The Care and Feeding of Strobe Lights

The Care and Feeding of Strobe Lights by Tom Fredericks November 1999 Astrobe light is a capacitive discharge, high energy device, often used to meet aircraft anti-collision requirements. In general, an inverter circuit converts...


In the late 1980's, there was a development effort to utilize automated airborne recognition of aircraft strobe lights as a means of dealing with collision avoidance. Of course, in the years following, sophisticated TCAS systems have been designed and produced, leading to today's worldwide incorporation of such systems on commercial and business aircraft. However, in those early years, affordability was a major consideration during the research of viable alternatives and it appeared that a strobe recognition system might be the answer. During the process of this research it was discovered that all strobes are not created equal, resulting in varying intensities on a system-by-system basis. Unlike halogen and many other lighting systems, strobe intensity does, in fact, degrade over time. If a system were to be developed that could recognize strobe flashes for collision avoidance purposes, there would have to be some standard established regarding acceptable strobe light intensities.

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The FAA broached the topic at an air carrier association meeting in the early nineties and was shocked to discover the level of resistance to ACL testing in the industry. At the time, air carriers had been recently overwhelmed with other requirements and were not in the mood to take on any more "unfunded mandates." They were especially disinclined to conduct any testing which, at the time, would have been invasive, time-consuming and expensive. While the FAA chose not to pursue the issue any further in a forum environment (and the strobe TCAS concept faded away), the FAA never the less recognized the need to establish some guidelines for the future. Consequently, the FAA published FSIB 94-25B to address the issue of ACL intensities and requirements.

These intensities are measured in candela at levels of 100, 150, or 400; depending on aircraft type (as outlined in the FARs). Measurements are taken for 360 degrees in the horizontal plane within +5 degrees in the vertical. Modern ACL's utilize xenon bulbs, which meet these requirements when new. Over time, though, they typically exhibit a pronounced degradation of light output, often dimming below minimum regulatory intensities long before complete failure. Given this requirement, operators are faced with two options: outright replacement (hard times) or periodic measurements.

Based on the apparent need for an affordable solution to this problem, DeVore Aviation developed an accurate, portable and inexpensive hand-held strobe-measuring device, called the Flask Measuring Gun (FMG4400D). The FMG quickly and accurately identifies ACL strobes whose intensity level has dropped below FAA minimums.

While FMG's are in service with over 30 air carriers and 20 repair stations worldwide, many operators remain unaware of the strobe intensity requirement. Historically, aircraft lighting systems have experienced inconsistent levels of reliability based upon bulb or lamp design, mounting location, environmental wear and tear, etc. ACL systems have proven themselves to be of incredible value when it comes to matters of safety of flight. It is important to remember that strobes can degrade in intensity over time, thus compromising the degree of safety enhancement they provide. There are less costly solutions to hard time replacement and it would benefit everyone who shares the same airspace to know that all aircraft are operating on a level playing field when it comes to "see and be seen."

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