NTSB Speaks out on Collision Warning System Failure Warnings

The prime responsibility for air traffic separation is with Air Traffic Control. When either pilots or ATC fail, that's when Traffic Alert and Collision Avoidance Systems (TCAS) are the vital fallback safety measure. The NTSB has now pointed out, in the aftermath of the GOL 737/Legacy mid-air collision, that any failure mode of transponders or the TCAS itself is being insufficiently alerted to pilots. The fact that TCAS depends upon both aircraft's transponders operating has tended to elude the aviation world's "threat and error" risk management experts. It is also starting to look as if the reason why the Legacy transponder was inoperative, leading to the collision (after Brazilian ATC failed their task) will forever remain a mystery. The NTSB concern is that future "silent avionics failure" scenarios shouldn't be allowed to generate similar collision outcomes. The Board has asked the FAA to require, for all aircraft required to have TCAS installed and for existing and future system designs, that the loss of collision avoidance system functionality, for any reason, should provide an inflight enhanced aural and visual warning requiring pilot acknowledgment.