This is an excerpt from a report made to the Aviation Safety Reporting System. The narrative is written by the pilot, rather than FAA or NTSB officials. To maintain anonymity, many details, such as aircraft model or airport, are often scrubbed from the reports.
Shortly after takeoff, at approximately 200 feet, we experienced almost total electrical failure in our Mooney M-20F.
A few days before, turning on the landing light recycled power to my Garmin GNS530W; all other systems operated normally.
My initial thought was that the landing light was on its last legs and drawing higher-than-normal current. Runup was normal and I deactivated the GNS530W for takeoff with the landing light.
Gear came up slightly slower than usual and shortly later in the climb the backup radio and transponder died. Im- mediately we lowered the gear to make sure we had gear down to return to the airport. At that point it became apparent we were at the end of battery power.
By midfield downwind we only had the NAV lights and the electro/hydraulic flaps were inoperable. Following light gun signals we landed uneventfully.
Human Factors: I made one assumption about the landing light and resolved that was the answer. I was wrong and excluded other possibilities.
I worked around the problem with that assumption and it became worse.
Primary Problem as determined by an ASRS analyst: Aircraft.
Do it right or do it cheap.
Pulleys must line up. Alernators and generators must have 20- 25 % more amps than installed equipment.
Homes in the 40-50 ears had 40amp service and 15 GA wire. To and modern A/C, electric range, range hood, TVs, computers requires a complete rewiring.
CFIS and salesmen just don’t care or know.
Neighbor of mine has a 66 Mooney with the STC alternator. It might be just his or that particular STC, but it doesn’t fit very well, the pulleys don’t line up properly and not only does it eat belts, it eats the aluminum pulley on the alternator. He was able to buy a new pulley and was told it was the last one in existence.
He sometimes flies IFR so having a good, reliable electrical system isn’t optional – it HAS to work.
I’ve seen some downright horrendous wiring on airplanes and I cannot imagine how they pass inspection, but somehow they do.
Nice exercise – go through YOUR airplane and figure out what instruments and accessories won’t work when the power goes out. Then figure out what to do if it does.
A quick check found that Plane-Power offers 4 different kits for Mooney M20s, depending on engine model. I’m sure that there are others as well, so it can be easy to choose the wrong kit.
I also have seen some very badly ‘cobbled’ wiring in aircraft. One, had the owner complaining that the alternator tripped off as the rpm went above 1,500, so he added a 2nd battery and flew it that way.
It turns out that it had 2 overvoltage relays and NO voltage regulator. It makes me wonder who did the ‘re-wire’, and why would a pilot fly an aircraft under those conditions ?
Regarding incandescent lights, when they are reaching end of life, the filament becomes thinner, ergo higher resistance, therefore lower current draw.
The 250 watt par46 lamp in the Mooney uses about 18 amps. The original certified DC generator will not charge the battery at less than about 1,500 rpm.
An led landing light will help, but the more reliable solution is to use an stc’d alternator.
Most pilots have a very poor knowledge of the aircraft electrical systems. Most cannot tell you the voltage of a fully charged ’12 volt’ battery !
When the Garmin 530 rebooted after the landing light was turned on should have been a clear indication that the battery was incapable of handling the additional current load and investigated immediately. Many things could have caused that issue, including a corroded battery terminal, charging system failure, battery failure, etc. So many times I’ve heard people say the battery was ok because they checked the voltage and it was over 12 volts. What they don’t realize is that voltage alone does not indicate a battery’s condition, it must be loaded to see the true capacity. I’m guessing that the landing light on this Mooney was incandescent or halogen and put a substantial load on the battery causing the Garmin to reboot due to low voltage.
The article never gave the actual cause of the electrical failure.
My comment is not to criticize the pilot here, as many people don’t understand the relationship between voltage and current, or electrical issues in general. My goal is to encourage pilots to investigate thoroughly any odd electrical events. The easiest way to check this would be to put a volt meter on the battery and turn on some high current devices and see what the battery voltage does. If you see a substantial voltage drop, especially if the voltage goes below 12 volts you most likely have a problem.
++1
And to emphasize this even more — in my prior post, the airplane I was talking about — and cutting a long story as short as I can — shredded the alternator belt in DAY IMC.
The pilot elected to divert immediately because the G530 went black and nothing electrical was working. This means its internal battery didn’t fully charge either.
I got a phone call from xxx Center asking about the plane because the transponder died while the plane was over an airport. They didn’t even have a primary echo.
A few text messages and I called them back to confirm aircraft landed at airport it had circled due to complete electrical failure.
Why did I get a call from a Center? The joys of ADS-B out/in. My phone number is associated with that plane. It was one of my partners flying it.
So now you have the rest of the story as why my other earlier post.
I doubt that this is the root cause of this report, but, we have just been looking at our plane and have noticed that our load meter (Piper) is at max with a 60A Alternator. How did we get here? Well, the panel was upgraded to have a G530W (and I don’t know the sub model which specifies the output power of the radio).
And there are a few other things that were added to the plane as upgrades since it was built (all before we bought it).
So, with all the lights on and the G530 running, the alternator does not have enough “surplus” to charge the battery. And so, if one has an alternator failure in flight, you may not have 30 minutes of battery power. And that is after changing the landing light to be an LED unit.
Oh, and guess what? Turn on the pitot heat and you will discharge the battery in this case. Cold, moisture, IFR, Night. Very bad combination.
It is probably wise to check the specs on one’s electrical system after doing panel upgrades to make sure that one is only using a MAX of 80% of alternator output. And I think that is based on “regularly used” devices. Don’t forget your regularly used tablets that you plug in….
Can one get an STC for an 80A alternator? Possibly. But, is the wiring system from the alternator to the battery heavy enough to carry the extra 20Amps? A lot to give thought to.
Great point !
NEVER ASSUME anything when it comes to preflight checks. If you see an anomaly, anything out of the ordinary check it before flying. Even it if means taking it to a shop.