How common is that a sensor froze ?

[Swiso]

http://avherald.com/h?article=47d74074

Wow.
Is really that common for sensors to froze ?
I know about Pitot tubes but never heard of those ones to happen.

[cagarini]

That's why I always feel better flying Boeing.... Fokker, Embraer, ATP, Canadair....

I can never forget that Airbus A320-100 accident in Alsace, due to the FBW system...

And they want us to fly without pilots in the cockpit in the future too...

[OmniAtlas]

AF447
That AirAsia Indonesian flight.

I still fly on an Airbus.

I'm building an Airbus home cockpit (Sorry Hardy! But your software is fantastic and I wish all avionics suites were up to the same fidelity).

[John H Watson]

Is really that common for sensors to froze ?

It's not common, but Airbus is working on a fix, and pilots are being trained how to handle the problem (in the meantime).
From what I've read, the sensor is like a pitot tube. This is quite different from the common vane type (which rarely freezes up).

I've been told that Airbus were given incentives by the French government to come up with different ways of doing things (probably to avoid copyrights/patents). This hasn't always been good for them. From what I saw on the A380, some of the simplest things were made ridiculously complicated.

[Swiso]

Is this a problem (the freezing)  mainly affecting only Airbus , or is more frequent with Airbus ?
Just to know...
I saw a Pilotseye documentary, a flight from Wien to Tokio, in a 777, where the Captain mention that the outside temperature to be like -62 deg. C !
Now...that's cold !!!!

[JRBarrett]

Is this a problem (the freezing)  mainly affecting only Airbus , or is more frequent with Airbus ?
Just to know...
I saw a Pilotseye documentary, a flight from Wien to Tokio, in a 777, where the Captain mention that the outside temperature to be like -62 deg. C !
Now...that's cold !!!!

-62C is not at all uncommon, especially in winter. The real "danger zone" for icing up of sensors (pitot tubes, AOA vanes etc) is actually when the OAT is considerably warmer - i.e. above approx -35 C.

It is possible, under the right conditions, for supercooled cloud droplets to still be in liquid form even at temperatures well below zero C. These will freeze instantly on impact with the aircraft structure, and can accumulate very rapidly.

At temps below -40 C, supercooled water cannot exist - any moisture will be in the form of ice crystals. Although ice crystals (if dense enough) can block a pitot tube - especially if the tube's heating element is inadequate, freezing of an AOA vane, where it becomes "locked" in place, likely occurs in warmer air - conducive to the accumulation of clear or rime ice.

I have no familiarity with Airbus AOA probes. Most of the aircraft I have maintained in the corporate world have AOA vanes which resemble miniature airfoils - this is true of Dassault, Hawker and Bombardier (Lear) aircraft. The vanes have a reasonable "dense" structure (weight) and pivot on mounts which have a reasonable amount of clearance around the periphery - in other words, it would take a LOT of ice, collecting at the base of the vane, to lock it in place.

An exception to this is the Gulfstream IV, which has an AOA probe shaped like a cone. The cone has slots cut into its surface which catch the air flowing past, and cause it to rotate. The cone is extremely light - very little mass at all, and VERY little clearance at its base with the surrounding fuselage. They appear to be custom made to catch ice. I don't know the history of AOA probe icing on the GIV - but it is not a fly-by-wire aircraft. If both probes froze into a high AOA position, it might cause a false stall warning - but the stall barrier system is easily disconnected. Their other function is to affect the amount of static source error correction being applied by the ADCs, which could lead to an error of displayed altitude by a few hundred feet - but other than that, they are not critical to aircraft auto flight.

I wonder if the Airbus AOA probes are of a similar slotted-cone design. Obviously the AOA readings are far more critical to the proper functioning of a FBW Airbus.

[nicolas]

Being a European I hate to say that I trust Boeing's systems more. The level of automatization at Airbus is too high and when things go wrong the pilots may be overwhelmed. Fortunately the LH pilot was well trained to recover the control of his plane.
IMO.

Nic

[Swiso]

Is this a problem (the freezing)  mainly affecting only Airbus , or is more frequent with Airbus ?
Just to know...
I saw a Pilotseye documentary, a flight from Wien to Tokio, in a 777, where the Captain mention that the outside temperature to be like -62 deg. C !
Now...that's cold !!!!

-62C is not at all uncommon, especially in winter. The real "danger zone" for icing up of sensors (pitot tubes, AOA vanes etc) is actually when the OAT is considerably warmer - i.e. above approx -35 C.

It is possible, under the right conditions, for supercooled cloud droplets to still be in liquid form even at temperatures well below zero C. These will freeze instantly on impact with the aircraft structure, and can accumulate very rapidly.

At temps below -40 C, supercooled water cannot exist - any moisture will be in the form of ice crystals. Although ice crystals (if dense enough) can block a pitot tube - especially if the tube's heating element is inadequate, freezing of an AOA vane, where it becomes "locked" in place, likely occurs in warmer air - conducive to the accumulation of clear or rime ice.

I have no familiarity with Airbus AOA probes. Most of the aircraft I have maintained in the corporate world have AOA vanes which resemble miniature airfoils - this is true of Dassault, Hawker and Bombardier (Lear) aircraft. The vanes have a reasonable "dense" structure (weight) and pivot on mounts which have a reasonable amount of clearance around the periphery - in other words, it would take a LOT of ice, collecting at the base of the vane, to lock it in place.

An exception to this is the Gulfstream IV, which has an AOA probe shaped like a cone. The cone has slots cut into its surface which catch the air flowing past, and cause it to rotate. The cone is extremely light - very little mass at all, and VERY little clearance at its base with the surrounding fuselage. They appear to be custom made to catch ice. I don't know the history of AOA probe icing on the GIV - but it is not a fly-by-wire aircraft. If both probes froze into a high AOA position, it might cause a false stall warning - but the stall barrier system is easily disconnected. Their other function is to affect the amount of static source error correction being applied by the ADCs, which could lead to an error of displayed altitude by a few hundred feet - but other than that, they are not critical to aircraft auto flight.

I wonder if the Airbus AOA probes are of a similar slotted-cone design. Obviously the AOA readings are far more critical to the proper functioning of a FBW Airbus.

Thank you very much for the detailed explanation, very helpful.

Aris

[United744]

IIRC the Airbus has the vane type. If that is what was fitted to this one, that is very concerning.

Even worse, is how ONE parameter can be off to cause this (though two sources said the same thing). If the airspeed was low as well, then likely a stall, but a normal airspeed, g around 1.0 and climbing VS should have caused a sensor alert, not pitch down to recover from a "stall".