N3254E

HISTORY OF FLIGHT

On July 21, 2017, at 1211 Pacific daylight time, a Robinson R44 II helicopter, N3254E, landed hard during an autorotation near Van Nuys Airport (VNY), Van Nuys, California. The commercial pilot sustained minor injuries, the three passengers sustained serious injuries, and the helicopter was substantially damaged during the landing. The helicopter was registered to and operated by National Helicopter Service and Engineering Company, as a Title 14 Code of Federal Regulations Part 91 revenue sightseeing flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight departed Van Nuys about 1112.

The three passengers and pilot boarded the helicopter at 1100 for what was to be a 1-hour tour around the Los Angeles area. The pilot reported that the tour was uneventful, and as they approached the airport for landing, he heard an unusual sound. He glanced down at the engine tachometer, and it was higher than normal, indicating above 110%.

The pilot began manipulating the engine throttle to reduce power and bring the engine and rotor speeds into alignment, but the rotor RPM began to decay. He was concerned that the engine might overspeed if he adjusted the throttle higher, and presumed that there was likely an unrecoverable failure in the transmission system, so he initiated an autorotation.

He stated that trees and power poles blocked his landing approach, and he therefore did not have sufficient speed or space to perform an adequate flare, and the helicopter landed hard.

The helicopter came to rest on a street at an elevation of 672 ft mean sea level, in a densely populated residential neighborhood between the Los Angeles River and the 101 Freeway, about 3 miles southeast of VNY (See Figure 1). The landing skids had spread during the impact, and were level with the belly, and the emergency pop-out floats had deployed. The entire airframe exhibited buckling damage, and the belly was crushed. The tail rotor gearbox struck a fence, and had partially detached. Both main rotor blades remained attached to the mast, but one was bowed downward and the other was bent slightly upward.

Figure 1 – Helicopter at Accident Site

The pilot stated that at no point during the flight did he receive any instrument panel annunciations or indications of a problem. He did not scan the instrument panel during the descent because his focus was on flying the helicopter and looking for a landing spot. He reported that the engine continued to operate during the descent, and that although he has trained for emergency events, he was shocked at how quickly everything transpired.

The floats had been armed for the flight, and they appeared to have deployed during the hard landing. All the doors opened on impact, and the occupants were able to egress on their own. Prior to exiting the helicopter, the pilot secured the helicopter by pulling the fuel mixture control to the out position, and turning off the magnetos and the fuel selector valve.

WRECKAGE AND IMPACT INFORMATION

Examination

The engine and airframe were examined following the accident by the NTSB investigator-in-charge, and technical representatives from Robinson Helicopters, and Lycoming Engines. Complete examination reports are contained in the public docket.

No anomalies with the flight controls, drive train or engine were noted, the governor switch was found in the "ON" position, and witness signatures indicated that the engine was producing power at the time of ground impact.

The low rotor RPM warning horn was tested by the application of electrical power directly to its input, and it did not produce a sound. The filament of the low rotor RPM warning light on the instrument panel was still intact and operational.

The magnetos were removed, along with the clutch actuator assembly, overrunning clutch, tachometer voltage regulators, engine and rotor tachometer, and governor control unit for examination and testing at the facilities of Robinson Helicopters. All components performed nominally.

Examination of the tachometer breaker point wires in the right magneto revealed that they were twice the designed length, and made of slightly thicker gauge wire, which did not have any identification on its sheath. The female spade connectors which connected the tachometer breaker points to the wires were of slightly heavier gauge than standard. Neither had any strain relief tabs, and closer examination revealed that the wires had been soldered to the spade connectors, rather than crimped. The wire on the moving side of the points had completely separated at the solder joint, with soldered strands still attached to the connector (See Figure 2). The wire on the fixed side of the points was still attached to the spade, however about 1/3 of its strands had frayed and separated in a similar manner.

The helicopter was fitted with the fuel tank bladders required in Robinson Helicopters Service Bulletin SB-78B. The bladders were not compromised during the landing.

Figure 2 – Separated Tachometer Points Wire

Maintenance History

The helicopter was maintained by mechanics employed by National Helicopter Service and Engineering Company at their base on Van Nuys Airport.

The mechanics stated that about two weeks before the accident the rotor and engine tachometer needles were intermittently binding against each other, particularly on startup as the needles climbed (the needles were housed in a dual gauge), but they would then usually unbind and work correctly once operating speeds had been reached.

The tachometer was therefore replaced at the 100-hour inspection. However, as soon as they started the helicopter, neither the engine tachometer nor the governor worked. They performed some troubleshooting steps and determined the right magneto, which contained the tachometer breaker points, was the problem, so they replaced the magneto with a unit loaned by a maintenance facility in Oxnard. It was their understanding that the replacement magneto had accrued about 5 hours of total time since overhaul.

Maintenance records indicated that the inspection and magneto replacement was complete on July 7, 2017, 26.2 flight hours before the accident.

Both mechanics from National Helicopter Service stated that they did not replace the tachometer wires at any time, and the owner of the maintenance facility who loaned the magneto stated that he was not aware of the cables ever being replaced while the unit was in his possession, and added that he would not have used solder to connect the wires.

During the investigation, the right magneto was taken to the facility who performed the last overhaul. The owner of the facility inspected the magneto, and confirmed that the breaker points cable and spade connectors were not the type he used, and that the cables were longer than standard. He then provided exemplar copies of the cables and connectors, and demonstrated how the tachometer points are typically assembled and wired. None of the methods matched those observed in the accident magneto. He stated that wires were always crimped, and solder was never used.

Governor and Tachometer System

The collective control for the R44 II series is conventional, and includes a twist grip throttle. When the collective control is raised, the engine throttle is opened automatically by an interconnecting linkage. In addition, the helicopter is equipped with an engine governor system, which senses engine RPM and applies corrective input forces to the throttle to maintain engine RPM as needed.

The governor system is composed of a solid-state electronic controller, which determines engine RPM from the tachometer points in the engine's right magneto. When the governor senses the need to adjust engine RPM it activates a motor which drives the throttle directly through a worm gear drive and friction clutch. The clutch can be overridden by the pilot through the throttle twist grip.

The governor is engaged via a switch located on the pilot's collective control. A "GOV-OFF" warning light in the instrument cluster will illuminate if the governor has been turned off by this switch. The light will not indicate a governor failure or error.

According to the maintenance manual, "The governor is active from 79% - 111 % engine RPM and can be switched on or off by the pilot using the toggle switch on the end of the right seat collective control. The governor system is designed to assist the pilot in controlling the RPM in the normal operating range. It may not prevent over- or under-speed conditions generated by aggressive flight maneuvers. Within the active range there is a 1 %-wide deadband from 101 % - 102%> where the governor will not take action provided the RPM is steady."

The helicopter is equipped with one electronic dual (engine and rotor) tachometer. The sensor for the engine tachometer is the same set of magneto breaker points used by the governor. The sensor for the rotor tachometer is an electronic Hall Effect device which senses passage of two magnets attached to main rotor gearbox input yoke assembly. The engine and rotor tachometer circuits have separate circuit breakers and are completely independent from the other.

According to technical representatives from Robinson Helicopters, if the magneto breaker point signal is lost completely, the governor controller will no longer send power to the governor motor, which will therefore remain at the last set position. Should the signal be partially interrupted, the governor may interpret the signal as a command to increase or decrease engine RPM, depending on the intermittency of the failure. None of these failure modes would trigger the "GOV-OFF" indicator light.

ADDITIONAL INFORMATION

Onboard Recording System

The helicopter was equipped with a "Tourmaster" GPS enabled video recording unit, manufactured by Rugged Video LLC. The unit was typically used by air tour operators to record video, audio, and GPS data for customers as a memento of their flight...