It did happen on take off run at low speed as well.
Airbus published following bulletin:
Description
Why conventional BSCU logic does not allow making the distinction between a simple auto brake fault and an auto brake fault combined with a wheel braking loss?
Further to pilot remarks, the operator would like to obtain some clarifications about BSCU behaviour regarding tachometer signal failure, compared to the 3 different configurations of Atheir fleet (conventional BSCU, EMM BSCU fitted on conventional A/C and full EMM BSCU and A/C).
The main point is about flight crew information during flight when an AUTO BRAKE FAULT warning is displayed. In this case failure can be originated by a tachometer failure (TACHOMETER (XX) GG OR BSCU) or another equipment of the auto brake system.
On conventional BSCU, a tachometer signal failure with BRAKE AUTO BRAKE FAULT warning leads to loss of the auto brake function but also loss of the braking on affected wheel. In this case the crew is not formally aware of the wheel braking loss.
On EMM A/C and BSCU, according to operator's experience this failure is also associated with warning "BRAKE RELEASED"
Solution
With the BSCU EMM, a specific discrete sent to the SDAC has been created to monitor the "brake release". This discrete (brake release fault) is true in case of a tachometer failure or servovalve failure without a normal brake fault. This discrete allows to indicate to the pilot an "autobrake fault" due to a tachometer or a servovalve failure.
The ECAM message is the alert BRAKES RELEASED if FWC std E4 (or following) is installed with the pin program "NORM BRK IMPROV OPTION INSTALL" grounded on pin AA11C.
With the BSCU OLD, the distinction is not realized with for example an autobrake fault due to a COM/MON disagreement or an ELAC failure.
However, the ECAM display will inform pilot that brake is released :
BRAKES AUTOBRK FAULT
BRAKE RELEASED
Hope that helps a bit.
