Narrative:

On ZZZ-mhlm leg; we briefed the VOR DME ILS 22. The captain had never flown into mhlm; so I did as thorough and complete a briefing as possible; including the possibility of circling to runway 4 if the winds pick up. Also briefed was the hill about 4 miles southwest of the airport; and the fact it is not charted on the area chart; but is as an antenna on the approach chart. Also during the approach brief; I mentioned that the visibility would not be as good as perceived from the metar; as it was extremely hazy. When in contact with la mesa approach; they informed us of the winds which were at our maximum tailwind component; so the captain and I elected to circle to runway 4 in case they continue to increase. ATC cleared us for the 'visual circling approach runway 4.' I elected to fly the full VOR DME ILS runway 22; followed by a visual circling maneuver at 1300 ft. The initial approach was flown well; and deliberately slow so as not to get behind. I decided to use right traffic because with the restricted visibility; I wanted to have a good view of the runway. I had the captain insert the visual approach runway 4 in the FMS. On downwind; I was planning to turn base and descend inside of the hill which is about 4 NM southwest of the airport. I had done this same exact approach and maneuver two days prior (ATC directed us to use right traffic then); and felt it worked out very well. However; the captain preferred to extend the downwind beyond the hill; then turn base. I feel there is no right or wrong way to do this; as it is personal preference -- so we then continued downwind as per the captain's suggestion. Throughout the entire maneuver; we had the hill in sight. Bt the way; this hill does not appear on the egpws terrain display. This has also been briefed; as I noticed this peculiarity two days prior. While on the base leg and descending (hand flying); we received a single 'terrain ahead' alert; immediately followed by a 'pull up' warning; immediately followed by no warning. The entire sequence lasted about 2 seconds. During the 'terrain ahead;' I began to level our descent; and after the 'pull up;' I began to add power and pitched up. The entire warning was over by the time the engines began to spool up. We were still in a position to maintain our projected path to the runway; so the captain and I decided to continue the approach; and I believe we met all stable approach criteria at 1000 ft. This hill was not in the terrain database; so I believe the GPWS was triggered by the RA; and the upslope of the hill's base as I began my turn and descent. In the future; I will consider left traffic; but left traffic has its own set of hills north of the airport. Therefore; I don't know which pattern offers greater safety margins; but feel it is important to maintain proficiency on both patterns as sometimes ATC will dictate the pattern.callback conversation with reporter revealed the following information: the reporter stated that it is likely that the terrain in the aircraft database does include the hill which triggered the warning. The aircraft terrain representation displays terrain in a pie-shaped area ahead of the aircraft; showing terrain 45 degrees azimuth right and left of the nose. Therefore; since the base turn was over the valley; the hill may have been outside the limits of the display; but the GPWS triggered the warning for closure to the rising terrain. His company does provide a topographic display of the airport area; but the reporter would prefer a multicolored graphic of the area. Hazy conditions often exist in the area; and in most cases; the direction of the circling approach is at the discretion of the flight crew.

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Original NASA ASRS Text

Title: ACR FLT CREW RECEIVED A GPWS TERRAIN WARNING WHILE CONDUCTING A CIRCLING APCH TO RWY 4 AT MHLM.

Narrative: ON ZZZ-MHLM LEG; WE BRIEFED THE VOR DME ILS 22. THE CAPTAIN HAD NEVER FLOWN INTO MHLM; SO I DID AS THOROUGH AND COMPLETE A BRIEFING AS POSSIBLE; INCLUDING THE POSSIBILITY OF CIRCLING TO RUNWAY 4 IF THE WINDS PICK UP. ALSO BRIEFED WAS THE HILL ABOUT 4 MILES SOUTHWEST OF THE AIRPORT; AND THE FACT IT IS NOT CHARTED ON THE AREA CHART; BUT IS AS AN ANTENNA ON THE APPROACH CHART. ALSO DURING THE APPROACH BRIEF; I MENTIONED THAT THE VISIBILITY WOULD NOT BE AS GOOD AS PERCEIVED FROM THE METAR; AS IT WAS EXTREMELY HAZY. WHEN IN CONTACT WITH LA MESA APPROACH; THEY INFORMED US OF THE WINDS WHICH WERE AT OUR MAX TAILWIND COMPONENT; SO THE CAPTAIN AND I ELECTED TO CIRCLE TO RUNWAY 4 IN CASE THEY CONTINUE TO INCREASE. ATC CLEARED US FOR THE 'VISUAL CIRCLING APPROACH RUNWAY 4.' I ELECTED TO FLY THE FULL VOR DME ILS RWY 22; FOLLOWED BY A VISUAL CIRCLING MANEUVER AT 1300 FT. THE INITIAL APPROACH WAS FLOWN WELL; AND DELIBERATELY SLOW SO AS NOT TO GET BEHIND. I DECIDED TO USE RIGHT TRAFFIC BECAUSE WITH THE RESTRICTED VISIBILITY; I WANTED TO HAVE A GOOD VIEW OF THE RUNWAY. I HAD THE CAPTAIN INSERT THE VISUAL APPROACH RWY 4 IN THE FMS. ON DOWNWIND; I WAS PLANNING TO TURN BASE AND DESCEND INSIDE OF THE HILL WHICH IS ABOUT 4 NM SOUTHWEST OF THE AIRPORT. I HAD DONE THIS SAME EXACT APPROACH AND MANEUVER TWO DAYS PRIOR (ATC DIRECTED US TO USE RIGHT TRAFFIC THEN); AND FELT IT WORKED OUT VERY WELL. HOWEVER; THE CAPTAIN PREFERRED TO EXTEND THE DOWNWIND BEYOND THE HILL; THEN TURN BASE. I FEEL THERE IS NO RIGHT OR WRONG WAY TO DO THIS; AS IT IS PERSONAL PREFERENCE -- SO WE THEN CONTINUED DOWNWIND AS PER THE CAPTAIN'S SUGGESTION. THROUGHOUT THE ENTIRE MANEUVER; WE HAD THE HILL IN SIGHT. BT THE WAY; THIS HILL DOES NOT APPEAR ON THE EGPWS TERRAIN DISPLAY. THIS HAS ALSO BEEN BRIEFED; AS I NOTICED THIS PECULIARITY TWO DAYS PRIOR. WHILE ON THE BASE LEG AND DESCENDING (HAND FLYING); WE RECEIVED A SINGLE 'TERRAIN AHEAD' ALERT; IMMEDIATELY FOLLOWED BY A 'PULL UP' WARNING; IMMEDIATELY FOLLOWED BY NO WARNING. THE ENTIRE SEQUENCE LASTED ABOUT 2 SECONDS. DURING THE 'TERRAIN AHEAD;' I BEGAN TO LEVEL OUR DESCENT; AND AFTER THE 'PULL UP;' I BEGAN TO ADD POWER AND PITCHED UP. THE ENTIRE WARNING WAS OVER BY THE TIME THE ENGINES BEGAN TO SPOOL UP. WE WERE STILL IN A POSITION TO MAINTAIN OUR PROJECTED PATH TO THE RUNWAY; SO THE CAPTAIN AND I DECIDED TO CONTINUE THE APPROACH; AND I BELIEVE WE MET ALL STABLE APPROACH CRITERIA AT 1000 FT. THIS HILL WAS NOT IN THE TERRAIN DATABASE; SO I BELIEVE THE GPWS WAS TRIGGERED BY THE RA; AND THE UPSLOPE OF THE HILL'S BASE AS I BEGAN MY TURN AND DESCENT. IN THE FUTURE; I WILL CONSIDER LEFT TRAFFIC; BUT LEFT TRAFFIC HAS ITS OWN SET OF HILLS NORTH OF THE AIRPORT. THEREFORE; I DON'T KNOW WHICH PATTERN OFFERS GREATER SAFETY MARGINS; BUT FEEL IT IS IMPORTANT TO MAINTAIN PROFICIENCY ON BOTH PATTERNS AS SOMETIMES ATC WILL DICTATE THE PATTERN.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT IT IS LIKELY THAT THE TERRAIN IN THE ACFT DATABASE DOES INCLUDE THE HILL WHICH TRIGGERED THE WARNING. THE ACFT TERRAIN REPRESENTATION DISPLAYS TERRAIN IN A PIE-SHAPED AREA AHEAD OF THE ACFT; SHOWING TERRAIN 45 DEGREES AZIMUTH RIGHT AND LEFT OF THE NOSE. THEREFORE; SINCE THE BASE TURN WAS OVER THE VALLEY; THE HILL MAY HAVE BEEN OUTSIDE THE LIMITS OF THE DISPLAY; BUT THE GPWS TRIGGERED THE WARNING FOR CLOSURE TO THE RISING TERRAIN. HIS COMPANY DOES PROVIDE A TOPOGRAPHIC DISPLAY OF THE ARPT AREA; BUT THE REPORTER WOULD PREFER A MULTICOLORED GRAPHIC OF THE AREA. HAZY CONDITIONS OFTEN EXIST IN THE AREA; AND IN MOST CASES; THE DIRECTION OF THE CIRCLING APCH IS AT THE DISCRETION OF THE FLT CREW.

Data retrieved from NASA's ASRS site as of May 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.