shielded installations because the metal conduit is at ground  potential and close to the ignition wires throughout their  entire length. In low-tension systems, however, this leakage is  reduced considerably because the current throughout most of  the system is transmitted at a low-voltage potential. Although  the leads between the transformer coils and the spark plugs of  a low-tension ignition system are short, they are high-tension  high-voltage conductor, and are subject to the same failures  that occur in high-tension systems. Low-tension ignition  systems have limited use in modern aircraft because of the  excellent materials and shielding available to construct high- tension ignition leads and the added cost of a coil for each  spark plug with the low-tension system. certain problems with carrying the high-voltage from the  magneto internally and externally to the spark plugs. In early  years, it was difficult to provide insulators that could contain  the high-voltage, especially at high altitudes when the air  pressures were reduced. Another requirement of high-tension  systems was that all weather and radio-equipped aircraft have  ignition wires enclosed in shielding to prevent radio noise  due to high-voltages. Many aircraft were turbosupercharged  and operated at increased high altitudes. The low pressure at  these altitudes would allow the high-voltage to leak out even  more. To meet these problems, low-tension ignition systems  were developed. Electronically, the low-tension system is different from the  high-tension system. In the low-tension system, low-voltage  is generated in the magneto and flows to the primary winding  of a transformer coil located near the spark plug. There,  the voltage is increased to high by transformer action and  conducted to the spark plug by very short high-tension leads.  [Figure 4-20]  The low-tension system virtually eliminates flashover in both  the distributor and the harness because the air gaps within the  distributor have been eliminated by the use of a brush-type  distributor, and high-voltage is present only in short leads  between the transformer and spark plug. Although a certain amount of electrical leakage is characteristic  of all ignition systems, it is more pronounced on radio- A FADEC is a solid-state digital electronic ignition and  electronic sequential port fuel injection system with only  one moving part that consists of the opening and closing  of the fuel injector. FADEC continuously monitors and  controls ignition, timing, and fuel mixture/delivery/injection,  and spark ignition as an integrated control system. FADEC  monitors engine operating conditions (crankshaft speed, top  dead center position, the induction manifold pressure, and  the induction air temperature) and then automatically adjusts  the fuel-to-air ratio mixture and ignition timing accordingly  for any given power setting to attain optimum engine  performance. As a result, engines equipped with FADEC  require neither magnetos nor manual mixture control. Figure 4-20.  Simplified low-tension ignition system schematic.  4-12 S T1 L1 L2 L3 C2 C3 C1 R1 R2 R3 V1 R4 Off S3 On L R Both Off Retard breaker Main  breaker Main breaker Spark plug T2 Spark plug L4 L5 Starter solenoid Starting vibrator Magneto switch Left magneto Right magneto FADEC System Description