Performance Data Errors in Air Carrier Operations: Causes and Countermeasures (7/31/2012)

 Several airline accidents have occurred in recent years as the result of erroneous weight or performance data used to calculate V-speeds, flap/trim settings, required runway lengths, and/or required climb gradients. Only one of these accidents incurred fatalities, but the potential for future accidents with large numbers of fatalities prompted the French and the Australian aviation authorities to conduct reviews of the risks. We have recently completed an FAA-sponsored study in which we examine and extend studies by accident investigation organizations, report our own study of ASRS-reported incidents, and provide a broad set of countermeasures that can reduce vulnerability to accidents caused by performance data errors.

Performance data are generated through a lengthy process involving several employee groups and computer and/or paper-based systems. Although much of the airline industry’s concern has focused on errors that pilots make in entering flight management system (FMS) data, we determined that errors occur at every stage of the process and that errors by ground personnel are probably at least as frequent and certainly as consequential as errors by pilots. Although relatively few major accidents have yet been caused by performance data errors, our study suggests that more accidents are likely to occur unless existing measures to prevent and catch these errors are improved and new measures developed.

Six kinds of error are of greatest concern: 1) ground personnel errors in obtaining, calculating, and entering weight data; 2) FMS data entry errors by flight crew; 3) errors made in checking against limitations; 4) flap and trim configuration errors, 5) fuel weight errors by either ramp personnel or pilots; and 6) errors by pilots using cockpit laptop performance computers and electronic flight bags (EFBs). Cutting across several of these six categories were errors made either by ground personnel or by pilots while manually entering data.

Most of the errors we examined could in principle have been trapped by effective use of existing procedures or technology; however, the fact that they were not trapped anywhere in the chain of developing and applying the data indicates a need for better countermeasures. Existing procedures are often inadequately designed to mesh with the ways humans process information and their associated vulnerability to error—and procedures often fail to take into account the ways in which information flows in actual flight operations and the time pressures experienced by both pilots and ground personnel.

Because data entry errors are so prevalent, we suggest that airlines employ automated systems (feasible with current technology) that eliminate the need for manual data entry wherever possible in the process. For instance, this could include entering data by scanning passenger and cargo documents and eliminating the need to re-enter data by providing direct communication that allows sharing of data between the various computer systems.

Without effective countermeasures, errors will inevitably creep into the data process because of human cognitive vulnerabilities and operational exigencies. Many error-trapping procedures fail because the various data checks all use the same source of data and thus produce the same erroneous output. To make error-trapping procedures as effective and reliable as possible, they should be designed to validate the performance data process by using independent sources of information, data entries, calculation processes, and data transmission. To preserve the independence and maximize the reliability of error-trapping procedures, airlines should design and implement these procedures in enough detail to explicitly guide the personnel performing them; for example, specifying the forms, displays, and control indicators to be looked at for verification. Airlines can further improve reliability by training personnel in methods to control rushing, to enhance deliberate execution of procedural steps, and to encourage deliberate review of status.

An autonomous onboard weight-and-balance sensing system—as an independent source of information—can serve as an effective cross-check for the weight and balance values derived from the performance data process. With the capability to update its calculations in real time, this technological intervention can effectively prevent errors caused by last minute load changes.

Even with weight and balance verified by onboard sensing, subsequent calculations and manual data entries, such as performance speed parameters, flap settings, and trim settings, can introduce additional errors downstream in the process. These can be trapped by additional verification procedures, such as well-designed cross checks conducted by pilots and by technological systems, such as automatically uplinking calculated performance settings into the FMS and programming the FMS to cross-check the uplinked values with its internal calculations. Regardless what approach to verification is taken, weight and balance information—as well as performance parameters derived from this information—should be compared between independent sources.

FMS interface design can be improved to prevent some types of data entry errors. For example, for those designs not already modified, it should be possible to modify FMS software so either zero fuel weight (ZFW) or gross takeoff weight (GTOW)—but not both weights—can be input by the pilots.

Throughout performance data processes it is critically important for both ground personnel and pilots to resolve discrepancies identified during cross-checks of performance data. Airlines should inculcate this practice into operational culture and line norms by proceduralizing, training, and encouraging it. Discrepancy resolution procedures should establish thresholds for specific discrepancies, such as fuel weight, defining those that are acceptable and those requiring resolution.

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