Blocked alpha probes

[tubby linton]

I was wondering how rare it is for multiple alpha probes to be blocked? In a recent incident an A321 experienced this and I was wondering where on the probe the blockage occurred as the probe is heated.It also seems strange that multiple probes were affected without other probes(pitots) also being blocked.
A previous thread was written about this two years ago(http://www.pprune.org/tech-log/50366...oa-probes.html) but doesn't reference the applicable OEB. My airline has just issued a notice about this and refers to OEB 48.Can someone upload images of the different kind of probes please.

[ACMS]

They don't actually block up, they ice up and can't move

[vilas]

AS ACMS stated there is no blockage as air doesn't go through it like Pitot tube. But water ingress can freeze or even otherwise they can get iced up due failed heating and they are unable to move. This was the reason for A320 fatal crash at Perpignan.

[tubby linton]

Do you think that only the vane and arm is heated and not the disc it is mounted on?

[rudderrudderrat]

Hi tubby linton,

I was wondering how rare it is for multiple alpha probes to be blocked?

Apparently, not as rare as you might think. EASA are concerned.
Pity Airbus never fitted a big red switch to simply disengage Normal Law.
http://www.caa.co.uk/docs/33/2014120...D20140267E.pdf
http://www.caa.co.uk/docs/33/2014120...D20140266E.pdf

[Winnerhofer]

Links

http://www.pprune.org/tech-log/50207...oa-probes.html
http://www.pprune.org/tech-log/50372...oa-probes.html

[Mad (Flt) Scientist]

Originally Posted by tubby linton

It also seems strange that multiple probes were affected without other probes(pitots) also being blocked.

Not that strange, unfortunately.

In the absence of a fault within a specific component which leaves it vulnerable (for example, a defect resulting in a blocked drain on a specific component), then the scenario is of a "common cause" environmental condition which defeats the design of the vanes. Basically, the conditions are more severe than what the vanes were designed for, or what they can in practice cope with. In which case, barring small variations in performance between the components (as is normal) it's not surprising that the same conditions would defeat all of the installations at once.

Similarly, since it is likely a function of the specific design (and design requirements) it also would not be a surprise that a specific component (say an AOA vane) was vulnerable to a set of conditions that other components could cope with. (Even if all designed to the same requirements, it wouldn't be unusual for them to have different capabilities - some might barely meet the requirement, some might have lots of margin)

[Winnerhofer]

Perpignan AOA: Danger For All!

A cruel area and 2 Rafales crashed a year on totalling 16 crashes!
A320, Rafales, DC4, PA-38 and many more!
Triangle des Bermudes Méditerranée Rafale Perpignan accident - leJDD.fr
http://aviation-safety.net/database/...0603-1&lang=fr

[tubby linton]

Thank you all for your replies. I am still looking for images of the different types of alpha probes fitted to Airbus aircraft and also which elements are heated.

[A33Zab]

AoA Probe (vane type, vane = heated)

[used on A320series;A340;A330 as AoA / A380;A350 as SSA / A350 as 4th AoA]

Goodrich:


Thales:





A380;A350 MFP (MultiFunctional Probe) I suppose both vane as base = heated.