N904CF

HISTORY OF FLIGHT

On January 17, 2010, at 1250 Pacific standard time, a Eurocopter AS350 B3, N904CF, landed hard on the helicopter pad at Renown Regional Medical Center, Reno, Nevada. The helicopter was operated by Air Methods, d.b.a. Care Flight, under the provisions of Title 14 Code of Federal Regulations, Part 91, as a positioning flight. The pilot and the two medical crew were not injured, and the helicopter was substantially damaged. Visual meteorological conditions prevailed, and a company visual flight plan had been filed. The flight originated at the Renown Regional Medical Center.

The pilot reported to the Safety Board investigator that the purpose of the helicopter emergency medical service (HEMS) flight was to fly to Humboldt General Hospital, Winnemuca, Nevada, to pick up a patient for an inner facility transfer to Renown Regional Medical Center. He lifted from the Renown helicopter pad and positioned the helicopter in to a high hover, 25 feet, per the normal operating procedures. Just as the pilot was beginning his transition to forward flight he heard a loud bang, and the helicopter experienced a partial power loss. The pilot lowered the collective slightly and landed hard on the helicopter pad.

Two of the Renown Medical Center's surveillance video cameras captured the accident sequence. The videos depicted the helicopter on the helicopter pad with the nose pointed to the northwest. A windsock in the vicinity of the helicopter pad was limp at the time of rotor engagement. The helicopter lifted into approximately a 30-foot hover over the pad and about 10 seconds after the helicopter lifts, the helicopter’s nose abruptly rotates right 90 degrees, then it descended vertically with the nose pitched down about 20 degrees, and the forward portion of the skids and cockpit chin bubble impact the ground. The helicopter rebounded from the ground impact, and came to rest on collapsed landing skids facing 180 degrees from the original takeoff orientation. The main rotor stopped turning after 1 minute 25 seconds, and the crew began to egress the helicopter about 2 minutes after the accident.

PERSONNEL INFORMATION

The pilot, age 61, held a commercial pilot certificate with rotorcraft-helicopter, and instrument helicopter ratings, issued October 23, 2008. He held a first-class medical certificate with the limitation that he wear corrective lenses and possess glasses for near and intermediate vision, issued on October 14, 2009. The pilot reported having 14,300 flight hours in helicopters, and 9,544 hours in the AS350. Over the last 90 days he had logged 46 hours, 11 hours of which were logged in the last 30 days.

AIRCRAFT INFORMATION

The AS350B3 is a main rotor-tail rotor configured single engine helicopter, serial number (S/N) 3676, manufactured in 2003. The interior was configured with the pilot seat on the right side; the patient litter was located on the left side and extended over the area where the copilot seat would traditionally be. There were two crew seats mounted along the rear cabin bulkhead. It was powered by a Turbomeca Arriel 2B1, 848 shaft HP engine. The engine power output is directed through a reduction gearbox, and to a drive shaft that is connected to the main gearbox at the forward end and the tail rotor drive shaft at the aft end.

Review of the maintenance records revealed that the airframe had 3,939.5 hours at the time of the accident. The most recent inspection was the A21, B61, and tail rotor (AD 2001-26-55) performed on January 17, 2010. The A21 inspection is a daily airworthiness inspection, the B-61 is a 20-hour engine inspection, and both were conducted in accordance with the Air Methods Approved Airworthiness Inspection Program (AAIP).

Examination of the helicopter maintenance records revealed that on August 3, 2009, at 3,880.4 hours total airframe time, the engine had been removed and the airframe was sent to the Gold Metal Paint Co. for paint finishing work. On October 29, 2009, the engine was reinstalled at the Air Methods certified repair station in Englewood, Colorado. On November 2, 2009, an A-26 (100-hour) inspection was performed, which included the Eurocopter ‘S’ interval maintenance inspection. The ‘S’ interval maintenance included inspection of both the flex couplings on the engine-to-main gearbox shaft. On November 11, 2009, an engine power assurance check was performed, with ‘Checked Good’ logbook entry noted. The helicopter was approved for return to service on December 1, 2009.

WRECKAGE AND IMPACT INFORMATION

The helicopter was removed from the Renown Helipad, and transported to the Air Methods maintenance facility in Reno, Nevada, and secured for further examination. On January 25, 2010, technical representatives from American Eurocopter, Turbomeca USA, Federal Aviation Administration (FAA), and Air Methods Corporation inspected the helicopter under the supervision of the Safety Board investigator-in-charge (IIC).

The left skid was collapsed into the forward fuselage area. The fuselage-tailboom junction exhibited buckled skin. The main fuselage structural beams were deformed. Full control continuity was established for the cyclic, collective, and anti-torque controls. External power was supplied to the cockpit avionics, and the Vehicle and Engine Multi-function Display (VEMD) energized. The VEMD data displayed the accident flight was flight number 7211. Flight 7211 total time was 2 minutes and 8 seconds. Three failures were recorded; test reference 69-OAT (left module), test reference 69-OAT (right module), test reference 124-amber gov OAT VEMD-OAT sensor FADEC (left module), and an NF over limit of 510 rpm. The outside air temperature (OAT) sensor is located under the nose of the helicopter and was impact damaged.

No main rotor blade damage was observed. The main gearbox (transmission) rotated freely in both directions with the corresponding rotation of the main gearbox input flange, but without the corresponding rotation of the engine and tail rotor. Hardware that is associated with the engine to main gearbox drive shaft flex coupling was identified on the engine deck. The engine-to-main gearbox shaft coupling tube was removed, revealing that the engine side flex coupling was detached from the engine-to-main gearbox shaft. Metal shavings were identified inside the perimeter of the aft side of the coupling tube. The flex coupling remained attached to the engine output spline. The three bolts that connect the flex coupling to the transmission shaft appeared sheared and the bolt fracture surfaces appeared smeared. The three nuts and two associated washers were loose and located clumped together just forward of the gimbal ring in the transmission input housing. No cotter pins were located on the bolts or in the main gearbox input housing. The three bolts attaching the flex coupling to the splined engine flange were present, with nuts, and cotter pins in place.

The engine was attached to the airframe at both the front and rear engine mounts. No apparent damage to the mounts was observed. The engine deck was clean, and no fluids were observed leaking from the engine. The aircraft to engine interface connections were intact and secure. All engine pipes, hoses, and harnesses were intact and properly connected and secured to the engine. The fuel shutoff lever in the cockpit was in the closed position. Oil was visible through the site glass on the oil tank and the level appeared to be within limits.

The engine was removed to facilitate examination of the transmission shaft. The oil filter and fuel filter by-pass indicators were not popped (systems not in by-pass). The electrical magnetic plug, oil filter, and fuel filter were clean. A small metallic sliver was found on the accessory gearbox (MO1) magnetic plug. The fuel pump and metering unit appeared to be undamaged. The free wheel shaft assembly rotated smoothly in both driving and freewheeling directions. Contact damage to the front face of the clutch housing was observed. The engine drive shaft splined nut and lock exhibited rotational scarring. Removal of the engine front support revealed damage to the inside surface of the support. The nose cone and axial compressor blades were unremarkable. The bleed valve was in the open position. The containment ring was unremarkable. The power turbine wheel assembly was easily rotated by hand. The free turbine blades were unremarkable. The reduction gear box casing (MO5) was unremarkable. The reduction gearbox (MO5) magnetic plug was clean. The flexible coupling to the tail rotor drive shaft was intact.

TESTS AND RESEARCH

Material Laboratory Examination

The engine-to-main gear box drive shaft and flex coupling assembly were sent to the Safety Board Materials Laboratory, and examined from April 14-16, 2010.

When assembled, three bolts attach the flex coupling assembly to the main gear box drive shaft. Castellated nuts are to be attached to the threaded end of the bolts. As additional safety feature, cotter pins are to be attached between the bolts and nuts. Bolts were found inserted in the through holes of the flex coupling. One bolt was intact. The two other bolts contained a fracture that intersected the cotter pin holes, and a thread fragment separated from these two bolts. The cotter pin hole for the three bolts did not contain a cotter pin or fragment of a cotter pin. Scanning electron microscope examination of the fracture faces from the bolt fragments revealed micro-void coalescence features typical of overstress separation with no evidence of fatigue cracking.

The bolts, washers, and nuts that were specified for the flex coupling-to-main gear box drive shaft connection were accounted for and recovered.

The flange portion of the main gear box drive shaft contained three arms. Each arm contained an impact mark at the same respective position. The impact marks are consistent with the threaded portions of the bolts from the flex coupling assembly a...