Beech C90 N14CP accident near Boise, Idaho

Probable cause

Excessive loading on the left wing, which occurred over a period of time. Contributing to the accident was maintenance personnel’s failure to adequately inspect and document the left wing damage.

NTSB analysis

The airplane had been contracted to the Bureau of Land Management (BLM) for 6 months, and it was primarily used in fire management activities in low-level lead airplane and air attack missions; these type of operations were susceptible to turbulent conditions. BLM provided the pilots, and the contract company provided the airplane and maintenance personnel. During a postcontract inspection, maintenance personnel found substantial damage to the outer left wing.

The BLM reported that, about 1 month into the 6-month contract period, a BLM pilot and contract mechanic noted deformation and wrinkling damage to the left wing; the mechanic inspected the area, and it was subsequently monitored for further damage. Three months later, the BLM pilot reported to a relief mechanic that he had encountered moderate turbulence. The mechanic subsequently completed a turbulent air inspection but noted no damage and considered the airplane airworthy. When the contract mechanic returned to work, he inspected the airplane and told the pilot that the wrinkle appeared to be "a little worse"; however, no actions were taken. The airplane was subsequently flown until the contract expired without incident. A review of the maintenance logbooks found no entries related to any maintenance actions or inspections of the damaged left wing.

About 2 months after the contract expired, the contract company's maintenance personnel observed that the damage had worsened. The damage was consistent with the wing assembly having experienced loading in excess of its normal operating limits, likely during turbulent conditions. The airplane was then taken out of service for repairs. The damage was likely cumulative as the airplane was flown in turbulent conditions.

If the maintenance inspections had been documented in the logbooks, it likely would have necessitated further inspection by maintenance personnel and resulted in the airplane's removal from service at an earlier date.

Text from the NTSB. Open the NTSB docket for WPR12TA445 for the full record.