
indicators rolled back to 60kts. The auto pilot and auto throttles
disengaged. The Master Warning and Master Caution flashed, and the
sounds of chirps and clicks letting us know these things were happening.
Jerry Staab, the Capt. hand flew the plane on the shortest vector
out of the rain. The airspeed indicators briefly came back but failed
again. The failure lasted for THREE minutes. We flew the recommended
83%N1 power setting. When the airspeed indicators came back. we were
within 5 knots of our desired speed. Everything returned to normal
except for the computer logic controlling the plane. (We were in
alternate law for the rest of the flight.)
We had good conditions for the failure; daylight, we were rested,
relatively small area, and light turbulence. I think it could have been
much worse. Jerry did a great job fly and staying cool. We did our
procedures called dispatch and maintenance on the SAT COM and landed in
Narita. That's it. IIRC, "alternate law" is Airbus-speak for a condition where the fly-by-wire software is in alarm mode so it turns off the envelope protection it normally enforces on the flight crew.
In instrument flying there is a technique called attitude flying where a known power setting and a known pitch angle with a known aircraft configuration will always yield a certain airspeed and rate of climb/decent. This is one way to deal with the loss of the airspeed indicator. Sounds like that occurred here.
In the several accounts I have read since this horrible disaster, I have not seen a single mention if the navigation system has a groundspeed reading available to the pilot. That is commonly displayed on GPS systems. That would be another way of keeping your airpseed constant, and at least within the ballpark of where it was before your airdata system failed.
Maybe these aircraft have become so automated that they cannot be operated reliably in the event too much of the system becomes degraded.
In any case, there is a lesson here:
Airbus takes the approach that the engineers know what is best for aircraft operation. The pilot controls are filtered through rules and limits so that it is forbidden for him to command the aircraft to do something that would cause it to exceed the approved and tested envelope.
Boeing takes the approach that the pilot should have full authority, even when it might result in the aircraft being overly stressed. The reason I read was that they would rather have the pilot end up with a bent, but flyable aircraft than have a perfectly good one that crashed.
I think this is a great metaphor for the difference between the command-and-control attitude compared to the liberty-oriented approach to design
When an Airbus went down on Long Island shortly after 9/11, it was determined that the VS was lost due to excessive rudder authority being exercised during recovery from a wake turbulence encounter. The upshot? Train the crew not to use so much rudder!