N419JSDiamond Aircraft Ind DA 40 · 2004

On September 13, 2008, at 1000 Pacific daylight time, N419JS, a Diamond DA-40, had higher than normal revolutions per minute for the engine during flight (RPMs), and after trouble-shooting the problem, the pilot returned to his departure airport of San Carlos Airport, San Carlos, California. The pilot was the registered owner of the airplane and operating it under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed. The pilot was not injured and the airplane sustained minor damage.

According to the pilot, the run up was without incident. He noted that the RPMs dropped slower than normal when he cycled the propeller but did not feel that it was a problem. During the climb out, he noticed that the engine RPMs climbed to 2,800 so he leveled off his climb and pulled the propeller control back. He did not notice a reduction in engine RPM. He then pulled the power back and was able to reduce the RPMs below 2,700. He attempted to cycle the propeller twice but noticed no change in RPMs. At this time, the pilot decided to return to San Carlos and during the return flight, he heard and felt a thump forward of the cockpit. The engine continued to run smoothly, while developing adequate power, and the pilot landed uneventfully. The pilot then contacted his maintenance facility regarding the event. The pilot further stated that the maintenance facility contacted him several days later and indicated that they had found a blister in the engine casing and fragments of metal in the oil. The engine was then disassembled and a ball bearing from the propeller governor was located in the engine. The propeller governor was removed for further examination.

Further disassembly of the engine identified one ball bearing within the oil sump, as well as damage to the case and two camshaft lifters. Examination of the engine showed that the ball bearings from the governor were able to pass through the oil drain hole of the governor.

The four-seat, low-wing, fixed-gear airplane, serial number 40.439, airplane, was manufactured in 2004. It was powered by a Textron Lycoming IO-360-M1A engine, serial number L-31681-51A, equipped with a Hartzell HC-C2YR-1BF propeller, hub serial number CH38437B. At the time of the accident, the airframe and engine had operated 559 hours.

The Ontic governor (part number C210776, serial number 0200) was examined at the governor manufacturer’s facility. Initial visual inspection showed that the low speed adjustment screw was installed backwards and safety wired into place. The pilot valve plunger was loose in the governor and could be removed. The plunger was detached from the pilot valve race which normally retains the plunger in the governor assembly. During removal of the governor cover assembly, a ball bearing .125-inch in diameter was observed to fall out of the governor oil drain hole. After the governor cover assembly was completely removed, it was observed that the retainer-thrust bearing and head assembly-flyweight were lying in the governor body. The pilot valve race was still inserted into the speeder-spring. Examination of the thrust bearing retainer revealed that 5 of the 11 required ball bearings were missing from the retainer. The retainer displayed some scoring and deformation. Upon examination of the pilot valve race it was observed that the set screw was still installed into the race, and the tip of the screw was protruding approximately .015-inch into the internal diameter of the race. The tip of the set screw displayed some deformation as observed under 10X magnification. Examination of the pilot valve plunger revealed circumferential scoring or wear marks at the location of the pilot valve race insertion.

The components were then metallurgically examined. The ball cage, washer, bearing race and plunger were examined with the scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and with optical microscopy. The failed governor bearing race and plunger were assembled with the bearing race set screw and plunger set hole misaligned. When the bearing race set screw was torqued down, the set screw tip flattened against the harder plunger surface. The failed bearing race set screw point was flattened by contact with the harder plunger surface. According to an Ontic representative, a properly assembled bearing race/plunger assembly set screw should not show any signs of set screw tip flattening.

Review of the maintenance records for the airplane showed that no maintenance had been performed on the adjustment screw. Additionally, information obtained from Diamond showed that during the airplane assembly process, the only adjustment made to the propeller governor once it is installed on the airplane is to the cable.

Review of the service difficulty report (SDR) data showed that two similar events had been reported. The two events, as well as the governor assembly from the accident, were from a single batch of 74 assemblies.

As a result of this incident, the governor manufacturer issued a mandatory service bulletin (SB) DES-353, on December 18, 2008, for the affected assemblies. The SB required that the units be returned to Ontic for inspection and, if necessary, repair.