Accident Sequence
On June 1, 2024, at 1416 Atlantic standard time, a Cessna 150M, registration N6198K, was substantially damaged during an instructional flight conducted under Title 14 Code of Federal Regulations Part 91. The aircraft departed from Fernando Luis Ribas Dominicci Airport (TJIG) in San Juan, Puerto Rico. ADS-B data indicated the takeoff roll began on runway 9 at 1415:23. At 1415:57, approximately 1,000 feet before the departure end of the runway, the airplane initiated a climbing slight right turn, reaching a maximum altitude of 213 feet above ground level. Subsequently, it entered a left descending turn back toward runway 27. The last ADS-B target was recorded at 1416:23, and the airplane impacted the ground, coming to rest on the edge of a parking lot about 0.13 nautical miles before the runway 27 threshold.
Injuries and Damage
The student pilot and flight instructor sustained serious injuries. Postaccident photographs revealed substantial damage to the engine mounts, fuselage, both wings, right horizontal stabilizer, and elevator. Fuel samples collected from the wing fuel tanks by a Federal Aviation Administration (FAA) inspector showed no visible contamination and were consistent with 100LL aviation fuel.
Pilot Reports and Engine Examination
An FAA inspector interviewed the student pilot and instructor after the accident. The student pilot reported that shortly after takeoff, between 300 and 600 feet, the engine lost total power, and the instructor assumed control. The student had no recollection after that point. The instructor stated that the engine lost partial power around 400 feet, at which time he took control, turned right about 30 degrees, then executed a left 270-degree turn in an attempt to return to the airport. He had no further recollection after the left turn.
A postaccident teardown examination of the engine, conducted under FAA supervision, found that the No. 2 rocker shaft bosses were fractured and separated. The fractured components were sent to the National Transportation Safety Board (NTSB) Materials Laboratory for analysis. Examination revealed that a portion of the cylinder housing holding the rocker arm shaft had fractured from fatigue cracking initiated along the bore where the shaft sits. The bore showed wear marks consistent with rotational and lateral shaft movement, and the rocker and valve stem faces exhibited uneven wear patterns. Fatigue cracking started at multiple sites along the edge of the fracture surface within the shaft bore. Although the housing contained solidification voids, fatigue cracking had propagated through some but not initiated from them.
Maintenance History and Airworthiness Directive
On February 18, 1994, the FAA issued Airworthiness Directive (AD) 94–05–05, applicable to Teledyne Continental Motors (TCM) C75, C85, C90, C125, C145, O–200, O–300, and GO–300 series reciprocating engines. The AD required inspection of cylinder rocker shaft bosses for cracks and inspection for looseness, with replacement if necessary, prompted by reports of cracked or improperly repaired bosses, which could result in engine power loss and failure.
Aircraft maintenance records showed compliance with AD 94–05–05 on November 21, 1999, at an aircraft total time of 6,788.5 hours, but no engine logbook entries specified which cylinders were inspected. Additionally, three cylinders were replaced on December 4, 2017, at an aircraft total time of 7,937.6 hours, though the specific cylinders were not recorded. At the time of the accident, the engine had accumulated 8,600.3 total hours.