Schweizer SGS 2-33AK N17965 accident near Windsor, Virginia

Probable cause

The unauthorized installation of a battery and associated wiring and electrical components, which resulted in an in-flight electrical fire of undetermined origin.

NTSB analysis

On the morning of the accident, the pilot arrived at the gliderport to practice for a check ride he was scheduled to take later that afternoon. The pilot, who was not a mechanic, selected and installed a "Gel-cell" battery behind the forward pilot seat during the preflight inspection of the glider. The battery was used to power the radio in the instrument panel. The pilot completed a low-level, traffic pattern flight and was then towed to 3,000 feet msl for a second flight. The glider climbed to 3,400 feet, about 5 miles from the gliderport, where the pilot smelled an unusual odor. The odor got stronger, he felt heat, and observed fire in the back seat. The pilot then deployed the spoilers and initiated an emergency descent. During the descent, the cockpit filled with smoke, and the pilot opened the canopy to clear the smoke. The smoke cleared, but the increased airflow exacerbated the fire. The pilot completed a forced landing to trees short of the gliderport, during which the glider sustained substantial damage in the ensuing post-crash fire. Examination of the glider by an NTSB fire and explosion expert could not determine the exact source of ignition in the battery or its associated wiring. Examination of the maintenance logbooks revealed that there were no entries for the work performed to install the electrical system, and neither was there any approval paperwork from the FAA pertaining to the modification.

Text from the NTSB. Open the NTSB docket for ERA10LA387 for the full record.