LUSCOMBE 11A near Merced, CA — 2010-06-19

Final reportWPR10LA306

Date: 2010-06-19
Location: Merced, CA, USA
Aircraft: LUSCOMBE 11A
Registration: N1606B
Category: Airplane
Highest injury: None
Fatalities: 0
Phase of flight: Climb

Probable cause

The pilot’s inability to maintain airplane control during cruise flight due to the failure of the elevator trim tab as a result of missing hardware for the elevator control cable bellcrank to elevator torque tube attachment bracket.

NTSB narrative

The pilot reported that during cruise flight several minutes after departure he felt both the control yoke and airframe shake violently. The pilot looked out of his window toward the tail section and observed the elevator trim tab fluttering up and down with no corresponding movement to the trim wheel inside the cockpit. The pilot reduced engine power to slow the airplane and regain aircraft control. The airplane began to descend despite full aft elevator pressure. Realizing that he did not have elevator control, the pilot manually manipulated the throttle for pitch control and contacted air traffic control to report his situation. During the descent to a road, the left wing struck a heavy advertising sign and a fence post. After exiting the airplane, the pilot inspected the trim tab and stated that it had failed outboard of the trim cable control horn bracket attachment. He also reported that the upper bolt for the elevator control cable bellcrank to the elevator torque tube attachment bracket was missing. Further examination of the airframe revealed that bolts from the upper attachment and the aft attachment for the elevator control cable bellcrank to elevator torque tube attachment were missing. Damage to the airframe in the tail section included, on the right side torque tube, rub marks on the leading edge with corresponding damage to the adjacent airframe skin, and left side torque tube rub marks on the trailing edge with damage to the rudder skin behind it. What likely occurred was that the elevator attachment bolts on the elevator control cable bellcrank backed out, which then initiated flutter at the elevator, which transferred to the trim tab causing it to fail in overload. Maintenance records indicated that the applicable Airworthiness Directive for the inspection of the trim tab horn attachment was accomplished in December 1949. The airplane had flown 7 hours since its last annual inspection 6 months prior to the accident.