An in-flight investigation of workload assessment techniques for civil aircraft operations

The report deals with an in-flight study of assessing short-term pilot workload and focuses on the problemacy of drawing conclusions from a variety of experimental measures in an airborne operational environment. Several implications are pointed out such as the dealing with mutually different outcomes, the designating of artefacts, and the problem of formulating final conclusions. An experimental program is discussed which is based on (normal) approach conditions for fixed-wing transport aircraft. The considered measures include pilot and safety pilot ratings (McDonnell 10-point rating scale, SWAT 3x3 rating matrix), measures of pilot heart rate and measures reflecting control activity and task performance. Besides, the usefulness of two pilot-aircraft model-based assessment methods (one based on pilot control input demand and one based on crew procedural work demand) has been examined up to some detail. The experimental tasks consisted of flying procedural approaches (with an external view occluding visor) with each experimental run starting on “downwind” approximately 10 minutes before touchdown. The task variables include - different approach aids, that is, ILS, VOR+DME, or NDB; - the manner of pilot control, that is automatic, manual (in case of an ILS type of approach: with or without Flight Director information), or manual with simulated trim malfunction; - the number of crew members, that is two-man versus one-man crew. In total, 168 approach runs were completed using the NLR Swearingen Metro II laboratory aircraft. Five (ATPL/CPL) pilots participated as subjects in the experiment. The approach runs were carried out at three international airports: Amsterdam (EHAM: ILS approaches only), Rotterdam (EHRD) and Groningen (EHGG). The results show among other things the necessity of the use of a set of different measures to guarantee a reliable assessment. Several inherent pros and cons of different measures are discussed in detail. Finally a strategy is outlined to formulate final conclusions based on the outcomes of a variety of measures.