Q400
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter CFTT / CFIT
Flight Crew Took Evasive Action; Flight Crew Executed Go Around / Missed Approach
Weather; Aircraft
We were executing the RNAV GPS D approach into MFR. We crossed BRKET at 10;000 FT; then descended to 8;500 FT and were established level at 8;500 prior to SUXCI. We got a 'TERRAIN PULL UP' warning. We executed a missed approach and requested vectors for the ILS approach into MFR. Surface temperature at MFR had just dropped from 1 to 0 degrees C; and we neglected to temperature compensate. ASOS at MFR does not broadcast weather when ATIS is not broadcast. We were given weather from Center just prior to being cleared for the approach. A post flight debrief of this event was performed; and I determined that temperature compensation at that position would have put us at about 8;900 FT. Charted terrain where the event occurred shows a terrain feature in excess of 7;000 FT.The cause of this event was the flight crew's failure to anticipate a temperature drop into the temperature compensation range.
The flight crew of a commuter aircraft believe their failure to 'temperature compensate' for a one degree celsius drop in OAT was the proximate cause of an EGPWS Terrain warning experienced approaching SUXCI while performing the RNAV (GPS)-D IAP to MFR.