Lighting and Marking of Obstructions to Air Navigation

Three classes of obstructions present hazards to VFR flight: tall towers encroach navigable airspace, catenaries obstruct the paths of low flying aircraft, and structures near airfields endanger terminal area traffic. Study of the first class, tall towers, has produced recommendations for very bright, flashing white lights and wide bands of black and white paint to enhance detection. Objection has been taken to revision of the marking standard for tall towers only, because the importance of retaining simplicity in the international standard requires all three classes of obstructions to be considered together. Additional analysis reveals that orange and white bands and checkerboards, and lesser red obstruction lights are valuable as hazard identification signs, if detection is otherwise as assured. Under marginal VFR conditions, however, there is reason to predict superior detection of both tall towers and catenaries if brightness contrast rather than color contrast is given priority. Relatively, addition of very bright flashing lights offers more increase in detection range than any painting scheme, but painting remains important for correct interpretation of what is detected.