Naples, FL, USA
N8618F
HUGHES 369
The flight instructor and airline transport pilot were conducting a recurrent local public helicopter training flight and had performed several straight-in autorotations and two 180-degree autorotations. During the third 180-degree autorotation, when the helicopter was about 50 ft above ground level (agl), the pilot, who was manipulating the controls, initiated a recovery flare. During the flare, the helicopter's tail rotor contacted the turf runway. The instructor took over the controls and landed the helicopter. The helicopter sustained damage to the tail rotor blades, horizontal stabilizer, and tail rotor drive train. Postaccident examination revealed no preimpact mechanical malfunctions or anomalies that would have precluded normal operation. The pilot reported that he had initiated the flare to arrest the forward motion as he had done during the previous autorotations, but at some point during the flare, he felt a "bump," which he realized later was the tail rotor striking the ground. The flight instructor reported that, during the flare, the helicopter "suddenly lost altitude," and he "grabbed the controls." He then felt a "bump," followed by a "buzz." A witness who was watching the helicopter during the autorotations reported observing the helicopter descend more rapidly and aggressively during the accident approach than during the previous autorotations. When the helicopter was about 100 ft agl, it nosed up "aggressively," followed by the tail striking the ground. Two areas at the airport at which the accident occurred could be used for practice autorotations: a paved runway and the turf runway. At the time of the accident, only the turf runway was in use due to traffic; however, a suitable hard-surface runway was also available at a nearby airport and could have been used for the practice autorotations. The flight instructor reported that, after the accident, he could see where the tail stinger had touched the grass and dug into the dirt. He noted that, at the helicopter manufacturer's training facility, pilots always conducted autorotations to a hard surface not onto grass. He believed that if they had been operating on a hard surface, the tail stinger would have touched and slid along the pavement, instead of it digging into the dirt, and this may have prevented the tail rotor blades from striking the ground.
HISTORY OF FLIGHT On February 3, 2014, about 1350 eastern standard time, a Hughes 369D, N8618F, operated by the Collier Mosquito Control District (CMCD), was substantially damaged during a practice 180 degree autorotation to touchdown at Naples Municipal Airport (APF), Naples, Florida. The flight instructor and airline transport pilot were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local public use training flight. According to the flight instructor, prior to the last practice "fulldown" autorotation, they had performed two running landings, two stuck left pedal maneuvers, three stuck right pedal maneuvers, and eight successful autorotations. Just like the previous eight, the helicopter responded the same during the flare but this time it suddenly lost altitude and contacted the ground. The instructor "quickly grabbed" the controls and landed the helicopter which had yawed 90 degrees to the right. The airline transport pilot then asked him what happened. According to the airplane transport pilot (ATP), he was undergoing annual proficiency training, and after completing the simulated stuck pedal maneuvers, and run on landings, four straight in touchdown autorotations were performed, followed by 180 degree autorotations to touchdown. Two were performed successfully but, on the third one, the tail of the helicopter contacted the ground. The ATP believed that the entry to the maneuver was normal and that during the turn to achieve the rollout prior to touchdown that the helicopter was level and was "essentially" into the wind, at most 10 to 15 degrees left of the nose and landing direction. He was at the target speed of approximately 60 knots indicated airspeed, and the rotor rpm was in the "mid-green arc." The flare was initiated about 50 feet above ground level (agl) to arrest the forward motion as he had done on the previous autorotations but, at some point during the flare he felt a "bump." The procedure was continued per the profile with the forward motion having been arrested, the helicopter was leveled off and a "pitch pull" was initiated, resulting in a "normal" touchdown with little forward motion, coming to rest turned to the right from its flight path by approximately 60 degrees. According to a witness, who was watching the helicopter doing autorotations, he "took interest" in this particular approach as the helicopter seemed to be "falling a little more rapidly and aggressively" then during the previous autorotations. At approximately 100 feet agl, he then observed the helicopter "nose up aggressively," the tail strike the ground, dirt being thrown upwards on to the top of the helicopter, and then the helicopter come to rest with the main rotor still turning. PERSONNEL INFORMATION According to Federal Aviation Administration (FAA) and pilot records, the flight instructor held a commercial pilot certificate with ratings for rotorcraft-helicopter and instrument- helicopter. A flight instructor certificate with ratings for rotorcraft-helicopter and instrument-helicopter, and an instrument ground instructor certificate. His most recent FAA second-class medical certificate was issued on July 1, 2013. He reported that he had accrued 5,465 total hours of rotorcraft flight experience, 1,549 hours of which were in the accident helicopter make and model. He also reported that 3,884 of his total hours were as a flight instructor, and that 1,083 of those hours spent as an instructor in the accident helicopter make and model. According to FAA and pilot records, the pilot held an airline transport pilot certificate with ratings for airplane multi-engine land, commercial privileges for airplane single-engine land, and rotorcraft-helicopter. He also held a flight instructor certificate with a rating for airplane single-engine. His most recent FAA first-class medical certificate was issued on January 29, 2014. He reported that he had accrued 4,935.3 total hours of flight experience, 1061.5 of which were in the accident helicopter make and model. AIRCRAFT INFORMATION The accident aircraft was a light, single engine utility helicopter manufactured By Hughes Aircraft Corporation in 1977. It was powered by a 420 shaft horsepower, Allison 250-C20B gas turbine engine, and was constructed primarily of aluminum alloy. The main rotor was a fully articulated five-bladed system, with anti-torque provided by a 2-bladed semi-rigid type tail rotor. Power from the turboshaft engine was transmitted through the main drive shaft to the main rotor transmission and from the main transmission through a drive shaft to the tail rotor. An overrunning (one-way) clutch, placed between the engine and main rotor transmission permitted free-wheeling of the rotor system during autorotation. The airframe structure was egg-shaped and incorporated a rigid, three-dimensional truss type structure which increased occupant safety by means of its roll bar design. The airframe structure was designed to be energy absorbing and would fail progressively in the event of impact. The fuselage was a semi-monocoque structure that was divided into four main sections. The forward section was comprised of a pilot compartment equipped with 2 seats. Directly aft of the pilot compartment, separated by a bulkhead, a passenger/cargo compartment was in the center of the helicopter. It contained provisions for installation of a bench or individual folding type seats for two passengers. It normally contained components for a spray kit for mosquito control operations but, at the time of the accident, it had been removed for the training flights. The aft section included the structure for the tailboom attachment and engine compartment. The lower section was divided by the center beam and housed the two fuel cells. Provisions for the attachment of a cargo hook were located on the bottom of the fuselage in line with the center beam. The tailboom was a monocoque structure of aluminum alloy frames and skin. The tailboom was the supporting attachment structure for the stabilizers, tail rotor transmission and tail rotor. The tailboom also housed the tail rotor transmission drive shaft. The landing gear was a skid-type attached to the fuselage at 12 points and was not retractable. Aerodynamic fairings covered the struts. Nitrogen charged landing gear dampers acted as springs and shock absorbers to cushion landings and provide ground resonance stability. The skid tubes were equipped with skid shoes, and provisions for ground handling wheels were incorporated on the skid tubes. According to maintenance records, the helicopter's most recent annual inspection was completed on December 4, 2013. At the time of the inspection, the helicopter had accrued approximately 3344.6 total hours of operation. METEOROLOGICAL INFORMATION The reported weather at APF at 1253 about 57 minutes before the accident, included: winds 220 degrees at 12 knots, 10 miles visibility, scattered clouds at 2,400 feet, broken clouds at 5,500 feet, temperature 28 degrees C, dew point 22 degrees C, and an altimeter setting of 30.05 inches of mercury. The reported weather at APF, at 1353, about 3 minutes after the accident, included: winds 220 degrees at 12 knots, 10 miles visibility, scattered clouds at 2,500 feet, temperature 28 degrees C, dew point 21 degrees C, and an altimeter setting of 30.05 inches of mercury. AIRPORT INFORMATION Naples Municipal Airport was a tower controlled public use airport, located 2 miles northeast of Naples, Florida. The airport elevation was 8 feet above mean sea level and there were two paved runways oriented in a 05/23, and 14/32 configuration. There was also a turf runway located off the side of runway 05/23, which was oriented in a southwest northeast orientation, and paralleled runway 5/23. Total length of the turf runway was 1,850 long and 100 feet wide. Two areas at APF could be used for practice autorotations, a hard surfaced taxiway, and the turf runway. At the time of the accident, due to traffic, the turf runway was in use. WRECKAGE AND IMPACT INFORMATION Examination of the helicopter revealed that the tail rotor blades exhibited impact damage and were twisted and bent. The tail rotor driveshaft was also twisted and bent, the horizontal stabilizer was bent, the forward and aft tail rotor drive shaft couplings were damaged, the tail rotor driveshaft dampener was distorted, and the tail rotor output shaft on the transmission was bent. TESTS AND RESEARCH Previous Training Accident Review of NTSB records indicated that N8618F had been involved in a previous accident under similar circumstances (NTSB Case No. ERA10LA172), when on March 11, 2010, it had been substantially damaged following a landing at APF. The certificated commercial pilot and airline transport pilot-rated check pilot that both employed by CMCD, were not injured. The purpose of the flight was also to complete a yearly check ride, which included all basic flight maneuvers and autorotations to landing. On the third autorotation, after touch-down, the pilot heard a "thud" and "no longer had use of the anti-torque pedals." The check pilot visually observed damage to the tail section. The helicopter was shut down and both pilots exited normally. At the time of the accident, The weather was also similar with the APF automated weather observation, reporting winds from 130 degrees at 12 knots, 10 statute miles visibility, overcast clouds at 1,500 feet, temperature 22 degrees Celsius (C), dew point 20 degrees C, and an altimeter setting of 29.83 inches of mercury. The pilot noted that the accident could have been prevented if the cyclic was "forward to neutral on and after touchdown." And recommended in a written statement that they train in weather conditions that included light winds and minimal gust factor and to use power recovery to prevent excessive main rotor blade flapping. As a result of this accident, CMCD began contracting with outside vendors for recurrent training. Contract with MD Helicopters On November 5, 2013, CMCD entered into a contract with MD Helicopters to provide recurrent training from February 3, 2014 through February 6, 2014 for up to 5 pilots, each of which would receive ground school and 1.5 hours of flight time. Review of the MD Helicopters 500/600 Series Helicopters Pilot Recurrent Syllabus, revealed that the course was designed for pilots who had previously attended the MD Helicopters Pilot Transition Course or had equivalent training. Course duration was normally three days and included academics and flight procedures: - The academic segment was approximately 8 hours and included a review of helicopter systems and procedures. Each pilot also would complete a written open-book flight manual exam. - The flight segment covered normal and emergency procedures and included up to 3 flight hours. Reference materials used during the course consisted of the helicopter flight manual, recurrent training manual, as well as other publications from the MD Helicopters website. The flight training in addition to emergency procedures would also emphasize other areas of interest requested by the customer, and MD Instructor pilots would determine which maneuvers would be briefed, demonstrated and/or practiced based upon customer pilot experience and prevailing ambient conditions. Interview with the Flight Instructor According to the flight instructor, on the day of the accident, the ATP had done 5 "very nice" autorotations, and the flight instructor stated that if they are doing well, he would "give them an inch, and would not be as restrictive" otherwise he would be on the controls. The accident occurred on their 9th full touchdown autorotation. The ATP rolled out at 150 feet, He flared around 50 feet and the rpm began to build, and the flight instructor thought to himself that "this is going to be the best one of the day." The helicopter though, suddenly lost altitude. The flight instructor then "grabbed the controls," and "double pumped" the collective. He then felt a "bump" and then a "buzz." Afterwards, he could see where the tail stinger had touched the grass. He advised that at the factory they would always do autorotations to a hard surface and not onto grass. He believed that on a hard surface, they would have felt the tail stinger contact the pavement, instead of it digging into the dirt. Interview with the ATP According to the ATP, he woke up at 0600 on the day of the accident and started ground school at 0730. The flight instructor talked about what they would be doing in the training. The ground school also covered a systems review and also covered normal and emergency procedures. After the ground school they went flying. The flight instructor explained what his expectations were and that the standards would be similar to the FAA's Practical Test Standards (PTS). The flight instructor also briefed the ATP that during the flight if he did not like the way things were going that he would take control. They did not do any performance calculations prior to the flight and the flight instructor did not advise of any wind limitations. The flight began with a demonstration by the flight instructor. During the autorotations, the wind was quartering off the forward left side of the helicopter. The ATP stated that they had done 8 successful autorotations under the wind conditions but then on the 9th autorotation when he was about 50 feet above the ground, he initiated the flare to arrest the forward motion as he had done on the previous autorotations but, during the flare he felt a "bump," which he later realized was the tail stinger coming into contact with the ground. The helicopter was equipped with skid shoes but, during the accident flight they were preforming the autorotations to the turf runway, as it is very busy at APF, and the airport did not like them to use the paved taxiway for autorotations. The Marco Island airport did have a hard surface taxiway that they could have utilized but they did not use it. The ATP also stated that when CMCD pilots did practice autorotations and landings it was not unusual for them to do them to soft surfaces, as most of the area they operated over was unimproved, but since this happened he thought that they might want to mitigate practice autorotations to touchdown on soft surfaces. He did believe though that training was necessary as two weeks prior to the accident one of their pilots did have an engine failure light come on, and he entered a full autorotation to touchdown. The ATP also advised that doing 180-degree autorotations do not really bother him but he was more comfortable with power on recoveries as full autorotations to touchdown are "nail biting." Autorotation In a helicopter, an autorotative descent is a power-off maneuver in which the engine is disengaged from the main rotor system and the rotor blades are driven solely by the upward flow of air through the rotor. In other words, the engine is no longer supplying power to the main rotor. According to the Helicopter Flying Handbook (FAA-H-8083-21A), the most common reason for an autorotation is failure of the engine or drive line, but autorotation may also be performed in the event of a complete tail rotor failure, since there is virtually no torque produced in an autorotation. In an engine failure, the freewheeling unit automatically disengages the engine from the main rotor allowing the main rotor to rotate freely. The freewheeling unit will also disengage anytime the engine rpm is less than the rotor rpm (as is the case during a practice autorotation). At the instant of engine failure, the main rotor blades are producing lift and thrust from their angle of attack (AOA) and velocity. By lowering the collective pitch, which must be done immediately in case of an engine failure, lift and drag are reduced, and the helicopter begins an immediate descent, thus producing an upward flow of air through the rotor system. This upward flow of air through the rotor provides sufficient thrust to maintain rotor rpm throughout the descent. Since the tail rotor is driven by the main rotor transmission during autorotation, heading control is maintained with the antitorque pedals a
The pilot's inadequate flare during the termination of a practice 180-degree autorotation and the flight instructor's delayed remedial action, which resulted in the tail rotor contacting the ground.
Source: NTSB Aviation Accident Database
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