Robinson R22 N559DD

Summary

On 20 November 2002 at about 20:30 local time, a Robinson R22 registered N559DD was involved in an accident near St. Jacob, Illinois, United States. 2 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

20 November 2002 at 20:30

Classification

Accident

Location

St. Jacob, Illinois, United States

Coordinates

38.7750, -89.8092

Aircraft

Robinson R22

Registration

N559DD

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Instructional

Phase of flight

Not recorded

Route

Cahokia/St. Lou → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CHI03FA025

Nobody was injured.

Fatigue fracture of the clutch assembly fan shaft and the resulting complete loss of power to the rotor drive system. A contributing factor was the loss of tail rotor authority due to the secondary failure of the control tube assembly.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The helicopter was substantially damaged when the fan shaft failed causing a loss of power to the main and tail rotors. The instructor pilot reported that while in cruise flight the clutch light flickered several times. He stated that he pulled the clutch circuit breaker, "however the noise continued to worsen and [he] suspected the drive belts were loosening." He reset the clutch circuit breaker and the clutch light illuminated steadily. The instructor pilot reported, "Immediately afterward the engine and rotor RPM needles split indicating a drive train failure, and a loud metal to metal grinding noise began." The flight crew (instructor and dual student) immediately initiated an autorotation. At the termination of the autorotation, the helicopter yawed to the left and did not respond to right pedal inputs. A post-accident examination revealed a complete failure of the fan shaft. The portion of the engine cooling fan assembly aft of the fracture point had departed the aircraft. This component was subsequently found approximately 1.2 miles south of the forced landing site. In addition, the tail rotor blade pitch push-pull tube was completely severed at the forward rod end. Extensive scraping and gouging was noted on the rod end fitting. The fan shaft, fan wheel and bearing were sent to the NTSB Materials Laboratory for examination. The examination noted the fan shaft was fractured in a "V"shape from a transition in shaft diameter adjacent to the bearing at the aft end, forward to the attachment bolt holes. Fracture surface features were "indicative of fatigue propagation." According to the dual student, on the delivery flight one of the drive v-belts broke and an emergency landing under partial power was made. The helicopter was repaired by Robinson technicians who replaced the drive belts and clutch actuator. A visual inspection of the fan shaft and lower bearing was completed at that time and no discrepancies were found. The fan shaft and bearing were not disassembled. Therefore, the mating surfaces of the fan shaft and bearing race were not inspected.

Quoted verbatim from the NTSB record.