Techniques for Measuring Workload for the CH-47F Coupled Flight Director Developmental Testing

As part of the Army Aviation modernization effort, legacy helicopters such as the CH-47D and UH-60A/L are being upgraded with more advanced digital "glass" cockpits and advanced flight control systems. The CH-47F is the Army acquisition strategy to replace the aging CH-47D fleet. The upgrade includes a newly designed fuselage, a Digital Automatic Flight Control System, and the Rockwell Collins Common Avionics Architecture System (CAAS) cockpit. In this configuration, the aircraft is capable of not only displaying Flight Director (FD) cues to the pilot, but also fully coupling the aircraft to the FD cues to reduce pilot workload on long missions and alleviate pilot fatigue. Several subjective workload assessment techniques are used and generally accepted in the test community to quantify workload levels: the Bedford Rating Scale, Modified Cooper-Harper (MCH), NASA-TLX, and the Subjective Workload Assessment Technique (SWAT), to name a few. Each technique has strengths and weaknesses across administrative, procedural, and technical aspects. Traditionally, the Army Aviation Technical Test Center (ATTC) has relied greatly upon MCH for assessment of singlemodal tasks, which involve tasks mostly of the flying pilot. The Bedford Rating Scale has been effectively used to rate workload on the part of the pilot who is not flying but rather operating onboard systems. Both MCH and Bedford, however, can be cumbersome due to the flow-chart process; further, for accurate workload assessments, ratings need be given real-time without adversely impacting mission flow. Due to its unobtrusive nature, its validity, and the fact that it could be applied to both pilot and copilot tasking, SWAT was determined to be a viable choice for the assessment of the CH-47F workload. SWAT is a multidimensional scaling technique used for measuring workload in which subjects are asked to rate the workload of a task on the basis of the dimensions of time load, mental effort load, and psychological stress load. It is a two-step process that includes an initial scale development phase that allows an individual to create a personalized workload profile that can then be translated to a final scaled solution. In the winter of 2007, ATTC assessed the first major Boeing-Rockwell Collins CH-47F flight director upgrade, which was designed to permit fully coupled flight. Twelve missions conducted under instrument flight rules (IFR) and simulating instrument meteorological conditions were conducted across three test conditions: (1) basic navigation data (basic flight instruments/raw data), (2) displays using the flight director (uncoupled), and (3) displays using the flight director (coupled). Test condition order was randomly assigned to a group of four pilots (three experimental pilots and one operational pilot) with varying degrees of CH-47 flight time and "glass cockpit" experience. Test participants' subjective comments and quantitative ratings were then aggregated to provide an overall assessment of the CH-47F CAAS integration and functionality in terms of usability, performance, and interoperability. This paper describes the results of the CH-47F coupled Flight Director IFR workload assessment and ATTC's modern, repeatable approach to documenting cockpit workload both accurately and efficiently.