PC-12
Flight Crew Air Transport Pilot (ATP)
Confusion; Situational Awareness
Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Executed Go Around / Missed Approach
Aircraft; Human Factors
I was the pilot flying the BHM RNAV (GPS) Runway 36 approach. We were cleared direct to GOTBY (IAF) at or above 3;000 FT for the GPS Runway 36. At GOTBY we stepped down to 2;800 FT to IMOBY; then down to 2;300 FT to BERFY (FAF). We were handed off and checked in with Tower outside BERFY. The Tower cleared us number 1 to land Runway 36. Two minutes later the Tower issued us a 'Low Altitude Alert' and advised us to check our altitude immediately. At that time we were slightly above the MDA of 1;480 FT. I continued for a few more seconds until the aircraft issued an 'OBSTACLE; OBSTACLE' alert and the MFD indicated a yellow shaded circle directly in front of the aircraft. I again noted my altitude was correct at 1;500 FT however executed an immediate missed approach as we were solid IMC and there was no way to visually verify the situation outside the aircraft. We were issued a climb to 4;000 FT and vectored instead for the BHM ILS 24 approach to a landing. Perhaps of some relevance was that the aircraft that was following us on the BHM RNAV (GPS) Runway 36 approach; a Cessna Sovereign; was also issued a 'Low Altitude Alert' two minutes after mine; and advised to check their altitude immediately. As it's not clear why the TAWS indicated 'OBSTACLE; OBSTACLE' during this approach I cannot suggest how to avoid this in the future. We are required at night to utilize the TAWS screen on the MFD at night; but given the variety of airports we fly to in less than VFR conditions; it may be advisable to utilize the TAWS screen at all times in the terminal area at night or when IMC exist.
Turboprop pilot reports being issued a low altitude warning by the BHM Tower while at minimums on the RNAV (GPS) Runway 36. Within a few seconds the aircraft TAWS system issued 'OBSTACLE' alert and the MFD indicated a yellow shaded circle directly in front of the aircraft. A go-around is initiated; followed by an approach to a different runway. It was reported that the following CE680 was issued the same warning by the Tower.