Gentlemen, Start Your Engines

By David Schober, A&P, IA, DAR

Reciprocating engine manufacturers have been slow to incorporate new technology ignition systems. There are a few electronic systems available, and the only TC’d engines with electronic ignition are the TCM Continental IOF-240 and IOF-550.

Unison has STC’d Lasar systems (see image above) for most horizontally opposed engines, but beyond that we are still running primarily with magnetos that trace their lineage back to Robert Bosch and the first installation of a magneto on a moving vehicle in 1897. The homebuilt market enjoys the advantage of electronic ignition, but they aren’t hampered by the same certification requirements that Standard Category aircraft are. The very reliability and simplicity of magneto systems has been the downfall of drastic design changes in aircraft ignition systems.

Rather than sweeping changes, the design changes in our ignition systems have come slowly and for the most part unnoticed. Small changes in manufacturing techniques and materials, but the basic product still looks pretty much the same as it did 60 years ago. The names have changed, but the products remained the same. The old standby Bendix Scintilla magneto is now manufactured by TCM as Alpha Systems. The S20, S200 and S1200 systems are available, but the part numbering system is a little different. Their application catalog provides updates on the appropriate part number for an installation. Unison is the manufacturer of Slick, and its predecessor, Case magnetos. The old Case and early throwaway Slick mags are no longer supported, but Unison has a full product line for horizontal opposed engines that operate single magnetos. Eismann magnetos have been out of business for many years and parts are problematic. Support for American Bosch and early SF, SB, MN, and PN Bendix Scintilla mags can be difficult, but there are still some NOS parts out there (don’t expect 8130-3s with these parts).

Ignition System Inspection

The most common problems encountered with magneto-type ignition systems involve low utilization of the aircraft, lack of, or improper maintenance, and deteriorated components. A frequent customer complaint is a bad mag check. It’s amazing how many mechanics jump right in and change all the plugs without even troubleshooting the problem. The first step should be to go out and run the engine to verify the problem, and, which mag is running rough.

Once we’ve identified which mag, and that it is only an excessive RPM drop and not an outright magneto failure, we now have an opportunity to try cleaning the offending plug with heat. Operate the engine at a power setting high enough to bring the cylinder head temperature quite hot and lean the mixture, but do not exceed the limits. Hold that power there for a few minutes, while observing that all the engine temperatures stay within limits, then perform another mag check.

If the airplane is equipped with a multi-point EGT or graphic engine monitor, this is an ideal troubleshooting tool to determine which cylinder is not firing. Assuming that we can’t clean the plug with heat, and we don’t have a multi-probe EGT system, it’s time for a cold cylinder check. Turn the ignition switch to the mag that has the drop and leave it there while the engine is running for several minutes, long enough for the engine to cool and more specifically, long enough for the dead cylinder to cool. At the point the engine is shut down, there should be at least 100 degrees difference in the CHT from the running cylinder to the dead cylinder.

Quickly remove the cowl and check the temperatures of the exhaust stacks as close to the cylinders as possible. An infrared non-contact thermometer is best for this but saliva on your finger wiped quickly on the stack will also tell you. The final step is to determine which plug is supposed to be fired by that mag. Following the wires, or looking up the ignition system in the appropriate manual will tell which plug is the offending one. If cleaning or replacing the plug doesn’t do the trick, the next thing up the line is the plug wire. A quick check with a high tension lead tester will confirm the integrity of the lead.

While looking at plugs, the most common problems with plugs are fouling and over cleaning. Fouling is the result of either combustion products, or oil building up on the firing end of the plug. This is caused by the engine operating at too low a temperature and can be avoided by leaning while taxiing. Over cleaning is simply poor maintenance. When cleaning the plugs, don’t only clean the firing end. Get the barrel and the recess where the plug wire is inserted. There are two primary suppliers for spark plugs — Champion (www.championaerospac.com) and Autolite (www.autoliteannie.com/home.html). Each of the plug manufacturers have servicing data available online or from their distributors.

If the test outlined above has been performed and a cold cylinder still can’t be identified, a common problem is cross firing at the distributor, or worn distributor contacts. From a practical standpoint, it is usually more cost effective to replace the mag with an overhauled unit than to repair it in the field. Magneto repairs are labor-intensive and parts are expensive. Magneto failures can come from carbon tracking across the distributor, failure of the distributor gear teeth, worn bushings, dry bearings, worn points, failed capacitor and lost magnetism in the magnet. Keep in mind that to perform maintenance, or overhaul these products, special tools and test equipment are required, along with having the appropriate technical publications.

Hard starting, another complaint, can be related to either fuel or ignition. When ignition-related, the problem can be with the impulse coupling, or the "shower of sparks" system, depending on the installation. Some other common hard starting causes can be a weak magnet, worn points, bad condenser or faulty coil. Since hard starting has so many possible causes, it’s harder to diagnose the problem. Points can be inspected visually, the coil can be checked with a multi-meter for a rough indication of condition, but much beyond that, replacing parts is the usual route to cure the problem.

Magneto failures are most frequently due to lack of maintenance. Each magneto vendor has specific maintenance and inspection items listed in their manuals, yet the majority of the airplanes never have anyone look at the magnetos beyond checking the timing between engine overhauls. Aircraft that fly less than 30 hours a year are the worst, since corrosion can build up and the grease in the bearings dry out. For Bendix/TCM magnetos, SB643 contains the recommended overhaul and inspection intervals.

TCM Alpha has increased their warranty program to cover 36 months or 1,000 hours, and they also have a 500-hour exchange program for $99. See tcmlink.com for details on these programs or to obtain subscription information for TCM product manuals. Slick inspection recommendations are contained in SB2-80. The Slick Lasar ignition system inspection requirements are found in L-1500. Subscriptions information for Unison Ignition product publications can be found at https://unisonpubs.com.

While maintaining the ignition system, the ignition switch and "P" leads are often overlooked. While doing the mag check, also check that the switch will kill the engine prior to shutdown. This is for safety as much as anything else. If the mag switch doesn’t ground both mags, any movement of the propeller could result in the engine firing and the prop causing significant bodily injury.

Over the years, ignition systems have had a number of Airworthiness Directives issued against various components. Certain ignition switches require inspections or lubrication at set intervals. Impulse couplings on O-540 engines require inspections, coils and condensers have had issues, older magnets require replacement, and on and on. Don’t assume that the ADs on the accessories are up to date unless you verify it by part number and serial number.

Electronic Ignition Systems

With increasing fuel costs, customers are going to start asking how to improve efficiency of their aircraft. Unison has their Lasar system that advertises a 12 percent reduction is fuel burn for the same power output. The primary advantage of any electronic ignition system is the ability to vary the timing. A common problem of electronic ignition is the requirement to have a constant power source. If the electrical system fails, then the ignition system would also fail.

The Lasar system incorporates magnetos that are designed to isolate the traditional coil and points from the system as long as the microprocessor is operational. In the event of an electrical system failure, the isolation relay closes and normal magneto operation is restored. The Lasar system is available for installation on certified aircraft via STC. Contact your Unison distributor for applicability to your aircraft. The Lasar system can also be installed on non-certified aircraft. The system replaces both of the existing magnetos and has the processor contained in a box installed on the firewall. Most installations also require warning lights to be installed in the panel. This system requires a special test box for installation, testing, and troubleshooting. A laptop computer can also be used.

TCM has taken a different approach with Aerosance — a full authority digital electronic control (FADEC) system. Details are available at www.fadec.com/index.asp. This system incorporates electronic ignition, electronic fuel injection, and engine monitoring, and can be set up as a single lever system with throttle only. The major advantage of this system is that it not only controls spark advance, but also the fuel injection system.

The combined use of timing advance and electronic fuel injection results in fuel savings up to 15 percent. Continental engines are certified under their respective TCs for the installation FADEC.

These systems have been operating over 13,000 hours on certified aircraft, and more than 100 certified engines have been delivered. The Liberty XL-2 has the TCM IOF-240 as standard equipment. Certain Beech Bonanza aircraft are eligible for installation of the IOF-550 via STC. There are certification projects for several other airframe/engine combinations underway and expect either STCs or new production aircraft to have FADEC as an option shortly.

Aerosance also has FADEC kits available for homebuilt aircraft with either Continental or Lycoming engines. Some of the issues noted with this system to date are connectors and dirty fuel. Any particulates in the fuel seem to plug the injectors and cause problems. This system requires a backup battery, and has outputs available to drive multifunction displays. Troubleshooting this system is done with a laptop plugged into the USB connection in the cockpit.

Electronic ignition for the homebuilt market has been around for quite some time. Homebuilts aren’t hampered with certification requirements. A simple search on the Internet will provide multiple sources for electronic ignition systems designed for installation on homebuilt aircraft engines. These kits range from crude to very sophisticated. Most involve some sort of external crankshaft sensor, a coil pack and the associated wiring and electronics to replace one magneto. Keep in mind that the electronic ignition system still requires an external source of electricity to function. One design that stands out is E-Mag (www.emagair.com). They’ve come up with a magneto replacement packaged to mount were your current mags are, but in addition to the electronic ignition, the package also contains a brushless generator. Should the aircraft power fail, the brushless generator will supply sufficient electrical energy to power the electronic ignition system. E-Mag is currently working on certifying this system via the STC process so certified aircraft can take advantage of electronic ignition, but not worry about having a battery backup.

As with any system, an electronic ignition system is a complete system. Be sure that the entire system is installed and that the specified wires and spark plugs are used. Standard plug wires and plugs may not work with the high energy used in these systems. If you are installing an STC’d system, be sure that all the STC documentation, including the Instructions for Continued Airworthiness, are given to the aircraft owner, and explain the importance of keeping the documentation with the aircraft records and to present them any time the aircraft is maintained or inspected.

While our magneto-based ignition system has worked well throughout the history of aviation, the current fuel prices may well be the catalyst to drive the installation of current electronic ignition systems.

Lasar systems from Unison, FADEC from TCM Aerosance, and perhaps E-Mag, may well be the future of general aviation ignition systems. Mechanics working on these new systems will need new skills sets, troubleshooting techniques and tools to properly service these systems.