Narrative:

During night IFR level flight at 11000 ft while on the gardner 2 arrival into bos, east of gardner VOR (gdm) speed 250 KTS assigned. ATC advised us of traffic 1000 ft below proceeding left to right ahead of us. I advised them no visual contact, however we had traffic on TCASII. MEA in this area is 4000 ft on the gdm arrival. Very soon thereafter (10-15 seconds) 'too low terrain' warnings occurred. I noticed our radio altimeter reading 980 ft in red numbers. First officer was PF and he instantly initiated SOP's of maximum power, pitch up 15 degrees and climbed until warnings ceased at approximately 14500 ft MSL. We leveled off at 15300 ft then down to 15000 ft. Throughout this evasive action I attempted to advise approach control of our actions, ATC traffic was very heavy. Once we were level at 15000 ft I had time to fully explain why we had climbed. We proceeded to bos uneventfully. In retrospect it was a false warning for reasons unknown, possibly a faulty GPWS. Our maintenance crew couldn't locate problem. First officer did an excellent job as a procedure like this is not one that you situation and discuss prior to responding. Everything went well except that I had difficulty contacting ATC who later said we had traffic at 13000 ft above us as we climbed from 11000 ft up to 15000 ft. Callback conversation with reporter revealed the following information: reporter states that the radio altimeter really got his attention because not only did the numbers light up in red, but the entire radio altimeter was red and this is not something that he had experienced in training. The first officer initiated an evasive maneuver while the reporter (PNF and captain) related the GPWS response to the controller. The GPWS warning continued for about 1 to 1 1/2 mins as the flight crew 'climbed like crazy.' the reporter states that he supported the first officer's response as this was a night flight in IMC, and he had heard too many (post crash) cvr's of 'this can't be,' while in training, to not respond. The reporter still felt certain that they were established on the arrival and that the nearest terrain was 6000 ft below. The controller's only comment to the event was that there had been traffic above reporter's B737-300 when the first officer responded to the GPWS. Reporter states that he did not receive a TCASII on the higher traffic. The only TCASII was of the lower traffic and it was indicated in white, showing 1000 ft below. This captain believes that it is possible for the radio altimeter to pick up traffic that is stacked on the same track, but he has never heard of the altimeter picking up crossing traffic and then setting off a GPWS warning. The traffic first appeared on the TCASII display forward of the 9 O'clock position and it crossed behind the right wing.

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Original NASA ASRS Text

Title: A B737-300 FLC RECEIVED A GPWS WARNING WHILE ESTABLISHED ON THE BOS GARDNER 2 ARR. THE FO (PF) IMMEDIATELY RESPONDED ACCORDING TO STANDARD OPERATING PROCS, CLBING APPROX 4300 FT, WHILE THE CAPT NOTIFIED ATC. AFTER ARRIVING AT THE DEST, RPTR (CAPT) COORDINATED WITH AIRLINE MAINT, BUT THEY WERE UNABLE TO LOCATE A PROB. THE RPTR BELIEVES THAT THE WARNING RESULTED FROM A FAULTY GPWS. EVASIVE ACTION CLB.

Narrative: DURING NIGHT IFR LEVEL FLT AT 11000 FT WHILE ON THE GARDNER 2 ARR INTO BOS, E OF GARDNER VOR (GDM) SPD 250 KTS ASSIGNED. ATC ADVISED US OF TFC 1000 FT BELOW PROCEEDING L TO R AHEAD OF US. I ADVISED THEM NO VISUAL CONTACT, HOWEVER WE HAD TFC ON TCASII. MEA IN THIS AREA IS 4000 FT ON THE GDM ARR. VERY SOON THEREAFTER (10-15 SECONDS) 'TOO LOW TERRAIN' WARNINGS OCCURRED. I NOTICED OUR RADIO ALTIMETER READING 980 FT IN RED NUMBERS. FO WAS PF AND HE INSTANTLY INITIATED SOP'S OF MAX PWR, PITCH UP 15 DEGS AND CLBED UNTIL WARNINGS CEASED AT APPROX 14500 FT MSL. WE LEVELED OFF AT 15300 FT THEN DOWN TO 15000 FT. THROUGHOUT THIS EVASIVE ACTION I ATTEMPTED TO ADVISE APCH CTL OF OUR ACTIONS, ATC TFC WAS VERY HVY. ONCE WE WERE LEVEL AT 15000 FT I HAD TIME TO FULLY EXPLAIN WHY WE HAD CLBED. WE PROCEEDED TO BOS UNEVENTFULLY. IN RETROSPECT IT WAS A FALSE WARNING FOR REASONS UNKNOWN, POSSIBLY A FAULTY GPWS. OUR MAINT CREW COULDN'T LOCATE PROB. FO DID AN EXCELLENT JOB AS A PROC LIKE THIS IS NOT ONE THAT YOU SIT AND DISCUSS PRIOR TO RESPONDING. EVERYTHING WENT WELL EXCEPT THAT I HAD DIFFICULTY CONTACTING ATC WHO LATER SAID WE HAD TFC AT 13000 FT ABOVE US AS WE CLBED FROM 11000 FT UP TO 15000 FT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THE RADIO ALTIMETER REALLY GOT HIS ATTN BECAUSE NOT ONLY DID THE NUMBERS LIGHT UP IN RED, BUT THE ENTIRE RADIO ALTIMETER WAS RED AND THIS IS NOT SOMETHING THAT HE HAD EXPERIENCED IN TRAINING. THE FO INITIATED AN EVASIVE MANEUVER WHILE THE RPTR (PNF AND CAPT) RELATED THE GPWS RESPONSE TO THE CTLR. THE GPWS WARNING CONTINUED FOR ABOUT 1 TO 1 1/2 MINS AS THE FLC 'CLBED LIKE CRAZY.' THE RPTR STATES THAT HE SUPPORTED THE FO'S RESPONSE AS THIS WAS A NIGHT FLT IN IMC, AND HE HAD HEARD TOO MANY (POST CRASH) CVR'S OF 'THIS CAN'T BE,' WHILE IN TRAINING, TO NOT RESPOND. THE RPTR STILL FELT CERTAIN THAT THEY WERE ESTABLISHED ON THE ARR AND THAT THE NEAREST TERRAIN WAS 6000 FT BELOW. THE CTLR'S ONLY COMMENT TO THE EVENT WAS THAT THERE HAD BEEN TFC ABOVE RPTR'S B737-300 WHEN THE FO RESPONDED TO THE GPWS. RPTR STATES THAT HE DID NOT RECEIVE A TCASII ON THE HIGHER TFC. THE ONLY TCASII WAS OF THE LOWER TFC AND IT WAS INDICATED IN WHITE, SHOWING 1000 FT BELOW. THIS CAPT BELIEVES THAT IT IS POSSIBLE FOR THE RADIO ALTIMETER TO PICK UP TFC THAT IS STACKED ON THE SAME TRACK, BUT HE HAS NEVER HEARD OF THE ALTIMETER PICKING UP XING TFC AND THEN SETTING OFF A GPWS WARNING. THE TFC FIRST APPEARED ON THE TCASII DISPLAY FORWARD OF THE 9 O'CLOCK POS AND IT CROSSED BEHIND THE R WING.

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.