The right engine of a Saab 340 flamed out shortly after the aircraft reached cruising altitude, after the engine’s hydro-mechanical unit driveshaft decoupled from the accessory gearbox due to an incorrectly seated coupling, leading to a fuel pump failure, an ATSB investigation report details.
The aircraft, with 2 flight crew, 1 cabin crew and 32 passengers on board, was operating a scheduled Regional Express service from Perth to Albany, WA, on the evening of 21 December 2022.
After climbing to 15,000 ft and establishing a direct track to Albany, the flight crew felt 2 bumps pass through the airframe, and felt the aircraft yaw.
Identifying that the right engine had failed, they conducted the associated checklists, secured the right engine, and returned to Perth where the aircraft landed without further incident.
“The ATSB’s investigation found that the right engine’s hydro-mechanical unit was incorrectly seated, resulting in a misalignment with the engine’s accessory gearbox, leading to significant wear and the eventual decoupling of the hydro‑mechanical unit’s drive shaft from the accessory gearbox,” ATSB Director Transport Safety Stuart Macleod explained.
“As a result, the fuel pump within the hydro-mechanical unit could not function, leading to the engine flameout.”
The engine, a GE Aerospace CT7, was removed from the aircraft for inspection at an authorised CT7 maintenance facility.
“While this inspection put the ATSB investigation on hold for an extended period, it did reveal that the V-band coupling securing the flanges of the hydro-mechanical unit to the accessory gearbox had wear on its inner surface from contact with the accessory gearbox flange,” Mr Macleod noted.
“Interference wear in this area was evidence of a misalignment and non-seating of the hydro‑mechanical unit onto the accessory gearbox.”
Maintenance records showed that the last recorded maintenance that required installation of the hydro-mechanical unit onto the accessory gearbox was during an engine workshop visit at a contractor maintenance facility in February 2018.
“This incident highlights that the incorrect alignment or seating of an aircraft or engine component may not be readily apparent after the installation of a V-band coupling or clamp,” Mr Macleod said.
“As such it serves as a reminder to maintenance personnel installing V-band couplings to ensure the correct seating and alignment of flanges and the V-band coupling prior to the fitment and torquing of attaching hardware.”
Regional Express has since commenced a fleetwide inspection of its Saab aircraft to confirm the correct fitment of the V-band coupling, while GE Aerospace intends to share the learnings of this occurrence with its customers and maintenance facilities.
