To help reduce operating costs of a High Speed Civil Transport aircraft, our External Vision System Technology Development Team at Honeywell, along with teams at NASA, Boeing and McDonnell Douglas, is investigating the feasibility of replacing forward windows with a synthetic version. The synthetic window will capture the greatest part of information normally visible to pilots. Ideally, it would capture the “look, feel, and functionality” of traditional windows.This paper discusses optical characteristics of certified windows. Measurements were taken from commercial aircraft windows at various stages of service up to and beyond 20,000 hours. Fundamental system attributes, relating to visual performance, were measured and evaluated. Measurement techniques are described. The resultant data provide the synthetic window systems designers a foundation on which to base their work and design goals.