History of Flight
On October 6, 2022, at approximately 1229 eastern daylight time, a Seamax Aircraft Ltd M-22, registration N46PD, sustained substantial damage in an accident near East Hampton, New York. The private pilot was fatally injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Surveillance video from East Hampton Town Airport (JPX) showed the pilot arriving at the airplane's hangar at 1159. At 1206, he pulled the airplane from the hangar, performed a preflight inspection, entered the airplane, closed the canopy, and started the engine at 1209. The airplane began taxiing for departure at 1214.
ADS-B data indicated the airplane departed runway 28 at 1219, proceeded south to the Atlantic Ocean, turned east paralleling the shoreline, then turned north. ADS-B contact was lost while the airplane was over Three Mile Harbor.
A witness reported hearing an airplane engine, then a loud “crack,” and saw a wing separate from the airplane, after which the airplane spiraled down into the water.
The main wreckage came to rest in 3 to 4 feet of water in Three Mile Harbor. The right wing was found in a tree about 770 feet from the main wreckage.
Aircraft Information
The accident airplane featured a foldable wing design offered by the manufacturer. On the ground, the wings could be detached from the upper fuselage and rotated about the wing strut attachment bolts to fold against the fuselage for transport or storage. The wing struts were structural members spanning from the lower fuselage to near mid-span on the lower side of each wing.
Wreckage and Impact Information
The engine was impact-separated from the fuselage but remained attached to the engine mounts. All four cylinders were attached. The propeller remained attached; one blade exhibited chordwise scratching and leading edge gouging, another was separated with similar scratching, and the third was not recovered.
Examination of the airframe revealed a fragmented fuselage. Flight control continuity was confirmed through multiple breaks and overload failures. The right stabilator remained attached with leading edge damage. The left wing was fragmented. The left wing strut was impact-separated but the strut attach point bolt remained secure with its nut.
The right wing was entirely separated and located in a tree. The aileron remained attached; the flap was separated. The bolt attaching the right strut to the wing remained attached to the wing and was not fractured, but the nut was missing. The bolt threads showed no significant damage.
Examination of the nut thread piece removed from the right wing strut outboard attachment bolt revealed 2 to 3 threads with deformation and contact patterns consistent with repeated contact loading. Scanning electron microscope examination showed smearing and ductile overstress fracture features.
The nut from the left strut outboard attachment also had 2 to 3 threads with deformation and twisting, and similar battered appearance indicating repeated contact loading.
Subsequent Service Actions
Following the accident, the FAA issued Special Airworthiness Information Bulletin (SAIB) 2022-24 on December 23, 2022, recommending compliance with all pertinent Seamax service bulletins and repetitive inspections of strut attachment hardware before each flight.
On February 23, 2023, Seamax Aircraft issued Service Alert SA_001_23, requiring a one-time inspection of the attachment bolts and nuts at the outboard ends of the left and right struts. The hardware specified was an AN5-10C bolt and an AN364-524 nut.
On September 19, 2023, Seamax Aircraft issued SD_003_23, recommending replacement of AN5-10C bolts and AN364-524 nuts on the wing strut upper terminal attachment points with an AN5-7 drilled bolt, AN310-5 castle nut, and MS24665-285 cotter pin.
The FAA updated SAIB 2022-24 to SAIB 2022-24R1 on November 14, 2023, recommending continued inspection of wing strut hinge points before each flight and replacement of nuts and bolts per SD_003_23.
According to AN Standard AN364 revision 4, the standard was inactive for design after March 13, 1957, and canceled on October 21, 1991. It was superseded by MS21083.
MS21083 revision H stated that these nuts were intended for shear applications only and subject to limitations of MS33588. MS33588 revision E stated that self-locking nuts shall not be used where loss of the bolt would affect safety of flight unless secured by a positive locking device, nor on externally threaded parts serving as an axis of rotation unless loads do not relieve initial stresses or the nut is secured with a positive locking device.
The axial height of the recovered nut was 0.250 inch, the maximum for an AN364-524 nut. The corresponding MS21083N5 steel nut had a specified height range of 0.235 to 0.266 inch.