Narrative:

I was a flight engineer on a B727 scheduled carrier flight on sept xx into eugene, or. Scattered clouds at approximately 5500 ft MSL bases. Approach control cleared us to descend and maintain 4300 ft MSL and fly a radar vector of 265 degrees which was meant as a left base vector to runway 16. As we descended on that vector to the cleared altitude of 4300 ft (we did respond to approach with 'descend and maintain 4300 ft' as we are required). We were able to get below those scattered clouds with bases at 5500 ft MSL and level off at 4300 ft MSL in VMC and with 20 plus mi of visibility. Level at 4300 ft MSL we could see that approach control had cleared us to an altitude that was below the 5100 ft minimum safe altitude for that sector but surely was at their minimum vectoring altitude (of course pilots do not have access to MVA's). This 4300 ft MSL cleared altitude was near a ridge of hills northwest of the eugene airport. Knowing we were at an MVA altitude and also could visually see that we were not dangerously near terrain we remained at 4300 ft and 265 degree heading as cleared by ATC. Over the ridge of hills we were startled to hear our GPWS announce 'terrain, terrain' this startled us since as I mentioned earlier we were at an ATC cleared altitude and heading and could visually see that we were in no danger of being near terrain. Of course the captain reacted to the warning immediately as we are trained to do. Our flight manual states verbatim, 'if terrain induced warnings are encountered under day visual conditions with terrain and obstacles clearly in sight: immediately take positive corrective action until warning ceases or terrain clearance is assured.' the GPWS only announced 'terrain, terrain' once as best as I can remember. With excellent knowledge of the flight manual and good judgement the captain reacted immediately to the warning. Unfortunately in his startled state while attempting to add power and increase pitch he initially lost 200 ft from 4300 ft (by this time we were past the ridge and in no danger of terrain and the GPWS had ceased its announcement) but immediately recognized this and made an adjustment to be assured of terrain clearance (as stated in the flight manual) by climbing to 500 ft above 4300 ft to 4800 ft. Realizing right away that we were clear of conflict (assured of terrain clearance and no GPWS announcement) he immediately went back to the cleared altitude of 4300 ft. The GPWS warning and required reaction definitely overrode the necessity to hold 4300 ft but as a pilot with a healthy respect for rules and safety not only do I feel our action was appropriate but that I have a moral obligation to report our deviation of altitude. Approach control did not query us in any respect and we perhaps should have offered the information. In retrospect as a crew we discussed that it would have been in the best interest for everyone to have shared our event. That way approach control would have understood our necessity to deviate from 4300 ft. Also, they may adjust their MVA or use a different vectoring technique to alleviate terrain announcement by an aircraft's GPWS. This event also teaches me to query a controller about MVA in the future if I can visually see that it is unusually close to terrain. Supplemental information from acn 317287: the PF was cleared to 4300 ft and went to 4000 ft back up and then down to 4000 ft again. I reminded him both times of his cleared altitude as the deviation was happening. Also he had a 1000 ft call. We got 'too low, terrain' he went to 4500 ft when I said we're too low and tried to sound urgent. Explaining before we started down that in 5 months of flying into eugene I've never been that low over that hill. Turning final we were told about traffic and couldn't see them outside. On TCASII, 100 ft below and 2 mi ahead. We got warned (TCASII) to climb and didn't. We never saw the traffic.

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Original NASA ASRS Text

Title: HAD ALTDEV EXCURSION, B727 FLC BELOW MSA, HAS GPWS ACTIVATE.

Narrative: I WAS A FE ON A B727 SCHEDULED CARRIER FLT ON SEPT XX INTO EUGENE, OR. SCATTERED CLOUDS AT APPROX 5500 FT MSL BASES. APCH CTL CLRED US TO DSND AND MAINTAIN 4300 FT MSL AND FLY A RADAR VECTOR OF 265 DEGS WHICH WAS MEANT AS A L BASE VECTOR TO RWY 16. AS WE DSNDED ON THAT VECTOR TO THE CLRED ALT OF 4300 FT (WE DID RESPOND TO APCH WITH 'DSND AND MAINTAIN 4300 FT' AS WE ARE REQUIRED). WE WERE ABLE TO GET BELOW THOSE SCATTERED CLOUDS WITH BASES AT 5500 FT MSL AND LEVEL OFF AT 4300 FT MSL IN VMC AND WITH 20 PLUS MI OF VISIBILITY. LEVEL AT 4300 FT MSL WE COULD SEE THAT APCH CTL HAD CLRED US TO AN ALT THAT WAS BELOW THE 5100 FT MINIMUM SAFE ALT FOR THAT SECTOR BUT SURELY WAS AT THEIR MINIMUM VECTORING ALT (OF COURSE PLTS DO NOT HAVE ACCESS TO MVA'S). THIS 4300 FT MSL CLRED ALT WAS NEAR A RIDGE OF HILLS NW OF THE EUGENE ARPT. KNOWING WE WERE AT AN MVA ALT AND ALSO COULD VISUALLY SEE THAT WE WERE NOT DANGEROUSLY NEAR TERRAIN WE REMAINED AT 4300 FT AND 265 DEG HDG AS CLRED BY ATC. OVER THE RIDGE OF HILLS WE WERE STARTLED TO HEAR OUR GPWS ANNOUNCE 'TERRAIN, TERRAIN' THIS STARTLED US SINCE AS I MENTIONED EARLIER WE WERE AT AN ATC CLRED ALT AND HDG AND COULD VISUALLY SEE THAT WE WERE IN NO DANGER OF BEING NEAR TERRAIN. OF COURSE THE CAPT REACTED TO THE WARNING IMMEDIATELY AS WE ARE TRAINED TO DO. OUR FLT MANUAL STATES VERBATIM, 'IF TERRAIN INDUCED WARNINGS ARE ENCOUNTERED UNDER DAY VISUAL CONDITIONS WITH TERRAIN AND OBSTACLES CLRLY IN SIGHT: IMMEDIATELY TAKE POSITIVE CORRECTIVE ACTION UNTIL WARNING CEASES OR TERRAIN CLRNC IS ASSURED.' THE GPWS ONLY ANNOUNCED 'TERRAIN, TERRAIN' ONCE AS BEST AS I CAN REMEMBER. WITH EXCELLENT KNOWLEDGE OF THE FLT MANUAL AND GOOD JUDGEMENT THE CAPT REACTED IMMEDIATELY TO THE WARNING. UNFORTUNATELY IN HIS STARTLED STATE WHILE ATTEMPTING TO ADD PWR AND INCREASE PITCH HE INITIALLY LOST 200 FT FROM 4300 FT (BY THIS TIME WE WERE PAST THE RIDGE AND IN NO DANGER OF TERRAIN AND THE GPWS HAD CEASED ITS ANNOUNCEMENT) BUT IMMEDIATELY RECOGNIZED THIS AND MADE AN ADJUSTMENT TO BE ASSURED OF TERRAIN CLRNC (AS STATED IN THE FLT MANUAL) BY CLBING TO 500 FT ABOVE 4300 FT TO 4800 FT. REALIZING RIGHT AWAY THAT WE WERE CLR OF CONFLICT (ASSURED OF TERRAIN CLRNC AND NO GPWS ANNOUNCEMENT) HE IMMEDIATELY WENT BACK TO THE CLRED ALT OF 4300 FT. THE GPWS WARNING AND REQUIRED REACTION DEFINITELY OVERRODE THE NECESSITY TO HOLD 4300 FT BUT AS A PLT WITH A HEALTHY RESPECT FOR RULES AND SAFETY NOT ONLY DO I FEEL OUR ACTION WAS APPROPRIATE BUT THAT I HAVE A MORAL OBLIGATION TO RPT OUR DEV OF ALT. APCH CTL DID NOT QUERY US IN ANY RESPECT AND WE PERHAPS SHOULD HAVE OFFERED THE INFO. IN RETROSPECT AS A CREW WE DISCUSSED THAT IT WOULD HAVE BEEN IN THE BEST INTEREST FOR EVERYONE TO HAVE SHARED OUR EVENT. THAT WAY APCH CTL WOULD HAVE UNDERSTOOD OUR NECESSITY TO DEVIATE FROM 4300 FT. ALSO, THEY MAY ADJUST THEIR MVA OR USE A DIFFERENT VECTORING TECHNIQUE TO ALLEVIATE TERRAIN ANNOUNCEMENT BY AN ACFT'S GPWS. THIS EVENT ALSO TEACHES ME TO QUERY A CTLR ABOUT MVA IN THE FUTURE IF I CAN VISUALLY SEE THAT IT IS UNUSUALLY CLOSE TO TERRAIN. SUPPLEMENTAL INFO FROM ACN 317287: THE PF WAS CLRED TO 4300 FT AND WENT TO 4000 FT BACK UP AND THEN DOWN TO 4000 FT AGAIN. I REMINDED HIM BOTH TIMES OF HIS CLRED ALT AS THE DEV WAS HAPPENING. ALSO HE HAD A 1000 FT CALL. WE GOT 'TOO LOW, TERRAIN' HE WENT TO 4500 FT WHEN I SAID WE'RE TOO LOW AND TRIED TO SOUND URGENT. EXPLAINING BEFORE WE STARTED DOWN THAT IN 5 MONTHS OF FLYING INTO EUGENE I'VE NEVER BEEN THAT LOW OVER THAT HILL. TURNING FINAL WE WERE TOLD ABOUT TFC AND COULDN'T SEE THEM OUTSIDE. ON TCASII, 100 FT BELOW AND 2 MI AHEAD. WE GOT WARNED (TCASII) TO CLB AND DIDN'T. WE NEVER SAW THE TFC.

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.