As we move into the colder part of the year, we begin to consider winter weather and its implications for aviation here at GoFly. Whilst it’s not all extra chores and precautions – the winter months offer some of the most spectacular and breath-taking flying days – there are a few key extra points that all students and private hirers should be aware of. In the second of a four-part article series on winter aviation, we look at winter preflight checks.
During the A-check (the check performed on an aircraft before the first flight of the day) normal procedure is to turn the battery, exterior lights and pitot heater from the cockpit, then get out, walk around the aircraft and check that each system is functioning properly. The battery, most of the lights and pitot heat are then turned off from inside the cockpit. One light, normally a red flashing beacon atop the tailfin, is always left on. This is to provide an obvious visual signal if the battery master switch is left on inadvertently; this red light will still be flashing, and will hopefully draw attention to itself before the battery goes flat.
Clearly, it’s important to check that external lights are functioning correctly, as well as the electric stall warner. These systems tend not to use too much electrical power, so leaving these systems selected on will not excessively drain the battery. However, the pitot heat will.
The pitot (shown right) senses air pressure, which is then used determine airspeed, altitude and vertical speed. These are then displayed to the pilot via the cockpit instrumentation, but if this probe becomes iced up in flight, the information can become unreliable.
An electric heating element is embedded with the pitot probe, which allows it to be warmed up to such a degree that any ice will melt off during flight. Since during flight the pitot is experiencing a 100-mph wind chill (due to the forward motion of the aircraft) the amount of heating supplied is sufficient to overcome this – and also destroy the ice. This requires a lot of electrical power, which is solely supplied by the battery when the aircraft engine isn’t running. In fact, if the pitot heat is left on without forward airflow for over two minutes, the heating element will overheat and burn out!
Therefore, if a student takes a long time to check the lights, stall warner, and pitot heat, then the battery can be excessively drained. The main culprit for a drained battery is nearly always the pitot heat, due to the large current it draws.
A drained battery will make it a lot harder to start the aircraft’s engine later on; cold temperatures mean that the aircraft’s battery is less efficient, and therefore will have to work much harder to drive the starter motor. This can (and has recently) lead to failed attempts to start the engine, which completely drains the battery. A battery change will of course produce tech delays and problems for students, which is not desirable when trying to make the best of a good winter weather day!
So please try to keep the amount of time that the battery is switched on for during the A-check to a safe minimum. The lights, stall warner and pitot can be checked correctly in less than one minute, and it can mean the difference between being able to start the aircraft and therefore miss out on flying during glorious winter flying days.
Happy winter aviating!
Ben Koprowski, FI