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| Date: | Saturday 1 June 2024 |
| Time: | 14:16 |
| Type: |  Cessna 150M |
| Owner/operator: | Private |
| Registration: | N6198K |
| MSN: | 15077583 |
| Year of manufacture: | 1975 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Other fatalities: | 0 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | near Fernando Luis Ribas Dominicci Airport (SIG), San Juan -
 Puerto Rico
|
| Phase: | Take off |
| Nature: | Training |
| Departure airport: | Ponce-Mercedita Airport (PSE/TJPS) |
| San Juan-Fernando Luis Ribas Dominicci Airport (SIG/TJIG) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
On June 1, 2024, at 1416 Atlantic standard time, a Cessna 150M, N6198K, was substantially damaged when it was involved in an accident near San Juan, Puerto Rico. The student pilot and flight instructor sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.
The student pilot and flight instructor reported that the engine lost power shortly after takeoff. ADS-B data showed that the airplane reached a maximum altitude of 213 ft above ground level (agl) before entering a descending left turn back toward the runway. The airplane impacted the ground before reaching airport property. Examination of the wreckage found substantial damage to the engine mounts, fuselage, both wings, the right horizontal stabilizer, and elevator.
Examination of the engine revealed that the rocker shaft bosses for the No. 2 cylinder had failed. Metallurgical examination found that a portion of the cylinder head, which contained the rocker arm shaft, fractured due to fatigue cracking that had initiated along the bore for the shaft. Once this section of the cylinder head fractured, the remainder of the cylinder head holding the rocker shaft fractured from overstress, freeing the shaft and rocker arms. These fractures would prevent the proper function of the drivetrain, preventing the valves from opening and leading to the failure of the No. 2 cylinder.
The housing boss bore walls exhibited wear significant enough to allow for movement of the bushings and shaft. The bore exhibited wear marks consistent with rotational and lateral movement of the shaft, and the adjacent bushings exhibited lateral wear marks. Many of these marks matched those observed on the shaft, indicating movement along these surfaces. This uneven wear likely led to the rocker arms pushing erratically on the valves, as evidenced by the off-center wear marks on the rocker arm and valve stem faces. This uneven movement and wear likely led to wobbling and sliding. This created more wear, which eventually resulted in fatigue cracking and the subsequent failure of the rocker shaft bosses.
A review of maintenance records was unable to determine the number of hours on the cylinder. The review found no record of the No. 2 cylinder being removed and reinstalled on the engine. While the logs described that about 7 years before the accident three unspecified cylinders had been removed and replaced, no information regarding which position they were installed to, or their serial numbers were recorded. The engine was subject to an FAA airworthiness directive (AD), which stated that the cylinder rocker shaft bosses must be inspected “At the next cylinder removal from the engine, or engine overhaul, whichever occurs first, after the effective date of this AD, inspect the cylinder rocker shaft bosses for cracks….” Based on the records, it could not be determined whether the No. 2 cylinder had been inspected in accordance with the AD.
Probable Cause: A partial loss of engine power due to the failure of the No. 2 cylinder rocker shaft bosses from fatigue cracking.
Accident investigation:
 |
|
Sources:
https://www.elnuevodia.com/noticias/seguridad/notas/se-estrella-avioneta-cerca-del-aeropuerto-de-isla-grande-en-san-juan/
https://data.ntsb.gov/Docket?ProjectID=194363
https://www.flightaware.com/live/flight/N6198K/history/20240601/1502Z
https://www.flightradar24.com/data/aircraft/n6198k#357a7a77
https://cdn.jetphotos.com/full/6/64532_1660140505.jpg (photo)
https://cdn.jetphotos.com/full/6/1450233_1717295901.jpg (photo)
Location
Images:
Photo: NTSB
Media:
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 01-Jun-2024 22:07 | Captain Adam | Added |
| 03-Jun-2024 05:56 | Anon. | Updated [Source, ] |
| 12-Jun-2024 18:17 | Captain Adam | Updated [Time, Location, Narrative, Category, Accident report, ] |
| 06-Apr-2025 23:51 | Captain Adam | Updated [Phase, Source, Narrative, Photo, ] |
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