Why Our Assumptions are Important

Published on: Sept 20, 2022 Updated on: Oct 21, 2022 2 minutes read

by Dr. Reginald Hammah

Some of us may have encountered a well-known anecdote about the US Federal Aviation Administration (FAA) and an aviation engineering test. The FAA developed a device for testing the strength of windshields on airplanes against bird strikes.

The testing involved a device, essentially a gun, that launched a dead chicken at an airplane windshield at the speed at which the plane flies. If the windshield did not crack from the impact of the chicken carcass, it would survive an actual collision with a bird during flight.

A European country, it is said, became very interested in this experimental setup because they needed to test the windshield of a high-speed train under development against similar bird strikes. The engineers borrowed the FAA's device, loaded it with a chicken, and fired.

The outcome was stunning! Against all expectations, the chicken shattered the windshield, broke the engineer's chair, and struck the cabin’s rear wall.

The European engineers asked the FAA to analyze their test to see if they did everything correctly. After a thorough investigation, the FAA arrived at the following: “Next time, please use a thawed chicken.”

This short anecdote highlights an essential aspect of our geotechnical engineering work: applying assumptions in our work. Assumptions always underly our work and can pose dangers, especially when we do not explicitly or carefully consider them and evaluate their impacts on outcomes.

Two researchers [1] once wrote, “the power of an experiment is only as strong as the clarity of the basic assumptions which underlie it.” This principle equally applies to our design and modelling work.

Prof. Dick Stacey shared similar insights on this and more in his keynote address (which we publish in this RocNews Africa issue) he delivered at the recently concluded Rocscience Africa Conference, held in Accra. Happy reading.


  1. Mitroff, I., & Bonoma, T. V. (1978). Psychological assumptions, experimentation, and real-world problems: A critique and an alternate approach to evaluation. Evaluation Quarterly, 2(2), 235–260.
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