Research into aircraft handling qualities is aimed in part at ascertaining which vehicle parameters influence pilot acceptance. It is obvious that the number of possible combinations of parameters is staggering, and conse­quently attempts are made to study one particular aspect of the vehicle while maintaining all others in a “satisfactory” configuration. Thus the task is formulated in a fashion which is amenable to study. The risk involved in this technique is that important interaction effects can he overlooked. For example, it is found that the degree of difficulty a pilot finds in controlling an aircraft’s lateral-directional mode influences his rating of the longitudinal dynamics. Such facts must be taken into account when interpreting test results. Another possible bias exists in handling qualities results obtained in the past because most of the work has been done in conjunction with fighter aircraft.