REX SF34 at Perth on Dec 21st 2022, engine shut down in flight

Last Update: September 12, 2024 / 06:52:29 GMT/Zulu time

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Photo of REX Regional Express VH-RXE, SAAB 340 — REX Regional Express VH-RXE, SAAB 340 (Photo credit: Alec BHX/KKC / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Dec 21, 2022

Classification
Incident

Cause
Engine shut down in flight

Airline
REX Regional Express

Flight number
ZL-2133

Departure
Perth, Australia

Destination
Albany, Australia

Aircraft Registration
VH-RXE

Aircraft Type
SAAB 340

ICAO Type Designator
SF34

A REX Regional Express Saab 340B, registration VH-RXE performing flight ZL-2133 from Perth,WA to Albany,WA (Australia), was climbing through about FL150 out of Perth when the right hand engine (CT7) failed and was shut down. The aircraft returned to Perth for a safe landing on runway 21 about one hour after departure.

Australia's ATSB reported they opened an investigation into the occurrence rated an incident.

On Sep 12th 2024 the ATSB released their final report concluding the probable causes of the incident were:

Contributing factors

- An incorrectly seated and misaligned hydro-mechanical unit resulted in significant wear of the hydro-mechanical unit drive shaft and accessory gearbox internal shouldered shaft. This resulted in the hydro-mechanical unit slipping and decoupling from the engine accessory gearbox.

- The slipping and decoupling of the hydro-mechanical unit drive shaft from the engine accessory gearbox resulted in a loss of fuel pump function and metered fuel output, leading to a failure of the engine.

The ATSB summarized the sequence of events:

On 21 December 2022, at 2108 local time, a Regional Express Saab 340B aircraft departed Perth Airport, Western Australia, for a passenger transport flight to Albany, Western Australia. The flight crew climbed the aircraft to a cruising level of 15,000 feet. Shortly after leveling off, the captain felt 2 bumps pass through the airframe prior to the aircraft noticeably yawing. The flight crew identified a right engine failure, conducted the associated checklists, and secured the right engine. The aircraft was returned to Perth Airport and landed without further incident.

The ATSB analysed:

On 21 December 2022, at 2108 local time, a Regional Express Saab 340B departed Perth Airport, Western Australia, for a passenger transport flight to Albany, Western Australia. During cruise the right engine failed, and the aircraft was returned to Perth.

Post-occurrence troubleshooting, component testing, examination and analysis were conducted on the right engine. Wear and deformation were identified on the splines of the HMU drive shaft and the internal splines of the AGB shouldered shaft.

Significantly, the polished O-ring land on the HMU drive shaft and the corresponding circumferential wear marks within the AGB shouldered shaft indicated that the drive shaft had decoupled and was spinning within the shouldered shaft during operation. Damage identified on the HMU drive shaft splines, along with corresponding wear and damage to the AGB shouldered shaft receptacle also indicated that rotation had occurred between the 2 shafts. Additionally, the measured minimum internal diameter between the splines of the AGB shouldered shaft receptacle was larger than the maximum HMU spline diameter, indicating a physical impossibility of the AGB to drive the HMU.

When the HMU was functionally tested, no faults were detected with the HMU and the high-pressure fuel pump. The most likely reason for serviceable operation during testing was that the HMU drive shaft was being driven by the shouldered shaft of the test stand and not the worn shouldered shaft within the engine’s AGB.

Wear marks from the AGB flange were observed on the inner surface of the V-band coupling. These wear marks were located on an area of the coupling that, when the flanges of the HMU and AGB are correctly aligned and the coupling is aligned correctly prior to and during torquing, an apex gap is maintained between the flanges and the inner surface of the V-band coupling. The presence of interference wear marks on the inner surface of the V-band coupling demonstrated that the flanges, or the V-band coupling, were misaligned during installation.

Also noted during the post-occurrence inspections was damage to the threads on the fuel line that connected to the HMU. This line was connected as part of the HMU installation and the presence of damage to the threads was a possible further sign of the fuel line being connected to a misaligned HMU.

This misalignment of the HMU, taking into consideration that the HMU drive shaft was not bent, likely translated to an uneven loading of the splines of the HMU drive shaft and the AGB shouldered shaft receptacle during operation. This in turn probably caused wear, damage, and subsequent decoupling of the HMU drive shaft during operation.

The ATSB released following safety message:

The incorrect alignment or incorrect seating of an aircraft or engine component may not be readily apparent after the installation of a V-band coupling or clamp. Personnel installing V-band couplings are reminded to ensure the correct seating and alignment of flanges and the V-band coupling prior to the fitment and torquing of attaching hardware. The incorrect alignment of a component may induce a fault and subsequent failure of a critical component after an extended period of operation.