La Belle, FL, USA
N3038W
ROBINSON R44
The pilot reported that he was conducting a flight at a low altitude and speed when he heard a light tapping sound followed by the low rotor rpm warning horn. He attempted to simultaneously initiate an autorotation and maintain forward speed to reach a clearing. The tail boom and tail rotor struck trees, and the pilot lost directional control of the helicopter. The helicopter touched down in the clearing, spun about 180 degrees to the right, and rolled onto its left side. A postaccident examination revealed that one of the rotor drive belts was separated and that each of the remaining three belts was frayed and partially displaced from at least one of its respective sheaves. According to a representative for the helicopter manufacturer, the fraying was typical of a drive belt that was displaced from the sheave while the engine was running. The fraying could be caused by the belt being too loose, by abrupt maneuvering of the helicopter, or by the helicopter striking the ground when the engine was running. The representative also stated that when a drive belt starts to fail, it tends to make a repetitive noise similar to that reported by the pilot, and that drive belt failure could result in low rotor rpm. The reason(s) for the drive belt failures could not be determined and maintenance records were not available during the investigation.
HISTORY OF FLIGHT On October 15, 2009, about 1751 eastern daylight time, a Robinson R44 helicopter, N3038W, was substantially damaged during a forced landing near La Belle, Florida. The commercially-rated pilot and two passengers sustained minor injuries, and one passenger sustained a serious injury. The personal flight was operated under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the flight. According to the pilot, the flight was a personal sightseeing flight with a friend of his, and two acquaintances of that friend. The pilot flew from the airport where the helicopter was based to a private farm in Punta Gorda, Florida, to pick up the passengers. The helicopter departed the farm about 1730. None of the helicopter's four doors were installed for the flight, and the majority of the flight was conducted at or below 300 feet above ground level (agl). After approximately 30 minutes, while in cruise flight at about 60 knots and 150 feet agl, the pilot heard what he variously described as either a "light tapping" or a "thump," and then "a horn went off." The pilot did not observe any other annunciations or problems with the helicopter. The helicopter began to lose altitude, and the pilot "immediately proceeded into an auto-rotation toward a pasture." The tail of the helicopter struck trees, and the pilot reported that he "lost [anti-torque] pedal" at that point, but that he continued the auto-rotation to the ground. Two of the passengers provided a different account of the accident flight. In a telephone conversation with the Federal Aviation Administration (FAA) inspector, two passengers reported that most of the flight was conducted "below tree top level" at a "slow" airspeed. The passengers also stated that the flight was uneventful until the helicopter began to spin and descend. The passenger in the front seat stated that the helicopter struck "something," and immediately after that, the pilot pulled up on the collective control briefly, and then pushed it down. Neither passenger noticed any warning horns or lights. According to the pilot, after it struck the ground, the helicopter spun in the horizontal plane approximately 180 degrees to the right, and then rolled onto its left side. When the helicopter came to a stop, the engine was not running, and the pilot switched off the fuel and the master switch. The pilot and two passengers exited the helicopter, but the remaining passenger, who seriously injured his foot in the impact, decided to remain in the helicopter until assistance arrived. The pilot contacted assistance via 911 on his mobile telephone, but the poor quality of the connection precluded successful communication of the accident situation and location. He then called an acquaintance of his who was familiar with the local area. The acquaintance drove to the accident location, and then led law enforcement personnel to the site. An emergency medical services (EMS) helicopter was dispatched to remove and transport the injured passenger, but the EMS helicopter did not arrive until approximately 2 hours after the accident. The injured passenger was airlifted from the accident site approximately 3 hours after the accident. PERSONNEL INFORMATION FAA records indicated that the pilot held a commercial pilot certificate with a rotorcraft-helicopter rating, and a private pilot certificate with an airplane single-engine land rating. His most recent FAA second-class medical certificate was issued in October 2009, and his most recent flight review was completed in June 2009. The pilot had approximately 3,000 total hours of flight experience, including approximately 900 hours of rotary-wing experience, and 720 hours in the R44. About 4 months after the subject accident, the pilot was fatally injured while piloting another R44 in the Dominican Republic. The owner of N3038W was also fatally injured in that accident. AIRCRAFT INFORMATION According to FAA records, the helicopter was manufactured in 2007, and was equipped with a Lycoming O-540 series piston engine. The helicopter was registered to a corporation. The pilot stated that the owner of the helicopter permitted him to fly the helicopter for his personal use. The pilot indicated that the most recent 100-hour inspection was completed in July 2009, and the helicopter had accrued a total time in service of 720.8 hours at the time of the accident. The maintenance records were not provided for the investigation. METEOROLOGICAL INFORMATION The 1753 recorded weather observation at Southwest Florida International Airport (RSW), Fort Myers, Florida, located approximately 21 miles south-southwest of the accident site, included winds from 260 degrees at 8 knots, 10 miles visibility, few clouds at 3,500 feet, temperature 30 degrees C, dew point 22 degrees C, and an altimeter setting of 29.83 inches of mercury. WRECKAGE AND IMPACT INFORMATION According to information provided by the Federal Aviation Administration (FAA) inspector who responded to the accident scene, the helicopter came to rest in a grassy field that was bordered by a treeline. The accident site was about 10.5 miles southeast of the flight's origination point. The helicopter sustained substantial damage to the tail boom, the main rotor system, and the fuselage. One of the tail rotor blades, as well as the horizontal and vertical stabilizer tailplane assembly, and were fracture-separated from the helicopter. The tailplane assembly was found at the treeline, about 120 feet from the helicopter. The left side of the fuselage was crumpled, the main rotor blades were bent, and the main rotor mast was deformed. Control rods and other components of the main rotor control system were bent or otherwise damaged. One of the drive belts, which mechanically connected the engine output sheave to the rotor input sheave, was broken, and each of the remaining three drive belts had come off at least one of its respective sheaves. All drive belts exhibited fraying damage to their tie bands. The landing skids did not exhibit any significant deformation or damage. ADDITIONAL INFORMATION Global Positioning System (GPS) Data According to the pilot, his handheld Garmin Global Positioning System (GPS) unit was in the helicopter and operating during the accident flight. The unit was sent to the NTSB Recorders Laboratory for data download, and it was determined that the unit had recorded multiple flights, including the accident flight. In interviews and written statements, the pilot had provided a variety of times for the departure, the accident, and the duration of the accident flight. Examination of the GPS data indicated that the helicopter departed the Punta Gorda farm about 1626, and that the accident occurred about 1751, for a total flight duration of approximately 90 minutes. The data indicated that entire flight was conducted below a GPS altitude of 300 feet, and most of the flight was conducted at GPS altitudes between 50 and 150 feet. The ground track of the helicopter was highly irregular and circuitous. The overall trend was in a southeast direction, but the ground track was included multiple turns, course reversals, and irregular-shaped circuits of varying diameters. Many circuits exhibited a maximum diameter of less than 500 feet, and several had a diameter of approximately 150 feet. The majority of the flight was conducted at ground speeds below 50 mph, and the average ground speed was approximately 30 mph. Telatemp Decals The helicopter was equipped with factory-installed, heat-sensitive "Telatemp" decals affixed to certain critical components. According to the R44 maintenance manual (MM), the purpose of the decals was to provide pilots and maintenance personnel with a visual indication of "changes to the operating temperature" of the components. Each decal was white, and contained a series of six hollow squares arranged in a row. Each square was designed to darken to black when it was exposed to a certain threshold temperature. The squares on each decal were arranged so that the threshold temperature of a given square was higher than that of the square to its left. Each square represented a 10 degree F increment, and the temperature values of the squares were imprinted on the decals. The darkening process was irreversible; the squares did not revert to white when the decal or its parent component cooled. The MM indicated that three different decals, each with a unique part number, were available. All decals had a temperature span of 50 degrees F, but each part number designated a specific temperature range, and the different part numbers (and thus decals) were location-specific. Telatemp inspection and usage guidance was provided in the POH and the MM. The basic procedure required that soon after a helicopter was first flown, or a new decal was installed, a mechanic was to mark a reference line to the right of the right-most darkened square on each decal. Each installed decal was then to be examined during subsequent preflight inspections, and darkening of any square to the right of the reference line was to prompt an attempt to account for the additional darkening. A representative of the helicopter manufacturer stated that pilots were typically advised of the Telatemp decal information in the MM at the manufacturer's pilot safety course, and also during their flight training. The representative also stated that squares tended to turn gray before they turn black, that the manufacturer did not have any specific information on the temperature increment required to turn a square gray but not black, and that a temperature midway between the black square and the gray square was likely a valid estimate. He also stated that it was not unheard of for two adjacent squares to turn gray. The representative stated that the number of blackened squares on any Telatemp decal was not necessarily indicative of a problem. The Telatemp decal on the upper clutch actuator bearing of the accident helicopter contained four black squares and one gray square. A black line was observed to the left of the left-most square on the decal. That line was presumed to be the initial reference line, which indicated that at some point in time, all six squares on the decal were white. According to the MM, two different Telatemp decal part numbers were acceptable for installation on that component. The "-2" had a temperature range from 140 degrees F to 190 degrees F, and the "-3" had a range from 180 degrees F to 230 degrees F. The installed decal was the "-3," and the decal indicated that the component had reached an operating temperature of approximately 215 degrees F. No indications of upper clutch actuator bearing distress or malfunction were noted. Main Rotor RPM According to the Robinson R44 Pilot Operating Handbook (POH), the helicopter was equipped with a single aural warning horn system; the system was designed so that the horn would sound whenever the main rotor rpm decreased to a value of 97 percent or less. The helicopter was also equipped with a low rotor rpm cockpit warning light designed to illuminate at the same rotor rpm threshold. The POH "Starting Engine and Run-Up" checklist in the "Normal Procedures" section required the pilot to verify the proper activation of the warning horn and light prior to every flight. According to a representative of the helicopter manufacturer, the horn and the light each received their signal on a shared circuit from the Low RPM Warning Unit. The Warning Unit received a signal from one of the two Hall Effect transducers on the input (drive) yoke of the main rotor gearbox, and the other transducer provided a signal to the rotor tachometer. The "Tachometers" paragraph in the POH "Systems Description" section contained a "Caution" which stated that "Installation of electrical devices can affect accuracy and reliability of electronic tachometers, low RPM warning system, and governor. Therefore no electrical equipment may be installed unless specifically approved by the factory." According to the helicopter manufacturer's representative, the manufacturer defined "installed" as "set up for use or service," irrespective of whether the installation was temporary or permanent. In other words, if an electrical device was present in the helicopter and was operating for use in flight, it was considered to be "installed," and therefore required explicit approval by the manufacturer. The helicopter manufacturer provided a list of all approved electrical devices on its website, and all were tested for interference prior to approval for installation. To date, all approved devices were console-mounted units, and the manufacturer has not approved the installation of any handheld or portable GPS devices. However, the manufacturer has not received any reports of a handheld GPS affecting a tachometer. Drive ("Vee") Belts Power transfer from the engine to the rotor system was accomplished via four flexible "vee-belts," each of which linked the engine (lower) and rotor system (upper) sheaves. Each drive belt consisted of two V-shaped belts arranged side-by-side, joined by a continuous "tie-band" that spanned the top (wide) parts of the two Vs. The bottom (narrow) part of each V rode in one of eight circumferential grooves in each sheave. The upper sheave was equipped with an overrunning clutch which permitted the sheave to rotate the main and tail rotor shafts, but prevented the reverse action. An electric actuator automatically maintained proper drive belt tension by moving the upper sheave towards or away from the lower sheave. The actuator was enabled by a clutch switch in the cockpit. The helicopter manufacturer's representative stated that the damage signature on the tie band of each drive belt was typical of a drive belt that was displaced from the grooves on one or both of the sheaves. He stated that a drive belt could be displaced from the grooves if the drive belt was too loose, by abrupt maneuvering of the helicopter, or by the helicopter striking the ground when the engine was running. A failing drive belt can become too loose. Also, since the four drive belts were installed adjacent to one another on each sheave, displacement of one drive belt could result in displacement of one or more of the other drive belts. The representative also stated that when a drive belt starts to fail, it tends to make a repetitive or continuous thumping or tapping noise, and that drive belt failure could result in low rotor rpm.
The loss of main rotor rpm due to the failure of one or more of the drive belts for undetermined reasons.
Source: NTSB Aviation Accident Database
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