On August 4, 2015, about 0830 Pacific daylight time, a Grumman G-164B agricultural airplane, N48452, was substantially damaged during a forced landing due to a loss of engine power near Princeton, California. The airplane was operated by Valley Air Service, LTD. The commercial pilot, the sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed for the local aerial application flight, which was being operated in accordance with 14 Code of Federal Regulations Part 137, and a flight plan was not filed. The flight departed Colusa County Airport (O08), about 0800.
In a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that the accident occurred on the second load of the morning while applying a fungicide to a rice field. The pilot stated that during a spray run the engine lost power, and unable to maintain altitude, he made a forced landing to the rice field he was treating. The pilot added that the airplane nosed over during the landing, which resulted in substantial damage to the airplane's rudder, and right upper and lower wing panels.
On August 18, under the supervision of a Federal Aviation Administration (FAA) Aviation Safety Inspector, the engine was examined by a licensed FAA airframe and powerplant mechanic. The examination revealed that the number 2 cylinder head had cracked and lifted under the cooling fins on the left side of the cylinder. The crack then continued across the top and inside of the head to the intake valve seat, which resulted in the loss of power after the hot gases entered the induction system. The examination revealed no other anomalies with the engine or the airframe that would have precluded normal operation.
An examination of the airplane's maintenance records revealed that the most recent annual inspection was performed on March 7, 2015. Records further revealed that on March 16, 2015, FAA Airworthiness Directive (AD) 99-11-02, a mandatory 100-hour repetitive visual inspection to prevent cylinder head cracking, was performed at an engine tachometer time of 3,661.4 hours. At the time of the accident, the engine tachometer read 3,728.1 hours, or 66.7 hours since the AD had been complied with.