Cessna 150 N6198K

Summary

On 1 June 2024 at about 18:16 local time, a Cessna 150 registered N6198K, operated by Ace Aviation, was involved in an accident near San Juan, United States. 2 people were on board and 2 were seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

1 June 2024 at 18:16

Classification

Accident

Location

San Juan, United States

Nearest airport

Fernando Luis Ribas Dominicci (SIG)

Coordinates

18.4574, -66.0886

Aircraft

Cessna 150

Registration

N6198K

Category

Airplane

Year built

1975

Engines

1

Operator

Ace Aviation

Operating rule

Part 91: General Aviation

Purpose of flight

Instructional

Phase of flight

Not recorded

Route

San Juan → Ponce

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ERA24LA239

2 people were seriously injured.

A partial loss of engine power due to the failure of the No. 2 cylinder rocker shaft bosses from fatigue cracking.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.