Assessments of Flight and Weather Conditions during General Aviation Operations

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Authors: Ulf Ahlstrom
Kevin Hallman
Nicole Racine

Ahlstrom, U., Racine, N. & Hallman, K. (2019). Assessments of Flight and Weather Conditions during General Aviation Operations. (DOT/FAA/TC-19/33). Atlantic City International Airport, NJ: FAA William Hughes Technical Center.



We investigated pilot weather assessments and pilot ability to assess the out-the-window visibility. Specifically, we assessed if sectional map distance training or the use of a slant-range rule of thumb could improve pilot visibility assessments.


One of the causes behind VFR into IMC flights is GA pilot difficulty in correctly assessing the out-the-window visibility. Simulation studies frequently find that pilots fly into areas with rapidly decreasing visibility or fly into areas of IMC where VFR-only pilots are not permitted to fly. This indicates that pilots have difficulty assessing weather conditions and determining if their flight is compatible with VFR requirements.


Sixty-six private pilots participated in the study. The pilots were randomly allocated to one of three simulation conditions (Map distance training, Slant-range training, or Control). Results: The result showed that the visibility estimate errors for the Slant-range group were on average half the size compared to the visibility estimate errors for the Control and the Map distance training groups. This shows a benefit of using the Slant-range rule of thumb when estimating in-flight visibility.


Based on the lack of weather training reported in the current pilot sample (9%), we believe there is a need for training in both how to correctly interpret weather conditions and how to translate these interpretations into flight decisions. We believe that with training on the Slant-range rule of thumb, coupled with a set of decision-making rules, pilots would be in a much better position to correctly assess the out-the-window visibility and make more informed flight decisions rather than continue flight into IMC.


We recommend that weather interpretation training and Slant-range rule of thumb should be incorporated into basic pilot training.