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Altitude deviation when an approaching A320's GPWS senses a closure rate warning on an unobserved mountain top near the approach route while at MVA altitude of 5100 ft, 8 mi northeast of las.
| Attributes | |
| ACN | 639632 |
| Time | |
| Date | 200412 |
| Day | Thu |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : las.airport |
| State Reference | NV |
| Altitude | msl bound lower : 5100 msl bound upper : 6000 |
| Environment | |
| Flight Conditions | Marginal |
| Aircraft 1 | |
| Controlling Facilities | tracon : l30.tracon |
| Operator | common carrier : air carrier |
| Make Model Name | A320 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent : approach descent : intermediate altitude |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 175 flight time total : 19500 flight time type : 4600 |
| ASRS Report | 639632 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude other anomaly other |
| Independent Detector | aircraft equipment : gpws |
| Resolutory Action | flight crew : took precautionary avoidance action flight crew : returned to assigned altitude |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Aircraft Airspace Structure |
Narrative:
We were being vectored for a visual approach to runway 19L at las. WX was reported as 3000 ft overcast, but ceilings were ragged. We were level at 5100 ft MSL per approach control and approximately 8 NM northeast of the airport. Suddenly, we got a GPWS warning of 'pull up, pull up, terrain.' I had briefly noticed a large mountain at this approximately location between clouds earlier. We were IMC, so we immediately climbed in response, approximately 900 ft. We told the controller we were responding to a GPWS warning and to verify we were at the proper at. She responded that yes, her MVA for that area was 5100 ft, but she would have lower for us soon. We returned to our previous altitude of 5100 ft, and then descended further when cleared and made a normal visual approach when we were clear of clouds. We assumed that when we went over the mountain, we got a closure rate GPWS warning. I called ATC on the ground and told them our story. We recommended that although the 5100 ft MVA may be a legal altitude for ground clearance, it may not provide adequate clearance to avoid these closure rate GPWS warnings.
Original NASA ASRS Text
Title: ALTDEV WHEN AN APCHING A320'S GPWS SENSES A CLOSURE RATE WARNING ON AN UNOBSERVED MOUNTAIN TOP NEAR THE APCH RTE WHILE AT MVA ALT OF 5100 FT, 8 MI NE OF LAS.
Narrative: WE WERE BEING VECTORED FOR A VISUAL APCH TO RWY 19L AT LAS. WX WAS RPTED AS 3000 FT OVCST, BUT CEILINGS WERE RAGGED. WE WERE LEVEL AT 5100 FT MSL PER APCH CTL AND APPROX 8 NM NE OF THE ARPT. SUDDENLY, WE GOT A GPWS WARNING OF 'PULL UP, PULL UP, TERRAIN.' I HAD BRIEFLY NOTICED A LARGE MOUNTAIN AT THIS APPROX LOCATION BTWN CLOUDS EARLIER. WE WERE IMC, SO WE IMMEDIATELY CLBED IN RESPONSE, APPROX 900 FT. WE TOLD THE CTLR WE WERE RESPONDING TO A GPWS WARNING AND TO VERIFY WE WERE AT THE PROPER AT. SHE RESPONDED THAT YES, HER MVA FOR THAT AREA WAS 5100 FT, BUT SHE WOULD HAVE LOWER FOR US SOON. WE RETURNED TO OUR PREVIOUS ALT OF 5100 FT, AND THEN DSNDED FURTHER WHEN CLRED AND MADE A NORMAL VISUAL APCH WHEN WE WERE CLR OF CLOUDS. WE ASSUMED THAT WHEN WE WENT OVER THE MOUNTAIN, WE GOT A CLOSURE RATE GPWS WARNING. I CALLED ATC ON THE GND AND TOLD THEM OUR STORY. WE RECOMMENDED THAT ALTHOUGH THE 5100 FT MVA MAY BE A LEGAL ALT FOR GND CLRNC, IT MAY NOT PROVIDE ADEQUATE CLRNC TO AVOID THESE CLOSURE RATE GPWS WARNINGS.
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.