Yesterday, 02:09 PM
I have received a bunch of messages requesting more information on the Fatal Flaw in the overhead electrical wiring panel on the 162Fs and Talons. What made me aware of this wiring issue occurred when I was flying with a student in his 162f when suddenly the entire electrical system shut down. Since the engine ignition, fuel pumps and FADECs are all controlled by the electrical system, the helicopter got real quiet at 500' AGL.
I was able to perform a safe auto to a grass field below us and upon inspection found that both of the 30 amp fuses at the Alternator were blown. Looking further I found that the 30 amp fuses in the overhead panel had also blown cutting off all power from the battery. How could this happen? We have redundant systems to prevent just such a dangerous condition from occurring.
I got the wiring diagram out and traced out the power feeds from the alternator to the overhead pane, the feed from the battery to the overhead panel, and the feed from the alternator to the battery. What I noticed was that both of the "REDUNDANT" systems shared the same power feeds from the alternator and the battery, they were not separated but jumpers went from one 30 amp fuse to the next to the next in the overhead panel. The designers idea was that if one supply failed the jumpers would carry the power from the other supply over to the other system and the pilot would not ever know that there was a failure of one power feed.
This worked but... what if one of the power feed wires should short out to ground...Power would surge to the short blowing every fuse in the path between the short and the power source. Now that made sense so we began inspecting the power feed wire originating at the alternator and traveling up along the frame to the overhead. At one point the wire was rubbing on the sharp metal edge of a frame bracket and when the insulation rubbed through, the wire shorted directly to the frame taking out every fuse in the power feed system to critical components needed to run the engine.
The fix for this flaw in the wiring was to isolate one FADEC, fuel pump, and ignition system completely from the other, not by just switches but by separating the power feeds themselves. After replacing the alternator feed wire that had shorted out, and the blown fuses, we change the wiring overhead. We ran the alternator power through one 30 amp fuse in the overhead then to the individual fuses that protected one FADEC, one fuel pump and one ignition system. We then ran the power feed from the battery through a 30 amp fuse to the other fuses that protect the other FADEC, fuel pump and ignition system. With this new wiring routing if one power feed would short out, one system would shut off and the pilot would immediately know that there was an issue as they would get a FADEC warning light, but the other system would continue to keep the engine running and the occupants safe.
I was able to perform a safe auto to a grass field below us and upon inspection found that both of the 30 amp fuses at the Alternator were blown. Looking further I found that the 30 amp fuses in the overhead panel had also blown cutting off all power from the battery. How could this happen? We have redundant systems to prevent just such a dangerous condition from occurring.
I got the wiring diagram out and traced out the power feeds from the alternator to the overhead pane, the feed from the battery to the overhead panel, and the feed from the alternator to the battery. What I noticed was that both of the "REDUNDANT" systems shared the same power feeds from the alternator and the battery, they were not separated but jumpers went from one 30 amp fuse to the next to the next in the overhead panel. The designers idea was that if one supply failed the jumpers would carry the power from the other supply over to the other system and the pilot would not ever know that there was a failure of one power feed.
This worked but... what if one of the power feed wires should short out to ground...Power would surge to the short blowing every fuse in the path between the short and the power source. Now that made sense so we began inspecting the power feed wire originating at the alternator and traveling up along the frame to the overhead. At one point the wire was rubbing on the sharp metal edge of a frame bracket and when the insulation rubbed through, the wire shorted directly to the frame taking out every fuse in the power feed system to critical components needed to run the engine.
The fix for this flaw in the wiring was to isolate one FADEC, fuel pump, and ignition system completely from the other, not by just switches but by separating the power feeds themselves. After replacing the alternator feed wire that had shorted out, and the blown fuses, we change the wiring overhead. We ran the alternator power through one 30 amp fuse in the overhead then to the individual fuses that protected one FADEC, one fuel pump and one ignition system. We then ran the power feed from the battery through a 30 amp fuse to the other fuses that protect the other FADEC, fuel pump and ignition system. With this new wiring routing if one power feed would short out, one system would shut off and the pilot would immediately know that there was an issue as they would get a FADEC warning light, but the other system would continue to keep the engine running and the occupants safe.