Board Says "Critical Safety Issue" Exists With TCAS

In response to last year's midair collision over Brazil involving a private Embraer Legacy 600 business jet, and a Gol Airlines 737, on Wednesday the National Transportation Safety Board issued three safety recommendations geared at solving what the Board calls a "critical safety issue" when traffic collision avoidance systems (TCAS) fail, without the flight crew's knowledge.

As Aero-News reported, Gol Airlines flight 1907 plunged into a thickly-jungled region September 30, about 18 miles from Peixoto de Azevedo, Brazil. All 154 persons onboard the 737-800 were killed; the pilots of the Embraer were able to make an emergency landing following the collision.

The NTSB noted the bizjet's transponder was not being received by ATC radar prior to the collision... and such a failure could have compromised safety alerts in the cockpits of both aircraft.

"The investigation of this accident is ongoing," the NTSB states in its report, "however, preliminary findings suggest that a critical safety issue exists regarding the loss of functionality of an aircraft’s collision avoidance system (comprising a transponder and a traffic alert and collision avoidance system [TCAS] and resulting cockpit warnings to flight crews. Flight data recorder (FDR) and cockpit voice recorder (CVR) information from both airplanes revealed no indication of any TCAS alert on board either airplane (both airplanes were equipped with mode S transponders and TCAS II computer units), no evidence of pre-collision visual acquisition by either flight crew, and no evidence of evasive action by either crew."

To address the possibility a failed or inoperable transponder may compromise TCAS warnings, the NTSB issued the following recommendations:

• Require, for all aircraft required to have a traffic alert and collision avoidance system installed and for existing and future system designs, that the airborne loss of collision avoidance system functionality, for any reason, provide an enhanced aural and visual warning requiring pilot acknowledgment. (A-07-35)
• Evaluate the feasibility of providing enhanced aural and visual warnings for future systems that may provide ground collision avoidance functionality. If feasible, require that future design criteria include such warning functionality. (A-07-36)
• Inform all pilots who use transponders or transponder/traffic alert and collision avoidance system (TCAS) units about the circumstances of this accident and the lack of a conspicuous warning to indicate the loss of collision protection resulting from a compromise in functionality of either the transponder or TCAS unit and ask all pilots who use transponders or transponder/TCAS units to become familiar with the annunciations currently used to indicate failure or lack of active functionality of these components. (A-07-37)

FMI: Read The NTSB's Complete Recommendation Letter (.pdf)