Avionics & ELT Weirdness

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machkhatib

Pre-takeoff checklist
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Mach
This morning my avionics stack (radios, GPS, transponder) would not come on during start up (master, then engine startup, then avionics switch). These items were all connected to the avionics switch and did not power on. Everything else was working fine, such as the beacon, Garmin G5 attitude indicator, cockpit lighting, etc.

We did some troubleshooting with the fuses and circuit breakers, and also checked for a loose wire to the avionics switch. No issues. Finally, I got out my portable radio as I thought about doing a hop from one untowered airport to another nearby untowered airport. Between my portable radio and ADSB-in on my iPad / Garmin GDL-50, I could manage.

But when I turned on the portable radio, I heard the ELT signal going off, even though the portable was on the local CTAF - maybe the portable monitors both the selected frequency and 121.5 simultaneously? I switched to 121.50 and heard the ELT signal there, of course. I took the tail panel off and confirmed it was my ELT. I reset it and rearmed it and confirmed the ELT signal was off.

I then started up the airplane again and began taxiing with the avionics switch ON but the avionics stack was dark. Halfway down the taxiway to the runway, all the radios, GPS, and transponder came on, and everything worked perfectly for the rest of the flight. I landed at a couple other airports, shut down, and everything came back on normally when I restarted.

What on Earth could explain this weirdness?

What set off the ELT? Did the ELT coming on prevent the rest of the avionics stack from coming on? Why did the avionics stack come on later?

Other items to note which may have been a factor...

1. The FBO fueled my airplane that morning shortly before my preflight.

2. I attached a GoPro camera to a tail bracket associated with the old ADF "clothesline" antenna. The antenna and ADF were uninstalled long ago, but the bracket is still present on the tail.

3. There was rain and thunderstorms the night before.
 
ELT isn’t part of the electrical system so coincidental. Percussion from thunder may have set it off. It demonstrated how effective that technology is. Nobody was looking for you.

My avionics switch has acted like yours. I turn it off, cycle the split alternator-battery switch off and back on, and magically the avionics circuit works. Mine’s not broken enough to worry about it.
 
Lightning strike?

I always wired 2 Radio Masters in parallel to reduce single point of failure.

ELTs can be strange though. 70’s Cessnas came with the Cessna ( Leigh Sharc 7).

A local AM radio station (1520 ) would bleed through the COMM loudly.

Cessnas fix was to replace the Cessna unit with a Narco ELT 10.

It worked !
 
machkhatib said:
What on Earth could explain this weirdness?
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Worn master switch, bad ground, chafed wire, loose connections, etc. Hard to tell.
machkhatib said:
maybe the portable monitors both the selected frequency and 121.5 simultaneously?
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To add, being that close the ELT will be picked up by any AM radio. Some OEMs even recommend to use a regular portable AM radio to check ELTs and save the aircraft battery.
machkhatib said:
What set off the ELT?
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As mentioned above the ELT should be separate from your electrical system. However, it may be connected to a GPS. Have seen thunder set off ELTs in the past but not on a regular basis. What type ELT and how is it mounted?
 
machkhatib said:
Ameri-King AK-450
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Given the issues and AD against these ELTs, you may want to look at buying one of the available ELTs that are a drop in replacement for the 450, especially since it activated in this manner. Perhaps discuss with your mechanic?
 
ELT is close enough to the ship’s comm radios that, because it is so strong at that close distance, it will bleed over to whatever freq is dialed in; so ‘normal’ weirdness there.
 
My ELT will trip on, if I broadcast on comm radio when between two rows of metal hangars, maybe yours too?
They can also trip on due to internal defects as well.
 
I’m convinced I should replace the ELT. Even though the AD states replacement is optional, this incident shows its problematic nature.

So ELT aside… should I be worried about the avionics not coming on until half way down the taxiway? I’ve never come across such a problem and I have no idea how it solved itself.

It may be a coincidence but my passenger said the avionics all came on the moment I turned on the Garmin GDL-50, which is connected to the cigarette lighter. But I’ve had it connected to the cigarette lighter at least 3 flights before this without any such issue.
 
A lot of responses missed the point that the avionics stack DID NOT COME ON. The ELT can’t bleed into a radio that is not on. Certainly you have a problem. I once had a rental that did this. I found individually turning all avionics off before turning the power on to the stack and the in a particular sequence turning each on would work every time. I wrote it in the squawk book and the maintenance person called me out to demonstrate what I found. With the stack power off and all avionics on when the stack power was applied nothing would come on and no circuit breaker popped. By using my technique it worked every time. I don’t know what was fixed but when the plane came out of maintenance the problem never happened again. My theory is a bad power connection. Each avionics unit has capacitors that need to charge up when power is applied. A poor connection could not provide enough current to charge all the caps at the same time. The sequence allowed each unit’s caps to charge before turning on the next one powered up. Once all the caps were charged the stack stayed on. If you don’t know a discharged capicator looks like a short until it is charged. I suspect a similar problem with your setup which is a poor connection in the power connections to the stack. Try turning the avionics on one star time and different sequences to prove my theory.
 
RonP said:
Each avionics unit has capacitors that need to charge up when power is applied. A poor connection could not provide enough current to charge all the caps at the same time. The sequence allowed each unit’s caps to charge before turning on the next one powered up. Once all the caps were charged the stack stayed on. If you don’t know a discharged capicator looks like a short until it is charged. I suspect a similar problem with your setup which is a poor connection in the power connections to the stack. Try turning the avionics on one star time and different sequences to prove my theory.
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This is an interesting theory. A couple variations on this - it’s possible my Garmin GDL-50 was drawing too much power from the cigarette lighter, preventing the avionics capacitors from fully charging until I cycled the GDL-50. Alternatively, if there was a nearby lightning strike (to set off the ELT?), maybe all the capacitors were discharged, and the avionics stack needed the aircraft to run long enough to recharge them (unrelated to the GDL-50). If I find myself with discharged capacitors in the future, then I could cycle each radio on one by one, like you did, until I get my plane into the avionics shop.
 
RonP said:
A lot of responses missed the point that the avionics stack DID NOT COME ON. The ELT can’t bleed into a radio that is not on.
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I think you missed that many are responding to his report of the ELT being heard on his handheld.
 
Let'sgoflying! said:
I think you missed that many are responding to his report of the ELT being heard on his handheld.
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Yeah there’s two problems: (1) the ELT going off, which I heard in my handheld, and (2) the delayed-startup of the avionics stack, which turned on midway through my taxi. I thought they might be related but from the feedback here, it sounds like it is coincidental.
 
The ELT can go off from a hard landing. It may not seem excessive hard but enough to set off the ELT. Had mine go off when I bumped it taking a tool box out of the luggage compartment. The power outlet, I.E. cigarette lighter socket, should be on a breaker or fuse. If it is not providing enough current then the fuse or breaker would fault. If there is a poor connection limiting the current and the fuse or breaker did not fault them it is a wiring problem.
 
RonP said:
The ELT can go off from a hard landing. It may not seem excessive hard but enough to set off the ELT. Had mine go off when I bumped it taking a tool box out of the luggage compartment. The power outlet, I.E. cigarette lighter socket, should be on a breaker or fuse. If it is not providing enough current then the fuse or breaker would fault. If there is a poor connection limiting the current and the fuse or breaker did not fault them it is a wiring problem.
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If a landing of any kind set off my ELT, then it was running continuously for a whole week since my last flight. I doubt the battery would last that long.
 
You ask a good question regarding how long an ELT battery should last. There should be some requirement it last X hours so you could be found in a day, week or month? If it is more than 1 week then it certainly could have been squealing for a week. Regardless of the answer the battery should be replaced since it is unknown how long it has been activated.
 
RonP said:
You ask a good question regarding how long an ELT battery should last. There should be some requirement it last X hours so you could be found in a day, week or month? If it is more than 1 week then it certainly could have been squealing for a week. Regardless of the answer the battery should be replaced since it is unknown how long it has been activated.
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Fair points, though I strongly suspect it went off that morning and had only been running a few minutes. The mechanic I talked to was surprised when I walked in with the ELT signal blaring in my handheld - the FBO monitors 121.5 and in his words, “they would immediately send someone to check it out.” Additionally, CAP is based at my field. If they can’t find an ELT going off at their home base for a week, well, we’re all screwed if we ever need their help. :D
 
ELT batteries may have to be changed after it has been transmiiting for an undetermined amount of time.
 
AmeriKing is a piece of ****. A stolen knock-off of the ACK design. The remote unit is particularly problematic and susceptible to RF interference which is surprising given how dumbass simple it is. First thing to check is to make sure it's wired up properly. The thing is wired up with a two RJ-11 plugs, but you need to make sure they have the right orientation. I found mine was installed in a way that always made it trip.

I originally thought that it had something to do with the battery, but the battery is solely there to light up the LED when the relay closes in the ELT unit. There's one common and the other two wires are wired to the set/reset buttons.
 
AK and ACK both use similar telephone type modular plugs on the lead to the Remote. However; plug orientation is different between the 2. I’m unsure which is
made per “ Telephone Standard”.
 
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