A B737-800 had an apparent TCAS null bus failure which caused them to take evasive action from a tar...

Narrative:

[The event was a] TCAS RA altitude deviation with no traffic separation issue. TCAS RA at FL400 we had a sudden TCAS RA showing traffic on the nose less than 1 mile and same altitude. We immediately responded per the operations manual and hand flew the aircraft in a climb. The target aircraft stayed at our altitude the entire time as we climbed +700 ft and notified ATC. The controller stated that no other aircraft were in that airspace and he noted our RA climb. We then selected the TA only mode on the transponder and returned to assigned altitude. When we turned the transponder to TA only; both nd on captain's and first officer's maps went blank. Both faults were written up in the logbook. Since no traffic separation was noted by ATC; we did not believe a [incident report] was required; however both the map blanking and the TCAS malfunction were noted in the maintenance log.

Original NASA ASRS Text

Title: A B737-800 had an apparent TCAS Null Bus failure which caused them to take evasive action from a target at FL400 less than a mile from their aircraft. ATC reported no other traffic in the area.

Narrative: [The event was a] TCAS RA altitude deviation with no traffic separation issue. TCAS RA at FL400 we had a sudden TCAS RA showing traffic on the nose less than 1 mile and same altitude. We immediately responded per the operations manual and hand flew the aircraft in a climb. The target aircraft stayed at our altitude the entire time as we climbed +700 FT and notified ATC. The Controller stated that no other aircraft were in that airspace and he noted our RA climb. We then selected the TA only mode on the transponder and returned to assigned altitude. When we turned the transponder to TA only; both ND on Captain's and First Officer's maps went blank. Both faults were written up in the logbook. Since no traffic separation was noted by ATC; we did not believe a [incident report] was required; however both the map blanking and the TCAS malfunction were noted in the maintenance log.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	984385
Time
Date	201111
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Traffic Collision Avoidance System (TCAS)
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

A B737-800 had an apparent TCAS null bus failure which caused them to take evasive action from a target at FL400 less than a mile from their aircraft. ATC reported no other traffic in the area.