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 mother of pearl! Who knew time travel would require so much power – or invoke such a muddled, mollusk metaphor? Since we typically fly our airplanes within just a one-time continuum, our electrical requirements are less daunting – no plutonium-fueled flux 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 actual 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 operates 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 breakers. 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 flows.
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 components, systems and avionics. To quickly identify circuits, a common technique is to install colored circuit breaker “collars” 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, resetting 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 automatic 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 inflight procedure.
My Generator is Bigger Than Your Generator
The battery(s) and generators/alternators 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.
Without getting into an electrical engineering discussion about joules vs. watts vs. amps vs. the amount of time in use, etc., the bottom line as far as we pilots are concerned is this: Amps (current ‘flow’) and wattage along with voltage (potential for electron ‘movement’), wire size and material (aluminum, copper, gold, etc.) generate varying amounts of heat – enough heat and you get fire. An open circuit is cold (literally, room temperature). An in-use circuit should produce virtually no heat. A circuit that has too much current for the size of wire will get hot – possibly hot enough to start a fire. And fire + airplane = bad. Even more so than an engine failure, an electrical fire will get your attention, so we need to recognize the early signs of an overheat or fire.
Ozone, Hot Plastic and Smoke
Electrical smell, vapor, smoke and flames will be our indication of a serious electrical problem. And you may notice one or more of these before your carbon monoxide/smoke detector sounds an alarm. When electricity arcs through air, as it sometimes does with a DC electric motor or between a bare wire and ground, it splits oxygen and nitrogen into a form of oxygen called ozone. This creates a smell – it’s the electric, model train smell. You may also encounter this smell from an electric drill or other electric motor with brushes if it doesn’t have a fan to blow away the smell. In an electrical fire scenario, this “electric motor” smell is followed quickly (or sometimes preceded by) the smell of hot or burning plastic, rubber or insulation. Sometimes you may even hear electrical popping, arcing or sizzling. Do not ignore these signs or second guess yourself if that is what you smell or hear. If it’s a developing electrical fire, you may only have a few minutes to find and put out the fire before much worse things happen.
My first inflight electrical fire was aboard my trusty 1959 Cessna 150. I was stationed at MacDill Air Force Base in Tampa while going through initial F-16 training and kept the plane at
Peter O. Knight Airport across the bay. One sunny day I took it out for a couple laps around the patch. Just after liftoff, the reverse current relay light came on and I smelled both electrical smell and battery acid. My voltage regulator overheated, failed to regulate and allowed 1.21 gigawatts (thereabouts) into my battery, which caused it to “boil over.” I shut off the master, landed immediately and ran into the FBO for a bucket of water to rinse the battery box and belly.
I also had an incident where a partially bare wire once arced against my pressurization controller in the Duke, causing the electric smell and burning rubber. And there were a couple of incidents with a recirculating fan while on the ground in the MD-80, but nothing like my Northwest/Delta friend Bob Hoffman experienced. He was flying a B-757 en route from JFK to MCO. A recirculating fan overheated inflight causing an electrical fire that filled the cabin with smoke. Bob landed 12 minutes after the checklist began, with no damage and no injuries. Here are some other published reports of electrical incidents.
Accidents and Incidents
- North American Aviation, Command Module, Apollo 1 – an electrical short started a fire which was exaggerated by an O2 saturated environment resulting in loss of the module and crew in just 17 seconds.
- MD11 belonging to Swissair – crashed into the sea off Nova Scotia following an inflight electrical fire caused by the inflight entertainment system.
- A321 operated by British Midland – during cruise in night IMC had an electrical malfunction accompanied by intermittent loss of the display on both pilots’ EFIS and an uncommanded change to a left-wing low attitude.
- A319 operated by British Airways, London Heathrow to Edinburgh – experienced an electrical malfunction during a night pushback, which blanked the EFIS displays following the second engine start and produced some electrical smell but no smoke.
- B752 operated by American Airlines from SEA to JFK – lost significant electrical systems functionality en route. After making a visual daylight approach, the aircraft was intentionally steered off the landing runway when the captain perceived that an overrun would occur.
- DH8B while descending into BDL – had an inflight fire that originated at a windshield terminal block.
- B747 near Dubai UAE – had a main deck cargo fire 22 minutes after takeoff resulting in a rapid build-up of smoke in the cockpit. An unsuccessful attempt to land was followed by loss of control due to fire damage.
- B747 operated by TWA – exploded over the Atlantic 12 minutes after takeoff due to arcing of the fuel quantity indication system in the center fuel tank.
Some fires are difficult to locate and fight. The time delay can allow fires to take hold and do plenty of damage. It may also be difficult to confirm that you even have a fire, which can cause a delay in the decision to land (this delay may allow the fire to become non-survivable). Accomplish the procedures in your POH or QRH and do your best to find and extinguish the fire. FAA Advisory Circular 120-80A uses the words “aggressively pursue” in reference to finding and fighting a fire. But while aggressively pursuing the fire, also make a mad dash, bee-line, emergency descent or whatever euphemism you like to use that means nearest suitable airport, and do it right now – even if you think the fire is out or that it’s under control. If your avionics are still working, use the “nearest airport” function of your navigation system, then make the Mayday call, ask ATC for a vector and request ARFF.
Fire extinguishers (Aircraft Spruce, $200 & up).
Carbon monoxide/smoke detector (Home Depot, $36.97).
CB collars (Aircraft Spruce,$2.51 ea.).
Provita smoke hood (Aircraft Spruce, $189.00).
According to 14 CFR 91.513, we need one extinguisher for seven to 30 seats – I have two in my six-seat Duke. One or two carbon monoxide/smoke detectors is a good number for four to 10 seats. Two to four CB collars should work in most GA aircraft. And in Part 121, we have smoke hoods for all crew members in order to allow us to function in a smoke environment while we fight the fire. These are also a great tool for GA. And aircraft with more than 19 seats need a crash ax to assist with egress if exits are jammed.
Remember, aircraft electrical systems can be our savior or our slayer. Learn your electrical system, where critical breakers are located, and go shopping for the above safety equipment. Because even without a Flux Capacitor, we’re “runnin’ with the devil,” and it won’t take 1.21 gigawatts to create a fire that can roast our joules.