NTSB Factual Report

HISTORY OF FLIGHT

On August 7, 2002, at 1026 central daylight time, a Hughes 369A helicopter, N98MP, operated by the Missouri State Highway Patrol, was substantially damaged during a forced landing shortly after takeoff from the Springfield Downtown Airport (3DW), Springfield, Missouri. The two highway patrol officers on-board, a pilot and an observer, sustained serious injuries. The flight was being conducted under the provisions of 14 CFR Part 91 and was not on a flight plan. Visual meteorological conditions prevailed at the time. The intention was to conduct a local surveillance flight and return to the Downtown Airport.

The pilot stated: "Approximately one minute after departure, I felt and heard a noise in the aircraft. We were approximately 200 to 300 feet above the ground and our airspeed was approximately 60 knots. The aircraft immediately began to yaw to the right. The anti-torque pedals immediately became ineffective. I lowered the collective to prevent the aircraft from yawing all the way around. This was effective, but resulted in a loss of altitude."

The pilot went on to note, "At an altitude of approximately 100 feet, the aircraft began to spin around the vertical axis. I immediately lowered the collective fully. As we neared the ground, I rolled the throttle off to flight idle, and pulled full collective to cushion the fall. The aircraft hit the ground on its skids. The left skid collapsed."

The observer reported, "After takeoff we were gaining altitude when I heard a loud bang. My side of the helicopter seemed to drop and we began flying sideways for a short time. Then we started spinning. After the pilot decreased the throttle, apparently, we started dropping but quit spinning. Before impact with the ground we slowed but hit hard, breaking the skid on my side."

PERSONNEL INFORMATION

The pilot held a commercial pilot certificate, issued by the Federal Aviation Administration (FAA), with rotorcraft - helicopter, airplane - single engine land, and instrument - airplane ratings. He also held a flight instructor certificate with an airplane - single engine rating. His Second Class medical certificate was issued on April 4, 2002 without limitations.

The pilot reported a total flight time of 3,063 hours, with 693 in rotorcraft, all of which were in the same make and model as the accident aircraft. His most recent flight review was completed on March 9, 2002.

AIRCRAFT INFORMATION

The helicopter involved was a Hughes 369A, serial number 680542. According to FAA records, it was registered to the Missouri State Highway Patrol on February 24, 1995. It was reportedly being used in support of the Highway Patrol's law enforcement activities.

A review of the aircraft maintenance records indicated that the most recent 100/300 hour inspection was completed on February 1, 2002. At the time of the accident, 79 hours had elapsed since the inspection. Total engine time at the time of the accident, was 3,181 hours, with 211 hours since overhaul. Total airframe time was 3,838 hours, at the time of the accident.

According to the records, the tail rotor gearbox was replaced on July 7, 2000. At installation, component times of 1661 total and 620 since overhaul were recorded. At the time of the accident, an additional 385 hours had been put on the gearbox. The manufacturer's documentation specifies the overhaul interval for the tail rotor transmission as 1,800 hours.

WRECKAGE INFORMATION

The accident site was located immediately west of US Highway 65, approximately 5/8 mile south of Division Street, in Springfield, Missouri. The location of the site was determined using a global positioning system (GPS) receiver to be 37 degrees 12.90 minutes north latitude, 93 degrees 13.57 minutes west longitude. This was 1.25 statute miles east-southeast of 3DW.

The main wreckage was oriented on a 202 degree magnetic heading. The aircraft was upright, although the left skid was collapsed causing it to lean to the left approximately 15 degrees. The main rotor blades exhibited bending and twisting. The fuselage skin was buckled and warped on the right side, immediately aft of the passenger door.

The upper vertical stabilizer was extensively damaged. The upper 22 inches of the stabilizer had separated and was found with the tail rotor assembly. The skin was torn in the area of separation and showed multiple dents. Also noted were discolorations consistent in color and texture with paint on the tail rotor blades.

The lower vertical stabilizer remained attached to the tail boom. It was intact, however, it was bent upward and to the right.

The canted horizontal stabilizer was attached and intact. The strut installed between the upper vertical and the horizontal stabilizer was slightly bent. It was separated completely from the upper vertical stabilizer at the inboard end.

The tail rotor transmission housing separated and the tail rotor assembly had departed the aircraft. It was subsequently located along the flight path, approximately 3/8 statute mile prior to the impact site. The location was determined using a GPS receiver to be 37 degrees 13.16 minutes north latitude and 93 degrees 13.82 minutes west longitude.

The tail rotor transmission housing was fractured circumferentially across the 90-degree angle of the housing. The transmission gears were free of debris and appeared undamaged. The drive shafts were free to rotate. The tail boom mounting holes on the forward half of the transmission were intact and appeared undeformed. The tail rotor drive shaft was intact and free of any bending or twisting.

The tail rotor blades were damaged, but remained attached to the hub. The hub remained with the drive fork and appeared undamaged, however the bolt, which secured the tail rotor assembly to the hub was broken. Half of the bolt was found with the assembly. The mating half had separated from the fork along with the elastomeric bearing. This bolt half, as well as the bearing, were found in the vicinity of the tail rotor assembly.

The elastomeric bearings from the tail rotor assembly appeared intact. No evidence of deterioration was noted. The outer bearing race and the drive fork bearing holes showed traces of adhesive, however, no evidence of scrim cloth was present. Both the bearing races and the bearing holes appeared undamaged. No signs of wear between the bearing race and the fork - scrapes, gouges, or galling - were noted.

One tail rotor blade was intact, with the exception of a mid-chord leading edge tear and a dent running along the trailing edge for the entire length of the blade. Chordwise wear marks were also noted. The other blade was severely damaged. The outboard 9-inch span of the blade was separated from the remainder of the assembly. The outboard closure rib and counterweight were also separated from the blade. They were both located with the tail rotor assembly. The inboard section remained secured to the hub.

The tail rotor pitch control assembly was attached to the drive fork and transmission housing. The bellcrank was attached to the transmission housing and was free to rotate. The pitch change control tube was fractured approximately 6 inches forward of the bellcrank attach point. The aft rod end, common to the bellcrank, was intact and free to rotate. The pitch change links remained attached, but were bent slightly. Otherwise, they were attached and intact.

Due to the time of year, the flight was operating without cabin doors installed. A post-accident inventory of the cabin contents revealed no missing items.

No evidence of a bird strike was present on the helicopter components. No debris associated with a bird strike was present at the accident site or the tail rotor assembly impact site.

The Hobbs meter indicated 438.3 hours at the accident site.

RESEARCH AND TESTING

The NTSB Materials Laboratory examined the tail rotor transmission housing and tail rotor assembly mounting bolt. Features of the fracture surfaces on both components were consistent with overload failures. No indications of fatigue were found.

The manufacturer's documentation indicated that the elastomeric bearings are to be inspected during 100 and 300 hour inspections. This specifically included verifying the integrity of the fork-to-bearing bond line and any sign of discontinuity in the elastomer material. Aircraft logbook entries indicated that the applicable 100 / 300 hour inspections were completed as required.

In addition, the elastomeric bearings are a preflight inspection item. The pilot stated that he inspected the bearings prior to flight and he determined them to be airworthy. No sign of unusual wear or deterioration was noted, according to the pilot. The pitch change linkage assembly was inspected as part of the preflight with no problems noted, according to the pilot.

The Component Overhaul Manual notes a requirement for one ply of scrim cloth is to be placed between the bearing and the fork when installing new elastomeric bearings. In addition, replacement of the bearings is based on condition only. A mandatory component replacement time is not specified for the bearings.

ADDITIONAL INFORMATION

Parties to the investigation were the Missouri State Highway Patrol -- Aircraft Division and Boeing Helicopter Company.

NTSB Probable Cause

Overload failure of the tail rotor transmission housing (gearbox) for undetermined reasons, which resulted in an inability to adequately control the aircraft.