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16th of June 2012, Metal Fatigue, Blog #656

An ATR 42-320 had departed a Guernsey Airport for a short flight to Jersey-States Airport (both in the Channel Islands) at 07:05 lt (local time) on this day in aviation history. The captain was the Pilot Flying, performing line training of the co-pilot, who was Pilot Monitoring for the flight.

The failed landing gear (Source; ©; Unknown)

The weather was reported good;

  • Wind - 210º at 16 knots

  • Clouds - Few at 2000 feet

  • Visibility - more than 20 kilometres

A visual approach for Runway 27 at Jersey was briefed, with an approach speed of 107 knots with the flaps selected to 30 degrees for landing. After the gear was selected down during the approach all three green "gear down and locked" indications were illuminated.

After a stable approach, the aircraft touched down with a recorded acceleration spike of 3g (significantly higher than normal), with a vertical speed of 3,1 feet per second (slightly higher than normal).

Just after touchdown an abnormal noise was heard and the crew noticed that the aircraft settled in a somewhat abnormal attitude. Reverse (propellor blade) Pitsch was selected. At 70 knots the PM took control of the ailerons (as per standard procedures), allowing the Captain to take control of the (Nose Wheel) steering tiller. Although corrective inputs were given by the copilot, the aircraft continued to roll its left wing down more and more the left wingtip and left propellor struck the runway.

The aircraft remained on the runway, rapidly coming to a halt to the left of the centreline, approximately abeam Holding Point D. Both propellers continued to rotate and the commander selected the condition levers to the fuel shutoff position and pulled the fire handles to shut both engines down. The tower controller, seeing the incident, pressed the crash alarm and airfield emergency services were quickly in attendance.

The aircraft in its final position (Source; © G. Hocquard)

An evacuation of the aircraft was initiated, and all passengers and crew safely vacated the aircraft.

It became obvious that the left-hand landing gear had failed. The Air Accidents Investigation Branch (AAIB) was notified and an investigation was initiated. It was found that the side brace upper arm of the left main landing gear had suffered a structural failure causing the landing gear to fail. Fractured parts of the side brace were recovered from the runway.

Metallurgical analysis of the (aluminium) side brace upper arm revealed a small metallurgical feature at the crack origin which was consistent with titanium-rich particles (TiB2 ) particles which were introduced as a grain refiner during the casting of the billet prior to forging. The size of the feature was within the defined specifications for AL7010-T74. Analysis of the area surrounding the crack origin revealed an area of static loading before propagating a crack in fatigue, indicating that there may have been a single overload event at some point in the history of the side brace upper arm.

The AAIB bulletin (10/2013) on which this blog is based did not contain

a probable cause as recommended by the ICAO. It can be accessed to obtain more detailed information by clicking on the .pdf file below;

16Jun2012 ATR Gear Failure
Download PDF • 1.84MB

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