brien23
Cleared for Takeoff
Before start and at shutdown turn off all the radios. I believe it to be good advice can't seem to get others to do it as I find the avionics in the on position all the time before start.
Turn off the radios
- Thread starter brien23
- Start date
bnt83
Final Approach
I agree. There are lot of avionics now that have no power switch so a master avionics switch needs to be installed. The Garmin GTN series and probably the G5s don't have a power switch.
you are correct. Even more annoying about the G5 is that is auto-powers on, so without an avionics master, you have to wait for it to power on enough to power it back off (another 5 seconds to do that) before you start the engine.
Needless to say, my Mooney now has an avionics master switch.
To be honest, I don't think there is any point it powering the G5 off without an avionics master, since the circuitry really isn't protected by a "switch" anyway.
bnt83
Final Approach
That would be very high on the list to install if buying one without an avionics master.
I remember climbing into a rental to go night cruising and the damn power & mode select switch was busted on a KT76A transponder. This memory made me happy when I discovered my new GTN had no damn switch to break like that KT76A did. You know darn good & well if it did break on a GTN it would be like $800 to fix and of course shipping and downtime. Good riddance! My avionics master switch is around $40 if it ever breaks.
bnt83
Final Approach
I do have breakers that can actually be pulled/tripped manually on the whole avionics bus so they can be handy. The avionics blower is loud so I disable that during maintenance.
IMHO, a PFD or electronic attitude indicator should be on the main electrical bus, not on the avionics bus. In fact, I suspect that the install manuals call for this. If the master is on, the PDF/AI (G5, Sandia, etc.) should be one. I don't think modern electronics are as sensitive to voltage fluctuations as the older stuff.
Clark1961
Touchdown! Greaser!
- Joined
- Jun 7, 2008
- Messages
- 17,737
- Display Name
Display name:
Display name:
The folks who wrote and approved the STC for the Aspen have a slightly different opinion since a separate switch is required. At least that is what the folks at Autopilot Central told me about the PFD master switch they installed.
Zeldman
Touchdown! Greaser!
One possible explanation is that just about everyone started driving cars and listening to the radio or other music playing device. We did not turn those off before shutting off the engine, nor did we make sure they were off before engine start. So that my carry on to the plane.
It may be switched, but I bet it's switched on the main bus and not the avionics bus.
Edit: Actually, here's what the Aspen install manual says:
"An 'EFIS MASTER' switch or switch breaker to the PFD may be installed if the customer desired to isolate the PDF during engine starts. The PFD breaker must be a pull type breaker and should be connected to the switched battery bus."
Clark1961
Touchdown! Greaser!
- Joined
- Jun 7, 2008
- Messages
- 17,737
- Display Name
Display name:
Display name:
How much money do you have?
See my edit above. The Aspen install manual calls for the PFD to be wired to the main battery bus (not the avionics bus), and a switch is optional.
Stewartb
Final Approach
My Cub's G3X is powered through a battery backup/power conditioner so that it can be turned on with the master and not cycle from a voltage fluctuation when the engine is started. Pretty handy since the instrument takes a while to initialize when powered on. I figure that's how all glass instruments should work.
As for radios? I have a radio master in my Cessna. I've forgotten it plenty of times and have turned the plane off with radios on. I figure it out before the next engine start, though, and that's probably where the bigger risk is. So far no problems.
As for radios? I have a radio master in my Cessna. I've forgotten it plenty of times and have turned the plane off with radios on. I figure it out before the next engine start, though, and that's probably where the bigger risk is. So far no problems.
tspear
En-Route
- Joined
- Dec 10, 2010
- Messages
- 3,587
- Display Name
Display name:
Timothy
Shawn
En-Route
To prevent avionics electronics from exposure to brown out from voltage dips and voltage spike surges during start up and shut down procedures. Put a volt meter on the buss and see what voltage does when you are cranking. Many electronic have a pretty low threshold of voltage variations before they take their own lives or start having power supply issues.
Easy way to fry electronics and that applies to more than just airplanes.
WILL they fry?...probably not. COULD they fry?...absolutely under the right set of conditions. Easy habit to get into to prevent that possibility and lessens that risk.
Last edited:
tspear
En-Route
- Joined
- Dec 10, 2010
- Messages
- 3,587
- Display Name
Display name:
Timothy
Maybe vacuum tube electronics, but any avionics since the late 90s is probably solid state. Solid state is just not nearly susceptible to such issues.
Further, even the old C172 I have rented a few times has an avionics master. So I could see your advice applying to the J3 Cub and a few other planes, but as general advice? Nah.
Tim
Shawn
En-Route
Could't disagree more. I work with a lot of electronics in temporary applications and chit gets blown up all the time do to voltage variation issues on generators, inverters and temporary power supplies. Most of the time it just strikes the power supply, but those are internal to the units on board.
...but go ahead, keep that avionics switch on if you believe your entire stack is invincible. I have already replaced a com panel due to a bad power supply.
bnt83
Final Approach
IMHO avionics master switch and using it is extremely cheap insurance. One radio repair would pay for it. Even if you have older stuff like an MX300. Repaired one of those a few years ago to the tube of around $600 and took two months to get it back. It works but golly talk about throwing away $$$ on a radio that may stay in the airplane for 5 more years before it gets retired during panel upgrade.
thomasdr72
Pre-takeoff checklist
Totally agree, I can only think of one instance that I didn't install an avioncs master when installing new avionics in the panel (if it didn't already have one). I remember a certain Cessna 150B, and the solid-state transponder went back to the manufacturer several times for work due to voltage spikes and other weird stuff... Never again!
SkyDog58
Ejection Handle Pulled
- Joined
- Jun 11, 2015
- Messages
- 14,600
- Location
- My own special place.
- Display Name
Display name:
Canis Non Grata
So, what if your engine instruments (i.e. oil pressure) are only on the EFIS? Do you still want to wait until the engine is running to switch on the instrumentation?
Shawn
En-Route
You are right...of course ALL avionics are invincible because some EFIS systems are less suceptable...silly me.
idahoflier
Pattern Altitude
- Joined
- Jul 21, 2017
- Messages
- 1,731
- Display Name
Display name:
idahoflier
You have this backwards. Tubes are extremely robust when dealing with voltage transients. Semiconductors are much less forgiving...
tsts4
Pattern Altitude
Well if the avionics in question are certified and tested to RTAC DO-160 standards (which all of the Garmin boxes are, don't about other brands) the chances should be remote, but I'll never say zero. So how many radios have been fried in the plane because they were on during engine starts? I'm guessing thousands based upon these posts.
Last edited:
tspear
En-Route
- Joined
- Dec 10, 2010
- Messages
- 3,587
- Display Name
Display name:
Timothy
Could be. But from audiophile friends, solid state is much more tolerant now; sure it started out as rather delicate. But now, tubes are much more fragile.
Note: I am going on complete hearsay, this is way outside my actual knowledge base.
Tim
GlennAB1
Ejection Handle Pulled
- Joined
- Oct 5, 2015
- Messages
- 4,889
- Location
- Home will always be Vandalia, OH
- Display Name
Display name:
GlennAB1
I happen to have been taught to turn everything off before starting an automobile, so that all available amperage was provided to the starter and reducing the overall load on the battery. It's even in many owner's manuals along with switching your air source from recirculation, to fresh. when turning the vehicle off.
ThatAviator
Filing Flight Plan
- Joined
- Aug 11, 2017
- Messages
- 3
- Display Name
Display name:
ThatAviator
I'm not sure why anyone would risk frying their electronics. It's not that hard to flip one more switch.
Many people, including myself have always shut off the car radio before the engine. I was just always taught to do that. It just seems to me that it could put more strain on an electric system, even if systems are more advanced in the recent years... but outside my expertise field as well.
Many people, including myself have always shut off the car radio before the engine. I was just always taught to do that. It just seems to me that it could put more strain on an electric system, even if systems are more advanced in the recent years... but outside my expertise field as well.
tspear
En-Route
- Joined
- Dec 10, 2010
- Messages
- 3,587
- Display Name
Display name:
Timothy
@ThatAviator @GlennAB1
With the first vehicle I drove on a regular basis was a 1970s pickup truck. I was taught to do the same.
Since the mid 90s; every car I have owned has fit into one of two categories. Either over powered battery, like on my diesel truck with two batteries where either one could start the truck and the radio would stay on; or like my current Subaru which automatically disconnects radio, lights whatever before the starter engages. So, I no longer bother.
Further, look at hybrids, and other cars that shutdown the motor at lights. You do not see any of them worried about such items. The after market radios for all the cars are not specially designed for it. At this point, until someone can provide some real data on a modern glass panel avionics system, I am not gonna bother.
Tim
With the first vehicle I drove on a regular basis was a 1970s pickup truck. I was taught to do the same.
Since the mid 90s; every car I have owned has fit into one of two categories. Either over powered battery, like on my diesel truck with two batteries where either one could start the truck and the radio would stay on; or like my current Subaru which automatically disconnects radio, lights whatever before the starter engages. So, I no longer bother.
Further, look at hybrids, and other cars that shutdown the motor at lights. You do not see any of them worried about such items. The after market radios for all the cars are not specially designed for it. At this point, until someone can provide some real data on a modern glass panel avionics system, I am not gonna bother.
Tim
GlennAB1
Ejection Handle Pulled
- Joined
- Oct 5, 2015
- Messages
- 4,889
- Location
- Home will always be Vandalia, OH
- Display Name
Display name:
GlennAB1
In the past, someone might have commented that real airplanes don't ever have to worry about it, but I won't go there.
455 Bravo Uniform
Final Approach
Do I remember a thread a while back about shutting off the master before the mags go off?
I learned "off" in the following order: Av master, alt/batt master, full lean, mags.
Obviously you can't leave batt master off before start up (maybe the thread was about leaving alt master off at startup).
I learned "off" in the following order: Av master, alt/batt master, full lean, mags.
Obviously you can't leave batt master off before start up (maybe the thread was about leaving alt master off at startup).
ThatAviator
Filing Flight Plan
- Joined
- Aug 11, 2017
- Messages
- 3
- Display Name
Display name:
ThatAviator
I think it was Friendly Skies Film on YouTube once shared a quote he learned somewhere... "The checklist on my knee: Mixture, master, key." But don't forget the electrical equipment switch!! 
denverpilot
Tied Down
As others have said, Avionics Master. Yes.
Generally incorrect. But...
Also can be incorrect. Because...
Stuff got "more tolerant" because of what was put on the schematic to handle transients and what components were chosen for the device's power supply section and quality of those components.
Example: Low Voltage Dropout linear voltage regulators didn't exist once. Now they exist but the manufacturers will skimp and save $0.01 per part on a cheap consumer electronics design. Usually at avionics price points, the circuit is much closer to "no expense spared" than "they left out, WHAT?"
And good luck getting a schematic from anyone making consumer electronics these days. Or even just opening up the device and reading the component part numbers so you can reverse engineer the gizmo.
Manufacturers have to obfuscate components or order them in quantity from the original manufacturer with custom part numbers on them, to avoid reverse engineering in China making a copy of the thing for less than half the price and shipping it to consumers directly in about a week.
But anyway... both tube and solid state designs have been both good and bad at handling the noisy voltage drops and spikes caused by electric motors on a battery bus. Doesn't really matter what was used if the design doesn't account for it.
Avionics, most manufacturers don't want anyone doing component level troubleshooting anymore. They know the depth of electronics knowledge has shrunk considerably. They just want someone who can swap a whole board or a whole box now. Ship it to them, they'll deal with component level fixes at some central facility somewhere.
So again. Good luck seeing a schematic.
Anything that can be off when the starter motor is engaged or when the engine is slowing below the normal speeds of the alternator, probably should be. That's the easy way to remember it.
The reality is, most avionics are going to be designed to handle it. But... some won't. So why risk it?
I've done a few repairs of modern VHF/UHF transceivers on the bench here for ham radio friends over the years.
The first most common way to blow things up (even with "fold back" RF power protection circuits in the designs) is transmitting into a bad antenna system.
The second most common failure is blowing up something in the power supply section. Sometimes from vehicle spikes. Sometimes from someone plugging something in with reverse polarity -- again even with protection circuits designed into the radios.
Third most common failure, displays or display lighting.
Fourth most common is random destruction by static discharge (it's dry here)...
I haven't done any avionics bench work, but I suspect with similar design engineering techniques and similar board layout techniques, the failure modes will be similar.
The major variable you won't see in most avionics that happens in the radios I've seen on my bench -- freaking idiots who don't know how to properly troubleshoot, let loose inside the radio with a soldering iron and overconfidence.
Those are the worst.
You have to reconstruct the original circuit just to figure out what was really wrong before they started screwing with it.
Zeldman
Touchdown! Greaser!
I learned to drive an old truck that had nothing but a heater. It was a 12 volt system but no A/T, P/S, P/B, P/W, P/Seats, A/C or radio. I didn't have anything to turn on or off. If it would not start we would just push it enough to get it rolling, jump in, clutch, 3rd gear, key on, let out the clutch and go. But when I turned the key to start the engine, the headlights if on, would momentarily turn off until I released the key.
It did have electric windshield wipers....I'm not that old....
About 20 years ago I had a 47 Chevy PU That had a foot pedal to push for starting. No electronics on it either. And it had vacuum wipers.... Plus the steering wheel was HUGE..!!!
I never took the key out of it because 99.996% of the people did not know how to start it, or shift it, or could turn the steering wheel.....
I do remember my dads cars had vacuum tube radios. It would take several minutes for the tubes would warm up enough for the radio to play, usually to the end of the road we lived on. No need to turn off the radio to start.
Modern cars turn off the accessary electrical during the starting sequence to put available amperage to the starter.
An instructor I flew with years ago used three 3Ms for shutdown. Master, Mags, Miller Time.I think it was Friendly Skies Film on YouTube once shared a quote he learned somewhere... "The checklist on my knee: Mixture, master, key." But don't forget the electrical equipment switch!!
Hmmm. I don't think I ever switched off the car radio for start and shutdown. But maybe I just haven't driven enough in 50 years to see a problem. (Yes, I do switch/check the avionics master.)
deonb
Pattern Altitude
- Joined
- Aug 17, 2015
- Messages
- 2,266
- Display Name
Display name:
deonb
This has caused a lot of my gray hair. I could probably diagnose most digital boards (excluding the really high frequency stuff) but then you have stupid manufacturers that scrape the part numbers of really basic components like flip flops and shift registers.
That's why I always source boards directly from China - they mostly don't bother with that and you can actually diagnose and repair stuff yourself.
If you have some unique design that you DON'T want copied - don't send it to China for manufacturing in the first place!
Last edited:
SkyDog58
Ejection Handle Pulled
- Joined
- Jun 11, 2015
- Messages
- 14,600
- Location
- My own special place.
- Display Name
Display name:
Canis Non Grata
Mixture is the first M or at least that is how I do it.
Maybe it was 4 M's
I never think in terms of "Mixture." That how the prop stops turning so it's pretty much automatic.
SkyDog58
Ejection Handle Pulled
- Joined
- Jun 11, 2015
- Messages
- 14,600
- Location
- My own special place.
- Display Name
Display name:
Canis Non Grata
Maybe it was 4 M's
Yeah, I was taught by one CFI to use the 3 Ms, Mixture, Mags, Master. Yours probably added a fourth for Miller TIme but he may have substituted as well and kept it at three.
Good! lol