Which Radios to Switch On?
 

Do you teach your students to only switch on the radios they require and/or know how to use or do you require them to turn on ALL the radios for all flights?

For example, for a circuit detail do you teach them to turn the DME and ADF, as well as COM and TXPDR?

Can you list any reasons supporting your views please.

Finally, does switching, for example, the DME on and off on every flight significantly effect time before failure?

Thanks.

I was always taught (and hence I teach) to turn them all on - the reasoning behind this was that it warmed them through and helped get rid of any condensation that may have formed, thus helping prevent corrosion. I don't know how much truth there is in this - be good to hear a radio mechanics view.:suspect:

Can't help to have them on and set for local nav aids just in case you need them unexpectedly

Airport closure / divert

Rapid weather deterioration

Other ?

Apologies !

Please swap \"help\" for \"harm\" in the above and it should then make sense !

Given the absurdly low MTBF for most GA avionic displays, I think that it makes good sense to keep them powered up to dry them out during flight when the aircraft have to parked out in the damp at this time of year.

Interesting. I always leave radios off when I'm not planning on using them, but I've never really thought about it or tried to justify it.

I do make sure that transponder is always on Standby, even if only doing circuits. And I make sure my IMC students turn on, tune and identify all navaids, even if they're not planning to use them. But for a VFR flight, I don't bother.

Maybe based on the other replies so far, I should change that?

FFF
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I'm in the "turn 'em on, warm 'em up and dry 'em out" camp - but whether it makes any real difference ... :confused:
I also believe that a briefing on the avionics should be part of any type conversion, even if the bod only has a vanilla ppl.

Edited: hey, I've reached 150 posts - and on my birthday too. How exciting. :D

HFD

Just a suggestion:Why not?

Happy Birthday!

Isn't the compass swung with all radios and electrical equipment on. So there's another reason to switch them on and warm them up.

Also if you are going to switch them on you may as well check they work. Trying to get an RNAV out of PAR mode in the air is 20 times harder than on the ground (if you've never done it before).

Sounds like I am not the only one who has heard that turning them on dries them out!

I take it you turn on the pitot heat before T.O. (I also do this, but have flown with many PPLs who do not).

Why do you turn the Pitot Heat on before TO Foxmoth? Says it's optional on my checklist and I only use it if there is a risk of it icing. That said, my FIC instructor always switches it on... Interested to know the debate here.

As was said the compass is swung with all electrics on - including the pitot heat :hmm:

Leave them on, then you know if they still work.

Also quite like having a avionics master then you can leave them all switched on thus stopping the wear and tear of the on/off switchs getting fannyed about with every trip. I don't know if this is a good idea though as you might get funny eddie currents getting at the avionics back through the earth.

Must admit my ex CFI used to say leave the pitot heater off because it burns out the element. Never heard of a pitot heater burning out yet on a light aircraft and the engineers said it was a pile of !!!!e as well so you might as well have it on. Better to have it on than think later bugger i wish i had turned it on earlier.

If the weather is 25 deg. C and dry, then the Pitot heat won't usually be required unless you plan to go IFR, but if in doubt, then turn the damn thing on. If having it on burnt out the heating element, what the hell's the point of having one? I have to say I've never noticed, but what's the average life of the pitot heat anyway?
Pretty long I would assume, as long as you have some airflow over it and don't let it just sit there on the ground heating away.

With regards to radios, I always like them on at this time of year for the reasons already stated, but I also like to know that they all work before going off, just in case you need them.

Pitot heater
 

Ahhhhh...

I've had the 'Turn it on all the time because the check list says' comment (which never made sense because it was not backed with an explanation).

I was also told its designed to work in a 100 mile per hour wind and doesn't like being turned on for long times on the ground - which did make sense so turn it on at take off and off when you land.

One instructor once said 'since we are not going to get near 5000' on the trip we will only turn on the heater if the OAT says less than 10degrees'. That seemed to make good sense but then I remember my first comment about the compass.

So now after 700 hours the 'Turn it on all the time argument seems to make sense'. But I can now explain why.

Friends of mine owned a Partenavia which, being a twin didn't get a lot of use. Pilots who used it were always moaning about randon avionics faults which could never be traced, just cost the owners a mint in trying to get 'em fixed. Then they sold it and had to deliver the aircraft somewhare in Southern Spain. As they continued their long flight south the avionics problems disappeared one by one and they delivered a fully functional aircraft. Obviously it was not used to doing long flights and this had dried out the avionics. In my book therefore, all avionics must be switched on before departure. This will minimise the problem due to damp and if some of it doesn't work then it is up to the PIC to decide whether to continue with the flight. Furthermore, any non working avionic boxes can be reported.

P.P.

With regard to the DME. Pilots should keep the DME off when they do not require it i.e. in the circuit. The reason is that DME stations have a capacity limit and when that limit is reached they stop stations at the greatest distance (affected by power) from obtaining information. This means that while you blast round the circuit with the DME blazing out the distance from some VOR/DME, the poor sod at the limit of the range may not get a DME indication when they need it because you are.

When it comes to drying out the avionics - turn up the heater! Many avionics faults are fixed by re-racking the equipment - moisture on the contacts. Turning up the heat or taking the aircraft to a better climate will help the avionics even when switched off.

Now to the biggest load of cobblers.

Could the person who thinks that the compass will only read correctly when the pitot heat and every bit of electrical equipment is on please tell me how they can tell what direction the aircraft is pointing after an in-flight electrical failure?

The Airworthiness procedures require that - The most adverse combinations of electrical loads must not cause deviation in
excess of 2° (5° for light aircraft).

When completing a compass swing, electrical equipment, e.g. radio, instruments and pitot tube heaters, should be
switched on to ascertain that there are no adverse effects on the compass.

Thus having the pitot heat on or off will have little effect. Since most light aircraft pitot heats are powered by DC then even having the cable passing by the compass, there would be no change in effect by having the switch on or off.

Do those pilots who require the pitot heat to be on so that the compass is reliable ensure that the instrument pannel light in the compass is also on and serviceable? :D

Next time someone trotts out that kind of rubbish, ask them if they had 4 dummies wearing david clarkes in the C172 so that the efects of 8 magnets waving round the cabin was checked during the compass swing! :D :D

Regards,

DFC

Up here in Scotland the avionics need all the help they can get at this time of year! Especially if the a/c are left sitting for a while and you only do short flights anyway.

Good point about the DME though!

DFC:
The comment about DME was fair but some of the rest is harsh and a bit suspect.

I didn't understand the bit about: "Since most light aircraft pitot heats are powered by DC then even having the cable passing by the compass, there would be no change in effect by having the switch on or off." - one of us needs to re-read their electromagnetism books :O

I didn't know about the 5 degree deviation limit from electrical services but the deviation card WILL only be CORRECT when all the services are on. 5 degrees may or may not be significant based on what you're trying to achieve at the time. There's an old story:
Nav to pilot: turn 1 degree port
Pilot to Nav: I can't fly that accurately
Nav to Pilot: OK, turn 5 degrees to stbd
Pilot to Nav: steady
Nav to Pilot: turn 4 degrees to port. :)

The comment about permanent magnets in headsets is certainly true if they're very close to the compass but they're fairly well shielded and I seem to recall that the field decays as an inverse cube law (may be wrong), so at normal distances the effect would be negligible.

HFD

hugh flung_dung,

How do you get DC power to the bulb inside the compass, vary the brightness and switch it on an off while having no significant effect of the compass reading?

If I remember correctly the right hand rule applied to DC. However, if one has the positive and negative cables side by side the magnetic effect is according to the UK CAA "usually insignificant"

The compass deviation card should say if the swing was done with the radio equipment on or off.

If the engineer checked that the radios, pitot heat etc had no significant effect on the compass as required by the airworthiness procedures and then did the compass swing with everything off as allowed (recorded on the dev.card). Would you say then that all flights should be completed with the radios off?

Why do the radios get special treatment? - Simple - many sources of alternating voltages and currents as various frequencies. Some of which - DME, Transponder, WX Radar can be high powered.

But please do not turn on the wx radar during the compass swing while the engineer is out front unless you want to endanger them.

Regards,

DFC

right so I have to have all the electrics on all the time then HFD :uhoh:? Pitot heat, all radios, nav lights, landing lights, taxi lights, dome lights, instrument lights, strobes, beacons every damm switch on in the plane has to be on all the time so the compass will read correctly?? Sorry but I have to agree with DFC, the point of a compass swing is to make sure that it stays within limits when all the services are turned on on; but that doesn't mean that you have to fly with them on all the time to get max accuracy! If I flew with everything on in the old heaps I instruct on there's no way the battery wouldn't be able to hack it! (and thats if even if all the lights and nav aids work, which is a rareity :rolleyes: )