This page intentionally left blank. HUMANFACTORS une 1, 1999 — American far beneath the airplane as the captain ly completed U.S. National Aeronautics Airlines Flight 1420 was seconds nosed Southwest Airlines Flight 1455 and Space Administration (NASA) study from landing at Little Rock, Arkan- down at a steep angle to try to land near of these and 17 other recent accidents sas, U.S., when the captain’s view of the beginning of the 6,032-ft (1,840- gives a different perspective on pilot error, Jthe runway was obscured by heavy rain m) strip. Air traffic control (ATC) had and this perspective holds keys to making lashing the windshield. “I can’t see it,” he brought the Boeing 737-300 in high flights safer in the future.3 said, but the runway quickly reappeared. and fast, and there was a shearing tail- Our analysis suggests that almost From 200 ft to the ground, he struggled wind aloft. As the captain looked at the all experienced pilots operating in the against the thunderstorm’s crosswinds situation on final approach, he thought same environment in which the accident to align the McDonnell Douglas MD-82 he could make it; in quick succession, crews were operating, and knowing only with the centerline, and the ground- he called for gear and flaps to try to what the accident crews knew at each proximity warning system (GPWS) slow the 737. The first officer could moment of the flight, would be vulner- produced two warnings of excessive see that the airplane was exceeding the able to making similar decisions and sink rate. The first officer thought about limits for a stabilized approach. How- errors. Our study draws upon growing telling the captain to go around, but if he ever, he said nothing because he could scientific understanding of how the spoke, his voice was too soft to be heard. see that the captain was doing all he skilled performance of experts, such as Saturated with high workload during the could to correct it. The jet landed near airline pilots, is driven by the interaction last stages of the approach, the crew had the normal touchdown point — but of moment-to-moment task demands, forgotten to arm the jet’s ground spoilers at 182 kt, the airspeed was more than the availability of information and the pressingBY BENJAMIN A. BERMAN anD R. KEY DISMUKES, PH.D. approach for automatic deployment and had not 40 kt faster than the computed target social/organizational factors with the completed the last steps of the landing speed. The pilots were unable to stop inherent characteristics and limitations checklist, which included verification the airplane, and it crashed through of human cognitive processes. Whether of the spoilers; consequently, braking a blast fence at the end of the runway, a particular crew in a given situation performance was greatly degraded. crossed a street and came to a stop near makes errors depends as much, or more, During the landing rollout, the airplane a service station. Two passengers were on this somewhat random interaction veered left and right by as much as 16 seriously injured, and the airplane was of factors as it does on the individual degrees before departing the left side substantially damaged.2 characteristics of the pilots. of the runway at high speed. The crash Flights 1420 and 1455 came to grief, into the approach light stanchions at the in part, because of two of the most far end of Runway 04R destroyed the Why did these experienced common themes in the 19 accidents airplane and killed 11 people, including professional pilots make these errors? studied: plan continuation bias — a the captain.1 The U.S. National Transportation Safety deep-rooted tendency of individuals to Board (NTSB) concluded that the crews continue their original plan of action caused both accidents. It’s true that the even when changing circumstances arch 5, 2000 — pilots’ actions and errors led to the ac- require a new plan — and snowball- Runway 08 at Burbank, cidents — and that in the final moments ing workload — workload that builds California, U.S., would have they were in a position to prevent the on itself and increases at an accelerat- Mappeared very short and very crashes but did not. However, our recent- ing rate. Although other factors not 28 | FLIGHT SAFETY FOUNDATION | AVIATIONSAFETYWORLD | DECEMBER 2006 HUMANFACTORS © Scroggins Aviation/Jetphotos.net A NASA study of 19 recent accidents yields a new the perspective on pilot error. pressing approach © Joe Pries–ATR Team/Airliners.net © Joe Pries–ATR www.FLIGHTSAFETY.ORG | AVIATIONSAFETYWORLD | DECEMBER 2006 | 29 HUMANFACTORS discussed here played roles in these on-board weather radar to identify a ibility. In hindsight, assembling all the accidents, the problems encountered thunderstorm cell northwest of the field. cues that were available to the crew, one by the crews seem to have centered on At that point, the crew had no way of can readily infer that the thunderstorm these two themes. knowing whether they could land before had arrived at the airport. Yet the crew the thunderstorm arrived. of Flight 1420 persevered, accepting a Plan Continuation Bias Later, as Flight 1420 continued its change of runways to better accommo- The pilots of Flight 1420 were aware from approach, the pilots received a series date the winds, attempting a close-in vi- the outset that thunderstorms could affect of ATC radio transmissions suggesting sual approach to expedite their arrival, their approach to Little Rock. Before be- that the thunderstorm was beginning and then, as conditions continued to ginning the approach, they saw lightning to affect the airport: reports of shifting deteriorate, changing to an instrument and rain near the airport, and they used winds, gusts, heavy rain and low vis- landing system (ILS) approach and Radar Data and Partial Air Traffic Communication Southwest Airlines Flight 1455, March 5, 2000, Burbank, California, U.S. 9,000 18:03:33 SOCAL: SW 1455, turn left heading 190, vector to final, descend and maintain 6,000. 8,000 18:04:05 SOCAL: SW 1455, maintain 230 or greater until advised. 7,000 6,000 18:05:10 SOCAL: SW 1455, turn left heading 160. 18:05:56 SOCAL: SW 1455, descend and maintain 5,000. If you’d like the visual, you will be following company. Right now they’re your 1 o’clock and 12 miles, turning onto the final out of 4,600. 18:07:45 SOCAL: SW 1455, descend and maintain 3,000. Company’s over Van Nuys now at 3,000. 5,000 18:08:21 SOCAL: SW 1455, cross Van Nuys at or above 3,000. Cleared visual approach Runway 8. Altitude (ft)Altitude 4,000 3,000 18:09:53 Tower: SW 1455, wind 210 at 6, Runway 8, cleared to land. 2,000 1,000 BUDDE OM & Van Nuys VOR/DME VINEE MM 0 10 8 6 4 2 0 2 Distance From Runway Threshold (nm) MM = Middle marker OM = Outer marker SOCAL = Southern California Approach Control Source: U.S. National Transportation Safety Board Figure 1 30 | FLIGHT SAFETY FOUNDATION | AVIATIONSAFETYWORLD | DECEMBER 2006 HUMANFACTORS pressing that approach to a landing instead of ingly similar to Flights 1420 and 1455.5,6,7 executing a missed approach. Our study suggests that, when standard op- Similarly, the pilots of Flight 1455 tried to cope erating procedures are phrased not as require- in a situation in which their airplane was obviously ments but as strong suggestions that may appear high and fast, and they continued their approach to tacitly approve of bending the rules, pilots despite numerous cues that landing safely would may — perhaps without realizing it — place too be challenging (Figure 1). For example, 1,000 ft much importance on schedule and cost when above touchdown elevation, where company op- making safety/schedule/cost tradeoffs. Also, erating procedures specified that flights should be pilots may not fully understand why guidance stabilized, this flight was unstabilized, far above the should be conservative; that is, they may not glide path, more than 50 kt too fast and descend- recognize that the cognitive demands of recov- ing at more than three times the desired rate; flaps ering an airplane from an unstabilized approach were at the approach setting because of excessive severely impair their ability to assess whether airspeed, and idle thrust was set. Below 1,000 ft, the approach will work out. For all these rea- the GPWS repeatedly annunciated “SINK RATE” sons, many pilots, not just the few who have and “PULL UP,” and the approach remained highly accidents, may deviate from procedures that unstabilized through touchdown. the industry has set up to build extra safety into Too often, pressing an approach in these cir- flight operations. Most of the time, the result of cumstances is attributed to complacency or an these deviations is a successful landing, which intentional deviation from standards, but these further reinforces deviant norms. terms are labels, not explanations. To under- Our study suggests that as pilots amass expe- stand why experienced pilots sometimes con- rience in successfully deviating from procedures, Many pilots, not tinue ill-advised approaches, we must examine they unconsciously recalibrate their assessment the insidious nature of plan continuation bias. of risk toward taking greater chances. This just the few who Plan continuation bias appears to underlie recalibration is abetted by a general tendency of have accidents, what pilots call “press-on-itis,” which a Flight individuals to risk a severe negative outcome of Safety Foundation task force found to be in- very low probability — such as the very small risk may deviate from volved in 42 percent of accidents and incidents of an accident — to avoid the certainty of a much they reviewed.4 Similarly, this bias was apparent less serious negative outcome — such as the procedures that in at least nine of the 19 accidents in our study.