St. Petersburg, FL, USA
N78BM
Velocity Elite RG
The pilot of the experimental amateur-built airplane stated that the first part of the takeoff roll was normal, but he noticed a sudden lack of acceleration and that the indicated airspeed was not increasing past 60 knots. He aborted the takeoff, reduced engine power to idle, and applied maximum braking. The airplane departed the end of the runway and came to rest on top of a rock embankment, resulting in substantial damage. Examination of the engine revealed no preimpact anomalies that would have precluded normal operation. Examination of the electrically-controlled variable pitch propeller system revealed that the propeller exhibited signs of inadequate maintenance as the gaps between the three propeller blades were not sealed in accordance with manufacturer guidance. Also, corrosion was present on the propeller slip rings (which would have increased electrical resistance), supercams, and spool. Additional examination revealed that the propeller would not change pitch when the switch lever was operated, though electrical continuity was confirmed from the battery to the carbon brushes that were in contact with the slip rings. Examination of the spool that controlled propeller blade pitch angle indicated that the propeller was not in the fine-pitch, high-rpm takeoff position. The planetary gearbox contained very little lubricant and there were areas that were visibly dry. Examination of the electric motor (gear motor), which powered the propeller pitch mechanism, revealed intermittent operation due to worn carbon brushes. Internal examination of the electric motor revealed a broken end on one of the armature coil windings that surrounded one of the three electromagnetic coils in the electric motor, indicating that the motor needed replacement. Review of propeller system maintenance records revealed no entries regarding preventive maintenance of the system in the approximate 2 years before the accident. The propeller manufacturer’s written guidance regarding operation of the propeller revealed that, before takeoff, the engine should be run at wide open throttle and the propeller blade pitch adjusted to the maximum horsepower rpm. Had the pilot performed this check, it would have been apparent that the propeller was not in the correct takeoff setting. Wind conditions at the time of the accident were consistent with a 9-knot tailwind, which would have increased the distance necessary for takeoff and placed the airplane farther down the runway when the pilot aborted takeoff.
HISTORY OF FLIGHT On January 14, 2020, about 1600 eastern standard time, an experimental amateur-built Velocity Elite RG, N78BM, was substantially damaged when it was involved in an accident in St. Petersburg, Florida. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The accident occurred during a rejected takeoff at Albert Whitted Airport (SPG), St. Petersburg, Florida. The flight was destined for Orlando Executive Airport (ORL), Orlando, Florida, where the pilot, and his two passengers had departed from earlier in the day and had flown to SPG for lunch. According to the pilot, prior to the return flight, he completed a normal preflight inspection, boarded the passengers, started the engine, and requested to taxi to runway 7. He performed an engine run-up with no anomalies and prepared the airplane for takeoff. The air traffic controller requested that he use the D2 intersection for departure, which the pilot declined and stayed at the D1 intersection to have more available runway for the takeoff roll. When cleared for takeoff, he taxied on to runway 7, held the brakes and increased engine power. All indications showed normal, and he released the brakes and commenced the takeoff roll. The first part of the takeoff roll was normal, but he then noticed a sudden lack of acceleration, with the indicated airspeed not increasing past 60 knots. He aborted the takeoff, brought the power to idle, and applied maximum braking. The airplane remained on the extended centerline of the runway; however, it departed the end of the runway and came on top of a rock embankment, just short of where the embankment met the waters of Tampa Bay. AIRCRAFT INFORMATION The accident airplane was a four-passenger canard of composite construction. It was equipped with retractable landing gear in a tricycle configuration, a swept wing with wingtip rudders, and a 205-horsepower Franklin 6A-350-C1R, air cooled six-cylinder engine, mounted in a pusher configuration, driving a 3-blade in-flight adjustable pitch, Ivoprop Magnum propeller. According to FAA and airplane maintenance records, the airplane received its special airworthiness certificate in 1998. The airplane's most recent condition inspection was completed on June 22, 2019. At the time of the inspection, the airplane and engine had accrued about 443 total hours of operation. According to FAA records, the airplane received its special airworthiness certificate in 1998, and was originally registered as N104MW. On February 20, 2018, it was sold by the original builder to the owner/operator. One June 4, 2018, the airplane was assigned the special registration number of N78BM at the owner’s request. METEOROLOGICAL INFORMATION The recorded weather at SPG at 1505, included wind from 260° at 9 knots, 10 miles visibility, few clouds at 2,800 ft above ground level, temperature 26°C, dew point 21°C, and an altimeter setting of 30.18 inches of mercury. Crosswind component calculations indicated that, around the time of the accident, the airplane would have been subject to about a 9-knot tailwind during the takeoff roll. AIRPORT INFORMATION Runway 7 was asphalt, in excellent condition, and measured 3,677 feet long and 75 feet wide. WRECKAGE AND IMPACT INFORMATION Examination of the airplane revealed that the nose structure and the canard were substantially damaged. Examination of the engine revealed no preimpact anomalies that would have precluded normal operation. Examination of the electrically-controlled variable pitch propeller system revealed that the airplane had two switches which controlled the propeller. The first switch had two positions (“MANUAL” and “AUTO”); this switch was found in the “MANUAL” position. The second switch also had two positions (“CLIMB” and “CRUISE”); this switch was found in a neutral position. When in the “MANUAL” position on the first toggle switch, pressing the second toggle switch in the “CLIMB” direction would send electric current through a set of graphite brushes to hub-mounted slip rings, and through the slip rings to the electric motor. Pressing the second toggle switch in the “CRUISE” direction would reverse the polarity of the current and the rotation of the electric motor. If the second toggle switch was held in one direction, the propeller blade pitch would change in that direction and the pilot could observe the result by an indication of change in rpm. Torque from the electric motor was multiplied in a planetary gear drive which turned a lead screw. The lead screw was supported by a thrust bearing and converted its rotary motion into axial movement of a spool. The spool was linked to cams which turned torsional rods. The torsional rods transmitted the movement from the center of the propeller to the outside section of each blade. This would cause the blade to twist, which would change the propeller blade pitch. Movement of the spool was restricted each way by washers on the lead screw. This limited maximum and minimum pitch and prevented engine over-revving. Further examination revealed that the gaps between the three propeller blades were not sealed with silicone as required by the propeller manufacturer’s written guidance, and corrosion was present on the propeller slip rings, supercams, and spool. Additional examination revealed that the propeller would not change pitch when the switch lever was operated, though electrical continuity was confirmed from the battery to the carbon brushes that were in contact with the slip rings. Examination of the spool which controlled propeller blade pitch angle indicated that the propeller was not in the fine pitch, high rpm position that is used for takeoff. Examination of the planetary gearbox revealed that very little lubricant was present and there were areas that were visibly dry. When rubbed between two fingers, the lubricant that was present was sticky to the touch. Examination of the electric motor (gear motor) which powered the propeller pitch mechanism revealed that, when power was applied directly to the leads of the electric motor, it would operate intermittently. Further examination revealed that the electric motor’s carbon brushes, which served as electrical conductors to pass electrical current between the electric motor’s stationary and rotating wires, were worn to the point that the metal brush housings were contacting the electric motor’s commutator. The electric motor would operate intermittently until the output shaft was turned by hand. This indicated the presence of a dead spot (broken wire/etc.) on the armature as it appeared to fail “open” (infinite resistance between two nodes) vs “closed” (short circuit). Internal examination of the electric motor revealed a broken end on one of the armature coil windings that surrounded one of the three electromagnetic coils in the electric motor. ADDITIONAL INFORMATION Propeller System Maintenance Review of maintenance records revealed that, between May 28, 1998, and October 16, 2017, the builder of the airplane performed both regular and preventive maintenance of the propeller system, including replacement of motor brushes, replacement of the gear motor, torque checks on the propeller bolts, replacement of the tape between the propeller blades, replacement of propeller blades, and replacement of the stainless-steel leading edges. No other entries regarding regular or preventive maintenance were recorded in the maintenance records for the propeller system after October 16, 2017. Propeller Manufacturer’s Records Review of the propeller manufacturer’s records indicated that, around July 18, 2019 (about 1 ¾ years after the last recorded regular and preventive maintenance on the propeller system), the pilot (who managed the LLC that owned and operated the airplane) sent a propeller assembly to the factory for repair. The propeller blades; however, were beyond repair, so the pilot was sold a new set of blades, the propeller core was inspected and repaired, and a new gear motor was also provided. The propeller manufacturer’s records also indicated that, on July 25, 2019, the pilot ordered a magnet for the propeller governor and instructions, as well as a brush assembly. On August 7, 2019, the pilot ordered more parts, this time for a gear motor and a pickup coil. On January 10, 2020 (ten days before the accident), the pilot ordered another gear motor. No entries that reflected installation of any of these propeller system components was recorded in the propeller system maintenance records. Propeller System Operation The propeller manufacturer’s written guidance regarding operation of the propeller stated: Run the prop W.O.T [wide open throttle] on the ground and adjust pitch to your maximum [horsepower] rpm. It also cautioned: Assume that In-flight pitch adjustment can quit on you anytime in which case the pitch stays where it is. Corrective Actions After the accident, the propeller manufacturer added continued airworthiness instructions to their published guidance for their in-flight adjustable propellers, which included: Before starting the engine, to cycle through the pitch range and listen for abnormal sound from the gear motor. If it sounds louder or slower than usual or makes a grinding sound find the cause and correct it. Annual Inspection: Clean the lead screw and spool thread with acetone and lubricate lead screw and groove in the spool with white lithium grease. Check the brushes, and if they are too short, replace them. Check the plastic bumper washers for deformation and limit washers for wear and replace them if necessary. Anytime you reinstall the prop, refer to the warning instructions in our service bulletins for proper torqueing, re-torqueing and monitoring. 500 Hour / 5 Year Inspection: Send the gear motor unit to us for inspection and lubrication.
A failure of the propeller pitch change electric motor, which resulted in an improper setting for takeoff and a subsequent runway overrun. Also causal was the inadequate maintenance and inspection of the propeller system and the pilot’s failure to follow the propeller manufacturer’s pretakeoff guidance, which would have indicated that the propeller was not in the takeoff position. Contributing to the accident was the pilot’s decision to depart with a tailwind.
Source: NTSB Aviation Accident Database
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