Accident Overview
An airplane conducting an instrument landing system (ILS) approach in instrument meteorological conditions at the end of a cross-country flight impacted terrain about one nautical mile left of the localizer centerline. The airplane was in a left-wing-down, slightly nose-down attitude at a groundspeed of approximately 90 knots. A postimpact fire ensued.
Sequence of Events
The pilot had been cleared to land, but the tower controller canceled the clearance because the airplane appeared not to be established on the localizer as it approached the locator outer marker. The approach controller asked the pilot if he was having an issue with the airplane’s navigation indicator; the pilot replied, “yup.” The controller suggested using an approach surveillance radar (ASR) approach instead, but the pilot chose to fly the ILS approach again.
After being vectored again for the ILS, the controller issued an approach clearance after the pilot confirmed he was receiving localizer indications. The airplane joined the localizer and descended toward the runway. Shortly after being instructed to contact the tower, the airplane entered a left descending turn away from the localizer centerline, about three nautical miles from the locator outer marker. The pilot told the tower, “we’ve got a prob.” The tower instructed the pilot to climb to 3,000 ft msl and turn left to 180°, but the pilot did not respond. During the final five seconds of recorded track data, the descent rate increased from 1,500 to about 5,450 ft per minute.
Investigation Findings
Examination of the remaining wreckage revealed no anomalies. Acoustic analysis of doorbell security videos showed propeller speed at 2,500 rpm before a sudden reduction to about 1,200 rpm approximately two seconds before impact. The airplane’s flightpath was consistent with receiving a valid localizer signal during both instrument approaches.
About five months before the accident, the pilot had told the airplane’s maintainer that the horizontal situation indicator (HSI) displayed erroneous heading indications. The maintainer reported that a replacement HSI was purchased and shipped to the pilot, but it could not be determined if it was installed before the flight. The HSI installed at the time of the accident sustained significant thermal and fire damage, preventing testing.
During both ILS approaches, the pilot was cleared to maintain 3,000 ft msl until established on the localizer. During the second approach, the airplane descended immediately, even though it was below the lower limit of the glideslope. A descent to the glideslope intercept altitude (2,100 ft msl) would have been acceptable after joining the localizer, but that was not consistent with the pilot's previous approach, in which he maintained 3,000 ft msl until intercepting the glideslope.
If the HSI provided erroneous heading information, it could have increased the pilot’s workload and contributed to a breakdown in his instrument scan and ability to recognize deviation left of course and descent below the glideslope. However, it is unknown if the pilot had replaced the HSI.
Probable Cause
The pilot’s failure to follow the instrument landing system (ILS) course guidance during the instrument approach.