May 28, 2018
While in cruise flight, the radio and GPS lights flickered, followed by a total loss of engine power. The pilot attempted to troubleshoot the loss of power and then conducted a forced landing to a field, during which the airplane impacted a fence; the wings were substantially damaged.
Examination revealed that the wire connection from the main battery to the engine’s electronic ignition had melted just above the terminal attachment. Although the airplane was equipped with a backup battery, the connection from the backup battery to the ignition was disconnected, with the wire connection from the electronic ignition to the backup battery not connected to the battery terminal.
While the melted wire that connected the main battery to the electronic ignition would still have allowed power to the electronic ignition from the backup battery, the lack of connection to the backup battery provided no power to the electronic ignition and resulted in the total loss of engine power.
Any more info about the homemade gel cell battery? I guess that was the source of overheating that melted the wire?
Don’t have any more information, though there was a picture in the NTSB docket.
I saw the photo, but on my phone, it was too small to see detail. To me, it looks like maybe the crimp was bad, making a high resistance connection which heated up when current was flowing? There appears to be no surrounding damage (overheating)? Just a speculation.
In the pic, it sure looks like one of the small gauge white wires connected to the battery positive (+) terminal goes straight up to ground!!! This is probably the main cause of the problem, and the reason the terminal melted at the battery. I don’t see that even mentioned in the report.
I have been wondering about the quality of the battery cable crimp terminals, if they are done poorly they can create heat.
This RV-4 accident has a similar electrical system meltdown which resulted in ignition system loss. In this case, the mechanical backup ignition failed to respond when the electronics failed.
Ironically, I was working in the hangar next to this RV-4 the day before the accident. I had discussed electrical issues with the pilot as he intended to fly to a maintenance shop the next morning. The electrical system failed and took out the ignition system and the RV-4 was landed, with damage, on a golf course in the wee hours of the morning. Reference NTSB CEN25LA309
There are also accidents in which the electronic ignition fails, and the backup magneto fails, due to lack of maintenance or damage induced by the electronic ignition set up. The root cause for most ignition failures remains to be poor installation and maintenance practices.
Someone once posted a most interesting column on the current carrying capacity of wires and switches that I can’t toggle up just yet. A/C current ratings are “big deal” different than direct current ratings and that’s important stuff if you’re wiring up your flying chariot. There must be a number of “Sparkies” out there who have something to say about this.
Ampacity (current-carrying value) isn’t different for ac vs dc. What may have bearing is type of wire (stranded or solid) and jacket/insulation. Automotive wires @ 12V are generally a different specification than 120/240/600 volt specs. Mostly to do with vibration I think.
Then there’s the connectors- if loose or otherwise improperly performed, can heat up & fail.
It’s been awhile since I flew an aircraft with electronic ignition. Isn’t there a step during run-up checks when you check the engine operation on the backup system alone? Wouldn’t that catch the problem of the wire disconnected from the backup battery?