History of Flight
On February 25, 2008, at 2116 mountain standard time, United Airlines flight 267, an Airbus A-320 (N442UA), departed the right side of runway 19 during landing at Jackson Hole Airport (JAC), Jackson, Wyoming. The 119 passengers and 6 crew members evacuated via emergency slides. One passenger received minor injuries during the evacuation; the airplane was not substantially damaged. The flight operated under 14 CFR Part 121 as a scheduled domestic passenger flight from Denver International Airport (DEN). Visual meteorological conditions prevailed during the nighttime landing.
The crew reported that takeoff, climb, cruise, and descent to JAC were normal. The captain was the flying pilot. After descending through a high overcast ceiling at about 12,000 feet, the airplane was in clear conditions.
The captain stated that prior to the night visual approach, he performed an approach briefing. He noted that Mu readings indicated "good" braking and that if the airplane did not touchdown in the first 2,000 feet of runway, they would go around. Weather at the time was calm wind, 1 mile visibility, and no precipitation. Both crew discussed landing distance numbers. The captain could see the airport from about 15 miles away and configured the airplane early with full flaps and autobrakes set to "medium."
The captain stated that touchdown was "firm" and speedbrakes auto-deployed quickly; he believed the airplane touched down in the first 2,000 feet. Deceleration was normal until about 80 knots and 2,000 feet from the runway end, when the airplane started to slide. He applied maximum manual braking, and the airplane slid to the right. He applied maximum left rudder, maximum braking, and reverse thrust as the airplane exited the right side of the runway end. The airplane came to rest against snow banks. The first officer said the engines "flamed out" when they ingested snow. As the flight crew shut off fuel levers, they heard a passenger yell "fire" and passengers began a self-initiated evacuation.
Personnel Information
The captain held an airline transport pilot certificate with multi-engine land, commercial single-engine land, flight engineer, and airframe and powerplant mechanic certificates, plus a CFI with single, multi, and instrument ratings. He was type-rated in the Airbus A-320 and Boeing 737, 757, 767. He had about 10,000 total hours, including 2,414 in the A-320. His most recent FAA first-class medical was issued September 24, 2007, and his last proficiency check was January 2007.
The first officer held an airline transport pilot certificate with multi-engine land and commercial single-engine land and rotorcraft privileges, with type ratings in the A-320 and Boeing 757/767. He had about 10,000 total hours, including 2,072 in the A-320. His most recent FAA first-class medical was March 28, 2007, and his last proficiency check was August 2007.
At the time, the crew had been on duty about 13 hours 30 minutes; the first officer noted their maximum allowed duty day was 14 hours.
Runway Documentation
Jackson Hole Airport has one asphalt runway (1/19), 6,300 feet long by 150 feet wide.
Examination revealed rubber transfer marks leading to disturbed snow on the right side of the runway. The longest mark began about 576 feet from the departure threshold of runway 19 and 67 feet from the left edge, arcing right. It was light for 55 feet, heavy for 76 feet, then light for 332 feet, stopping about 111 feet from the threshold and 17 feet 4 inches from the right edge. The heavy mark crossed the centerline at about 31 degrees. A second set of light marks began about 389 feet from the threshold and 39 feet from the right edge, parallel and separated by 40 inches, ending at disturbed snow. At the runway edge, three sets of parallel tracks through snow matched the landing gear. The center of the right main landing gear (RMLG) tracks was 149 feet from the threshold, nose landing gear (NLG) tracks 99 feet, and left main landing gear (LMLG) tracks 36 feet. Perpendicular distances between tracks were 13 feet 9 inches (LMLG to NLG) and 10 feet 3 inches (RMLG to NLG).
The airplane came to rest in snow on the right side of the overrun. RMLG and NLG tires left distinct impressions; LMLG outboard tire left a distinct impression while inboard left only a light impression. The center of RMLG was 140 feet from extended centerline, LMLG 137 feet 4 inches, and NLG 42 feet 2 inches forward of a line connecting both MLG centers. Distance between RMLG and LMLG was 28 feet. A point midway between MLG was 116 feet beyond the threshold.
Runway friction measurements taken before and after the incident using a SARSYS Saab Friction Tester: at 20:43 MST on 2/25, readings were 0.45, 0.46, 0.51; at 21:38 MST, readings were 0.62, 0.64, 0.69.
According to the airport's director of operations, it had snowed earlier but stopped before the incident. The runway was swept prior to arrival. Patchy, thin packed snow and ice (less than 1/8 inch) was on the runway, mostly along edges, covering not more than 25%.
Aircraft Documentation
Leading edge slats and trailing edge flaps were extended. Spoilers 3 and 4 on each wing were extended. Both engine thrust reversers were deployed. Snow was packed in both engines from fan area through thrust reversers and in aft fan air ducts; a frozen pool of water was in the left engine tail pipe.
Snow and ice were packed around all landing gear and into wheel wells. The LMLG inboard tire had a large flat spot with a rupture through the aft end from sidewall to sidewall. The outboard tire was intact with minor abrasions. RMLG tires were intact with minor abrasions and small cuts. No other obvious landing gear damage.
Anti-Skid System
Power was applied to check status messages on the Multipurpose Control Display Unit (MCDU). The maintenance post-flight printout showed no failure messages around the incident time. The Brake Steering and Control Unit (BSCU) last leg report showed no relevant faults. Both BSCUs tested with no failures.
Wheel tachometers were pulled from axles without removing wiring. Examination revealed the wires were cross-connected on the LMLG. Testing per the AMM confirmed the cross-connection. After correct installation, the system operated normally.
Maintenance Records
N442UA was purchased new by United Air Lines from Airbus on February 26, 1998. It had accumulated 34,587 flight hours and 13,631 cycles at the incident. No open Minimum Equipment List (MEL) or deferred items were in the logbook.
Main Landing Gear (MLG)
Both MLG and nose landing gear were replaced on February 2, 2008, due to approaching overhaul time limits. The left-hand main landing gear was an "enhanced" type; the right-hand was standard or "pre-enhanced." According to Airbus, Service Bulletin for retrofit required replacement as a set; a "mixed" configuration required case-by-case approval. United was unaware of the mixed configuration, and no records indicated a request for mixed gear.
Overhaul of MLG
United contracted Hawker Pacific Aerospace to overhaul A320/A319 landing gears. All work used United's joint documents and Messier-Dowty Component Maintenance Manuals. Wiring harnesses were overhauled and installed into overhauled gear components. Hawker Pacific shipped the gear to United.
During installation, United personnel installed tachometers to the overhauled gear before installation on the airplane. The Maintenance Manual and task cards were not clear on correct tachometer position. The mechanic who installed all four tachometers had never installed one before but was guided by a more experienced coworker. He reported no issues.
Removal and installation of landing gears required a full check of landing gear systems. Records showed all tasks were accomplished and signed off; a functional test of tachometers was done with no discrepancies. Maintenance personnel noted that the functional spin-up test could be complex and confusing.
After the incident, United performed a functional check of tachometers on three airplanes that had undergone gear changes between October 2007 and February 2008. No discrepancies were found.
Subsequent to the incident, United made numerous modifications to their maintenance program regarding MLG wheel speed transducers, including changes to FOQA monitoring, receiving inspection, installation, inspection, and functional test procedures.
Previous Event
On October 9, 2007, about 2030 central daylight time, United Airlines flight 628, an Airbus A320-232 (N431UA), received minor damage when it exited runway 22R and impacted runway lighting while landing at O'Hare International Airport. Of 125 passengers and crew, one flight attendant and one passenger reported minor injuries. The flight was operating under 14 CFR Part 121 from Seattle-Tacoma to Chicago. During that investigation, it was determined that the tachometer functional test was overlooked during the accomplishment of an Airworthiness Directive at a contract maintenance facility.