November 01, 2012
The airport at Jackson Hole, Wyo., is both beautiful and challenging. JAC sits on a small plain at an elevation of 6,451 ft., some 7 mi. north of Jackson. The airport, which is surrounded by the Rocky Mountains and is in a noise-sensitive area, has one asphalt runway (1/19) that is 6,300 ft. long, 150 ft. wide and features a 0.6% gradient with the Runway 19 threshold on the high end. A four-light PAPI generates a 3-deg. glidepath for visual guidance into Runway 19.
The published approach plate remarks includes this cautionary note: “Aircraft that fail to touch down within the first third of Runway 01/19 sometimes fail to stop on the runway and are at risk for a runway excursion.” In fact, there were 20 runway excursions at JAC from 2007-2010 — half by air carriers, half by general aviation aircraft. Advisory Circulars and SAFOs have been issued for operators to help them avoid such unhappy arrivals.
This month we'll look at a Dec. 29, 2010, incident involving an American Airlines Boeing 757-200 that ran off the departure end of Runway 19, coming to a stop in deep snow some 730 ft. beyond the runway's end. None of the 179 passengers or six crewmembers were injured and the airplane sustained only minor damage.
This accident is worth reviewing not so much because someone erred, but rather because it points out that multiple system failures can occur when least expected — a timely reminder as we begin to depend on the protections usually offered by automated systems in modern transports. What follows is primarily from the NTSB report on the incident.
The pilots operating American Flight 2253 were well experienced both in type and in JAC operations. The captain had logged 19,645 hr. flight time, 10,779 of them in the 757. He had also logged 300 to 400 trips into JAC. The first officer had accumulated about 11,800 hr. of total flight time, including 3,582 hr. in the 757. He had flown into JAC frequently including four times with the captain during the month of the accident. Investigators found no evidence of fatigue or medical/behavioral conditions that might have adversely affected the pilots' performance.
The en route phases of the flight had been routine and the crew had checked conditions for JAC several times at they approached the destination. IMC prevailed. The first officer was the pilot flying (PF) and the captain was the pilot monitoring (PM). Both pilots later told investigators that they were familiar with the challenging landing conditions that could exist at JAC in the winter (for example, slippery runway conditions and relatively high landing weights, which were common during the ski season). As a result, they said they were especially vigilant and began preparing for the approach and landing at JAC early during what they described as an uneventful flight from Chicago O'Hare International. These guys were on their game.
American's Boeing 757/767 Performance Manual requires pilots to confirm landing performance limits just before landing, using the actual runway conditions at the time. If the runway braking action is determined to be less than good, pilots “must use the most adverse reliable and appropriate braking action report or the most adverse expected conditions for the runway, or portion of the runway, that will be used for landing when assessing the required landing distance.” The crew of Flight 2253 gathered the most current information about the JAC weather and runway conditions, including wind, MU runway friction values and pilot braking action reports.
The pilot of a corporate jet that landed on Runway 19 about 1 hr. before the incident airplane reported “poor” braking action on the last one-third of the runway, but “good” braking action on the first two-thirds of the runway. The American crew obtained the most current MU friction values for the runway when the flight was 18 min. out. The values were 0.43, 0.43 and 0.39 for the first, second and third sections of the runway, respectively. The pilots also reviewed information about potential delays and/or alternate airports for various circumstances. In addition, they specifically discussed the airplane's performance at high-density altitude airports.