Aircraft Mishap Investigation Course (AMIC) 26-F Practice Test

When a bulb is energized, heat signs appear as the filament and glass show evidence of high temperature. The filament can stretch as it softens when hot, the globe can discolor from scorching, and the filament ends may ball up or neck as they heat and fail. These heat-related changes point to the bulb having been on at impact because they require the filament to be hot when the crash occurs.

Shattering or fracturing, on the other hand, is primarily a mechanical outcome of the impact itself. Glass can break from a crash regardless of whether the bulb was powered, so this sign does not reliably indicate the bulb was on at the moment of impact.