Whitley City, KY, USA
N11HX
Bell 407
The pilot was conducting a fire suppression flight. While indicating approximately 100 knots of airspeed, with an empty water bucket that was occasionally unstable during the flight, the pilot heard a "bang." The helicopter yawed to the right, and the tail rotor quit spinning. The pilot jettisoned the bucket, and because there was no place to land, he continued to the dip-point. At the dip-point, the pilot selected an open area. The area was sloped, but the pilot was uncertain of the airworthiness of the helicopter and did not want to look for another area. He entered a "needles joined autorotation." As the helicopter slowed, it started to spin to the right. The spin stopped, the helicopter impacted the ground, and then rolled onto its right side with little or no power applied to the main rotor. Examination of the wreckage revealed that the bucket had entered the arc of the tail rotor, and that the tail-rotor driveshaft was severed consistent with overload. The operating manual for the bucket stated that the bucket had been proven stable up to an airspeed of approximately 96 knots, and that a bucket with a overall length greater than the distance from the cargo hook to the front arc of the tail rotor could result in a tail rotor strike. The emergency procedure for a complete loss of tail rotor thrust in-flight was reduce throttle to idle, and immediately enter autorotation. If a suitable landing site was not available, the vertical fin may permit controlled flight to a suitable area.
On November 12, 2001, at 1420 eastern standard time, a Bell 407 helicopter, N11HX, was substantially damaged during a precautionary landing near Whitley City, Kentucky. The certificated commercial pilot was seriously injured. Visual meteorological conditions prevailed for the local fire suppression flight. Flight following was used to track the helicopter, and the flight was conducted as Public Use. According to several witnesses, the pilot had just made a water drop, and was returning to a pond in an open area. While the helicopter was in cruise flight and approximately 100 feet agl, an individual videotaping the fire fighting operation captured a loud "pop" on the audio portion of the recording. The witness then focused the video recorder on the helicopter. Examination of the video revealed that the tail rotor was stationary, and a portion of the "BLUE" tail-rotor blade, along with the last driveshaft cover, had separated from the helicopter. According to the pilot, he had just completed his 46th water-drop of the flight, and was returning to the "dip-point" to refill. While in level flight and indicating approximately 100 knots, he heard a "bang." The helicopter yawed right with enough force to push him into the left seat. The pilot immediately jettisoned the bucket, rolled the throttle to idle, and entered an autorotation. He then realized there were no suitable landing areas, so he rolled the throttle back to "FLIGHT." The pilot maintained 70 knots, and felt the vertical fin was providing enough directional control to make the dip-point. While en route, he felt a "strong" continuous vibration in the airframe that made him unsure of how long he could maintain control of the helicopter. Once at the dip-point, the pilot had to choose between two landing areas. The first was relatively flat, but occupied by personnel. The other area was free of personnel, but sloped. Uncertain of the airworthiness of the helicopter, the pilot did not want to look for another place to land, so he set up an approach to the sloped area. He entered an autorotation, but did not reduce the throttle, adding that he was doing a "needles joined autorotation." The pilot could not remember anything associated with the accident sequence past that point. According to several witnesses, while on approach, the helicopter started to spin to the right. It then impacted the ground, and rolled onto its right side. Earlier in the day, the pilot conducted a preflight, but did not insure that the bottom of the bucket could not reach the forward arc of the tail rotor. The pilot added that he flew between 90 and 100 knots, en route, and remembers the bucket being occasionally unstable. The pilot planned to conduct three more drops before having to refuel, estimating he had 45 minutes of fuel remaining when the tail rotor lost thrust. According to a Federal Aviation Administration (FAA) inspector, the main wreckage was located in an open area. The area was surrounded by trees and comprised of several different down slopes that joined approximately in the center of the area. The helicopter came to rest on its right side with the nose pointing partially down an 8-degree slope. The main cabin area was intact. All four of the main-rotor blades were attached to the hub, with three of the blades displaying impact damage. In addition, all four blade-flap stops displayed impact marks. The tailboom displayed impact damage, and was fragmented. The tail rotor driveshaft also displayed impact damage and fragmentation. The tail rotor was equipped with two blades. The "ORANGE" blade displayed impact damage, and a portion of the blade tip, approximately 8-inches square, was missing. The "BLUE" blade displayed severe impact damage, and the majority of the blade outboard of the blade root was missing. All of the major components for the helicopter were recovered, except for the last tail-rotor-driveshaft cover and the missing section of the "BLUE" tail rotor blade. Flight control continuity was verified from the pilot controls to the main rotor and tail rotor. Examination of the fracture surfaces on the tail rotor driveshaft revealed no evidence consistent with fatigue. Examination of the water bucket revealed a tear approximately 2 feet long, and impact damage to the internal metal frame. Inside the bucket were fragments of fiberglass. The threads in the fiberglass were purple in color and similar in appearance to the thread used to manufacture the tail-rotor blades. During the examination of the bucket, it was reconnected to the cargo hook, and pulled towards the tail rotor. With the line extended, the damage on the bucket was within the arc of the tail rotor. According to the operator's manual for the water bucket, the bucket had been proven stable up to an airspeed of approximately 96 knots; however, the manufacturer suggested that airspeed be increased slowly in order to determine a safe operating speed for a particular helicopter. A warning in the manual stated that using a bucket with a greater overall length than the distance from the cargo hook to the front arc of the tail rotor could result in a tail rotor strike, and possibly a loss of control. The preflight section of the Helicopter Flight Manual stated that the cargo sling should be checked for condition, and proper length. In addition, VNE for external loads was 100 knots. The emergency procedure section for the helicopter flight manual stated, "There is no single emergency procedure for all types of antitorque malfunctions. One key to a pilot successfully handling a tail rotor emergency lies in the ability to quickly recognize the type of malfunction that has occurred." The flight manual described a complete loss of tail rotor thrust as a break in the drive system, wherein the tail rotor stops turning and delivers no thrust. Indications were listed as an uncontrolled right yaw, a nose down tuck, and a possible fuselage roll, with the severity of the initial event depending on airspeed, center of gravity, power applied, and density altitude. The emergency procedure for a complete loss of tail rotor thrust in-flight was published as "Reduce throttle to idle, immediately enter autorotation, and maintain a minimum airspeed of 55 KIAS during descent." A note in the flight manual stated that if a suitable landing site was not available, the vertical fin might permit controlled flight at low power settings and sufficient airspeed. The pilot held a commercial pilot certificate with a rotorcraft-helicopter rating, and a flight instructor certificate with a rating for rotorcraft-helicopter. His last FAA second-class medical certificate was dated May 15, 2001, and was issued with no limitations or waivers. The pilot reported to the Safety Board that he had 7,500 hours of total flight experience, all in rotorcraft. In addition, the pilot had 900 hours in the accident helicopter make and model, with 100 hours of that being within 90 days of the accident.
The pilots decision to operate the helicopter at an airspeed in excess of the maximum demonstrated stable airspeed for the water bucket. A factor in the accident was the pilot did not follow the published emergency procedure.
Source: NTSB Aviation Accident Database
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