History of Flight
On July 27, 2012, at about 1400 mountain daylight time, Southwest Airlines flight 1871, a Boeing 737-3H4 (registration N379SW), was on approach to El Paso International Airport (KELP), El Paso, Texas. The flight was a regularly scheduled passenger service from Las Vegas McCarran International Airport (KLAS), Las Vegas, Nevada, operating under Title 14 Code of Federal Regulations Part 121. Visual meteorological conditions prevailed.
The captain was the pilot flying, and the first officer was the pilot monitoring. At 1400:37, after receiving clearance for a visual approach to runway 8R, the captain requested landing gear extension. At 1400:40, as the gear extended, two loud snapping sounds were heard; the captain described them as a very loud bang. The flight crew discussed the sound and expressed concern about the nose gear condition. At 1401:17, the first officer requested a fly-by from the tower to inspect the nose gear. The crew conducted a fly-by at 500 feet above ground level. At 1404:32, the tower controller reported the nose gear appeared normal. The crew then entered a right traffic pattern for a visual approach and landed on runway 8R, taxiing to the gate uneventfully. Post-flight inspection revealed a puddle of hydraulic fluid under the nose gear and reduced A hydraulic system quantity.
Injuries to Persons
There were no injuries to the 71 passengers and 5 crewmembers.
Damage to Airplane
The airplane sustained minor damage. The lower T chord of the actuator retract beam was fractured across the horizontal leg and into the radius of the vertical leg, about 16 inches aft of the nose wheel forward bulkhead. The beam comprised four web bays; bay 1 was undamaged, bays 2 and 3 were buckled along 45-degree angles, and the vertical stiffener was cracked. A gap of about 3/8 inch was present between the stiffener and web. The lower T chord was displaced outboard and left by up to 2 inches. All fracture surfaces exhibited overstress features with no evidence of fatigue. The nose landing gear retract actuator hydraulic line was ruptured about 8.5 inches from the forward end, with 3.18 inches of outer spiral wrap missing. Abrasion marks were evident on the corrosion resistant steel braid, with broken strands and a ruptured Teflon inner liner.
Personnel Information
The captain, age 47, held an FAA Airline Transport Pilot certificate with B737 type rating and first-class medical certificate with near-vision glasses limitation. He reported about 15,110 hours total time, including 7,500 hours as pilot-in-command and 9,960 hours on the B-737. The first officer, age 36, held an FAA ATP certificate with multiple type ratings and a first-class medical certificate with no limitations, reporting 9,500 hours total time.
Aircraft Information
The incident airplane, manufacturer serial number 26586, was a Boeing 737-3H4 equipped with two CFM International CFM56-3B2 turbofan engines, delivered in 1994. It had about 59,939 hours total time and 49,780 cycles. The most recent inspection was on November 5, 2011, under the operator's continuous airworthiness maintenance program.
Meteorological Information
The METAR at 1951 indicated wind from 110 degrees at 16 knots gusting to 23 knots, visibility 10 statute miles, few clouds at 5,500 feet, scattered at 10,000 feet, broken layers at 15,000 and 25,000 feet, temperature 29°C, dewpoint 16°C, altimeter 30.09 inches of mercury.
Airport Information
El Paso International Airport is 4 miles northeast of El Paso, Texas, at elevation 3,962 feet. Runway 8R is grooved asphalt, 150 feet wide and 9,028 feet long, with a 4-light precision approach path indicator and runway end identifier lights.
Flight Recorders
The cockpit voice recorder (Allied Signal Model 6022) had 2 hours 5 minutes of good-quality audio. The flight data recorder (same model) contained about 27.2 hours of data; the event flight was the last recording, lasting about 1 hour 37 minutes.
Tests and Research
Examination of the NLG hydraulic hose showed rupture 8.5 inches from the airplane end, with missing spiral wrap and abrasion on the CRES braid. The transfer cylinder had no damage except a broken tag tab; leakage and operational tests found no faults. The retract actuator appeared normal during functional tests; disassembly revealed the restrictor fitting was installed in the head end instead of the rod end cap, contrary to engineering drawings. The hydraulic modular package had no defects. A functional demonstration on a similarly equipped 737-300 showed that the hose could contact the NLG tire when the hose was twisted during installation.
Maintenance Records
The retract actuator support beam was original. The union and restrictor were normally replaced during actuator overhaul. An overhauled actuator was installed on August 18, 2006. There was no required maintenance program for the NLG retract hydraulic hose; it was replaced on condition. Records indicated the hose was removed and reinstalled on October 30, 2008.
Organizational and Management Information
Southwest Airlines Co., based in Dallas, Texas, operated the flight. The company merged with AirTran Holdings in 2011. As of December 31, 2011, the combined fleet included 610 Boeing 737s and 88 Boeing 717s.
Additional Information
Following the event, Southwest Airlines developed a special inspection procedure for the NLG retract actuator hydraulic hose and the union and restrictor installation. Boeing issued an operator publication recommending examination for chafe damage and correct installation, and amended the Component Maintenance Manual.