Jetstar A320 at Sydney on Aug 1st 2019, landing gear trouble after departure

Last Update: March 9, 2022 / 20:03:41 GMT/Zulu time

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Incident Facts

Date of incident
Aug 1, 2019

Classification
Incident

Flight number
JQ-420

Aircraft Registration
VH-VFN

Aircraft Type
Airbus A320

ICAO Type Designator
A320

A Jetstar Airbus A320-200, registration VH-VFN performing flight JQ-420 from Sydney,NS to Coolangatta,QL (Australia), departed Sydney's runway 34L and was climbing out when the crew stopped the climb at 4000 feet due to a problem with the landing gear, metallic debris (unclear which parts of the departing aircraft) was found on the runway prompting all approaches to runway 34L swing over to runway 34R. The occurrence aircraft returned to Sydney for a safe landing on runway 34L about 30 minutes after departure.

Emergency services the metallic debris looked like a "locking pin".

The airline reported the aircraft was unable to retract the landing gear.

A replacement A320-200 registration VH-VQL reached Coolangatta with a delay of 3:45 hours.

On Aug 5th 2019 the ATSB reported the left main gear torque damper pin sheared, the gear could not be retracted. The pin was found on the runway. After return to Sydney a post flight inspection revealed three hydraulic lines were damaged. The occurrence was rated an incident, a short investigation estimated to conclude in 4th quarter 2019 has been opened.

On Mar 8th 2022 the ATSB released their final report concluding the probable causes of the incident were:

Contributing factors

- During the manufacture of the apex pin, the initial machined profile led to unintended stress concentrations at the quench stage of the material heat treatment process that resulted in the part cracking. The crack was not removed by the final machining process. (Safety issue)

- Despite apex pins being subject to magnetic particle non-destructive inspections during manufacture, for reasons that could not be identified, this inspection did not detect the crack that was present in the occurrence pin.

- The head of the apex pin failed due to cyclic structural fatigue, which led to disconnection of the left main landing gear (MLG) torque link. This left the MLG strut free to rotate out of fore/aft alignment.

Other factors that increased risk

- The MLG brakes failed due to the strut rotating and a wheel contacting and fraying a hydraulic hose. This most likely occurred during take-off.

- Despite the failed part and aircraft being positively identified by elements within Jetstar, a message was unable to be conveyed to the flight crew who returned for landing unaware of the true nature of the undercarriage defect and the associated risks. The additional information would have improved crew decision making.

Other findings

- The undercarriage failed to fully retract by not engaging the gear uplocks and not permitting the gear doors to fully close. This was likely due to the wheels and axle being out of alignment.

- The torque link disconnect, the consequential landing gear misalignment and brake failure had the potential to reduce directional control and braking performance on touchdown. However, the degradation was manageable and the aircraft landed safely.

- The failed apex pin was temporarily reinstalled by engineers to enable the towing of the aircraft off the taxiway and back to a gate for disembarkation. This had the potential to damage evidence on the fracture surface. At that time, the pin shank was the only piece of evidence available to understand the failure mechanism as the pin head had not yet been located.

The ATSB analysed:

Apex pin manufacturing

The apex pins were manufactured by initially machining an oversize profile, which was then heat treated and finally machined to size including a large relief radius under the pin head. The identification of temper scale on the crack face from the heat treatment was conclusive evidence that the crack found on the occurrence pin (and several others) was induced as part of the quenching process. The initiated cracks were large enough they were not completely removed by the subsequent machining process.

While it was established that the radius of the initial machining under the head was too small to prevent heat-related cracking, most pins did not crack. It was concluded that another factor, or factors, were required, in combination with the size of the radius, to initiate a flaw. These factors included variations in cutting tool sharpness, undercut surface roughness and/or the quenching bath temperature, even though these features may have been within prescribed tolerances.

Manufacturing inspection

The manufacturer’s investigation of the post-manufacturing inspections focused only on the initial batch of 12 pins, two of which had failed in service and five pins were subsequently found cracked. The review of the human factors and organisational elements of the company at the time could not determine why these cracks were not found in this batch during the routine non-destructive testing (NDT) magnetic particle inspection (MPI).

Before the manufacturer’s investigation was completed, and as a result of the airworthiness directive, 15 pins were found cracked from adjacent batches and four pins found cracked from other batches. These additional pins indicate it was unlikely cracking in pins at manufacture was a one-off event. The identification of cracks in 2014 that resulted in a manufacturing change also indicates that it was possible for cracks to be identified at manufacture.

Torque link disconnect

Following initiation of a crack during manufacture, the head of the apex pin fractured from the shank due to cyclic fatigue. The exact time of this event could not be determined. This left the apex pin shank free to migrate from the MLG upper and lower torque links thereby allowing them to disconnect just after pushback from the gate. The apex pin shank was shed onto the taxiway approximately 250 m from the pushback position.

The consequence of the torque link disconnection during the taxi and take-off was the misalignment of the MLG. During the flight the MLG was retracted twice. In both cases, either the MLG failed to lock in the retracted position or the MLG did retract successfully but the aircraft failed to sense this, i.e. sensor failure. Given the potential for misalignment without the apex pin, incomplete retraction of the MLG was considered the most likely reason. That conclusion is reinforced by the Captain’s comment regarding the unusual airflow noise. Damage to other systems including the brake lines on the MLG was further evidence the wheel set rotated out of alignment, contacting the upper torque link and adjacent equipment.

Risk analysis conducted after the incident regarding the loss of brakes on one wheel set concluded that an aircraft would remain directionally controllable at high speed due to the effectiveness of the fin and rudder, and at low speed with the nose wheel steering. The braking distances were determined to have increased by approximately 10-15 per cent.

While the disconnected torque link reduced the directional stability and braking performance due to the misaligned axle and failed left brake set, the degradation was manageable and the aircraft landed safely. The use of runway 25 would have been acceptable, however the crew’s choice to request and use the longer runway 34L was prudent.

...

Failed apex pin temporarily reinstalled

Due to unavailability of spares, Jetstar temporarily reinstalled the failed apex pin shank into the torque link. This action was to enable safe towing of the aircraft to the maintenance hangar however, it had the potential to damage evidence on the fracture surface. At that time, the apex pin shank was the only piece of evidence available. Ultimately, the apex pin head was located, and analysis of both fracture surfaces determined the failure mechanism.

Notwithstanding unavoidable situations, where possible, preservation of evidence is vital in determining the circumstances of an occurrence and identifying safety issues that may present a hazard to continued operations.
Aircraft Registration Data
Registration mark
VH-VFN
Country of Registration
Australia
Date of Registration
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Airworthyness Category
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TCDS Ident. No.
Manufacturer
AIRBUS INDUSTRIE
Aircraft Model / Type
A320-232
ICAO Aircraft Type
A320
Year of Manufacture
Serial Number
Maximum Take off Mass (MTOM) [kg]
Engine Count
Engine
Cligfimmnhdfgjcllckdpchlp ckph qjgjcqnmiAgb Subscribe to unlock
Main Owner
Alpmebgdhinncej fgpjel fA g iljgb eflilcigqnidqgceggb bbmdhkiekhgggpmfifcgleepA jpgkhckf p lAqepmli bdmAdqcib pepncepekkbgf Subscribe to unlock
Main Operator
Jmppbphjqf nhqiehiffgffkpnAhlg e lefhdb fAiq fdhhpjmlgkee qAqmqnikmqfAinqfcfmf hAphcheAcfApbne Subscribe to unlock
Incident Facts

Date of incident
Aug 1, 2019

Classification
Incident

Flight number
JQ-420

Aircraft Registration
VH-VFN

Aircraft Type
Airbus A320

ICAO Type Designator
A320

This article is published under license from Avherald.com. © of text by Avherald.com.
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