What happened
The pilot reported experiencing issues with the instrument landing system (ILS) during his initial approach. The localizer needle fluctuated significantly to the left, prompting corrective turns. Upon reaching decision height and breaking through the clouds, the runway was visible to the right, leading to a missed approach. The pilot initially attributed this error to a cockpit distraction caused by switching on the landing lights.
During a second ILS attempt, the fluctuations were more pronounced. At decision height, both localizer needles indicated the aircraft was right of course. The pilot observed a row of lights to his left and mistakenly identified them as the runway lights. He turned left and began descending toward these lights before realizing they were actually street lights. While climbing back up for another approach attempt, the right wing struck a tree.
The investigation
An examination of the ILS transmitters and both aircraft receivers revealed no mechanical malfunction or failure. The aircraft was equipped with an autopilot front/back switch, which was reportedly set to the "front" position during the incident.
Findings
The primary factor was the pilot's misidentification of street lights as runway lights. This error occurred despite the ILS equipment functioning correctly. The localizer needle fluctuations may have contributed to confusion regarding lateral positioning, but the root cause was the visual misinterpretation of ground lighting.