Taking a look at aircraft lighting basics Robert N. Rossier
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ing resources will make night operations safer and more comfortable.
On the Outside Probably the most important function of aircraft lighting revolves around collision avoidance. An anti-collision light system must provide the FAA’s required minimum intensity light in either “aviation red” or “aviation white” throughout an envelope that extends 360 degrees horizontally around the aircraft, and 75 degrees above and below the horizontal plane (see sidebar for specific requirements). Any one of four basic configurations is typically used to meet these requirements, depending on the particular aircraft. The first, and simplest, is a single anticollision strobe light or rotating beacon mounted on the top of the vertical stabi-
JIM KOEPNICK
love night flying, but one gripe I have is the way the lighting systems in a lot of airplanes leave you in the dark. First there’s the issue of having other airplanes see you at night, and then there’s the matter of finding your way around a dark airport. Inside, you have to have enough illumination to see—but not so much that you destroy your night vision. There’s nothing worse than not being able to read the numbers on the OBS, see the position of the fuel selector clearly, read a sectional or approach plate, or even find the seat belts at night. The lights in many older aircraft seem more like an afterthought, with little concern to any real-world lighting requirements. For those building an aircraft, restoring an old one, or even upgrading a more modern aircraft, putting some thought into adequate light-
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lizer. Alternatively, two wingtipmounted strobes that extend beyond the wingtips can also meet the requirements. Enclosing the wingtip strobes reduces the angles over which they are visible, and generally means adding a third strobe either atop the tail or on the bottom of the fuselage to fulfill the FAA-required light envelope and meet the stated requirements. Forward facing, wingtip-mounted red and green position lights are required by the FAA to fill a light envelope of 110 degrees horizontally from the nose to the respective wing, and also 180 degrees vertically, with no obstruction caused by any part of the aircraft. The “avia-
tion white” taillight must shine 70 degrees to either side of the tail, and 180 degrees vertically. Delivering electrical power to lighting elements isn’t always as simple as you might think. While items like interior lights, landing lights, and position lights can draw power directly from the aircraft’s 14- or 28volt power buss, the same isn’t necessarily true for strobes and beacons. Strobes generally require a power supply to provide pulses in excess of 400 volts to generate the flashes. Different configurations are used to accomplish this, including self-contained strobe units that incorporate both the light head and the power supply, or remote power supplies
that can power multiple flashers. If multiple self-contained strobes are used (or multiple power supplies), it is generally necessary to interconnect the power supplies to synchronize the flashes in accordance with FAA’s maximum flashing requirements. Rotating beacons generally don’t have the same high-voltage requirements of the strobes. However, older versions have rotating mechanical components, and still require an external power source. Those beacons can suffer from high current draw and limited life. As these older beacons fail, they are often replaced with halogen flashers that incorporate a half-red/half-clear cover. This type of unit has a lower power demand and
Light Up the Night The specific requirements for aircraft lighting during night flight are spelled out in regulations. FAR Part 91 establishes the types of lighting systems required, and when they must be used. Specific details as to the design characteristics of those lighting systems are found primarily in FAR Part 23, to which builders of amateur-built aircraft are directed for such requirements. According to the regulations, an aircraft uses position lights (FAR 91.205(c)(2)) during the period from sunset to sunrise (FAR 91.209). The requirement also applies to moving the aircraft on the surface near night operations areas. Lighted position lights are required unless the airplane is otherwise clearly illuminated. Position lights are also required for aircraft operating on the water, such as seaplanes and floatplanes. FAR 91.209(a)(3) says a pilot can’t anchor an aircraft unless the aircraft has lighted anchor lights or is in an area where anchor lights are not required on vessels. The details on the design of position lighting systems are provided in FAR 23.1387-1399. The essence of these regulations is to define the lighting envelopes (angles through which the position lights must be visible) and the distribution and required lighting intensities of the position lights. These
regulations also define the proper colors for position lights, and specific requirements regarding anchor lights. Part 91 also spells out the requirements for anti-collision light systems. According to FAR 91.205 (b)(11), all aircraft certificated after March 11, 1996, must have an “approved aviation red or aviation white anti-collision light system,” regardless of whether the aircraft is operated day or night. For aircraft certificated prior to this date, the anti-collision light system is only required for night operations. In theory, if you have an aircraft certificated prior to that magic day in March 1996, and you don’t plan on night flying, you don’t need an anti-collision light system. Also important to note is the fact that the specific design parameters for anti-collision light systems change depending on the age of the aircraft. In essence, there are three different requirements, depending on when the aircraft was certificated. Over the years, the brightness of the lights, and the angles through which they must be visible, have been revised (see Table 1). Other characteristics of anti-collision light systems are also spelled out in the regulations, such as the colors, flashing characteristics (40 to 100 flashes per minute), and minimum flashing intensities as a function of viewing angles.
Table 1: Anti-collision Light System Requirements* Certification or Application Date April 1, 1957, to August 10, 1971 August 11, 1971, to July 18, 1977 After July 18, 1977 Source: FAR Part 23.1397; 23.1401 48
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Minimum Effective Power (candela)
Vertical Axis Visibility (degrees)
100 400 400
360 360 360
Horizontal Plane Visibility (degrees above and below) 30 30 75
greatly extended life compared to the older rotating beacons. A key point to consider when designing a lighting system or choosing components for an aircraft project is the overall electrical demands placed on the system. Both by regulation and common sense, the airplane should be able to provide enough electrical energy to run the installed components. That can be a problem if you have a decked-out panel, some creature comforts, and lots of exterior lighting. I struggled with this problem myself in my 1947 Bonanza, which was equipped with an anemic 35-amp generator. Adding new power demands would quickly exceed the capacity of the electrical system, forcing me to change to a bigger generator. Another way to tackle the problem is to choose lighting components that have less power-hungry designs. A Better Mousetrap In addition to the basic FAA requirements for position and anti-collision lighting systems, Part 23 goes into considerable depth regarding the characteristics of the specific lighting elements. The specifications for brightness and color have limited development of new lighting technology for years, but lately that has been changing. "When it comes to exterior aircraft lighting, LED technology is really where the industry is headed," says Jeff Argersinger, sales and marketing manager for Whelen Engineering in Chester, Connecticut. Light-emitting diode technology has evolved to where it meets the various requirements of the aviation industry, and it offers a number of significant advantages over traditional incandescent lighting, including greatly reduced power requirements and longer life. TSO'd LED technology is now available for position lights (28-volt systems only), and for anti-collision beacons (14and 28-volt systems). Significant improvements have been made in beacon design. Designs EAA Sport Aviation 49
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BONNIE BARTEL
JIM KOEPNICK
JIM KOEPNICK
that incorporate solid-state LED lighting technology surpass even the halogen flashers. LEDs don’t require external power supplies, use less power, and offer life limits that exceed 20,000 hours. Power consumption for the LED beacons is in the range of 0.85 amps for a 14-volt system, compared to 2.7 amps for a 14-volt halogen flasher. LED technology is now becoming more common in position lighting systems. If you’re looking for position lights for a project aircraft, consider TSO’d components, as other designs may not meet the airworthiness requirements that even amateur-built airplanes must meet. “A common misconception regarding amateur-built aircraft is that it isn’t necessary to meet all the FARs,” says Argersinger. “For lighting requirements, FAR 21 directs the builder back to the requirements of Part 23. We’ve put a lot of effort into making the LED position lights meet those requirements. LEDs tend to be bright, and it’s easy to have light spill over from one area to another.” Despite the advantages, LED technology is not a panacea; it has its limitations, and it doesn’t do everything. “For example,” says Argersinger, “I don’t see wingtip strobes going to LED technology. The FAA requirement for these is 400 candela, and we just can’t do that with current LED technology.” While this technology may sound great, it does come at a cost. While price varies from one application to the next, builders can expect to pay roughly double for LED lighting compared to traditional incandes-
cent lighting. But that difference is likely to decrease as LED technology matures. “As the technology evolves the lights become brighter, we need fewer of them, and the price goes down,” Argersinger says. The other factor in the price equation revolves around production. As more applications are found for LED lighting, the number of units manufactured increases, and the per-unit cost decreases. Before opting for less expensive lighting, consider that to a great extent, the acquisition cost of LED lighting is offset by a reduction in replacement cost. Manufacturers are quick to point out that LED lighting has a much longer life than incandescent bulbs and is virtually immune to vibration, which plays havoc with the filaments in incandescent bulbs. Still, there’s more to the picture than initially meets the eye. “Despite what you might hear or read, the question of life for an LED is really a loaded question,” warns Argersinger. “We can put an LED on the bench and get 100,000 hours out of it, but many factors come into play when using that light in an aircraft design. First is the heat sink. In order to dissipate the heat, these really need a proper heat sink design. Power is also important. If we drive these lights at their maximum capacity, they won’t last as long as when we reduce the power. Then there’s the issue of color. Over time, the color characteristics of the LEDs will shift.” Many experts in the field suggest that a more reasonable estimate on the life of LED components is in the order of 20,000 hours. For most general aviation aircraft, that’s still a lifetime. Anti-collision lighting systems are considered serious safety items, and the FAA emphasizes that in the regs. FAR 91.205 says a pilot can turn the system off if the safety of the flight requires it. However, if any anti-collision light fails, the pilot can only EAA Sport Aviation
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continue flight to a location where repairs can be made. Strangely, the regulations don’t seem as serious when it comes to landing lights.
Taxi/Landing Lights The regulations require an electric landing light only if the aircraft is operated for hire (read that as charter, rental, or instruction). However, the savvy pilot knows that having a taxi/landing light is critical to safe operations, regardless of whether it’s legally required. FAR 23.1383 includes a few more specifics about taxi/landing light design criteria, invoking four essential criteria. First, the landing light must be sufficient for night operations. What that really means is left to the builder, as the regulation provides no further guidance. The lights must not cause a fire hazard, which implies that the light be properly wired, and if designed as a retractable light, must have safeguards so that if the light is powered in the retracted position, it doesn’t get hot enough to ignite any part of the aircraft. This regulation also requires that the landing light not create any glare that could pose a problem for the pilot, and that the pilot not be seriously affected by halation (a halo or glow surrounding a bright spot). For the aircraft designer or restorer, a few additional considerations regarding taxi/landing lights can greatly enhance the safety of night operations. The first is redundancy. While landing an airplane on a 52
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runway at night without a landing light requires no extraordinary skills under good conditions, not having one at the wrong time can quickly put you way behind the proverbial eight ball. An operating landing light can reveal runway surface conditions, the existence of debris or “contamination” that could affect the landing, or reflections of the eyes of wildlife choosing to occupy the same real estate on which you plan to plant your tires. Murphy’s Law says that if you have only one light, it will most assuredly burn out just when you need it the most. In terms of the power or brightness of our landing lights, the general consensus is that higher takeoff and landing speeds translate to a need for a more powerful light capable of projecting farther down the runway. For a light general aviation aircraft, landing lights in the 100-watt range that deliver 100,000 to 150,000 candela are common. Finally, the location and type of mounting is critical to the life of the light. The biggest killers for any incandescent light are vibration, temperature, and voltage. As any of these variables increases, you can expect a significant decrease in the life of the light. Money saved in a simple but insufficient mounting system is soon spent on bulb replacement.
While LED lighting isn’t practical for landing lights, quartz halogen lamps will outshine standard incandescent lamps by a broad margin. Quartz halogen lamps generally provide 10 times the life of standard incandescent lamps (250 hours versus 25 hours, typically), and retain their rated intensity or light output over their entire life. Although more expensive to purchase, quartz halogen lamps can reduce overall maintenance costs, and at the same time provide improved performance. High intensity discharge (HID) lighting technology, which does not involve a filament and provides highly efficient lighting, is now available for some landing light applications as well.
Interior Lighting Design FAA requirements for instrument lights are found in FAR 23.1381. According to this regulation, instrument lights must meet three basic criteria. First, the lighting must “make each instrument and control readable and discernable.” Second, the lights must be installed in a manner that prevents them from shining into the pilot’s eyes, either directly or by reflecting off the windshield or other surface. Finally, there must be adequate insulation between current-carrying components and the housing to prevent shorting from
vibration. The regulations also stipulate that a cabin dome light is not considered an instrument light. Here again, we see a variety of products that can meet these requirements. Among the more popular designs today are those that incorporate LED lighting elements. “LED lighting has really matured in the past couple of years,” says Joe Ziadi, vice president of Avtec Inc., an aviation lighting manufacturer in Cahokia, Illinois. “A typical LED reading lamp has a life of 50,000 hours, and draws only 150 milliamps. LED lights are solid-state components, and since they have no filament, they aren’t affected by vibration. They also operate over a broad range of temperatures, and offer ease of installation.” The variety of lighting options can just about guarantee your abili-
Anti-Collision Concerns If being seen at night—either in the air or on the ground—is a major concern, a couple variations on the aircraft lighting schemes may give you peace of mind. One is DeVore Aviation’s upwash lighting system that illuminates the vertical stabilizer of the aircraft, providing enhanced visibility both on the ground and in the air. For more information, contact DeVore Aviation Corp. of America at 6104 Jefferson St. NE, Albuquerque, NM 87109 or call 505/345-8713. Another excellent tool for enhancing your visibility to other pilots is a flashing system for your taxi/landing lights. AvTek’s Pulsar system is designed to flash one or two separate lights of up to 100 watts to greatly enhance the visibility of aircraft both night and day. The system uses a solid-state electronic controller to flash the lights, and is designed to operate with both 14and 28-volt electrical systems. For more information, contact AvTek at 25230 45th Ave. S., Kent, WA 98032 or call 800/770-3265. EAA Sport Aviation
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Wiring Considerations Whichever system you decide to install, the lights are no better than the wiring that delivers power to them. All wiring must be properly sized, routed, and secured, with due attention given to all terminations and connections to assure security and electrical continuity. One warning for both builders and restorers: make certain a reasonable service loop is retained where the lights are 54
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ty to see what’s going on in the cockpit at night, although the selection available may depend to some extent on whether you have a 14- or 28volt electrical system. Standard 14and 28-volt instrument post lights can now be replaced with TSO’d LED versions that use a quarter of the energy and provide brighter illumination. Gooseneck lights, adjustable map lights, and fixed cabin lights are also available in both 14and 28-volt varieties, typically consuming one-quarter to one-tenth the power of their standard incandescent counterparts. For craft equipped with 28-volt electrical systems, LED strip lights can be installed above the instruments to provide highly effective downwash illumination. Other options include fiber-optic downwash lighting systems. Another item to consider as part of your interior lighting system is courtesy lights, designed to assist passengers in entering and exiting the aircraft. These can be installed in a variety of locations, both inside and outside the aircraft.
mounted to enable servicing the fixtures without tearing apart the airframe. Among the requirements imposed by the regulations is that position lights must be wired independently of the anti-collision lighting system. Obviously, you don’t want a single point electrical failure to leave you with neither the position lights nor the anti-collision lights. Of particular concern to some builders is the potential fire hazard posed by electrical wiring in a wing. In fact an incident that occurred two years ago highlights the consequences of igniting errant fuel vapors. The incident involved a Piper Navajo, the wing of which exploded just before rotation. As it turns out, a faulty fuel vent system allowed fuel to spill into the
wing and vaporize. Just as the aircraft was about to rotate, the stall warning system energized, and a spark was generated that ignited the fuel, causing an explosion that blew the wing apart. Fortunately, the pilot aborted the takeoff without injury. In general, proper wiring considerations will alleviate most concerns over such potential problems. Still, and without a doubt, things need to be done right anywhere fuel and electricity are mixed. A much more common problem is the electromagnetic interference that can occur with anti-collision lights and strobes. Fortunately, some of the common problems that lead to interference can be easily avoided. The first centers on the location of the beacon or strobe breaker on the electrical bus. If the radio breaker is located between the powered end of the bus and the strobe/beacon breaker, then the radios are much more likely to pick up noise generated by the power supply. Instead, position the strobe/beacon breaker as close as possible to the supply end of the buss. Second, add additional filtering to the radio power lead to limit the noise. Another way to get interference to the radios is via the ground. Voltage drops in the ground circuit caused by electric motors, strobes, beacons, fuel pumps, or even the alternator itself can be interpreted as signals by the radios. Isolating audio grounds from the airplane ground at the speaker, headphone, and microphone junctions can eliminate much of this noise. For the best results, ground these devices at a common point with the radio itself. As an extra measure, consider some filtering on the ground side of the radios as well. With today’s technology, there’s no need to be left in the dark when flying takes you into the hours after sunset. By giving thorough consideration to the requirements—both legal and otherwise—you can apply some truly illuminating concepts to light up your night.
