A BO 105 helicopter which had returned to land after the pilot detected abnormal airframe vibrations was found to have a crack in a main rotor blade, an Australian Transport Safety Bureau report details.
On 18 August 2021, the Surf Life Saving Queensland-operated helicopter took off from Archerfield with three crew on board.
During initial climb through about 40 kt, the pilot noticed the onset of abnormal airframe vibration. This worsened through 60 kt, with the pilot likening it to a significant rotor track-and-balance issue.
The pilot reduced power, levelled off at about 500 ft, and returned to Archerfield for an uneventful landing.
A post-flight inspection identified a crack in one of the main rotor blades, about 1,700 mm from the blade root.
The ATSB investigation determined the crack was consistent with the in-flight vibrations reported by the pilot. Minor damage was also present in the same location on the other three rotor blades.
The cracked blade was subsequently shipped to the manufacturer, Airbus Helicopters Deutschland, where it was examined in 2022, under the supervision of the German Federal Bureau of Aircraft Accident Investigation (BFU) on behalf of the ATSB.
The examination found that the crack on the underside of the blade went through the middle of a previous repair, which had been conducted in accordance with the applicable blade repair instruction, and there were no anomalies noted.
No specific reason for the blade cracking was identified, although it was noted that cracks at repair sites were not unusual. It was also determined that the cracked blade, in its post-occurrence condition, was within repair limits.
“This occurrence is a reminder to pilots of the importance of remaining vigilant for changes in aircraft noise and vibration,” ATSB Director Transport Safety Dr Stuart Godley said.
The report notes that mild vibration had been observed towards the end of the flight previous to the incident flight.
“While the threshold for acknowledgement of changes can be subjective, based on an individual’s familiarity and experience, mild deviations from normal flight conditions could still be an indication of a developing technical issue,” Dr Godley concluded.
Read the report: Main rotor blade cracking involving Airbus Helicopters Deutschland BO105 CBS-5, VH-NVH, near Archerfield Aerodrome, Queensland, on 18 August 2021