History of Flight
On June 2, 2010, at approximately 1630 Pacific daylight time, a Robinson R22 Beta, registration N522SA, experienced a main rotor blade strike that separated the tail boom while in the landing pattern at Felts Field in Spokane, Washington. The helicopter was operated by Inland Helicopters, Inc., under 14 Code of Federal Regulations Part 91 as a local instructional flight that had departed around 1600. Visual meteorological conditions prevailed, and no flight plan was filed.
The student pilot, accompanied by a certified flight instructor, flew the traffic pattern and performed a full stop landing on runway 21L. The instructor, deeming the student competent to continue solo, exited the helicopter. This was the student's fourth solo flight; he had completed approximately five additional touch-and-go landings prior to the accident.
On the accident flight, the student reported downwind to the air traffic control tower, and the controller cleared him for landing. The controller observed the helicopter on base leg at a normal altitude and attitude and saw no smoke or falling debris. After looking away for a few seconds, he did not see the helicopter upon returning his gaze.
Witness Observations
Ground witnesses saw the helicopter flying the base leg at altitudes similar to those of other helicopters. Several heard one or two popping sounds; one witness reported that the rotor sounds went silent and the engine sputtered before the pops. Some witnesses saw pieces separate from the helicopter, after which it began spinning clockwise. One witness described the helicopter as V-shaped before it pitched nose down and fell straight to the ground.
Aircraft and Pilot Information
The helicopter was a Robinson R22 Beta, serial number 3788. At its last annual inspection on January 2, 2010, the airframe had 2,600 hours; the last 100-hour inspection occurred on April 15, 2010, at a Hobbs time of 2,696. The Hobbs meter read 2,790.7 at the accident site. The engine, a Textron Lycoming O-360-J2A, had 1,219 hours total time and 496 hours since major overhaul at the last 100-hour inspection.
The 29-year-old student pilot held a combined student pilot and second-class medical certificate with a limitation requiring corrective lenses. His logbook showed an estimated total flight time of 32 hours, including 26 hours in the last 90 days and 11 hours in the last 30 days. He had completed three previous solo flights, totaling 3.3 hours, all in the same make and model. He had received an endorsement from a CFI on December 21, 2009, confirming awareness training for the R22 as specified in SFAR 73.
Wreckage and Impact
Investigators from the National Transportation Safety Board, the Federal Aviation Administration, and Robinson Helicopter Company examined the wreckage. The debris path stretched about 500 feet long by 200 feet wide in a northerly direction, with the fuselage oriented at an estimated 160 degrees. The tail boom separated into multiple pieces; the aft end with the tail rotor gearbox and a piece of driveshaft was found first. The forward section of the tail boom and drive shaft separated at a rivet line about 2 feet aft of the engine, bearing a 45-degree impression similar to a main rotor blade. One tail rotor blade separated about 4 inches from its attachment point.
The main wreckage came to rest on its right side in a residence's backyard. The cabin area was embedded in the ground, and the right side of the cockpit was crushed inboard to the helicopter's centerline. No damage was found to nearby structures or a child's play station. Ground scars beneath the main rotor blades were crisp and distinct, with no evidence of rotation.
Engine and Systems Examination
The engine crankshaft rotated freely, and all cylinders produced thumb compression in firing order. Both magnetos sparked at all posts. The carburetor sustained crush damage but had a clear fuel screen; the metal floats showed hydraulic crush damage. The oil filter was clean. Investigators found no preimpact anomalies that would have precluded normal operation of the airframe or engine.
The carburetor heat control knob was unlocked and pulled out 1.7 inches (56% of travel), and the carburetor heat slider valve was in the on position. The governor OFF light filament was broken but not stretched. The fuel system contained no debris or contamination.
Meteorological and Additional Information
The METAR at Spokane at 1653 PDT reported wind from 190 degrees at 12 knots gusting to 18 knots, visibility 10 miles, scattered clouds at 1,700 feet, broken at 3,000 feet, overcast at 5,000 feet, temperature 59°F, dew point 54°F, altimeter 29.70 inHg, and relative humidity 83%.
FAA Special Airworthiness Information Bulletin CE-09-35, published June 30, 2009, addressed carburetor ice prevention, noting that icing can occur above freezing with visible moisture or high humidity. The conditions at the time of the accident (59°F, 83% RH) fell in the area of serious icing at cruise power. The R22 Pilot Operating Handbook described a carburetor heat assist device that correlated heat application with collective changes; the CFI stated he stressed using carburetor heat during landing, and the student used it while the instructor was on board.
Robinson Safety Notice SN-25 (revised 1999) warned that carburetor ice could cause engine stoppage, especially with high humidity and temperatures below 70°F. SN-24 (revised 1994) discussed main rotor blade stall due to low rotor rpm, stating that stall could lead to an uncontrolled descent and, in some cases, allow the main rotor to strike the tail. An NTSB Special Investigative Report from 1996 noted that the low-inertia rotor could diverge to strike the helicopter within less than 0.5 seconds.