What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
On August 8, 2026 during a base to final turn on approach to the Lemhi County Airport in Salmon, Idaho on a 14 CFR part 135 passenger flight, the pilot in command (PIC) set the flaps to approach setting, heard a “bang” with a resultant asymmetrical flap setting when the left flap partially retracted. The PIC used full counteracting aileron to complete the landing with no additional damage to the aircraft. Post landing examination of the aircraft discovered the left; aft flap bell crank mounting bolt assembly had backed out of the self-locking nut plate in the doubler at the bottom of the left wing. This allowed the bell crank to move enough to allow the left flap to partially retract and the interconnection flange of the bell crank to puncture the left-wing aft spar web. Additionally, the interconnect rod between the forward and aft left wing flap bell cranks damaged the lower portion of the pass-through hole in the spar web. Further investigation revealed that the operator’s maintenance personnel had performed the 100 hour or 12 month flap system functional check task 27-50-00-720 but had failed to complete the required step of the task to torque check the flap bell crank mounting bolts. The maintenance personnel had failed to perform the flap bell crank mounting bolt torque check for at least the previous 600 flight hours.
As the FAA filed it
ON AUGUST 8, 2026 DURING A BASE TO FINAL TURN ON APPROACH TO THE LEMHI COUNTY AIRPORT IN SALMON, IDAHO ON A 14 CFR PART 135 PASSENGER FLIGHT, THE PILOT IN COMMAND (PIC) SET THE FLAPS TO APPROACH SETTING, HEARD A “BANG” WITH A RESULTANT ASYMMETRICAL FLAP SETTING WHEN THE LEFT FLAP PARTIALLY RETRACTED. THE PIC USED FULL COUNTERACTING AILERON TO COMPLETE THE LANDING WITH NO ADDITIONAL DAMAGE TO THE AIRCRAFT. POST LANDING EXAMINATION OF THE AIRCRAFT DISCOVERED THE LEFT; AFT FLAP BELL CRANK MOUNTING BOLT ASSEMBLY HAD BACKED OUT OF THE SELF-LOCKING NUT PLATE IN THE DOUBLER AT THE BOTTOM OF THE LEFT WING. THIS ALLOWED THE BELL CRANK TO MOVE ENOUGH TO ALLOW THE LEFT FLAP TO PARTIALLY RETRACT AND THE INTERCONNECTION FLANGE OF THE BELL CRANK TO PUNCTURE THE LEFT-WING AFT SPAR WEB. ADDITIONALLY, THE INTERCONNECT ROD BETWEEN THE FORWARD AND AFT LEFT WING FLAP BELL CRANKS DAMAGED THE LOWER PORTION OF THE PASS-THROUGH HOLE IN THE SPAR WEB. FURTHER INVESTIGATION REVEALED THAT THE OPERATOR’S MAINTENANCE PERSONNEL HAD PERFORMED THE 100 HOUR OR 12 MONTH FLAP SYSTEM FUNCTIONAL CHECK TASK 27-50-00-720 BUT HAD FAILED TO COMPLETE THE REQUIRED STEP OF THE TASK TO TORQUE CHECK THE FLAP BELL CRANK MOUNTING BOLTS. THE MAINTENANCE PERSONNEL HAD FAILED TO PERFORM THE FLAP BELL CRANK MOUNTING BOLT TORQUE CHECK FOR AT LEAST THE PREVIOUS 600 FLIGHT HOURS.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.