What happened
While parked on the ramp with electrical power applied, a crew was conducting minor corrective maintenance on an MD-11F freighter in preparation for departure. During standard flow checks, the captain was verifying that the windshield anti-ice was selected OFF and the windshield de-fog was selected ON. During this process, the forward windshield panel (R1) cracked. The crew observed flames emanating from the lower portion of the windshield.
The captain immediately de-powered the aircraft, which caused the fire condition to dissipate. There were no injuries reported during the incident.
The investigation
A post-incident examination of the R1 windshield anti-ice controller was conducted. The investigation revealed internal shorts within the controller unit. When electrical power was applied to the aircraft, these shorts caused an uncontrollable and continuous application of power to the R1 windshield anti-ice heating element.
Findings
The investigation concluded that the continuous power to the heating element led to overheating, which subsequently caused the windshield to shatter while the aircraft was parked on the ramp.