N61425Schweizer 269C-1 · 1996

On July 11, 2008, at 1232 eastern daylight time, a Schweizer 269C-1, N61425, was substantially damaged when it collided with terrain during a forced landing near Northumberland, Virginia. The certificated commercial pilot and the passenger were not injured. Visual meteorological conditions prevailed for the local flight that originated at Hummel Field (W75), Saluda, Virginia. No flight plan was filed for the aerial survey flight which was conducted under the provisions of 14 Code of Federal Regulations Part 91.

The pilot was interviewed by telephone, and he reported that the helicopter was full of fuel and hovering 100 feet above ground level, when it encountered "a pretty good headwind" that registered 20 knots on the airspeed indicator. The helicopter shuddered, the nose yawed to the right, and the pilot's application of the left anti-torque pedal "had no effect" as the helicopter began to rotate around the main rotor mast. The pilot initially increased collective pitch to climb up, and away from the trees. The pilot then applied forward cyclic, which lowered the nose of the helicopter and increased forward airspeed. According to the pilot, this slowed the rate of rotation during the descent, but upon ground contact, the landing skid "caught" and the helicopter rolled onto its side.

The pilot was asked how long the helicopter was in the 100-foot hover before he "ran out of left pedal," and the left pedal input lost effectiveness. He replied, "I didn't run out of pedal, I just didn't have any left or right."

Examination of Global Positioning System (GPS) track data extracted from the GPS unit on board the helicopter revealed an "S" shaped track that eventually oriented the helicopter into a quartering-tailwind condition above the crash site.

The pilot held a commercial pilot certificate with a rating for rotorcraft helicopter. He also held a private pilot certificate with a rating for airplane single engine land. His most recent second-class medical certificate was issued on May 29, 2008.

The pilot reported 424 total hours of flight experience, 200 hours of which were in helicopters, and nearly all of that in make and model.

The helicopter's most recent annual inspection was completed July 3, 2008, at 4,657 aircraft hours. According to the pilot, the helicopter had accrued about 4 hours of flight time between the inspection and the time of the accident.

At 1240, the weather recorded at Middle Peninsula Regional Airport (KFYJ), 20 miles west of the site, included clear skies with 10 miles visibility. The wind was from 160 degrees at 5 knots, the temperature was 30 degrees Celsius, and the dewpoint was 20 degrees Celsius. The altimeter setting was 30.09 inches of mercury.

The helicopter was examined in Clayton, Delaware on August 5, 2008. The main rotor blades had been removed for recovery of the helicopter prior to examination, but the remainder of the helicopter remained intact. Cyclic and collective control continuity was established from the cyclic and collective controls to the main rotor head. Tail rotor control continuity was established from the pedals to the tailrotor. Tail rotor rigging could not be positively established due to deformation of the airframe, and a break at the tailboom forward bulkhead attachment. The fracture surfaces at the bulkhead attachment displayed signatures consistent with overload. Tail rotor drive continuity was decoupled at the main transmission output due to impact. The locknut safety wire was broken and several threads were exposed.

The tail rotor driveshaft and tailrotor gearbox were removed. The main transmission pinion drive spline was secure and undamaged. The tailrotor driveshaft forward and aft splined couplings were intact, and showed no damage or abnormal wear. The driveshaft appeared straight, and undamaged. The output side of the tailrotor driveshaft displayed wear in the inner aluminum ‘dome' but maintained drive continuity.

The tailrotor pitch control was undamaged, and displayed no abnormal wear or play. The tailrotor blades were intact, and showed only minor damage to the tip caps. The belt drive transmission was intact, and undamaged. Electrical power was applied and the linear clutch actuated from the engaged to the disengaged position smoothly and continuously.

The main transmission was rotated by hand at the upper pulley of the belt drive transmission. The transmission rotated smoothly and continuously to the main rotor head.

An engine start was initiated on the airframe using battery power and the helicopter's own fuel system. The engine started immediately, and ran at idle continuously without interruption. The engine was accelerated to 2,500 rpm, the manifold pressure showed 11 inches, and the oil pressure was in the normal operating range. A check of both magnetos was completed within the manufacturer's parameters.

Examination of performance planning charts revealed that atmospheric conditions at the time of the accident would provide the helicopter in-ground-effect performance capabilities up to 2,000 feet mean sea level. Out-of-ground effect charts were not available, nor were they required, for this helicopter.

According to the U.S. Army's TH-55A (Hughes 269) Operator's Manual, Emergency Procedures, Chapter 9-24, Loss of tail rotor effectiveness:

"This is a situation involving a loss of effective tail rotor thrust without a break in the drive system. The condition is most likely to occur at a hover as a result of two or more of the following:

a. Out-of-ground effect hover.

b. High pressure altitude /high temperature.

c. Adverse wind conditions.

d. Engine rpm below 2900.

e. Improperly rigged tail rotor.

(1) Indications: The first indication of this condition will be a slow starting right turn of the nose of the helicopter which cannot be stopped with full left pedal application this turn rate will gradually increase until it becomes uncontrollable or, depending upon conditions, the aircraft aligns itself with the wind.

(2) Procedures: Lower collective to regain control and allow the aircraft to touchdown with little if any forward movement."

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."