Aircraft Maintenance: Cockpit lighting repair and improvement
Panel lighting, Part 2
In the last segment, we covered the different types of panel lighting and the importance of adequately lighting the instruments, controls, and everything else the pilot needs to be able to identify in the cockpit to minimize heads-down time searching for the right switch. However, the reality is that many older general aviation aircraft have terrible panel lighting.
In the 1960s, 1970s, and 1980s when most GA aircraft were built, manufacturers treated cockpit lighting as an afterthought. Even if the original system is still working fine, chances are that it doesn’t do a very good job illuminating everything that the pilot needs to be able to see in the cockpit at night. Compounding the problem, most aircraft I’ve flown in at night don’t have lighting systems that are in perfect working order. Dimmers get temperamental, bulbs burn out, and the lights that work are often not aligned with the items they are supposed to illuminate. Finally, most aircraft panels have evolved over the years with new avionics, switches, and circuit breakers to control new equipment. Often, those changes are made with little regard to using the new systems at night.
I like to begin with the flight instruments. If you have a traditional six-pack of instruments, it’s not uncommon to have a mix of internally lit instruments and those that need external lighting. For a consistent look and balanced appearance, you can install “light wedges” that provide 360-degree illumination using thin lighting elements sandwiched between the instrument and the panel. I’ve had great experience with UMA’s electroluminescent instrument light bezels.These have a very low current draw and employ a DC-to-AC inverter to provide power to the electroluminescent strips in the wedges. The result is a very uniform light projected onto the face of the instrument. They are also available in a variety of colors. UMA offers installation assistance through an approved data package for FAA approval that is available on their website.
After the flight instruments, move to the rest of the panel and look for the best ways to illuminate each area. Post lights are a good option to provide flexible lighting throughout the cockpit. My personal go-to source is Whelen Aviation for both post and flood light options for the cockpit. Depending on the application, Whelen offers a variety of colors and styles that can cover different applications. The different models vary in height and in the width of the light beam. For example, if you are lighting a fuel selector, you may want a post light that covers a wide area versus a shorter, tighter pattern post light for just one flight instrument. Whelen also has goose neck and reading-style cabin lights that can be added to help with checklist reading, kneeboard notes, etc. In our Titan Aircraft T–51D Mustang build project, we are using Whelen’s post lights to provide lighting for the panel as well as the gear lever, fuel controls, and radiator cooling door. We are using Whelen's 70820-series interior LED map reading lights mounted to the side of the cockpit to provide kneeboard lighting for pilot and co-pilot.
One of the most common failure points for the existing cabin lighting is the dimmer itself. If you find that your lights flicker or do not dim smoothly, chances are that the rheostat or potentiometer that controls the dimming at the dial is to blame. These are mechanical devices that consist of spiral-wound wire with a metal wiper sliding over it. Those devices were never meant to last the 30 to 50 years that most have been in service. Fortunately, these are usually parts you can find from electronics supply houses. So, if you can’t get the part from the aircraft manufacturer (or you don’t want to spend $250 for a $5 part), you still have options. You can follow the FAA’s guidelines for “owner produced parts.” Identify the commercial part number and specs for the original part and get a suitable replacement approved by your local A&P as a minor alteration. As long as the installer is vetting your homework and the paper trail, and they are comfortable that you conform to the regulations, you can often get your dimmers back in service without a big maintenance bill.
This last item is the most controversial, simply because I’ve seen so much inconsistency from both mechanics and the FAA. A brief search on eBay or Amazon will turn up a plethora of LED replacement bulbs with the same bulb bases and size as many of the old incandescent bulbs installed in glare shields, map lights, overhead cabin lights, etc. These are generally not direct replacements as far as the FAA is concerned, but you can get approval in many cases. They are much more reliable, produce less heat, and use less power than the originals, so there’s good reason to seek approval to use them. Check with your local mechanic to see if he or she recommends installation as a minor alteration or 337 field approval as a strategy for your particular situation.
Taking the time to map out your cockpit lighting needs and make the necessary repairs and improvements is critical for night flying safety. And, if you improve your lighting, you may find that your interest in night flying will increase as well. Next time, we will cover repairs to those pesky but beautiful electroluminescent panels! Until then, happy flying!
