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From the Flight Deck by Kevin R. Dingman 1.21 Gigawatts! Airplanes and electricity: the best of friends; the worst of friends. Popped CBs Who can forget Dickens’ primer from “The Tale of Two Cities” (modified here for relevance), or the iconic line from the 1985 blockbuster film “Back To The Future”? Christopher Lloyd, as Dr. Emmet Brown, delivers the classic 1.21 gigawatts line and its follow-on: “How could I have been so careless? 1.21 gigawatts; Tom, how am I going to generate that kinda power!” A gigawatt is one billion watts or 83,320,000 amps. Holy joules and moth- er of pearl! Who knew time travel would require so much power – or invoke such a muddled, mollusk metaphor? Since we typically f ly our airplanes within just a one-time continuum, our electrical requirements are less daunting – no plutonium-fueled f lux capacitor required. But even with our airplanes’ relatively refrained appetite for amperage, we are “Runnin’ with the Devil” (Van Halen, 1978). With a risk of fire and brimstone (OK, mostly fire), electricity can be the worst of friends if we fail to properly manage our volts, amps, ohms, watts and those oyster-joules. Electrons + Movement = Heat Heat + Combustibles = Fire Fire + Airplane = Bad Fortunately, our airplanes have no need for a time travel level of electrical power, nor is it necessary for pilots to demonstrate proficiency in using actu- al electrical circuit equations. But since aircraft electrical systems can be the best of friends or the worst of friends, it is necessary for us to understand how the system in our airplane oper- ates and where the threats are – and to have enough knowledge to isolate failed circuits or busses when they become the worst of friends. Isolation methods are generally composed of a master or battery switch, generator or alternator switches and circuit break- ers. All circuits should be protected with a circuit breaker or fuse. This is a device that senses the current flow, and when it reaches a predetermined level based on wire capacity (size), opens the circuit so that no current f lows. If we are going to isolate busses or components, we need to know what we lose when we isolate them with the master, the battery, a generator or alternator. Along with where the circuit breakers are for major compo- nents, systems and avionics. To quickly identify circuits, a common technique is to install colored circuit breaker “col- lars” or to paint the most important or high draw breakers. In my Duke, for example, the landing gear motor and electric trim CBs are painted white. While manually pulling a CB is an accepted isolation technique, reset- ting a popped breaker inflight can be problematic. From AC 25.137-1A: “Service experience has shown that attempts by the flight crew to restore power by resetting CBs after an auto- matic disconnect (popped breaker) can sometimes create a fire hazard and will often be unsuccessful because the majority of such disconnections are caused by faults that must be corrected by maintenance action.” So, don’t reset popped CBs unless needed for safety of flight and directed by the POH, QRH or the manufacturer’s inf light procedure. My Generator is Bigger Than Your Generator The battery(s) and generators/alter- nators are the sources of our electricity. The typical piston twin’s generators or alternators produce about 60-120 amp/hr, a turbine twin or small jet about the same, and a B-737 around 90 Kva (kilovolt-ampere). Each of the three fuel cells on the space shuttle generates 12 kilowatts, and your car uses about 400 amps to start and 45-50 amps while driving. A turbine engine can draw 1,000 amps to start. 28 • TWIN & TURBINE / May 2020