Part(s) separation from AC: Piper PA-28-140 Cherokee, N261FC, accident occurred on March 27, 2025, in Royal Kunia, Hawaii

• Location: Royal Kunia, Hawaii 
• Accident Number: ANC25LA028
• Date & Time: March 27, 2025, 12:00 Local 
• Registration: N261FC 
• Aircraft: Piper PA-28-140 
• Aircraft Damage: Substantial 
• Defining Event: Part(s) separation from AC 
• Injuries: 2 Minor 
• Flight Conducted Under: Part 91: General aviation - Instructional

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/199932/pdf

https://data.ntsb.gov/Docket?ProjectID=199932

On March 27, 2025, about 1200 Hawaii-Aleutian Standard time, a Piper PA-28-140, N261FC, was substantially damaged when it was involved in an accident near Royal Kunia, Hawaii. The flight instructor and student pilot reported minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. 

During an instructional flight, the flight instructor detected a vibration; shortly thereafter he heard a loud bang, the engine lost total power, and the nose dropped. He performed a forced landing to a heavily vegetated field.

After landing, the flight instructor noticed that the propeller was missing. It was later found in a nearby residence; no one was injured. The airplane sustained substantial damage to both wings, the fuselage, and the empennage.

Examination of the separated propeller revealed that the engine crankshaft had fractured and separated just aft of the crankshaft propeller flange (CPF). This flange is an integral part of the crankshaft and is where the propeller attaches to the engine; however, the CPF was found attached to the separated propeller and not the crankshaft where it belonged. The CPF was removed from the propeller and examined by an NTSB metallurgist to determine why the crankshaft had fractured and separated. The examination revealed that the CPF had been improperly modified by the drilling and installation of additional bolts. Investigators were unable to determine the purpose for the modification, when it was made, or by whom.

Available maintenance records did not include any entries noting that the propeller assembly had been removed or altered since initial installation. Additionally, there are no Lycoming maintenance instructions, repair instructions, or service bulletins that permit hole drilling and filling of the CPF.

- Probable Cause: Improper alteration of the crankshaft propeller flange at an unknown time, which resulted in an in-flight separation of the propeller assembly.