N61PJAutogyro Gmbh MTO SPORT · 2018

On October 27, 2011 about 1440 Pacific daylight time, a McDonnell Douglas MD-500D helicopter, N61PJ, was substantially damaged during an autorotation and forced landing about 6 miles west of Colusa, California, following a complete loss of engine power. The helicopter was owned and operated by PJ Helicopters, and was being utilized for communications cable installation and support activity for Summit Line Construction Company. The pilot received minor injuries. The work flight was operated under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the flight.

According to the pilot, he had flown the helicopter a total of about 5, non-continuous, hours on the day of the accident, operating from a remote landing zone near the job site. He had just transferred two construction personnel from one cable tower to another one, and was beginning to climb and translate the helicopter clear of the tower, when he heard a noise and felt a yaw that indicated to him that the engine had ceased developing power. The helicopter began to descend rapidly. The pilot began an autorotation, maneuvered the helicopter away from the tower, and attempted to flare for ground impact. The helicopter impacted in a freshly plowed field. The aft section of the tailboom and both landing skids were partially fracture-separated from the helicopter. The main rotor blades, flight control linkage, and the fuselage sustained substantial damage. The height of the towers was reported as about 165 feet.

The pilot held a commercial pilot certificate with a rotorcraft-helicopter rating. He reported a total flight experience of 1,980 hours, including 330 hours in the accident helicopter make and model. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued in January 2011, and his most recent flight review was completed in February 2011.

According to FAA information, the helicopter was manufactured and registered as a Hughes (Hughes Helicopters became McDonnell Douglas Helicopters in 1984) model 369D in 1977, and was equipped with an Allison/Rolls-Royce C20B series turboshaft engine. Operator-provided information indicated that the most recent 100-hour inspection was completed on October 19, 2011. At the time of the accident, the helicopter had accumulated a total time (TT) in service of 11,579 hours, and the engine had accumulated a TT of 15,515 hours.

The operator reported that the weather conditions about the time of the accident included clear skies; wind speed of 5 knots; and temperature about 27 degrees C.

The accident site was not located at an airport. Commercially-available geographic data indicated that the accident site elevation was about 430 feet above mean sea level.

The helicopter was landed and remained upright in a level, plowed field several hundred feet from the tower that it had just departed. The airframe was examined in detail about one week after the accident. The airframe incurred significant crush and deformation damage from the impact. No non-impact anomalies that would have precluded normal operation were observed. There was no evidence of fire or uncontained engine failure. No components were determined to be missing.

The skids were bent and/or fracture-separated, and the tail boom was almost completely fracture-separated from the fuselage. The tail boom separation was not consistent with a main rotor blade strike. The main and tail rotor blade and drivetrain damage was consistent with low energy and low rotational speed at impact.

The cockpit structure was intact but the door frame structure, windscreens, overhead transparencies, and floor exhibited varying degrees of damage. The instrument panel was intact and visibly undamaged. The crew seats were intact, with visible crush damage to the pilot seat pan. There was no obvious damage or deformation to the seat box structure. The seat damage was consistent with high vertical loading. The restraint system was intact and undamaged. The fuel tank was not compromised, and no fuel leaks were observed on site, or during the subsequent examination.

Drive continuity from the engine to transmission was established. There was no evidence of transmission failure. Due to impact damage, engine control continuity from the cockpit to the engine could not be fully established.

Refer to the NTSB public docket for detailed information.

Fuel

The helicopter was equipped with two interconnected fuel cells, which had a total fuel capacity of 64.0 gallons (about 428 pounds), of which 62.1 gallons (about 416 pounds) were usable. No representatives from the NTSB, FAA, or the airframe or engine manufacturers responded to the accident site. According to the operator, the helicopter fuel gauge indicated that there were about 300 pounds of fuel on board after the accident. Approximately that same quantity was observed by the investigators during the examination the week after the accident.

A fuel sample was obtained shortly after the accident and was tested for the presence of water, with negative results (no water). The fuel in the fuel truck which supplied the helicopter was subsequently used on other aircraft with no reported problems.

According to the pilot, about 25 minutes before the accident, the helicopter was hot-refueled to bring the total fuel quantity to about 350 pounds. The engine was not shut down between the hot refueling and the power loss. Between that refueling and the power loss, the helicopter idled on the ground for about 15 minutes, and flew for about 10 minutes. Calculations based on the engine manufacturer's fuel burn rate data indicated that the engine would have consumed about 55 pounds of fuel, which would have resulted in about 295 pounds remaining at the time of the accident.

Engine and Fuel System

There were no reported problems with the airframe fuel supply system prior to the accident. Subsequent to the accident, visual inspection of the fuel system did not identify any visible damage to the fuel cells, plumbing, and fittings, and there were no visible fuel leaks. All fuel lines were found to be at least hand tight, with undamaged torque stripes on the fittings. Two separate deviations from fuel system configuration requirements were observed on the helicopter. One was a wire-security issue related to the fuel quantity system. There was no evidence that the improperly-secured wire interfered with the fuel quantity system operation. The other was the presence of a drain valve that was eliminated by a mandatory 1994 Service Bulletin. Additional details are presented below.

The manufacturer's maintenance and operating guidance warned that air entering the fuel supply lines could result in a power reduction or an engine flameout. The manufacturer's maintenance manual required that subsequent to any maintenance which breached (opened) the fuel supply system for any reason, a fuel system vacuum leak check and fuel/air bleed procedures must be performed before the helicopter is returned to service.

As part of the investigation, it was decided to conduct the fuel system vacuum checks required by the maintenance manual. During those preparations, it was discovered that the operator's mechanics who were participating in the examination were unfamiliar with the required vacuum check procedures. The investigation did not determine whether any of the operator's other mechanics were familiar with the vacuum check procedures.

Vacuum checks of several fuel system sections were conducted, and the system repeatedly failed to hold vacuum, which was the pass/fail criterion. The engine was removed in order to gain better access to certain components and narrow down the location of the system leak which prevented it from holding vacuum, but with the necessary result that the system was breached. Subsequent to that, it was discovered that the test equipment was faulty. However, since the fuel system had already been compromised, the pre-disassembly integrity of the fuel system was unable to be determined. Testing of remaining and/or untouched system elements with known-good testing equipment resulted in satisfactory vacuum tests. Detailed testing information can be found in the NTSB public docket for this accident.

During the investigation vacuum testing, the fuel elbow at the station 124.00 firewall was observed to be a superseded design which had a drain valve installed. The presence of that drain valve indicated that the mandatory McDonnell Douglas Service Bulletin (SB) DN-186 "Firewall Fuel Fitting Modification," dated 26 September 1994, had not been completed on this helicopter.

The engine was shipped to Rolls Royce for detailed examination. Due to damage, the engine could not be test-run. The engine was disassembled, but no non-impact anomalies that would have precluded normal operation were observed. The engine main fuel control and the power turbine governor were removed from the engine. Impact damage was noted, and the units were sent to Honeywell for examination and testing. No other anomalies or defects that would have prevented normal operation were detected during the follow-up examination and testing of those units.

As a result of the fact that the detailed examinations of the engine, main fuel control, and power turbine governor did not reveal any anomalies, the investigation subsequently examined some additional components in the fuel system, even though they were historically reliable components. The start pump, fuel shut off valve, and fuel line to the start pump were examined during a re-visit to the operator's facility. No anomalies or deficiencies that would obstruct fuel flow to the engine, or allow air to enter the fuel system, were found.