Batteries – Jumping Hazards

If your airplane has an electric starter, you have a battery on board and, over time, a number of factors can help to rob the capacity from your battery, making it too weak to start your airplane. If you need to get from here to there with any sense of schedule or urgency this leaves you with few options and many pilots to turn to the same technique that they use for their cars — that is, to jump-start the airplane.

Caution: While you can jump your aircraft, it is usually not the best thing to do for the aircraft’s electrical system…

THE SETUP – You get your friend to pull his car up next to your airplane while you get ready to hook up the booster cables between your plane and his car. But wait! Is your plane a 24-volt model? If it is, hooking up even your weak battery to the car’s electrical system can cause immediate damage, including fire or an explosion, as the two voltage sources try to reach equilibrium with each other. The jumper cables will heat up — and can even melt off the insulation; all happening so fast that you can’t remove the now red-hot leads from your battery.

ANOTHER SETUP – Unknown to you, the battery in your airplane is internally faulted, and has discharged ‘hard to ground.’ When you connect your friend car to your 12-volt battery, current flows between the car’s electrical system, and your aircraft’s. BUT, in this case, the current will flow right to ground through the internal fault, and the fluid in the battery starts to heat up as the acid-water mixture begins to seethe and boil. Hydrogen gas is released by the rapid charge, and a minor spark between the battery’s plates, now exposed by the rapid boiling, sets off an impressive explosion that sprays you, your friend, and both your vehicles with battery parts and acid!

Contact your FBO and ask for help. Most reputable shops have battery equipment that is designed to charge batteries at variable rates. The A&P will usually start off with a low rate, to verify that the battery is not faulted, and then will up the rate when they are sure that there is no problem. They will also likely look for the cause of the problem, such as corroded terminals which can impede charging of the battery, long periods of inactivity, which are very hard on batteries, or too low of electrolyte level in the cell, which can rob their capacity.

WARNING – If your battery is more than two or three years old, and it goes dead on you, it is giving you fair warning that the time to replace it has arrived. Take that first warning seriously. The maximum life expectancy of an aircraft battery is about four years at the most. Unless you can trace the condition of the battery to a carelessly left on lamp or appliance, the right thing to do is have your FBO order a new battery, for installation at the earliest opportunity.