PA-31P Navajo P
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 100; Flight Crew Total 5640; Flight Crew Type 3000
Distraction; Situational Awareness
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Human Factors
On a coupled RNAV XX LPV approach to ZZZ the aircraft overshoot the turn to final. It started the turn but not fast enough to intercept. After correcting and intercepting final the aircraft began a descent as if following the glideslope. There was heavy rain between me and the airport and my attention was diverted to that and I lost situational awareness. It is obvious now that the descent was not following the glideslope when the terrain alert activated I climbed to a higher altitude and shortly broke out of the rain and landed in visual conditions. We were in contact with approach control until just before the turn to final; then switched to UNICOM. My mistakes were ones of complacency. When I had an abnormal turn to final I should have executed a missed approach. Something was not right. I allowed my attention to be diverted at a critical time from the task of monitoring the approach. I misinterpreted the weather situation. I used ASOS reports that may have been 5 - 10 minutes old in a rapidly changing weather situation. I should have requested the RNAV XY and accepted the tailwind even though the minimums were higher. The weather was moving west to east and conditions in the quadrant turned out to be much better.
Pilot reported getting a terrain alert after not noticing the aircraft was not on glideslope. Reporter stated they were focused on the poor weather conditions and did not monitor the approach progress.