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What happened

On 20 February 2014 at 1425 EDT, a Fairchild Industries Metro 23 aircraft, registered VH-UUB, was being operated on a charter flight from Avalon to Portland, Victoria with 10 passengers and two crew on board. Shortly after touch-down the torque link on the left, main landing gear (MLG) failed. The aircraft veered left as a result, and came to rest beside the runway. There were no injuries as a result of the occurrence.

What the ATSB found

The runway excursion resulted from failure of the lower torque link attachment lug on the left main landing gear’s yoke. This allowed the wheels to rotate through 90° with respect to the direction of aircraft travel and skid, producing a large braking effect on the left side. The flight crew were unable to counteract this and it resulted in the aircraft veering to the left and off the runway.

The failure of the lug on the yoke resulted from pre-existing cracks that had progressively grown until the part had insufficient strength to support normal landing loads. The cracks initiated principally from areas of pitting corrosion in the lug’s bore and were propagated by cyclic stresses imposed during operation.

The ATSB identified a safety issue whereby the maintenance and inspection program for the aircraft’s landing gear did not adequately provide for the detection of corrosion and cracking in the yoke lug bore.

What has been done as a result

The Civil Aviation Safety Authority (CASA) has released Airworthiness Bulletin AWB 32-023 to alert all Fairchild Swearingen Metro and Merlin operators of the need for detailed inspection of the internal bore of the landing gear torque link lugs for any signs of corrosion or wear outside of the manufacturer’s specified limits and to take appropriate action per the aircraft’s structural repair manual, where necessary.

In addition, the aircraft’s Type Certificate Holder has drafted service bulletins 226-32-083, 227-32-065, CC7-32-030 titled “inspection of Main Landing Yoke for Corrosion and/or Damage” that will significantly increase the effectiveness of maintenance inspections for the affected parts.

Safety message

This occurrence highlights the importance of developing and conducting appropriately detailed maintenance inspections on susceptible parts and assemblies.

UUB after veering off runway

UUB after veering off runway description
Source: airline operator

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Safety issue

AO-2015-028-SI-01 -  

Inadequate inspection procedures

The maintenance program for the aircraft’s landing gear did not adequately provide for the detection of corrosion and cracking in the yoke lug bore.

Safety issue details
Issue number:AO-2015-028-SI-01
Who it affects:All owners and operators of Fairchild Swearingen Metro and Merlin aircraft
Status:Adequately addressed

General details
Date: 20 February 2014 Investigation status: Completed 
Time: 14:45 ESuT Investigation type: Occurrence Investigation 
Location   (show map):Portland Airport Occurrence type:Landing gear/indication 
State: Victoria Occurrence class: Technical 
Release date: 22 March 2016 Occurrence category: Serious Incident 
Report status: Final Highest injury level: None 
Aircraft details
Aircraft manufacturer: Fairchild Industries Inc 
Aircraft model: SA227 
Aircraft registration: VH-UUB 
Serial number: DC-894B 
Type of operation: Charter 
Sector: Turboprop 
Damage to aircraft: Unknown 
Departure point:Avalon, Vic.
Destination:Portland, Vic.
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Last update 11 November 2016