A Very Halting Affair to Remember

What will have then happened is that the hot channel, Channel 2, will have relinquished control to the standby, Channel 1, which will have logged the same fault, but cannot relinquish control since it is operating without a standby. On sensing touchdown ("Weight on Wheels"), four seconds after the spoiler deployment signal, the Autobrake function of the BSCU calls the command function to apply current to open the Normal Selector Valve. The COM/MON disagreement fault becomes a failure; the Normal Selector Valve is not opened, the Autobrake function is lost and the Normal braking system is left inoperative. This is recorded in the CFDIU as a failure in the NSVs (although the actual failure was upstream), yet it is sent to the ECAM as a "BRAKES AUTO BRK FAULT" message, which is inhibited from display during landing until engine shut down (but is recorded for post-flight replay). So the crew never saw it --it was not there to be seen.

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At the end of the Ibiza overrun area, there is a sea wall and the Mediterranean Ocean. Rather than risk taking a swim, the captain swerved the aircraft from side to side to lose momentum through scrubbing the tires, and then finally managed to achieve 90 degrees of turn, bumping across the grass and into a low bank "to remain within the aerodrome boundary." The report describes the ride as "quite rough."

BSCU software Release 7 was on board; Release 8 provides a fix for the sensing discrepancy condition involved in this incident; Release 9 was released after in-service experience with Release 8. It's not known what release is presently current. But you do get the impression that one hasn't heard the last of the BSCU. It has a low-key habit of not halting one in one's tracks. With triple redundancy you at least get a referee and a fighting chance. With the twin ugly sisters of the BSCU, there's always the chance they'll not be talking to each other, or that one will be down for the count.

The G-UKLL Accident Report is available at: www.mfom.es/ciaiac/publicaciones/informes/1998/1998_019_A.pdf