N25VHRobinson Helicopter R44 II · 2004

On July 19, 2009, about 0840 Eastern daylight time, a Robinson R44 II helicopter, N25VH, was substantially damaged during a forced landing near Silver Spring, Pennsylvania. The student pilot, the sole person on board, was not injured. The instructional 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.

According to the pilot, she departed Frederick Municipal Airport (FDK), Frederick, Maryland, about 0745, with an intended destination of Lancaster Airport (LNS), Lancaster, Pennsylvania. The pilot reported that she conducted the cruise portion of the flight at an altitude of 3,000 feet above mean sea level (msl), at an airspeed of approximately 110 knots. After she established communications with the LNS air traffic control tower, and was getting ready to begin her descent to the airport, the pilot noticed that the vertical speed indicator was indicating a descent of approximately 1,000 feet per minute, and that the airspeed was approximately 120 knots. The pilot manipulated the collective, cyclic and throttle in an effort to reduce or stop the descent, but the helicopter did not respond as the pilot expected, and the descent continued. She determined that she would not be able to reach LNS, and selected a field suitable for a landing. Despite the fact that the engine was operating, the pilot stated that she conducted an autorotation. The helicopter landed hard in a soybean field, and remained upright. The engine continued to run after touchdown, and the pilot shut it down using normal shutdown procedures.

Federal Aviation Administration records indicated that the pilot held a private pilot certificate with an airplane single-engine land rating. She also held a senior parachute rigger certificate. Her most recent FAA third-class medical certificate was issued in April 2009. The pilot had approximately 212 total hours of fixed wing flight experience, and 64 hours of rotary-wing experience, 62 of which were in the R44.

According to FAA records, the helicopter was manufactured in 2004, and was equipped with a Lycoming IO-540 series piston engine. The helicopter was owned by a corporation, leased to a fixed-base operator (FBO) located at FDK, and rented by the pilot. According to the maintenance records, the helicopter had accrued a total time (TT) in service of 898.9 hours. The most recent 100-hour inspection was completed on May 30, 2009, when the airframe had a TT of 837.5 hours, and the engine had a TT of 899.0 hours.

The most recent maintenance entry was dated June 23, 2009, and indicated an engine TT of 859.3 hours. At that time the three hydraulic servos, which had been rebuilt by Robinson Helicopter Company (RHC), were reinstalled. At the same time, the FBO complied with RHC Service Bulletin (SB) 69, which replaced the fuel strainer with a new version. Also at the same time, the FBO complied with Lycoming mandatory SB 388C, which must be accomplished every 300 hours on engines installed in helicopters. SB 388C specified the measurement of the clearances between the exhaust valves and their guides, and correction thereof if the allowable limits were exceeded. The maintenance records indicated that the valve guide for the No. 3 cylinder was reamed to bring it into compliance with the specified limits. The previous accomplishment of SB 388C was completed in May 2008, at an engine TT of 544.1 hours. The most recent annual inspection was accomplished in February 2009, at an engine TT of 742.7 hours.

The 0856 LNS recorded weather observation included wind from 310 degrees at 9 knots, 10 miles visibility, clear skies, temperature 21 degrees C, dew point 13 degrees C, and an altimeter setting of 30.11 inches of mercury.

According to information provided by the Federal Aviation Administration (FAA) inspector who responded to the accident, the helicopter landed approximately 8 miles west-southwest of LNS. The landing skids were deformed upwards, and the right side and underside of the fuselage were buckled. One engine mount was deformed, and another one was fractured. The remainder of the structure appeared intact. A fuel sample was obtained; the fuel was clear and bright, with no visible contamination. Control checks resulted in full control travel, with no binding or obstruction. On-scene examination of the helicopter did not reveal any pre-impact failures or anomalies that could have resulted in an inability to maintain altitude. The main rotor blades, tail rotor assembly, and tail boom were removed for transport, and the helicopter was recovered to a secure facility.

The insurer of the helicopter determined that it was damaged beyond economical repair, and subsequent to follow-up examinations and tests, the helicopter was disassembled and parted out.

Follow-on Airframe and Engine Examination

Four days after the accident, the helicopter was further examined by FAA and National Transportation Safety Board (NTSB) personnel. All four main drive V-belts were in good condition, and the drive belt tension actuator operated normally. The hydraulic reservoir was full. The upper spark plugs on all six cylinders were removed and inspected; all were clean, and all exhibited normal wear characteristics. The engine intake air filter was clean and unobstructed. The fuel servo throat was clean, and when the cockpit throttle was manipulated, the servo throttle valve movement was directionally correct, with full travel. Fuel samples obtained from the fuel strainer were clear and bright, with no visible contamination. The fuel strainer was disassembled; the bowl and screen were clean. The fuel injector nozzles were clear.

The removed engine components were reinstalled, and the engine was test-run. It started quickly, and ran smoothly. Due to the fact that there was no load on the engine, it was only run to a maximum of approximately 90 percent engine rpm. The engine was run for about 5 minutes at varied throttle settings, and responded normally to throttle inputs. The engine was shut down, and an oil sample was obtained for possible subsequent analysis. The engine was then removed from the helicopter, drained of its oil, and shipped to the Lycoming facility in Williamsport, Pennsylvania for additional testing.

Engine Test Run at Lycoming

The engine was examined at the Lycoming facilities on October 14, 2009, under the supervision of the NTSB. Examination of the engine revealed that it visually appeared to be undamaged. For engine run testing purposes, the Robinson oil filter adaptor was removed and replaced to accommodate the Lycoming adapter. An adaptor between the fuel servo and fuel intake manifold was also removed and replaced, as well as were other miscellaneous fittings, such as the oil pressure gauge, manifold pressure gauge, fuel pump, and the air/oil separator drain.

The oil suction screen was clean, except for three small very small (about 1/16 inch diameter) black flakes which fractured readily under pressure, and were presumed to be carbon flakes. The residual oil on the screen appeared to be clean and fresh. The oil filter, which was replaced 10 days prior to the accident, was removed but not opened. Nominal magneto timing was 20 degrees (before piston top dead center), plus or minus 2 degrees; tested magneto timing was 22 degrees (within limits) for the left magneto and 23 degrees (1 degree early) for the right magneto. The spark plugs were removed and visually examined. All showed signs of normal wear.

The engine was then prepared for a test run. It was pressure-filled with oil and started with a slave starter installed. The engine was run under manual control for approximately 5 minutes, and then was transitioned to a computer-controlled production test program. It ran for about 50 minutes, and the target rpm values were achieved. Based on the test cell results, it was determined that further examination or disassembly of the engine was not warranted. The oil sample obtained during the airframe and engine examination was not analyzed due to the results of the engine test and the on-site examination at Lycoming.

Main Rotor Hydraulic System

According to the manufacturer’s pilot operating handbook (POH), the helicopter's main rotor flight controls are hydraulically boosted "to eliminate cyclic and collective feedback forces." The pilot's control for activating or deactivating the hydraulic system was located on a 2 inch by 1-1/2 inch panel on the pilot’s cyclic control stick. The control was a 1/4 inch, unguarded toggle switch mounted at the center-right of the panel, which also contained two momentary-type pushbutton switches for the radio communications system.

Normal procedures specified that the helicopter was always to be operated with the hydraulic system operating. The POH "Before Starting Engine" checklist contained a line item to turn the hydraulics on, and the POH "Takeoff Procedure" stated "Verify…hydraulics on." The POH "Shutdown Procedure" did not contain any instructions to turn the hydraulics off after flight, or after engine shutdown. However, it did contain a "NOTE" that stated "HYD switch should be left on for start-up and shutdown to reduce…[the] possibility of unintentional hydraulics-off liftoff. Switch off only for pre-takeoff controls check or hydraulics-off training."

The accident helicopter was not equipped with any annunciation system or indicator to alert the pilot that the hydraulic system had either failed or was selected off in flight, and no such option was available from the manufacturer. According to the POH, "Hydraulic system failure is indicated by heavy or stiff cyclic and collective controls," and that in the event that the hydraulic system failed or was turned off, "control will be normal except for the increase in stick forces." Discussions with an RHC representative indicated that if the hydraulic system was inoperative, the helicopter would remain flyable, but control forces, particularly in the landing hover, would increase noticeably. He also noted that hydraulic-system off operations, which included "run-on" landings, were part of the R44 pilot training, in order to familiarize pilots with the change in control forces and helicopter responses, as well as the appropriate procedures for such operations.

Examination of the pilot's training records indicated that she had practiced flight with the hydraulics off, and had practiced run-on landings also. Several interviews with the pilot were consistent in the fact that the pilot was certain that the hydraulic system was operating for the entire accident flight. Post-accident examination of the helicopter did not reveal any physical evidence of hydraulic system malfunction, or that the pilot had switched the hydraulic system off in flight.