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 DC input voltage into a high level output voltage of between 350 to 550 volts. This voltage is then applied to a xenon gas flash tube. In addition, a trigger voltage is pulsed to the glass envelope of the flash tube.
The trigger pulse causes the xenon gas to ionize, which allows the high voltage to conduct. This results in the high intensity flash of the flash tube. There are two basic types of aircraft strobes. A self-contained strobe consisting of a lens, flash tube and electronic power supply all housed in a single unit or a remote strobe consisting of a power supply, a three conductor cable and a remote lens and flash tube assembly. In both cases, the lens, flash tube and electronic power supply come in various sizes and power levels to fit a number of different applications.
Troubleshooting a self-contained strobe unit The first step in troubleshooting a self-contained strobe, that does not flash, is to check the circuit breaker in the aircraft. If the breaker is okay, then measure the voltage at the input to the strobe. Note that some early strobes emitted an audible sound when turned on. This was often used to determine that voltage was present, however, a meter is a more reliable method of checking.
If power is present at the unit, visually inspect the flash tube. Replace it if it is blackened or cracked. If the strobe flash tube is okay, then the power supply must be defective and the unit must be repaired or replaced.
For a self-contained strobe unit that operates irregularly, the first step is to check for a faulty power connection at the breaker or strobe unit. Make sure that the unit has a good ground connection all the way back to the aircraft power source. If the connections are okay, then the power supply must be defective and the unit must be repaired or replaced.
Troubleshooting a unit with a single remote strobe
Troubleshooting a single remote strobe unit is similar to a self-contained unit, with one obvious difference, the interconnect cable. For a strobe
that does not flash, the first step again, is to check the circuit breaker in the aircraft. If the breaker is okay, then again, measure the voltage at the input to the power supply.
If power is present at the power supply, visually inspect the flash tube. Replace it if it is blackened or cracked. If the flash tube appears to be okay, check the interconnect cable. One way to isolate the cable is to connect another cable and flash tube assembly at the power supply. If this works, then the power supply is good and the problem is with the remote flash tube assembly or the cable. Replace the flash tube assembly. If the unit still does not work, then replace the cable, as a last resort. If a flash tube darkens and fails within a short period of time, such as 30 minutes to a few hours, there may be a wiring problem. Check all three wires, at both ends of the cable, for proper connections.
Troubleshooting a unit with multiple strobes
Troubleshooting a power supply with multiple remote strobes is often easier than a single remote unit, since the remote flash tube assemblies can be swapped to isolate problems. In a case where neither strobe flashes, begin again with a circuit breaker and power supply voltage check.
If the power is okay and since neither of the strobes are flashing, the problem is most likely a defective power supply. Repair or replace it.
If one strobe is not flashing, swap the strobe connections at the supply to determine whether the problem is with the remote strobe assembly or the output section of the power supply. If the flash tube appears to be okay, check the interconnect cable. As a last resort, replace the interconnect cable.
If a flash tube darkens and fails within a short period of time, such as 30 minutes to a few hours, there may be a wiring problem. Check all three wires, at both ends of the cable, for proper connections.
Other Problems
Self-ionization is a condition where the flash tube fires, but the xenon gas stays ignited until the unit is shut off or the charge slowly drains
off. In general, this is caused by components degrading over time and is more common in relatively old designs. Repair or replace the power supply if self-ionization occurs. It is important to note, however, that in some cases replacing an old power supply with a new supply may appear to increase the occurrence of self-ionization. The reason for this occurrence is that some supplies, such as those manufactured by Whelen Engineering Company after 1980, have a deionization circuit that isolates the flash tube ground from the aircraft ground. To make this circuit operate correctly, the following wiring change must be made.
Both Grimes and SDI sometimes use MS (Cannon Type) connectors: A=RED (Anode), B= White (Trigger), C=Black (Ground).
Remember that wiring sequence varies between comparable equipment made by different companies. When intermixing anti-collision strobe light system equipment, make sure to check wire color and to connect Red to Red, White to White, and Black to Black.
In most pre-1980 aircraft, the three-wire conductor cable from the power supply to the remote strobe assembly had the bare shield wire pinned together with the flash tube ground wire, at both ends of the cable. When replacing an older supply, with this type of shield wiring, it is important to remove (carefully cut) the shield connection at the remote strobe assembly and leave this end unconnected. At the power supply, remove (carefully cut) the shield wire from the supply connector. Attach the bare wire from the cable to frame ground. Add a short piece of shield wire if necessary.
Radio frequency interface (RFI) is another problem associated with aircraft strobe installations. In many cases, an RFI problem will progressively worsen as components degrade over time. This was more common with older designs using older style capacitors. Repair or replace the power supply if this is the problem
Safety
Strobe power supplies generate high voltage. Caution must be used when
working with a strobe supply. Do not disconnect remote strobes with DC power applied to the strobe supply. Do not operate a strobe unit with the cover or lens removed. If a flash tube darkens and fails within a short period of time, such as 30 minutes to a few hours, there may be a wiring problem. Check all three wires, at both ends of the cable, for proper connections.
Stand out with no additional lighting.
A new enhancement in collision avoidance doesn't require installation of any additional lights on your aircraft.
A company called Precise Flight, Inc. has developed a system that utilizes existing lighting on aircraft to help the aircraft stand out.
Pulselite® alternately flashes existing landing, taxi and recognition lights 45 times per minute in a variety of patterns — dramatically increasing the visibility of your aircraft. According to the company, "Your aircraft is transformed into an immediately recognizable spectacle that can be seen for miles. The illusion of exaggerated motion distinguishes you from surrounding ground lights. In an instant, other pilots will see and avoid you.
For more information on this system, call Precise Flight at (800) 547-2558 or visit them on the Web at www.preciseflight.com.
Realted Article on Anti-Collision Light Maintenance Recquirements.
Anti-Collision Light (ACL) Maintenance Program Requirements
By Pete Alexander November 1999In 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.
DeVore's Flash Measuring Gun is a battery-powered device containing a retractable distance measuring cable, a precision CIE response photo diode and microprocessor-based measurement electronics. FMG electronics automatically compensate for ambient light, allowing measurements to be made under all lighting conditions. The digital readout display on the back of the gun provides large, bright LED data, indicating strobe intensity levels to the nearest candela up to 9,999. To measure ACL strobe light intensities, the FMG measuring cable is drawn out to it's full length - approximately 8 ft. - and attached to the center of the strobe light lens cover. An alternative carbon fiber extendable wand, which comes supplied with each kit, may be used as well. Once the unit is at the required 90-in. distance from the strobe, depressing the trigger will turn the FMG on. A microprocessor first performs a battery self-test and will not allow the system to operate if an insufficient charge condition exists. The unit is then ready to begin measuring intensities, quickly and accurately. DeVore provides an annual inspection, re-testing and certification service. This annual requirement includes replacement of the battery pack and a complete recharge. Typical turnaround times are within 48 hours.
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."
