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Procedural compliance


The first thing to consider is that batteries have their maintenance manual and their catalogue of parts; both the intervals and the maintenance procedures are codified. The maintainer has to diligently follow the instructions issued by manufacturers. “The helicopter


manufacturer liaises with the battery manufacturer in order to


establish the maintenance intervals. From a


maintenance standpoint the battery is treated as if it were an aircraft. Some batteries require a yearly check, whereas others require a check twice a year, depending on the model,” says Claudio Girardi, maintenance manager at Adria Air Services.


Different Types of Batteries


There are three main types of batteries that are most commonly installed on helicopters: lead, nickel-cadmium, and gel batteries.


Lead batteries are used in small aircraft and they are the easiest ones to maintain. It could even be said that - under certain circumstances - there is no need for maintenance at all. “Lead batteries, once positioned on board, have their own life cycle at the end of which - instead of performing maintenance by emptying the batteries and checking the cells – they are often replaced by new batteries. The advantage of lead batteries is that they are simple and safe. On the contrary, they do not maintain a constant charge level. The charge degrades over time; little by little the curve of the voltage decreases because the cells of the batteries progressively lose their holding ability,” says Fabrizio Segrè, quality manager at helicopter maintenance company Euroavia.


Nickel-cadmium batteries are installed most often on more sophisticated turbine-powered helicopters requiring a significant electric charge upon starting. These batteries also have pros and cons. An advantage is that they maintain a constant charge over time, but a disadvantage is nickel-cadmium batteries do not provide notice as to when their charge level is about to drop or when they are having issues in maintaining the nominal charge level.


“Nickel-cadmium batteries maintain their nominal charge level - e.g. 24 volts - and then, all of a sudden, this level drops to zero. Instead of having a descending curve like lead batteries, which allows one to predict their performance over time, nickel-cadmium batteries have a straight line, which at a certain point drops all of a sudden,” Segrè says.


“Also, thermal runaway is a second aspect of nickel-cadmium batteries


that needs consideration because it determines


maintenance cycles. Issues in the battery’s cells, internal short- circuits, and degrading insulation can potentially overheat the battery and produce a destructive result. Thermal runaway is due to the particular internal structure of nickel-cadmium batteries, which can continue to overheat even if the electrical load inducing an increase of the battery’s temperature in the first place is discontinued. It is for this reason that helicopters equipped with nickel-cadmium batteries must have a sensor connected to a warning light installed in the cockpit to monitor the battery’s temperature.”


“Lead and nickel-cadmium batteries are not compatible with one another; they need to be managed in two separate environments for health and safety reasons, since the gaseous emissions of these two different types of batteries can create an explosive compound. The two types are also to be disposed of separately,” Girardi says. “There is a recent evolution with regard to lead batteries. They are being increasingly manufactured without liquid acid inside, but rather with the electrolyte in the form of gel; this makes the handling of batteries safer.” Gel batteries are gaining momentum because they have the same simplicity as lead batteries, as well as the same effectiveness as nickel-cadmium batteries.


74 Nov/Dec 2017


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