Narrative:

I was the PF. During cruise flight at FL280, we were approximately 10 mi from bikkr intersection when we received a TCASII alert showing a target at 11:30 O'clock position and 20 mi. The target presentation had gone from white/small to yellow/large. The target was showing level at FL288. The scale on the moving map display was on 40 mi, so I changed it to 20 mi to increase the accuracy of the target's location. The aircraft remained at FL288 and there was no climb/descent arrow. With both crew members looking for the traffic, there was no time to contact ATC, nor did they contact us. I selected the 'flight level' mode for the TCASII display, and further reduced the scale to 10 mi as the target aircraft was within 9 mi of our position. At this juncture, the target aircraft was still level at FL288 and neither myself nor the first officer had visual contact with the target aircraft. As the intruder aircraft neared the 5 mi arc, I further reduced the TCASII scale to 5 mi and we received an RA commanding us to descend at a rate of 2000 FPM. I disconnected the autoplt from the altitude hold/RNAV mode to follow the command as the first officer made visual contact with the nearing aircraft. I hesitantly started the descent, for I noticed on the TCASII display a 'down arrow' and that the aircraft's altitude was descending. Something did not look right. I shallowed out the descent at FL277 while the first officer pointed out the aircraft at 10 O'clock position, 1-2 mi offset to our left. It was a small jet descending. Having just stopped the descent, the TCASII now commanded a climb to be executed at a rate of 1500 FPM. We climbed back to our cruising altitude of FL280. As the aircraft passed our left wing, ATC contacted us about the traffic. We informed them that the aircraft was in sight and that we had an RA. ATC thought that the aircraft was level, and we informed them that the other aircraft was not level and in fact was descending. A factor contributing to the confusion was that the intruder aircraft was in ZLA's airspace while we were in ZOA's airspace. The controllers were unsure if the target aircraft has followed a TCASII command. Had we aggressively followed the TCASII command to descend at 2000 FPM, we would have been at the same altitude as the small jet and had a difficult time trying to recover and follow the TCASII command. The controller asked us to call them upon arrival. I contacted dispatch, advised them of the event and asked if they wanted any recorder circuit breakers pulled. After conferring with duty control, dispatch just asked for us to call them upon arrival.

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Original NASA ASRS Text

Title: B737-700 FLC RECEIVES RA DURING CRUISE.

Narrative: I WAS THE PF. DURING CRUISE FLT AT FL280, WE WERE APPROX 10 MI FROM BIKKR INTXN WHEN WE RECEIVED A TCASII ALERT SHOWING A TARGET AT 11:30 O'CLOCK POS AND 20 MI. THE TARGET PRESENTATION HAD GONE FROM WHITE/SMALL TO YELLOW/LARGE. THE TARGET WAS SHOWING LEVEL AT FL288. THE SCALE ON THE MOVING MAP DISPLAY WAS ON 40 MI, SO I CHANGED IT TO 20 MI TO INCREASE THE ACCURACY OF THE TARGET'S LOCATION. THE ACFT REMAINED AT FL288 AND THERE WAS NO CLB/DSCNT ARROW. WITH BOTH CREW MEMBERS LOOKING FOR THE TFC, THERE WAS NO TIME TO CONTACT ATC, NOR DID THEY CONTACT US. I SELECTED THE 'FLT LEVEL' MODE FOR THE TCASII DISPLAY, AND FURTHER REDUCED THE SCALE TO 10 MI AS THE TARGET ACFT WAS WITHIN 9 MI OF OUR POS. AT THIS JUNCTURE, THE TARGET ACFT WAS STILL LEVEL AT FL288 AND NEITHER MYSELF NOR THE FO HAD VISUAL CONTACT WITH THE TARGET ACFT. AS THE INTRUDER ACFT NEARED THE 5 MI ARC, I FURTHER REDUCED THE TCASII SCALE TO 5 MI AND WE RECEIVED AN RA COMMANDING US TO DSND AT A RATE OF 2000 FPM. I DISCONNECTED THE AUTOPLT FROM THE ALT HOLD/RNAV MODE TO FOLLOW THE COMMAND AS THE FO MADE VISUAL CONTACT WITH THE NEARING ACFT. I HESITANTLY STARTED THE DSCNT, FOR I NOTICED ON THE TCASII DISPLAY A 'DOWN ARROW' AND THAT THE ACFT'S ALT WAS DSNDING. SOMETHING DID NOT LOOK RIGHT. I SHALLOWED OUT THE DSCNT AT FL277 WHILE THE FO POINTED OUT THE ACFT AT 10 O'CLOCK POS, 1-2 MI OFFSET TO OUR L. IT WAS A SMALL JET DSNDING. HAVING JUST STOPPED THE DSCNT, THE TCASII NOW COMMANDED A CLB TO BE EXECUTED AT A RATE OF 1500 FPM. WE CLBED BACK TO OUR CRUISING ALT OF FL280. AS THE ACFT PASSED OUR L WING, ATC CONTACTED US ABOUT THE TFC. WE INFORMED THEM THAT THE ACFT WAS IN SIGHT AND THAT WE HAD AN RA. ATC THOUGHT THAT THE ACFT WAS LEVEL, AND WE INFORMED THEM THAT THE OTHER ACFT WAS NOT LEVEL AND IN FACT WAS DSNDING. A FACTOR CONTRIBUTING TO THE CONFUSION WAS THAT THE INTRUDER ACFT WAS IN ZLA'S AIRSPACE WHILE WE WERE IN ZOA'S AIRSPACE. THE CTLRS WERE UNSURE IF THE TARGET ACFT HAS FOLLOWED A TCASII COMMAND. HAD WE AGGRESSIVELY FOLLOWED THE TCASII COMMAND TO DSND AT 2000 FPM, WE WOULD HAVE BEEN AT THE SAME ALT AS THE SMALL JET AND HAD A DIFFICULT TIME TRYING TO RECOVER AND FOLLOW THE TCASII COMMAND. THE CTLR ASKED US TO CALL THEM UPON ARR. I CONTACTED DISPATCH, ADVISED THEM OF THE EVENT AND ASKED IF THEY WANTED ANY RECORDER CIRCUIT BREAKERS PULLED. AFTER CONFERRING WITH DUTY CTL, DISPATCH JUST ASKED FOR US TO CALL THEM UPON ARR.

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.