OEB 48 abnormal v alpha prot

The OEB 48 abnormal v alpha prot  was made due to an incident of Lufthansa near Bilbao.

According with Aviation herald , the Lufthansa A321 had a conflict between what was happening and what the aircraft detected it was happening.

For explaining what happened we are going to start talking about the angle of attack probe (AoA). The AoA is mounted on the fuselage , by measuring the pressure  differential then it creates an electrical signal.

The airbus has different laws, with any failure the aircraft flyes in normal law which means it has some protections, such as :

• Normal law : load factor protection, pitch attitude protection, high angle of attack protection and high speed protection.
• Alternate law : the same protections mentioned before, less the pitch attitude protection , and the high angle of attack protection is replaced by stall warning.

What happened to the Lufthansa flight was that the AoA got frozen sending a high angle of attack signal to the aircraft, which means that the aircraft thought that it was on stall , so it applied for what it was programmed to. Which is to pitch down to recover the stall, but in fact it wasn´t.

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

How to know if we have had our probes frozen?

The red strip completely hides the black and ambar in a wings level flight path , with no load factor

If the black and amber strip moves by more that 30knt during flight maneuvers

How to react against it ?

To stop the uncontrolled descend due to frozen AoA is to apply a procedure which the pilot could take control of the situation, I want to remark that during that descend the aircraft don´t respond to the pilot orders because it things that the pilot wants it to be in a greater stall.
So under those circumstances there must be something that the pilot could do , which is forcing it to the alternate law.

How to force it to the alternate law ?

Now you can watch  all I have explained above