Alternator Inop Lamp Weak

Recently had a full electrical failure, fortunately it was Day VFR. The airplane was on downwind, and after putting the gear down, lost the radios and all electronics. Dark panel. On final received a RED light from the tower. Performed a go around and received a Green light from the Light gun and landed. After shut down tried to restart the engine. Dead battery. This is a 2004 Arrow III, PA-28R-201.
The A&P arrived 2 days later to look at the problem. As per his instructions I had the battery on a charger for several hours prior to his arrival. He tested everything and could not find anything wrong in the electrical system. Even the battery was good and not in need of replacement. His assessment is that the alternator had tripped off in flight for some reason and was not noticed or reset as per the electrical failure checklist. Excuses include; Bright CAVU weather in the Arizona sunshine while practicing VFR Commercial Pilot maneuvers, eyes up and outside the cockpit.
Another interesting component in the chain, is that the mechanic discovered that the "Alternator Out Lamp" on the annunciation panel, does not illuminate very brightly when the alternator is turned off with the engine running. However it does display as brightly as the Oil & Vacuum lamps when it it tested with the Annuniciator test button.
Is this something that can be fixed or is this normal for this lamp to display less brightly when activated by an alternator failure or disabled by the alternator On/Off switch? Is there a part that needs to be replaced in the electrical wiring system and if so what is the part name and number.

Sincerely yours, for a safer G.A.
Bristowe Pitts

Comments

  • The dim display is normal, sorry. However, you can connect a second annunciator light in parallel with the first. Here's a link. https://www.aircraftspruce.com/catalog/inpages/al1RED.php?clickkey=5011821

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Piper Owner Society Forum Moderator and Pipers Author.

    Need help? Let me know!

  • edited July 16

    Bristowe;

    I had a similar experience. It was winter, and I flew a 2 1/2 hr flight to MI. I parked the plane and plugged in the engine heater. I returned to the plane after only 2 - 3 hrs. The starter spun so slowly it would not engage the Bendix nor turn the propeller. There was not heavy grease on the shaft of the starter, nor was it that cold, but it behaved like your plane with a weak battery. My wife (who was already in MI) drove me to the local auto parts store where I picked up jumper cables and a car battery. I jumped the airplane and it started immediately confirming that the Bendix was not bound up. I needed to stop for fuel on the way home so I kept the battery and cables with me in case the engine wouldn't start after the fuel stop. The engine fired immediately after the fuel stop without jumping, and I flew home without a single problem. At home, we pulled the battery and my A&P performed a load test. It showed 97% capacity, so the battery was ruled out. A month later during the annual, we inspected the starter, the wiring, master/alt switch, and checked voltage drops, but found nothing. We agreed that even if the battery was weak prior to departure, a 2 1/2 hr trip should have been plenty of time to charge up. We came to a conclusion similar to your A&P that something may have tripped the alt off line, but like you, I never saw an annunciator light come on and my radios continued to work. The problem has never reoccurred. I'm chalking it up to a weak connection somewhere that was disassembled and reseated during the annual.

    Jim "Griff" Griffin
    PA28 - 161
    Chicago area

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