Avionics failure in IMC

[Brantel]

With my RV-7, the VP-X Pro turns on the primary display with the master similar to what Paul mentions above.

This is standard with the VP-X product.

[Southern Pete]

Another reason not to have an avionics master?
I do have a switch on my main EFIS, but only a breaker on the stand-by, because there are enough times I only want to power up the fuel gauges or a radio.

[Lycosaurus]

I replaced my avionics master switch with a locking toggle switch.

[snopercod]

Originally Posted by Ironflight

Why have switches for the EFIS screens at all?...

Extending that line of thought, why have an Avionics Master at all? Bob Nuckolls of Aeroelectric Connection makes a good case against them at Avionics Master Switches: Really Necessary?. His basic argument is that if the switch fails, you're well and truly screwed. After much consideration, I went ahead and installed an Avionics Master anyway in my plane. (I'm VFR only and carry a backup handheld radio and battery powered Stratus/iPad.)

P.S. I've accidentally hit the power button on a GPS by mistake - just when ATC was clearing me to a new destination. I faked it

[rmartingt]

Originally Posted by Ironflight

Here?s one additional thing for everyone to think about. Why have switches for the EFIS screens at all?...

I wish there was a like button sometimes...

I'm building an electrically-dependent airplane (EFI and glass, eventually IFR). One thing I'm trying hard to do is eliminate single-point failures on the electrical side, so that the failure of one component (or a single accidental switch bump) can't cause the pilot-cooling fan to stop working. I've already decided to do basically as Paul suggests--anything critical for flight comes on when its power bus comes on; the bus power switches and critical engine switches (coil power, fuel pumps) will be covered or be locking*.

I've killed everything in the panel once, in Dad's -6. I was trying to look up a frequency on the Skyview when I hit a bump and killed the avionics master (toggle switch below the Skyview). At the time there was a bug that kept the backup battery from activating, so everything went dark. I was VFR so it was no big deal, just an annoyance... but it made me think.


* depends on what kind of switches I decide to go with...

[maniago]

Originally Posted by Lycosaurus

I replaced my avionics master switch with a locking toggle switch.

+1.

If youre gonna have a master switch (and I do - one for each buss and the buss tie) a Cam-over-switch is pretty hard to accidentally actuate......

[dlloyd3]

Similar thing happened to me after an alternator failure on a low IFR day while flying my Bonanza. Meant to cycle the alt switch and got the master at the same time. NY Center sounded tense when they lost my transponder. RV has the master and alt switches by themselves and high on the panel. Radio master by it self about two inches down. All other switches in the conventional location at the bottom of panel. Fuel pump at one end, flap switch at other end. Lights, strobe, etc. in the middle of the row. I've got to look for the strobe or nav light switch but never have to look for the pump or flap.

[SuperCubDriver]

On my -7 the master and avionic switch (also ELT remote) is located far left on the panel hard to reach from the passenger, and during normal ops not used during flight. The switches are double pole so less chance of failure. There is a switch guard around it and they are high so no chance bumping them with the knee.
On my -8 the critical switches are locking toggle switches, also double pole, but grouped together with other switches.
I´m flying VFR only, however the planes are at least capable flying safely in IMC.

I found that on some certified airplanes like the Mooney the avionics master actually opens when the avionics are switched on. This makes the switch itself kind of redundant.

[Carl Froehlich]

For an IFR RV, I offer there are superior power distribution approaches - none of which have an Avionics Master.

Carl

[Walt]

Originally Posted by rmartingt

I wish there was a like button sometimes...

I'm building an electrically-dependent airplane (EFI and glass, eventually IFR). One thing I'm trying hard to do is eliminate single-point failures on the electrical side, so that the failure of one component (or a single accidental switch bump) can't cause the pilot-cooling fan to stop working. I've already decided to do basically as Paul suggests--anything critical for flight comes on when its power bus comes on; the bus power switches and critical engine switches (coil power, fuel pumps) will be covered or be locking*.

I've killed everything in the panel once, in Dad's -6. I was trying to look up a frequency on the Skyview when I hit a bump and killed the avionics master (toggle switch below the Skyview). At the time there was a bug that kept the backup battery from activating, so everything went dark. I was VFR so it was no big deal, just an annoyance... but it made me think.


* depends on what kind of switches I decide to go with...

Personally I'm a control freak and want to be able to turn things on/off when I want to. Lots of things these days lack on/off switches, EFIS/GTN etc., and I want to be able to control power to these units.

Starting your aircraft requires max energy from the battery, load it up with a full avionics panel and you just add to the burden the battery has to carry (do you start your aircraft with all your lights, strobes, pitot heat on?). So I want everything off for start, no other way to turn many things off than with an avionics master. Avionics power supplies are generally rated for 11-33 volts, running them outside these limits is not generally recommended, start voltages will always be less than 11v.

I even go one step further and add a "radio" master, this is just for the radios (GTN units have no on/off switch). This also has the advantage of redundancy as splits the avionics load between two switches.

Another reason I like avionics/radio masters is the ability to shut these power sources off in the event of a problem, like smoke in the CP. Shutting off these switches kills power before it even gets to the fuse/CB panel.

Essential equipment all has a seperate aux battery inputs, so turning off both the avionics/radio masters still leaves me with primary instruments, GPS and a single com.

These switches also let me do ground checks/updates etc. with only the equip I need running. Like I said, for me it's all about control.

PS: I've been around/used the Honeywell 'TL' series switches most of my career, I still use them and personally have never seen one fail and won't use any other switch if I can avoid it.