On November 16, 1985, a Cessna 421C (registration N124RS) was involved in an aviation accident near Idaho Falls, ID. Investigators recorded the probable cause as: The pilot's decision to continue the approach and land while relying on a limited visual reference caused by an inoperative windscreen heating system, which led to a loss of depth perception and a hard landing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot encountered inflight icing during approach, causing the windscreen heater to fail. Using a small cleared area for reference led to a hard landing.
What happened
During the initial phase of an instrument approach, the aircraft encountered inflight icing conditions. The primary windscreen heating system failed to function because the associated inverter was inoperative. Despite this failure, a small section on the right bottom portion of the windscreen remained clear due to heat from the defrost system.
The pilot elected to land the aircraft using only this small cleared area for outside visual reference. This limited field of view resulted in a loss of depth perception. Consequently, the aircraft touched down with excessive force, resulting in a hard landing.
Probable cause
The pilot's decision to continue the approach and land while relying on a limited visual reference caused by an inoperative windscreen heating system, which led to a loss of depth perception and a hard landing.