Narrative:

Upon takeoff at oak, runway 29L, we switched to departure control at 500 ft and was instructed to climb to FL230. At 800 ft we received a 'reduce climb, reduce climb' RA from the TCASII, with a red target displayed on the map, at 1 mi and level with us. At this time we entered the clouds, and reduced the pitch attitude to comply with the TCASII RA command. At 1200 ft we received a 'descend, descend' RA on the TCASII, with the target still on the nose, level. We pushed the nose over gently and began a descent to comply with the TCASII RA command. Below 1000 ft we got a GPWS 'too low terrain' and 'too low gear' warning at the same time the TCASII was telling us to descend. At 500 ft above the ground, we were clear of clouds, no visual traffic, and the TCASII target disappeared. During this descent, departure control repeated the 'climb to FL230' clearance, but we could not talk to him because of the conflicting aural warnings in the cockpit. We resumed the climb when it was apparent there was no traffic, the GPWS warnings stopped, and we notified departure of the conflict. He stated there was no radar traffic in the area, and there had been other false warnings caused by ship xponders in the bay area. We called them back later in the climb, and they told us another air carrier flight off sfo had also received a false 'descend' RA on their TCASII, and also took evasive action. Looking back, there is no doubt the target was false, as it followed us in the descent, and never changed position on the map until it went away. Also, there was no radar targets in the area. The TCASII did not announce 'clear of conflict' as it does for a passing target. Since we were in the clouds, we could not conform visually the target, we had to choice but to follow the RA as is our instructed procedure. We were over the bay, flat terrain, so I had no problem descending IFR to follow the alert. However, TCASII is not supposed to give 'descend' RA's below 1000 ft AGL. We wrote up the unit, and maintenance removed it. We were in the clouds, with conflicting commands from TCASII and GPWS. If I were unsure of the terrain, I would had disregarded the TCASII command, and followed the GPWS commands, possibly turning to avoid the target. TCASII resolutions provide for climbs on dscnts, not turns. Callback conversation with reporter revealed the following information: reporter could not add much to initial report. He stated that the safety division of his air carrier was contacted with the information relating to this incident. They said that they were assigning an individual to 'work with' ZOA regarding this problem of false TCASII RA's. Supplemental information from acn 280923: now we began to receive a 'don't sink' warning from the GPWS due to our low altitude. Departure control then called to inquire about our climb or lack of climb at about the same time the GPWS burped 'too low terrain' or 'terrain, terrain.' the confusion and tension in the cockpit was quite high as the captain told departure that we were responding to a TCASII RA. At about this time we descended out of the overcast and could not see any aircraft in our vicinity. We contacted both our maintenance base and dispatch to inform them of the event since we could not be sure if there was a problem with our TCASII hardware, software (which could affect hundreds of aircraft) or some kind of local electromagnetic interference. Although the entire event lasted 20-30 seconds, it felt longer at the time. The captain and I agreed that under different circumstances, say a low visibility takeoff or an engine failure after takeoff, that the conflicting commands ('descend, descend'/'terrain, terrain') could easily cause an accident.

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Original NASA ASRS Text

Title: EVASIVE ACTION DSCNT BASED UPON A LATER IDENTED FALSE WARNING ON TCASII RA EVOKES A GPWS WARNING.

Narrative: UPON TKOF AT OAK, RWY 29L, WE SWITCHED TO DEP CTL AT 500 FT AND WAS INSTRUCTED TO CLB TO FL230. AT 800 FT WE RECEIVED A 'REDUCE CLB, REDUCE CLB' RA FROM THE TCASII, WITH A RED TARGET DISPLAYED ON THE MAP, AT 1 MI AND LEVEL WITH US. AT THIS TIME WE ENTERED THE CLOUDS, AND REDUCED THE PITCH ATTITUDE TO COMPLY WITH THE TCASII RA COMMAND. AT 1200 FT WE RECEIVED A 'DSND, DSND' RA ON THE TCASII, WITH THE TARGET STILL ON THE NOSE, LEVEL. WE PUSHED THE NOSE OVER GENTLY AND BEGAN A DSCNT TO COMPLY WITH THE TCASII RA COMMAND. BELOW 1000 FT WE GOT A GPWS 'TOO LOW TERRAIN' AND 'TOO LOW GEAR' WARNING AT THE SAME TIME THE TCASII WAS TELLING US TO DSND. AT 500 FT ABOVE THE GND, WE WERE CLR OF CLOUDS, NO VISUAL TFC, AND THE TCASII TARGET DISAPPEARED. DURING THIS DSCNT, DEP CTL REPEATED THE 'CLB TO FL230' CLRNC, BUT WE COULD NOT TALK TO HIM BECAUSE OF THE CONFLICTING AURAL WARNINGS IN THE COCKPIT. WE RESUMED THE CLB WHEN IT WAS APPARENT THERE WAS NO TFC, THE GPWS WARNINGS STOPPED, AND WE NOTIFIED DEP OF THE CONFLICT. HE STATED THERE WAS NO RADAR TFC IN THE AREA, AND THERE HAD BEEN OTHER FALSE WARNINGS CAUSED BY SHIP XPONDERS IN THE BAY AREA. WE CALLED THEM BACK LATER IN THE CLB, AND THEY TOLD US ANOTHER ACR FLT OFF SFO HAD ALSO RECEIVED A FALSE 'DSND' RA ON THEIR TCASII, AND ALSO TOOK EVASIVE ACTION. LOOKING BACK, THERE IS NO DOUBT THE TARGET WAS FALSE, AS IT FOLLOWED US IN THE DSCNT, AND NEVER CHANGED POS ON THE MAP UNTIL IT WENT AWAY. ALSO, THERE WAS NO RADAR TARGETS IN THE AREA. THE TCASII DID NOT ANNOUNCE 'CLR OF CONFLICT' AS IT DOES FOR A PASSING TARGET. SINCE WE WERE IN THE CLOUDS, WE COULD NOT CONFORM VISUALLY THE TARGET, WE HAD TO CHOICE BUT TO FOLLOW THE RA AS IS OUR INSTRUCTED PROC. WE WERE OVER THE BAY, FLAT TERRAIN, SO I HAD NO PROB DSNDING IFR TO FOLLOW THE ALERT. HOWEVER, TCASII IS NOT SUPPOSED TO GIVE 'DSND' RA'S BELOW 1000 FT AGL. WE WROTE UP THE UNIT, AND MAINT REMOVED IT. WE WERE IN THE CLOUDS, WITH CONFLICTING COMMANDS FROM TCASII AND GPWS. IF I WERE UNSURE OF THE TERRAIN, I WOULD HAD DISREGARDED THE TCASII COMMAND, AND FOLLOWED THE GPWS COMMANDS, POSSIBLY TURNING TO AVOID THE TARGET. TCASII RESOLUTIONS PROVIDE FOR CLBS ON DSCNTS, NOT TURNS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR COULD NOT ADD MUCH TO INITIAL RPT. HE STATED THAT THE SAFETY DIVISION OF HIS ACR WAS CONTACTED WITH THE INFO RELATING TO THIS INCIDENT. THEY SAID THAT THEY WERE ASSIGNING AN INDIVIDUAL TO 'WORK WITH' ZOA REGARDING THIS PROB OF FALSE TCASII RA'S. SUPPLEMENTAL INFO FROM ACN 280923: NOW WE BEGAN TO RECEIVE A 'DON'T SINK' WARNING FROM THE GPWS DUE TO OUR LOW ALT. DEP CTL THEN CALLED TO INQUIRE ABOUT OUR CLB OR LACK OF CLB AT ABOUT THE SAME TIME THE GPWS BURPED 'TOO LOW TERRAIN' OR 'TERRAIN, TERRAIN.' THE CONFUSION AND TENSION IN THE COCKPIT WAS QUITE HIGH AS THE CAPT TOLD DEP THAT WE WERE RESPONDING TO A TCASII RA. AT ABOUT THIS TIME WE DSNDED OUT OF THE OVCST AND COULD NOT SEE ANY ACFT IN OUR VICINITY. WE CONTACTED BOTH OUR MAINT BASE AND DISPATCH TO INFORM THEM OF THE EVENT SINCE WE COULD NOT BE SURE IF THERE WAS A PROB WITH OUR TCASII HARDWARE, SOFTWARE (WHICH COULD AFFECT HUNDREDS OF ACFT) OR SOME KIND OF LCL ELECTROMAGNETIC INTERFERENCE. ALTHOUGH THE ENTIRE EVENT LASTED 20-30 SECONDS, IT FELT LONGER AT THE TIME. THE CAPT AND I AGREED THAT UNDER DIFFERENT CIRCUMSTANCES, SAY A LOW VISIBILITY TKOF OR AN ENG FAILURE AFTER TKOF, THAT THE CONFLICTING COMMANDS ('DSND, DSND'/'TERRAIN, TERRAIN') COULD EASILY CAUSE AN ACCIDENT.

Data retrieved from NASA's ASRS site as of July 2007 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.