Southwest B733 at El Paso on Jul 27th 2012, unsafe gear

Last Update: August 31, 2019 / 16:48:44 GMT/Zulu time

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Incident Facts

Date of incident
Jul 27, 2012

Classification
Incident

Flight number
WN-1871

Aircraft Registration
N379SW

Aircraft Type
Boeing 737-300

ICAO Type Designator
B733

A Southwest Airlines Boeing 737-300, registration N379SW performing flight WN-1871 from Las Vegas,NV to El Paso,TX (USA) with 71 passengers and 5 crew, was on approach to El Paso's runway 08R when the crew went around due to problems with the landing gear. The aircraft positioned for another approach and landed safely about 10 minutes later.

The NTSB opened an investigation into the incident reporting the nose gear actuator retract beam experienced a structural failure when the gear was extended on the approach to El Paso. The aircraft sustained minor damage.

On Aug 31st 2019 the NTSB released their brief final report concluding the probable causes of the incident were:

the rupture of the nose landing gear hydraulic line that resulted from abrasions due to contact with the nose landing gear tire. Contributing to the incident was the incorrect installation of union and restrictor on the actuator.

The NTSB reported:

The aircraft experienced a structural failure of the nose landing gear (NLG) actuator retract beam when the landing gear was selected down during approach. The flight crew heard a loud noise during gear actuation, performed a go-around, and then returned to land uneventfully. Examination of the aircraft revealed a fracture across the horizontal leg of the actuator retract beam that propagated into the radius of the vertical leg. The fracture surface features were consistent with overstress failure with no sign of fatigue. The NLG hydraulic line to the actuator was found ruptured with abrasion damage aligned coincident with the NLG tire.

Disassembly of the actuator revealed the restrictor fitting was installed in the head end of the actuator and the union fitting was installed on the rod end cap although engineering documentation requires the restrictor fitting to be installed in the rod end cap and the union fitting to be installed in the head end. The union and restrictor are normally placed in the actuator prior to installing the actuator on the airplane.

Hydraulic fluid leaking from the actuator through the ruptured line allowed air to fill the actuator cavity on the head end of the actuator while hydraulic system pressure remained on the rod end. When the landing gear was selected down, air in the actuator allowed the actuator piston to move rapidly toward the head end. Due to the union rather than the restrictor being installed on the piston end, higher than normal hydraulic flow was permitted in the rod end of the actuator increasing the rate of piston movement. When the piston reached the end of range of motion, the resulting force was transferred to the NLG retract actuator beam.
Aircraft Registration Data
Registration mark
N379SW
Country of Registration
United States
Date of Registration
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Manufacturer
BOEING
Aircraft Model / Type
737-3H4
Number of Seats
ICAO Aircraft Type
B733
Year of Manufacture
Serial Number
Aircraft Address / Mode S Code (HEX)
Engine Count
Engine Manufacturer
Engine Model
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Engine Type
Main Owner
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Incident Facts

Date of incident
Jul 27, 2012

Classification
Incident

Flight number
WN-1871

Aircraft Registration
N379SW

Aircraft Type
Boeing 737-300

ICAO Type Designator
B733

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