Narrative:

Briefing for ILS 19 complete inbound. Winds calm at jac; sky clear; moon bright. At approximately quirt; we were told by tower that the winds had shifted and were out of the north at 5 KTS. We pulled up new landing information to determine if we were legal to land. We were at approximately fapmo on the ILS 19; the tower said winds had increased from the north to 8 KTS and asked if we would like runway 1. Due to the concern about the tailwind increasing; the captain opted to accept runway 1. We were level at 9;700 ft at the time and remained tracking toward the airport at that altitude. As the first officer; I changed the box to reflect the new runway as well as pulling new landing data for runway 1. As we began to enter a downwind for runway 1; we also began to descend out of 9;700 ft. Again bright clear moonlit night and all terrain was in sight. As that descent was begun; we passed over a hill near the airport and due to a sudden decrease in RA combined with the aircraft descending; we received 1 terrain warning GPWS (not egpws). The captain turned off the autopilot and climbed until the warning went away (this was only for a few seconds because we were 1;500 ft AGL above the small hill at the closest and with the weather conditions; we had all terrain in sight). After this event; we continued a normal approach and landing. In a postflight discussion about the GPWS warning; we discovered that we had not followed the direction from the operations manual page indicating that at night no visual or circle approaches were to be made. While I know we were not allowed to do the visual approach at night (which is why we were on the ILS 19) when we started getting wind report and checking for legality (concern over short runway snow on runway); it did not occur to me until after that we should not have accepted the circle even with the very clear and bright conditions that existed.

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Original NASA ASRS Text

Title: A large transport jet crew realized after landing that the their company's operations manual does not permit night landings on JAC Runway 01 because of high terrain. A GPWS warning was received during the approach.

Narrative: Briefing for ILS 19 complete inbound. Winds calm at JAC; sky clear; moon bright. At approximately QUIRT; we were told by Tower that the winds had shifted and were out of the north at 5 KTS. We pulled up new landing information to determine if we were legal to land. We were At approximately FAPMO on the ILS 19; the Tower said winds had increased from the north to 8 KTS and asked if we would like Runway 1. Due to the concern about the tailwind increasing; the Captain opted to accept Runway 1. We were level at 9;700 FT at the time and remained tracking toward the airport at that altitude. As the First Officer; I changed the box to reflect the new runway as well as pulling new landing data for Runway 1. As we began to enter a downwind for Runway 1; we also began to descend out of 9;700 FT. Again bright clear moonlit night and all terrain was in sight. As that descent was begun; we passed over a hill near the airport and due to a sudden decrease in RA combined with the aircraft descending; we received 1 terrain warning GPWS (not EGPWS). The Captain turned off the autopilot and climbed until the warning went away (this was only for a few seconds because we were 1;500 FT AGL above the small hill at the closest and with the weather conditions; we had all terrain in sight). After this event; we continued a normal approach and landing. In a postflight discussion about the GPWS warning; we discovered that we had not followed the direction from the OPS Manual page indicating that at night no visual or circle approaches were to be made. While I know we were not allowed to do the visual approach at night (which is why we were on the ILS 19) when we started getting wind report and checking for legality (concern over short runway snow on runway); it did not occur to me until after that we should not have accepted the circle even with the very clear and bright conditions that existed.

Data retrieved from NASA's ASRS site as of April 2012 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.