VERO BEACH, FL, USA
N30397
Piper PA-44-180
While maneuvering the airplane at 4,000 feet above ground level, the flightcrew heard a loud noise from the left engine and saw that the left engine had dropped down about 45 degrees from the normal position. They returned to the departure airport for an emergency landing. When the landing gear was extended the left engine dropped down further. They were unable to maintain directional control due to the drag and made a forced landing in a wooded area. Post crash examination showed the left propeller hub had failed due to fatigue cracking causing a blade to separate. The remainder of the propeller separated when the propeller flange separated due to overstress and the engine dropped down when the engine mount separated due to overstress. The left propeller had sustained damage in a gear up landing 525 flight hours before the accident. The blades were bent beyond repairable limits and scrapped. The hub was inspected and returned to service with new blades. The manufacturer's procedures call for a hub to be retired if the blades receive damage beyond repairable limits and are scrapped.
On April 14, 1999, about 1139 eastern daylight time, a Piper PA-44-180, N30397, registered to and operated by Flight Safety International, Inc., crashed while attempting an emergency landing at Vero Beach, Florida, while on a Title 14 CFR Part 91 FAA check flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the commercial-rated pilot-in-command and the airline transport-rated check pilot were not injured. The flight originated from Vero Beach, Florida, the same day, about 1000. The check pilot stated he was giving the pilot-in-command the FAA check ride for the commercial pilot multiengine rating. While at 4,000 feet they simulated the failure of the right engine, shut down the engine, and placed the propeller in the feathered position. After completion of the maneuver, the pilot-in-command was instructed to restart the right engine. As they were doing this, they heard a loud bang from the left side of the aircraft and looked out to see the left engine hanging down about 45 degrees from the normal position. They completed starting the right engine and turned toward the Vero Beach Airport for an emergency landing. While on final approach to runway 22, he waited until about 300 feet agl before lowering the landing gear. After the gear was lowered, the left engine dropped down to about 65 degrees from the normal position. The increased drag caused the aircraft to veer to the left and he was unable to maintain directional control. A forced landing was made in a wooded area, about 1,000 feet from the runway. Postcrash examination of the aircraft by an FAA inspector and maintenance personnel from the operator showed the left propeller and propeller flange were missing. The left engine mount had separated in multiple locations and the upper portion of the engine fire wall had separated from the engine nacelle. Portions of the separated propeller and the propeller flange were located several days after the accident. The propeller hub had separated and one propeller blade and a portion of the hub were not found. Teardown examination of the left engine conducted by the operator maintenance personnel and an FAA inspector showed no evidence of precrash failure or malfunction of the engine assembly including the crankshaft counter weights. The only damage was the separated propeller flange and propeller. Examination was conducted by the NTSB Materials Laboratory of the recovered components of the left propeller, the left engine crankshaft, separated portions of the left engine mount, and a propeller hub from another aircraft, that had previously been installed on an aircraft with the separated hub during a gear up landing. The No. 1 blade was separated from the left propeller hub by a circumferential fracture around the hub arm. The hub fracture was located just inboard of the blade bearing retention flange and just outboard of the pre-load shelf. Visual examinations of the fracture surfaces revealed indications of fatigue progression on the fracture of the forward half of the hub. Fatigue features were visually apparent over about 3 inches of the fracture. The remainder of the fracture surfaces were consistent with overstress fracturing stemming from the fatigue area. The fatigue did not emanate from an origin area on the received piece of hub. The left engine crankshaft was fractured on the forward end just aft of the oil slinger ring. The fracture surface was consistent with overstress separation. Examination of the separated portions of engine mount showed fractures consistent with overstress separation. Examination of the propeller hub that had been installed on another aircraft during a gear up landing with the failed left propeller hub showed the hub had no crack indications present. (See attached NTSB Materials Laboratory Factual Report) Maintenance records show the left propeller, Hartzell model HC-C2YR-2CEUF, serial number AU6102, had been installed on another Piper PA-44 aircraft, N2247B, when in May 1998, the aircraft was involved in a gear up landing resulting in sudden stoppage damage to the propellers. The propellers were removed from the aircraft and sent to a propeller overhaul company for overhaul. The blades in both propellers were bent beyond allowable limits for repair and they were scrapped. The propeller hubs were inspected and new blades were installed. The propellers were then certified as overhauled and returned to service. One of these propellers was then installed in the left position on N30397. At the time of the accident, the left propeller had accumulated 11,355 total flight hours since new and 525 flight hours since overhaul after the May 1998 damage. (See attached maintenance records) The Hartzell Standard Practices Manual No. 202A, dated March 1997, states on page 1110, that aluminum "hubs must be retired if involved in a ground/foreign object strike in which the hub was exposed to severe abnormal loads. If visual inspection reveals one or more of the following indications listed, the hub must be retired. One or more aluminum blades retired because of bends beyond Manual No. 133C (61-13-33) repair limits." (See attached pages from Hartzell Standard Practices Manual)
The improper return to service of a propeller hub by a propeller overhaul company which according to manufacturer's procedures should have been retired due to damage to propeller blades from sudden stoppage. This resulted in undetected fatigue propagation through the hub and separation of a propeller blade in flight. This resulted in overstress separation of the propeller flange and the remainder of the propeller and overstress separation of the engine mount causing the engine to drop down making the aircraft uncontrollable.
Source: NTSB Aviation Accident Database
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