JACKSONVILLE, FL, USA
N29YV
Beech 1900D
Shortly after takeoff a counterweight and clamp separated from one propeller blade on the right propeller. The separated counterweight and clamp struck the adjacent blade and caused the blade to separate about 12 inches from the hub. The resultant imbalance caused severe vibration from the right engine. The propeller governor struck the engine cowling and broke into pieces. The flight crew shutdown the engine using the condition lever. The propeller did not feather when commanded by the flight crew, and it continued to windmill causing vibration and drag until landing. Metallurgical examination indicated a blade counterweight clamp screw failed causing the clamp to separate. The screw fracture surface initiated at the screw threads and had features typical of intergranular cracking. Cadmium, which is used as a plating on the screw after manufacturer, was present on the fracture surface.
On March 28, 1996, about 0616 eastern standard time, a Beech 1900D, N29YV, registered to Mesa Air Group, Inc., and operated by Mesa Airlines, Inc. dba Florida Gulf Airlines, as flight 5564, a Title 14 CFR Part 135 scheduled commuter service from Jacksonville, Florida, to Orlando, Florida, suffered separation of a propeller counter weight and adjacent propeller blade, during takeoff from Jacksonville. Visual meteorological conditions prevailed at the time and an instrument flight rules flight plan was filed. The aircraft received minor damage and the airline transport-rated pilot and first officer were not injured. There were no passengers. The flight was originating at the time of the incident. The flightcrew stated that after takeoff on runway 25, at about 200 feet, they felt a heavy vibration which they identified as coming from the right engine. They shut down the engine using the condition lever and placed the propeller control in the feathered position. The vibration was reduced about 50 percent. The propeller did not feather and continued to windmill, causing vibration. As they flew the traffic pattern to return for landing on runway 25, the propeller slowed and moved toward the feathered position; however, it did not feather. After about 2 to 3 minutes the drag from the right propeller was reduced. They landed without further incident and taxied to the ramp. Postcrash examination of the aircraft by an FAA inspector indicated the counterweight and clamp on one right propeller blade separated and exited through the propeller spinner in the direction of the adjacent propeller blade. The following propeller blade was impacted by the counterweight and clamp and separated about 12 inches from the propeller hub. The separated propeller blade was found to the right side of the departure runway, about 6,000 feet from the beginning of takeoff roll. The counterweight and part of the retaining clamp were located on the left side of the runway about 5,000 feet from the beginning of takeoff roll. After the right propeller blade separated, the engine imbalance caused the propeller governor to strike the engine cowling damaging the governor. The damage to the governor prevented the propeller from feathering. Representatives of Raytheon Aircraft Company, formerly Beech Aircraft, stated that "during production flight testing of the 1900D, a check is performed which involves shutting down one engine at a time with the propeller unfeathered and the airspeed about 120 knots. During that check, the propeller typically windmills at about 1400 rpm and does not feather. If not commanded to feather, the propeller will continue to windmill until the rpm decreases to a point where oil is no longer supplied to the propeller governor. At that point, the propeller springs take the blades to the feather position." See the Raytheon Aircraft Company letter. Examination of the separated blade clamp was performed by the NTSB Materials Laboratory, Washington D.C. One of two clamp retaining screws had failed. Metallurgical examination of the failed clamp screw indicated that the screw separated due to intergranular fractures which initiated in the thread area of the screw. Cadmium, which is used to plate the screw after manufacturer, was found on the fracture surface. See the Metallurgist's Factual Report.
Failure of a blade counterweight clamp retaining screw due to cadmium embrittlement which occurred during the manufacture process. This resulted in the counterweight clamp separating and striking the adjacent blade causing it to separate.
Source: NTSB Aviation Accident Database
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