Were flying along blissfully the smooth night flight conditions and the panorama of lights below. The engine is purring, and, for once, we have caught a tailwind. We think this is why we became pilots and then we proudly wonder out loud what the groundbound populace below is doing on such a pleasant evening when they could be aloft.
Its so serene even the radio chatter seems to be fading into the distance and the panel lights are slowly dimming making the vista outside the aircraft all the more spectacular.
Wait a minute. . . The panel lights are dimming? When was the last time we checked on the aircrafts electrical system? A quick glance at the meter confirms our fear. We are in the midst of an electrical system failure, and like countless pilots, we were guilty of not monitoring the electrical meter until we had eaten well into our battery supply.
Now What?
Unless we smell smoke, or see flames or sparks coming from behind the instrument panel, the electrical failure is likely not an immediately life- threatening emergency. However, we do need to take action. First, we determine if we are experiencing problems due to an insufficient rate of charge or an alternator overcharge situation, the latter is a condition which can become an onboard fire hazard if ignored. The aircrafts POH and most commercially created checklists will guide us through the process of addressing the electrical malfunction, but as with so many things in life, it all goes a lot smoother with a little advance planning and some basic knowledge.
What Is the Source?
Electrical power in most modern light aircraft comes from two sources. The primary is the engine-driven alternator. In other words it is a dynamic source of electrical energy (for the purposes of this discussion we will use the term alternator to include generator).
The second source is the battery, which is essentially a reservoir for electrical energy. The battery also acts as a quasi voltage regulator for the aircrafts electrical system, working alongside the voltage regulator, by absorbing spikes in voltage, but also compensating for voltage drops. Furthermore, the battery provides power for initial engine start, and back-up power should the alternator or the alternator belt attached to the engine fail.
The typical general aviation electrical system has a number of other components which allow the pilot to take simple peeks at the health of the electrical system, while the aircraft is in flight. These items include meters, circuit breakers and annunciator lights.
Ammeter vs. Loadmeter
The ammeter and loadmeter are two very different meters and are common- ly misunderstood. The misconception stems from the erroneous assumption that the two meters are telling us the same thing. That is, we tend to think that the battery is being charged by the alternator if the needle is right of center, or the battery is discharging because the needle is left of center.
The misperception is that battery charge or discharge is a proxy for the alternators health. This may be true for an ammeter, but is most assuredly not the case of the loadmeter used in a number of popular aircraft.
Rather than measuring battery charge or discharge, a loadmeter indicates the amperes of load being placed on the alternator by each electrical component which is turned on, including the battery. This makes detecting a failure of the alternator more difficult without knowing the normal needle position for a specific aircraft, or by checking the system in flight. Thus when f lying behind a loadmeter, knowing the normal position of the needle is a must know item.
Circuit Breakers
Circuit breakers are failsafe items. When the circuit breaker is overheated by too much electrical energy it will open the circuit and stop the flow of electricity. It works whenever a voltage regulator fails to regulate an overvoltage situation or when a component is drawing more power than it or its associated wiring can safely handle. Unlike fuses in older aircraft, circuit breakers have the added convenience of being easily and repeatedly reset.
Common wisdom used to say aircraft electrical systems are simple systems and thus prone to voltage spikes from time to time. As such it was normal procedure to reset a popped circuit breaker at least once and perhaps two times, so long as nothing was smoking or overheating.
Nowadays, after the 2004 tragedy of a Swiss Air MD-11 and the high profile 2007 crash of a NASCAR Cessna 310 in Florida, airline crews are discouraged and sometimes even prohibited from resetting a circuit breaker in flight, unless the circuit breaker is controlling a component that is absolutely essential for flight.
Fortunately, this smart approach has trickled down to General Aviation. If a circuit breaker popped, it did so for a reason, and that reason is not likely something you can fix in flight. If the related component is not absolutely essential for flight, you are best just leaving it alone and then making the decision whether or not to terminate the flight.
Many newer aircraft now have critical and non-critical electrical components on separate buses, which helps the pilot determine and isolate essential electrical components.
Whats Going To Fail?
This is where advance planning really comes into play. The specific aircrafts POH is the key source for information. Items such as lights, most panel gauges and radios are obvious items, but what about some items which can become critical during instrument flight such as the turn indicator, autopilot, pitot heat or heated windscreen elements.
Flaps and landing gear in certain aircraft are also affected by an electrical failure. These last two components and any heating elements are huge draws on power and worthy of additional consideration if the aircraft battery has any reserve energy left which needs to be conserved.
This is also where creating a list of the ampere draw for each component in your aircraft and knowing how to turn off each item is a smart advance planning move on the part of the pilot.
Stacking The Deck In Your Favor
Loadmeter
During the pre-flight inspection of the aircraft, pay special attention to the alternator belt. Check for looseness and its overall condition. Also inspect the alternator and bracket to make sure the components are tight and that no wires are loose or disconnected.
If the aircraft battery is accessible check its security and overall condition. Be especially wary of any leaks or corrosion on the terminals. If the battery has been sitting for a while, then it is also time to check to make sure there is the proper quantity and quality of electrolyte in each cell. Be sure to secure the vent caps when done.
As you start the aircraft, watch the aircrafts ammeter or loadmeter. It should jump to the right as the aircraft is started and then settle to a needles width right of center for an ammeter, or to its normal position for a load- meter. If, by the time you are ready for flight, this has not occurred, it is time to questions the integrity of the electrical system.
Charging?
When flying with a loadmeter, there is a way the alternator can be tested to make sure it is charging the battery. The procedure requires turning off all electrical equipment, but leaving the master switch on. The loadmeter will now indicate the amount of charging current demanded by the battery, usually about 2 amperes for a fully charged battery. Unfortunately, this test may not be practicable during instrument flight.
Then while in flight, make it a habit to keep the meter, or if the aircraft is so equipped, the voltage annunciator light in your instrument scan. A lit voltage light or a rapid fluctuation of the needle on a meter may be an indication of an alternator mal- function. Pull and run your electrical anomaly checklist.
Oh Say, Can You See?
On a final note, gone are the bad old days of the large, heavy flashlight. Now, LED flashlights are cheap, small, powerful, and long lasting. It only makes sense for each pilot onboard to have at least two of these flashlights in his or her flight bag for when things go dark.
Armand Vilches is a commercial pilot, instructor and FAASTeam member.
This article originally appeared in the October 2012 issue of IFR Refresher magazine.
