Mag switches "on" indication options

[Flying Scotsman]

I'm starting to wire up all the switches and whatnot on the panel, and doing my schematics (btw, ExpressSCH seems to work well for a free tool ).

I'm using the Aveo Rockrack switches which are internally lit by LEDs. Nice!

So here's my question...I have a keyswitch which must be ON in order for the mags to be ungrounded. No key in the switch, can't turn the system on, no way to get a hot mag. I also figured out how to wire a pushbutton starter switch (also internally lit with an LED ) so that during start, the non-impulse-coupled mag is grounded during starting.

So...I can have the L and R mag switches "light up" only when the keyswitch is on and the mag is in the ON position, or I can have them light up *whenever* the mag switch is in the ON position, as a sort of visual "HEY! YOUR MAGS ARE ON!" warning (even though they shouldn't be ungrounded due to the keyswitch safety interlock).

Hot mags scare me...I think I'd like the idea of a RED light on a mag switch whenever it's in the ON position, but maybe that's confusing?

Which do you think is the better option?

[az_gila]

Originally Posted by Flying Scotsman

....So here's my question...I have a keyswitch which must be ON in order for the mags to be ungrounded. No key in the switch, can't turn the system on, no way to get a hot mag....

Have you created a single point failure that would affect both mags at the keyswitch?

[Andy Hill]

As with Gil, the whole concept of what you are doing frightens me

Yes - a hot mag on the ground is not desirable, but discipline / training should keep it safe (a standard Cessna style switch is as good as any, and ensure the keys are "out" when cockpuit unoccupied). No mags in the air is definitely even less desirable / far more hazardous...

It's difficult to do at this time, but think resale value as well. Keep it (relatively) conventional.

Andy

[Snowflake]

My opinion is to do away with the keyswitch entirely. I got rid of mine because I hated having a key fob flopping around on the panel while flying. And personally I would want Green lighting for anything that is "on," regardless of whether that means the mag is "ungrounded."

If you want an external indicator that the mags are "off," wire up a simple LED flasher that pulses once every 5 seconds and hook it up to come on when the mags are "off." Then put the LED on the glare shield where you can see it during your walk around.

[aerhed]

I've been harping at guys for years: When you stop, pull the keys and throw them on the glareshield. When someone approaches the plane to hook up a tug or towbar etc. they look at the glareshield. Keys= warm-fuzzy. No keys, hair stands up on your neck.

[Flying Scotsman]

A single point failure...you mean like if the keyswitch suddenly mysteriously went from the "On" position to the "Off" position? Why would that make it any different than this part:



Basically, I'm doing *exactly the same thing*, but just with a keyed switch and two toggles, instead of everything all in one.

So let me take these in order, and then maybe someone will address the original question?

Failure: Yes, but it's no more of a single-point failure than the switch above. I'm not worried about that, as the worst failure other than the key turning itself in flight (which it is not wont to do, as this is a pretty sturdy keyswitch with very positive detents) would be a broken lead or contact, which would fail the mag *open*, not grounded.

Cessna style...correct me if I'm wrong, but all the Cessnas I've flown had the switch style shown above, which as I've said, would have the same potential for failure.

Getting rid of it...not an option, in my mind. A simple toggle switch which makes the mags hot is not safe, IMHO. A quick search here will find all sorts of horror stories of people at airshows and fly-ins dicking around with peoples' cockpits, even so far as to let their kids sit in the planes and diddle the switches. All it takes is ONE idiot like that to set up a potentially deadly situation. No thanks, I'll take something a bit more positive when it comes to safety.

Lastly, whatever color light it is is irrelevant, and I don't want to goober up the cockpit with blinky lights and whatnot. A flashing LED for hot mags is most certainly NOT any kind of standard.

I agree with aerhed, but not everyone around an aircraft is an experienced ground crew.

So...let me try this again. There will be a keyswitch, sorry if that worries anyone, but that's my decision. There won't be additional flashing lights and buzzers and stuff...the lighted toggles are already capable of being lit, why add more lights. The wiring I have is safe, and failure modes are such that in-flight loss of mags is no more of a probability than with the "standard" ignition switch.

Back to the original question, and maybe I won't get an answer, and I'll just make a decision...mag indicator lights (in the switch) on regardless, or only on when the interlock is "armed"?

[ChiefPilot]

I designed my panel so that a light means "Something may be wrong here, check it out.". It's less error prone than a system where sometimes a light means good, sometimes a light means bad as well as quicker to scan.

[RV8R999]

are the LEDs in those switches wired to the battery bus..in other words they are independent of your master switch otherwise the master switch will need to be on as well. You can have a hot mag with the master off and not see those lights if they are not connected directly to the battery - right?

I think the lights are useless to anyone careless enough to pull a prop around without checking the status of the mag switches since they will not be seen from the prop arc.

It would be better to wire up a really loud bullhorn that yells, "Mags are hot, mags are hot" be sure to buy lots of spare batteries though...

[jetjok]

Steve,
I have just the part you need! Master ignition switch and individual magneto controls!


Just my .02, but as one previous poster has already stated, keep it simple and develop a habit pattern of when the key switch goes off, the keys come out and go to the same place each time (in my case, hanging from the DG knob).

However, as one member's signature states...."Build the plane you want...."
Good luck!

[SteinAir]

Originally Posted by Flying Scotsman

......Back to the original question, and maybe I won't get an answer, and I'll just make a decision...mag indicator lights (in the switch) on regardless, or only on when the interlock is "armed"?

Here's the quick answer....NO. Why? Because all you manage to do is have an indicator that tells you the position of the switch, which you obviously can tell visually just by looking at it. It does little to tell you if the mag is hot or not. Also, if it's a light that you intend to only have on when the engine is not running (who wants to continuously look at a warning light during the normal phases of flight) how do you intend to tell the light to only illuminate when the engine is stopped or you are on the ground?

Also just a quick comment on switches (and mind you this is not personal at all, only my opinion)...just because it's a "key switch" looks like a key switch doesn't mean the internals of all switches are created equal and one shouldn't assume as much. Aircraft mag switches are actually fairly robust (look at their size) and aren't exactly identical to other simple "on/off" type switches. Perhaps you found one that is similar, but I don't know for sure as I've not seen it's guts so I very well could be speaking out of school on that.

I'm not trying to argue, but remember we should always design stuff primarily for the 99th percentile, not the 1th percentile. In some cases when you endeavor to increase safety you actually have a net negative effect on reliability. I'm not saying this is 100% the case, but some of what you're doing and the stated reasoning behind it does give me pause.

Just my blunt 2 cents as usual.

Cheers,
Stein