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On July 20, 2011, about 1126 eastern daylight time, a Robinson R22 BETA helicopter, N83509, was substantially damaged when it collided with terrain following an uncontrolled descent while maneuvering near Dayton, New Jersey. The certificated commercial pilot and the passenger were seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local photography flight that was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The helicopter departed Princeton Airport (93N), about 1045.
According to witnesses, the helicopter was orbiting at low speed and low altitude in the vicinity of an elementary school and some commercial properties. One witness was working on the roof of the school as he observed the helicopter orbit his position. He stated the helicopter engine sounded "fine" as the helicopter completed one and a half circuits around the school about 150 feet above the ground, as one of the occupants was taking photographs. At that point, the witness alerted his coworkers because it appeared that the helicopter "might crash into the school." He said the helicopter then descended quickly towards the ground while the helicopter itself was in a slow "spin." He said the engine ran "perfectly" the entire time up to ground contact.
Another witness stated that the helicopter caught his attention because of its low altitude and because it appeared "slightly out of control." He stated that he watched for only a few seconds before the helicopter descended in a spin, regained altitude momentarily, and then descended from view.
In an interview with a Federal Aviation Administration (FAA) inspector, the pilot stated he positioned the helicopter in an out-of-ground-effect hover about 400-500 feet above ground level (agl). The photographer asked for a different vantage point, but as the pilot explained that wind and high power demands would prevent him from accommodating the request, the helicopter began to "settle with power." The pilot attempted to arrest the descent with a reduction of power and a forward cyclic input.
As the pilot took corrective action, the helicopter yawed to the right and began to rotate around the main rotor mast. He reduced the throttle to idle to arrest the spin, the yaw rate slowed, but the spin continued as the helicopter descended through approximately 250 feet agl. The pilot remembered assuring the passenger of a safe landing but could not recall anything beyond that point in the flight.
In a statement that the pilot provided through his employer, he estimated that the onset of the event began at 150-200 feet agl, and that the helicopter was "spinning" when it hit the ground.
A video camera, two still cameras, and several data storage devices were recovered at the site and forwarded to the NTSB Recorders Laboratory for examination.
According to FAA records, the pilot held a commercial pilot certificate with a rating for rotorcraft helicopter. His most recent second-class FAA medical certificate was issued on January 31, 2011.
The pilot reported 430 total hours of flight experience, of which 90 hours were in the accident helicopter make and model.
According to FAA records, the helicopter was manufactured in 2001. It was a two-seat, two-bladed, single main rotor helicopter that was equipped with a Lycoming O-360 reciprocating engine. The most recent annual inspection was completed on March 16, 2011, at which time the airframe had accumulated 4,000 total hours.
The maximum allowable gross weight for the helicopter was 1,370 pounds. The operator estimated that the gross weight of the helicopter at the time of the accident was 1,282 pounds.
The 1153 recorded weather observation at Trenton Mercer Airport, located approximately 10 mile northeast of the accident location, included variable wind at 5 knots, clear skies, 10 miles of visibility, temperature 31 degrees C, dew point 22 degrees C, and an altimeter setting of 29.89 inches of mercury. The calculated density altitude was 2,555 feet.
The contents of the still cameras and data storage devices revealed no useful information other than 46 photographs that were taken during the flight prior to the accident.
The video camera was operating at the time of the accident, but during the actual accident sequence, it rested inside a camera case where audio and only a partial view were captured.
Examination of the video recording revealed that the recording began at 1120:16 as the helicopter was in forward, cruise flight above urban, residential neighborhoods.
Over approximately the next 5 minutes, audio and video evidence both suggested and depicted the helicopter alternately slowing and accelerating.
At 1125:51, sounds associated with the slowing of the helicopter were heard. Two seconds later, at 1125:53, an 800 Hz continuous warning tone, similar to the low rotor rpm audio alarm, began and continued beyond the sound of impact, which was recorded at 1126:00. The alarm was later silenced by emergency responders at 1132:14.
WRECKAGE AND IMPACT INFORMATION
FAA inspectors photographed the wreckage at the scene. Examination of the photographs revealed that the helicopter rested upright on its belly, and the landing gear skids were spread uniformly to each side. The fuselage displayed significant vertical crushing into the cockpit and cabin areas. The tailboom was wrinkled at its mount, and torn about three feet forward of the tailrotor and tailrotor gearbox. Both tailrotor blades were fractured near their respective blade grips. The main rotor blades, hub, and main rotor mast appeared undamaged. The wreckage was recovered from the site and moved to a recovery facility in Clayton, Delaware for a detailed examination that was conducted August 29, 2011.
Control continuity was established from the cockpit flight controls to the main and tail rotor through several breaks. The breaks were due to impact and overload.
The engine sustained minimal impact damage. The airbox and air filter were deformed around the carburetor, which was broken into several pieces. The float bowl was void of fuel. The float was made of blue foam and was shattered into many pieces. Small pieces of the same blue foam were found in the spark plugs.
The exhaust system was deformed due to impact.
The oil level was within limits and the oil appeared clean and was absent of debris.
The crankshaft was rotated by hand with no anomalies noted, and suction and compression were confirmed at all four cylinders using the thumb method. Both magnetos were secure and undamaged.
The cooling scroll sustained impact damage on the bottom, and the outer edge of the cooling fanwheel displayed rotational score marks. The forward face of the upper sheave exhibited rotational score marks as did the upper frame adjacent to the upper sheave.
Unanticipated Right Yaw (Loss of Tail Rotor Effectiveness)
The FAA issued Advisory Circular (AC) 90-95, Unanticipated Right Yaw in Helicopters, in February 1995. The AC stated that the loss of tail rotor effectiveness (LTE) was a critical, low-speed aerodynamic flight characteristic which could result in an uncommanded rapid yaw rate which does not subside of its own accord and, if not corrected, could result in the loss of aircraft control. It also stated, "LTE is not related to a maintenance malfunction and may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots."
Paragraph 6 of the AC covered conditions under which LTE may occur. It stated:
"Any maneuver which requires the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind creates an environment where unanticipated right yaw may occur."
Paragraph 8 of the AC stated:
"OTHER FACTORS...Low Indicated Airspeed. At airspeeds below translational lift, the tail rotor is required to produce nearly 100 percent of the directional control. If the required amount of tail rotor thrust is not available for any reason, the aircraft will yaw to the right."
Paragraph 9 of the AC stated:
"When maneuvering between hover and 30 knots: (1) Avoid tailwinds. If loss of translational lift occurs, it will result in an increased high power demand and an additional anti-torque requirement. (2) Avoid out of ground effect (OGE) hover and high power demand situations, such as low-speed downwind turns. (3) Be especially aware of wind direction and velocity when hovering in winds of about 8-12 knots (especially OGE). There are no strong indicators to the pilot of a reduction of translation lift... (6) Stay vigilant to power and wind conditions."
Vortex Ring State (Settling With Power)
According to the FAA Rotorcraft Flying Handbook, "Vortex ring state describes an aerodynamic condition where a helicopter may be in a vertical descent with up to maximum power applied, and little or no cyclic authority. The term 'settling with power' comes from the fact that the helicopter keeps settling even though full engine power is applied."
U.S Army Field Manual 1-203 defined Settling with Power as:
A condition in powered flight in which the [helicopter] settles in its own downwash.
Three things needed to get into settling with power:
1) Low airspeed
2) 20 to 100% of available engine power applied
3) A 300 foot per minute or greater rate of descent, with insufficient power
remaining to retard the sink rate
Contributing factors for a loss of tail rotor effectiveness include:
1) High gross weight/[Density Altitude]
2) Low indicated airspeed
3) Power droop
4) Right downwind turns