Investigation brief · generated 2026-10-09 · source: NTSB public docket and accident database
BOEING 737-3H4 — El Paso, TX, USA, 2012-07-27
NTSB number
DCA12IA113
Operator
SOUTHWEST AIRLINES CO
Registration
N379SW
Highest injury
No injury
Regulation
Part 121
Damage
Minor
Cohort
Part 121 airline
Recorder data
Tier 1 — decoded recorder tables
Every sentence below is taken directly from NTSB records — the accident database, the docket's recorder reports and the Board's findings — with its source noted. Nothing is paraphrased or inferred.
NTSB summary
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.
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.
Verbatim, NTSB determination.
Sequence of events (FDR factual report)
Time
Event
Page
about 12:41 MDT
Aircraft departed and climbed to flight level 370
3
about 13:35 MDT
Descent for El Paso began
3
14:00:39-14:00:45 MDT
At 7,836 ft pressure altitude the landing gear transitioned from up and locked to down and locked (gear lock parameters sampled only once every 4 seconds); coincident with the last sample of nose gear up and locked, the master caution sampled one warning at 14:00:39
3
after 14:00:45 MDT
Aircraft descended to about 4,240 ft pressure altitude (about 600 ft radio altitude) heading east
3
about 14:04:47 MDT
Aircraft began a climb to about 4,900 ft pressure altitude while turning right
3
about 14:07:15 MDT
Aircraft began to descend while turning right back toward an easterly heading
3
about 14:08:33 MDT
Vertical acceleration fluctuated between 1.24 g and 0.79 g in under one second
3
14:08:41 MDT
Nose gear weight-on-wheels transitioned from air to ground, about 8 seconds after the acceleration fluctuation
3
Extracted by claude-fable-5-1 (in-session); 0 of 1 stated events verified against the raw recorder data.