Embraer EMB120 N1110J accident near Iliamna, Alaska

Probable cause

the maintenance personnel's failure to install the cotter pins that secured castellated nuts on the left elevator vertical hinge bolts, which resulted in the left elevator partially detaching in flight. Contributing to the accident was the failure of maintenance personnel to document the non-routine maintenance procedure that was used to remove and reinstall the elevator during maintenance.

NTSB analysis

On February 16, 2012, at about 1308 local time, Everts Air Cargo flight 1291, an Embraer EMB-120, N1110J, experienced an uncommanded pitch down while descending into Iliamna Airport (KILI), Iliamna, Alaska. There were no injuries to the 2 crewmembers onboard but the airplane sustained substantial damage. The flight was operating under 14 CFR Part 121 Supplemental as a cargo only flight from Anchorage, Alaska (KANC) to KILI.

The Captain reported that the flight from KANC had been uneventful. The Captain reported that during the descent, while at about 250 knots airspeed with his hands on the controls and the autopilot engaged, the airplane pitched to about 20 degrees nose down. The captain reported he then disconnected the autopilot and adjusted the pitch trim while pulling back on the column to recover from the pitch excursion. The flight crew declared an emergency and slowed the airplane to about 200 knots. Approximately 5-10 miles from the airport, while in a slow left turn at 3000 feet msl altitude, the airplane pitched down a second time while the captain was hand flying. As he recovered from the pitch down, he was lined up for a 5 mile final approach for runway 35. The captain elected to make a high speed, flaps up landing and landed uneventfully on runway 35. Post-flight inspection revealed that the left elevator was bent at the mid span trim tab, had partially detached from the aircraft, and was missing two attachment bolts.

A review of the airplane maintenance history showed that while in "A" check maintenance, a dent was noted in the left elevator and the elevator was removed. The maintenance team did not follow the EMB 120 maintenance manual procedure for removal of the left elevator. During the non-routine maintenance procedures used by the maintenance team, cotter pin safeties that were removed from castellated nuts on the 2 outboard vertical hinge bolts on the left elevator were not reinstalled. The removal of these two bolts is not part of the EMB 120 maintenance manual procedure for removal of the left elevator. The maintenance team did not document the non-routine procedure they used to remove and reinstall the left elevator.

The Require Inspection Items (RII) inspector had inspected the elevator installation for the procedures in the manual and was not aware of the undocumented non-routine maintenance procedures used, and hence did not examine the nuts that did not have the required cotter pins, which were not to be removed as part of the approved procedure. The FAA found that the maintenance teams that removed and reinstalled the elevator were inexperienced in EMB 120 elevator removal and reinstallation procedures.

Text from the NTSB. Open the NTSB docket for DCA12CA042 for the full record.