Narrative:

On arrival into reno; we were given a vector from mustang (fmg) of 160 degrees; 210 KTS at 9000 ft. We knew we did not have a GPWS (MEL) and we reviewed the arrival; the terrain and the minimum safe altitudes. We noted that the MSA south of the fmg VOR was 12000 ft. We were night IMC during this vector and had no ground reference. Prior to the vector we discussed with the controller that we did not have GPWS and that he must keep us clear of terrain. He said that we would be fine on the vector but that we might get a terrain warning. We told the controller that we should be vectored clear of areas that would give us a warning. We were assured there would be no problem. Shortly thereafter; we received a terrain warning and a pull up command which surprised both of us. Given that we were in night IMC conditions and had no GPWS display; we honored the command and initiated a climb to 10800 ft at climb thrust. We advised the controller of our altitude deviation and why. The controller wanted us to level at 10000 ft because there was another aircraft behind us at a higher altitude; possibly 11000 ft but I don't recall exactly. We explained that it took some altitude to stop our climb passing through 10000 ft and descend back down to a lower altitude. There was no issue with vertical or horizontal separation with another aircraft at any time during this sequence of events. We were then given a vector to intercept the localizer DME (back course) runway 34L final. An uneventful 40 degree flap landing was made and we taxied to the gate. Once on the ground; the aircrew discussed the thought that we should not have an operating GPWS system per MEL which requires the system to be deactivated by pulling and collaring the ground proximity warn circuit breaker on the P18-1 panel. We knew we didn't have a terrain display because it didn't work and the MEL sticker was next to it. We then got out the QRH and found that the ground proximity warn circuit breaker was located at P-18-1-a-7. We then looked directly at the circuit breaker and saw that it was in and had not been pulled and collared. We then suspected that the system may have thought that it was in a different location; thereby giving us a false warning. Given our track over the ground; we should not have received a terrain warning since the highest peak near our track was 7864 ft and we were level at 9000 ft. We flew one more leg where we talked to someone in maintenance. That person said that the breaker should have been pulled and collared; but obviously was not. He also stated that it was not uncommon to have a breaker left out to see if the system would work on subsequent flts. If this does occasionally happen; it would require subsequent aircrews to check the system then report that the system worked or didn't work. If it didn't work then the circuit breaker would have to be pulled and collared. That is not procedurally correct and did not happen in this case as far as we know. Several actions attributed to this sequence of events. First; the circuit breaker was not pulled and collared while the maintenance write-up occurred and the MEL stickers placed in the GPWS display. Second; the aircrew did not check to see that the circuit breaker was pulled per the MEL. A few circumstances may have contributed to item #2. The plane was late arriving and the MEL/cdl text was 5 pages long and included a fuel MEL; which rushed the crew. The logbook write-up was correct and the display was MEL'ed correctly so the circuit breaker must have been pulled and collared. Also; panel P18-1 had many circuit breakers pulled and collared and the aircrew may have thought that one of the collared breakers was the GPWS breaker. The bottom line is that maintenance and the aircrew should check and ensure that all of the MEL is complied with. Had the MEL been fully complied with in this case; there would not have been a flight crew reaction to an erroneous GPWS cue in a night; IMC; mountainous environment with no GPWS display.

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Original NASA ASRS Text

Title: B737 CREW RECEIVES GPWS WARNING WHILE ON RADAR VECTORS DOWN WIND AT 9000 FEET EAST OF GINGER.

Narrative: ON ARR INTO RENO; WE WERE GIVEN A VECTOR FROM MUSTANG (FMG) OF 160 DEGS; 210 KTS AT 9000 FT. WE KNEW WE DID NOT HAVE A GPWS (MEL) AND WE REVIEWED THE ARR; THE TERRAIN AND THE MINIMUM SAFE ALTS. WE NOTED THAT THE MSA S OF THE FMG VOR WAS 12000 FT. WE WERE NIGHT IMC DURING THIS VECTOR AND HAD NO GND REF. PRIOR TO THE VECTOR WE DISCUSSED WITH THE CTLR THAT WE DID NOT HAVE GPWS AND THAT HE MUST KEEP US CLR OF TERRAIN. HE SAID THAT WE WOULD BE FINE ON THE VECTOR BUT THAT WE MIGHT GET A TERRAIN WARNING. WE TOLD THE CTLR THAT WE SHOULD BE VECTORED CLR OF AREAS THAT WOULD GIVE US A WARNING. WE WERE ASSURED THERE WOULD BE NO PROB. SHORTLY THEREAFTER; WE RECEIVED A TERRAIN WARNING AND A PULL UP COMMAND WHICH SURPRISED BOTH OF US. GIVEN THAT WE WERE IN NIGHT IMC CONDITIONS AND HAD NO GPWS DISPLAY; WE HONORED THE COMMAND AND INITIATED A CLB TO 10800 FT AT CLB THRUST. WE ADVISED THE CTLR OF OUR ALTDEV AND WHY. THE CTLR WANTED US TO LEVEL AT 10000 FT BECAUSE THERE WAS ANOTHER ACFT BEHIND US AT A HIGHER ALT; POSSIBLY 11000 FT BUT I DON'T RECALL EXACTLY. WE EXPLAINED THAT IT TOOK SOME ALT TO STOP OUR CLB PASSING THROUGH 10000 FT AND DSND BACK DOWN TO A LOWER ALT. THERE WAS NO ISSUE WITH VERT OR HORIZ SEPARATION WITH ANOTHER ACFT AT ANY TIME DURING THIS SEQUENCE OF EVENTS. WE WERE THEN GIVEN A VECTOR TO INTERCEPT THE LOC DME (BACK COURSE) RWY 34L FINAL. AN UNEVENTFUL 40 DEG FLAP LNDG WAS MADE AND WE TAXIED TO THE GATE. ONCE ON THE GND; THE AIRCREW DISCUSSED THE THOUGHT THAT WE SHOULD NOT HAVE AN OPERATING GPWS SYS PER MEL WHICH REQUIRES THE SYS TO BE DEACTIVATED BY PULLING AND COLLARING THE GND PROX WARN CIRCUIT BREAKER ON THE P18-1 PANEL. WE KNEW WE DIDN'T HAVE A TERRAIN DISPLAY BECAUSE IT DIDN'T WORK AND THE MEL STICKER WAS NEXT TO IT. WE THEN GOT OUT THE QRH AND FOUND THAT THE GND PROX WARN CIRCUIT BREAKER WAS LOCATED AT P-18-1-A-7. WE THEN LOOKED DIRECTLY AT THE CIRCUIT BREAKER AND SAW THAT IT WAS IN AND HAD NOT BEEN PULLED AND COLLARED. WE THEN SUSPECTED THAT THE SYS MAY HAVE THOUGHT THAT IT WAS IN A DIFFERENT LOCATION; THEREBY GIVING US A FALSE WARNING. GIVEN OUR TRACK OVER THE GND; WE SHOULD NOT HAVE RECEIVED A TERRAIN WARNING SINCE THE HIGHEST PEAK NEAR OUR TRACK WAS 7864 FT AND WE WERE LEVEL AT 9000 FT. WE FLEW ONE MORE LEG WHERE WE TALKED TO SOMEONE IN MAINT. THAT PERSON SAID THAT THE BREAKER SHOULD HAVE BEEN PULLED AND COLLARED; BUT OBVIOUSLY WAS NOT. HE ALSO STATED THAT IT WAS NOT UNCOMMON TO HAVE A BREAKER LEFT OUT TO SEE IF THE SYS WOULD WORK ON SUBSEQUENT FLTS. IF THIS DOES OCCASIONALLY HAPPEN; IT WOULD REQUIRE SUBSEQUENT AIRCREWS TO CHK THE SYS THEN RPT THAT THE SYS WORKED OR DIDN'T WORK. IF IT DIDN'T WORK THEN THE CIRCUIT BREAKER WOULD HAVE TO BE PULLED AND COLLARED. THAT IS NOT PROCEDURALLY CORRECT AND DID NOT HAPPEN IN THIS CASE AS FAR AS WE KNOW. SEVERAL ACTIONS ATTRIBUTED TO THIS SEQUENCE OF EVENTS. FIRST; THE CIRCUIT BREAKER WAS NOT PULLED AND COLLARED WHILE THE MAINT WRITE-UP OCCURRED AND THE MEL STICKERS PLACED IN THE GPWS DISPLAY. SECOND; THE AIRCREW DID NOT CHK TO SEE THAT THE CIRCUIT BREAKER WAS PULLED PER THE MEL. A FEW CIRCUMSTANCES MAY HAVE CONTRIBUTED TO ITEM #2. THE PLANE WAS LATE ARRIVING AND THE MEL/CDL TEXT WAS 5 PAGES LONG AND INCLUDED A FUEL MEL; WHICH RUSHED THE CREW. THE LOGBOOK WRITE-UP WAS CORRECT AND THE DISPLAY WAS MEL'ED CORRECTLY SO THE CIRCUIT BREAKER MUST HAVE BEEN PULLED AND COLLARED. ALSO; PANEL P18-1 HAD MANY CIRCUIT BREAKERS PULLED AND COLLARED AND THE AIRCREW MAY HAVE THOUGHT THAT ONE OF THE COLLARED BREAKERS WAS THE GPWS BREAKER. THE BOTTOM LINE IS THAT MAINT AND THE AIRCREW SHOULD CHK AND ENSURE THAT ALL OF THE MEL IS COMPLIED WITH. HAD THE MEL BEEN FULLY COMPLIED WITH IN THIS CASE; THERE WOULD NOT HAVE BEEN A FLT CREW REACTION TO AN ERRONEOUS GPWS CUE IN A NIGHT; IMC; MOUNTAINOUS ENVIRONMENT WITH NO GPWS DISPLAY.

Data retrieved from NASA's ASRS site as of January 2009 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.