What happened
During a night arrival, an aircraft was performing a localizer approach to runway 17. The flight was under the control of a developmental controller, who was being supervised by an instructor. The pilot had been instructed to descend and cross the STILL intersection at 3,000 feet. While level at this altitude and approximately 5 miles from the intersection, the pilot received clearance for the localizer approach.
Radar tracking indicated that the aircraft proceeded toward the STILL intersection and subsequently turned onto the localizer course toward the final approach fix (FAF). Shortly after passing the intersection, the aircraft began a descent while still inbound on the course. During this phase, the controller issued instructions to change frequencies. At this time, the instructor noticed a low altitude alert on the radar screen and verbally alerted the pilot that the aircraft's altitude was indicating 1,200 feet.
There was no response from the pilot to the altitude alert. Approximately 2 miles before reaching the FAF, the aircraft continued its descent. The aircraft eventually struck treetops at an altitude of 750 ft, roughly 0.5 miles before reaching the FAF. There were 0 fatalities and 0 injuries reported in the source text, though the impact occurred above the minimum descent altitude of 720 ft.
Findings
Investigation into the descent revealed that the instructor's verbal warning was based on an outdated approach plate that listed a lower minimum crossing altitude than the current requirement of 1,800 feet. The instructor had incorrectly stated the pilot should be at 1,500 feet. This discrepancy occurred because approach control management had failed to provide the current approach plate to the controllers. It remains undetermined if the use of the correct, current plate would have resulted in an earlier warning to the pilot.