THE DTSB
The DTSB determines the Probable Cause of this accident to be pilot error, in that the accident pilot elected to fly a night IMC approach into an area of known terrain, intending to land after midnight local time. The accident pilot requested the RNAV(GPS) Z RWY 32 approach and was cleared to fly the approach, with circle to land on runway 14. This approach was NA for night straight in and was also NA for night circle to runway 32. The accident pilot properly selected the approach and allowed the on board automation to fly both lateral and vertical guidance, thereby disregarding critical MDA constraint of 9100 feet at WDCHK intersection, as the on-board GARMIN system recognized the “Advisory Glideslope” data and followed that. The aircraft was travelling more than 180 KIAS and the on-board automation pitched the aircraft nose down in order to maintain the Garmin generated, non approved, advisory glideslope, thereby resulting in a vertical descent rate in excess of 1200 FPM. The accident pilot set 13,600 in his altitude window while descending, in anticipation of a possible missed approach, but in doing so, eliminated the hard level off required at WDCHK of 9100 feet. The aircraft tracked the lateral GPS course within a few feet, and the accident pilot monitored the vertical path by prioritizing the advisory glideslope over the published altitude constraint at WDCHK. The airport winds were from the southeast, so the accident pilot was issued a proper IFR approach clearance for this approach, with circle to land on 14. The aircraft would have received numerous nuisance terrain warnings as is common on these type approaches, and the accident pilot likely simply disregarded them all, as his confidence lay in the published FAA procedure, and the Garmin automation. The aircraft impacted at high speed and high ROD on the southeast side of the terrain ridge in solid IMC conditions, the accident pilot never aware of the danger that he was in.