Turboprop pilot reported an unexpected terrain warning on approach to bhm just prior to the MDA.

Attributes
ACN	1525201
Time
Date	201803
Local Time Of Day	1201-1800
Place
Locale Reference	BHM.Airport
State Reference	AL
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Small Transport Low Wing 2 Turboprop Eng
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	Captain
Qualification	Flight Crew Commercial
Events
Anomaly	Inflight Event / Encounter CFTT / CFIT Inflight Event / Encounter Weather / Turbulence

Narrative:

The weather at bhm was reported as ceiling 1;200. We chose to fly the RNAV 36; an LNAV approach with an MDA of 1;480 MSL (847 AGL). We were inside the FAF; descending to 1;500 on the autopilot at 1;000 FPM. At 1;500 MSL or just prior we heard 'caution obstacle'. I immediately began the missed as ATC called with a low altitude alert. After the missed we checked our setup and the vertical profile we had flown and found everything to be correct as far as we could tell. We did not use the advisory glideslope; opting instead to descend to MDA after the FAF. There are a few obstacles noted on the approach plate; however we didn't expect a warning from them. We circled around for the ILS 6 and landed uneventfully.

Original NASA ASRS Text

Title: Turboprop pilot reported an unexpected terrain warning on approach to BHM just prior to the MDA.

Narrative: The weather at BHM was reported as ceiling 1;200. We chose to fly the RNAV 36; an LNAV approach with an MDA of 1;480 MSL (847 AGL). We were inside the FAF; descending to 1;500 on the autopilot at 1;000 FPM. At 1;500 MSL or just prior we heard 'Caution Obstacle'. I immediately began the missed as ATC called with a low altitude alert. After the missed we checked our setup and the vertical profile we had flown and found everything to be correct as far as we could tell. We did not use the advisory glideslope; opting instead to descend to MDA after the FAF. There are a few obstacles noted on the approach plate; however we didn't expect a warning from them. We circled around for the ILS 6 and landed uneventfully.

Data retrieved from NASA's ASRS site 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.