Winder, GA, USA
N566BC
ROBINSON R22
The pilot was practicing touch-and-go landings during a personal flight in a helicopter. As the helicopter was turning onto a left crosswind during the fifth circuit around the pattern, the pilot heard a “metal against metal” noise, and the helicopter “jerked.” As he began to look for a clearing to land the helicopter, it jerked again, and the pilot thought that the helicopter was losing power. The pilot was unable to reach a clear area, and the helicopter descended “straight down” through trees and collided with the ground, resulting in substantial damage to the helicopter’s fuselage, tailboom, main rotor, and tail rotor and serious injuries to the pilot. Postaccident examination of the wreckage found that most of the drive system vee-belts were missing; only a small 2-ft portion of one vee-belt was found. Further examination of the wreckage revealed that the engine cooling fan attachment bolts were loose and could be easily turned with a wrench. The paint around the fanwheel-to-hub hardware was displaced, and surface corrosion and fretting residue were found on the exposed metal around the hardware. This evidence was indictive of the bolts having been loose for a period of time, and it is likely that the condition of the bolts would have resulted in the cooling fan imparting vibratory loads to the helicopter. The cooling fan vibration likely allowed the belt tension actuator to incrementally overextend, resulting in the failure of the vee-belts and the loss of power to the rotor system. The helicopter operator had not complied with a service bulletin that addressed an issue with the belt tension actuator. According to the airframe manufacturer, taking the action described in the service bulletin would have prevented the actuator from overextending by incorporating an electronic time delay. Also, there was no record of fanwheel replacement at the most recent overhaul, which was required by the manufacturer. The fanwheel hardware should also have been inspected by maintenance personnel at the last 100-hour inspection and by the pilot during the preflight inspection.
On October 18, 2020, about 1059 eastern daylight time, a Robinson Helicopter Company R22 Beta, N566BC, was substantially damaged when it was involved in an accident near Barrow County Airport (WDR), Winder, Georgia. The private pilot was seriously injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he flew from Gwinnett County Airport (LZU), Lawrenceville, Georgia, to WDR to practice takeoffs and landings. During the fifth circuit around the pattern, he performed a touch-and-go landing. After takeoff, as the helicopter was turning onto a left crosswind, he heard a “metal against metal” noise, and the helicopter “jerked.” As the pilot began to look for a clearing to land the helicopter, it jerked again, and the pilot thought that the helicopter was losing power. The helicopter then descended “straight down” through trees and collided with the ground. The helicopter came to rest on its left side. Structural damage to the fuselage, tailboom, main rotor, and tail rotor was observed. The engine sustained minimal impact damage. The crankshaft could be rotated by hand more than 360° using the cooling fan. No anomalies were noted. The alignment marks (torque stripes) on the cooling fanwheel were not aligned with the marks on the nut by about 90° and were misaligned with the roll pin by about 10°. The paint around the fanwheel-to-hub hardware was displaced, and surface corrosion and fretting residue were found on the exposed metal around the hardware. The threads of the attachment bolts extended more than two threads beyond the nuts. The bolts were loose and could be easily rotated with a wrench. The lower and upper sheave grooves were unremarkable. Most of the drive system vee-belts were missing; only a small 2-ft section of one vee-belt was found. Examination of the recovered 2-ft section found that the backing was not present, one end had a jagged surface, and the other end was frayed. The friction surfaces were smooth with no glazing or thermal damage noted. The belt tension actuator was extended 1.65 inch between the scissor mounts. The scissors were deformed, and the overtravel switch was damaged. The upper and lower actuator support bearings rotated smoothly. The actuator was removed and functionally tested at Robinson Helicopter Company. The load tension and the amperage draw were slightly above production specifications. The fuse installed in the actuator circuit protection fuse holder was a 2-ampere fuse. Specifications required a 1.5-ampere fuse. The spare fuse holder contained a 1.5-ampere fuse. The helicopter was not installed with an actuator time delay assembly, as prescribed by Robinson R22 Service Bulletin SB-113A, and the helicopter’s maintenance records did not show compliance with the service bulletin. The service bulletin stated the following: RHC [Robinson Helicopter Company] has received A051-1 actuators which have buckled due to overtensioning of the drive vee-belts. Normally, the actuator fuse will prevent an overtension. However, in some cases, a vibrating switch may allow the actuator to gradually overtension without blowing the fuse. Switch vibration can be aggravated by an out-of-balance cooling fan. RHC has designed an electronic time delay which prevents the actuator motor from running until spring switches contacts have been closed for approximately 1/4 second. The time delay will prevent the actuator from overtensioning and also prolong actuator switch life. According to the maintenance logbooks, the helicopter was overhauled in 2000, about 180 hours prior to the accident, and a 100-hour inspection was performed about 84 hours prior to the accident. According to Robinson Helicopter Company, the fanwheel should have been replaced with a new or overhauled unit at the time of the most recent overhaul. A replacement of the fanweel was not documented in the maintenance logbooks for the most recent overhaul. The fanwheel should have been visually inspected at the most recent 100-hour inspection. Also, inspection of the fanwheel was also required during any preflight inspection by the pilot.
Maintenance personnel’s failure to properly secure the engine cooling fan attachment bolts, leading to vibration of the cooling fan, the overextension of the tension belt actuator, the failure of the drive system vee-belts, and the loss of power to the rotor system. Contributing to the accident was the failure of the operator to incorporate the manufacturer’s service bulletin addressing the prevention of belt tension actuator overextension, and the failure of maintenance personnel and the pilot to observe the loose fanwheel bolts during the most recent 100-hour inspection and during the preflight inspection of the helicopter (respectively).
Source: NTSB Aviation Accident Database
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