[T67M]

Only in aviation could you design something so stupid that 'on' isn't really on, instead 'alt' is

Well, maybe that's a little more user-friendly than this transponder...

At least that one has a switch labeled "Mode-C"! Well, "M-C" to be precise, but still closer than "ALT".

[Crash one]

It strikes me that pilots do not understand the function of each switch position.
On, means on, but only basic.
Alt means everything else that the thing does whether it's alt only or alt plus dress size etc.
A bit like this iPad. If I switch it on it comes up with the home screen, nothing else. I have to select something else to get any sense out of it.
It beats me why transponder manufacturers don't just fit a switch marked Off--On (A)--On (C alt)--On (S alt).
There would still be the choice but perhaps understandable what is being delivered.
Just because the thing is a mode S unit doesn't automatically mean "On" does it all, any more than a mode C doesn't.
The amount of ambiguity and mis information on rules in this business is mind boggling.
The whole thing needs a complete rewrite.
I haven't read the Highway Code properly since 1957, so far I have managed to drive safely picking up the changes enroute but no comparison.

[mick w]

& why is everything off , when the Switches are in the on position .

[Crash one]

& why is everything off , when the Switches are in the on position .

Power to the unit only, God only knows why

[Dave W]

Only in aviation could you design something so stupid that 'on' isn't really on, instead 'alt' is

Well, maybe that's a little more user-friendly than this transponder...

At least that one has a switch labeled "Mode-C"! Well, "M-C" to be precise, but still closer than "ALT".

Except that it's in the "Test" group so probably doesn't set Mode C in flight anyway. (Assuming "M-C" does in fact mean "Mode C", which I suspect it doesn't!)

[flyingeeza]

& why is everything off , when the Switches are in the on position .

Power to the unit only, God only knows why

Not really. Anyone with a reasonable knowledge of electronics will know why it is a necessary practice to turn power on to any high stability piece of kit a while before use.
There are components such as reference diodes (voltage references) and precision filters etc that need a few minutes with power connected to warm up to the temperature at which their stability and accuracy will be within defined parameters.
So it is indeed good and proper procedure to switch to "On" after startup to allow a few minutes for its electronics to warm up while you fanny about with checks and taxiing and waffling on the wireless. Then when you finally line up and do your SPLIT checks, your kit is on spec and sending out accurate info on the exact frequency.

[Ben K]

Interesting - does that still apply to the newer digital-looking Garmins, for example?

[Miscellaneous]

There are components such as reference diodes (voltage references) and precision filters etc that need a few minutes with power connected to warm up to the temperature at which their stability and accuracy will be within defined parameters.
So it is indeed good and proper procedure to switch to "On" after startup to allow a few minutes for its electronics to warm up while you fanny about with checks and taxiing and waffling on the wireless. Then when you finally line up and do your SPLIT checks, your kit is on spec and sending out acc

Are you sure about that, flyingeeza? Is that not what standby is for, given the transponder will respond to Mode S interrogations when in the ON position (with the exception of altitude)?

That reads to me ON is functioning rather than 'warm up'.

[ianfallon]

Ours cycles through displaying STBY , AC, ACS - makes sense to me (Funke)

[Irv Lee]

The advantage of the old bit of kit was that it seriously improved primary returns as well

[flyingeeza]

There are components such as reference diodes (voltage references) and precision filters etc that need a few minutes with power connected to warm up to the temperature at which their stability and accuracy will be within defined parameters.
So it is indeed good and proper procedure to switch to "On" after startup to allow a few minutes for its electronics to warm up while you fanny about with checks and taxiing and waffling on the wireless. Then when you finally line up and do your SPLIT checks, your kit is on spec and sending out acc

Are you sure about that, flyingeeza? Is that not what standby is for, given the transponder will respond to Mode S interrogations when in the ON position (with the exception of altitude)?

That reads to me ON is functioning rather than 'warm up'.

Dead right there Misc. Typing in haste.
It is the "standby" position, first click I meant by switched ON, so powered but not yet transmitting owt as it does in the "On" position.
As a rule I always go to Alt once lined up for departure, and to go back to Standby on cleanup after landing.

[Mike Tango]

Isn't it incumbent for the pilot to understand how the equipment in the aircraft he/she is about to fly works?

Or is it routine to head off in to the wild blue yonder not knowing what the various bells, whistles and buttons in the steed you are meant to be captain of do?

The fact that the transponder may not be immediately intuitive is surely irrelevant as you should be familiar with its operation before you switch on the magnetos and start the engine. You owe it to yourself to be briefed/familiar with the equipment, never mind any passengers or other souls who may be adversely affected by any unfortunate outcome due to your ignorance.

Would make a good headline, 'serious incident/accident caused by amateur pilot who didn't know how his aircraft's equipment worked'.

From the ANO...

Responsibilities and authority of pilot in command

68.—(1) The pilot in command of an aircraft is responsible—

(a) before every flight, for defining the roles and duties of each crew member;

(b) for the operation and safety of the aircraft and for the initiation, continuation, termination or diversion of a flight in the interest of safety; and

(c) during aircraft operations, for ensuring the safety of all crew members, passengers and cargo on board.

If you don't know how your equipment and/or avionics work are you fulfilling the above responsibilities? Or are there excuses why private pilots should be exempt from the responsibility of being familiar with the equipment and avionics in the aircraft they are captain of?

[Paul_Sengupta]

As a rule I always go to Alt once lined up for departure, and to go back to Standby on cleanup after landing.

I switch mine off after landing. No need to keep it warm when you're about to park up and switch the master off anyway...

[flybymike]

It's not always just pilots who don't understand the operation of transponders.

I recall bimbling in the local area a few years ago when ATC asked the pilot of another aircraft to "Squawk standby" because of apparent erroneous position and altitude information from his transponder return.

The pilot, whose voice I recognised as that of the club CFI, acknowledged the request and confirmed that he was "squawking standby"

A short while later ATC called again and said that his transponder was still providing spurious information and repeated the request for him to sqawk standby.

The CFI said that he had been on standby ever since the first request, but that he would now switch the transponder off altogether.

The controller then became very irate and said that the phrase "squawk standby" means "turn your transponder off!"

The CFI, ever polite, remarked that he would be telephoning the controller for "educational purposes" once he got back on the ground.

[Paul_Sengupta]

Except that it's in the "Test" group so probably doesn't set Mode C in flight anyway. (Assuming "M-C" does in fact mean "Mode C", which I suspect it doesn't!)

I would suggest they are three position switches with OUT at the bottom, ON in the middle and TEST at the top, possibly momentary, that last bit. And the switches appear to be Mode 1 (with two digit Mode 1 code selectable below), Mode 2, Mode 3/A (with the four Mode 3/A digits below, same as our civilian ones), so then the next one logically would be Mode C.

https://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes
http://www.dean-boys.com/extras/iff/iffqa.html

Ah, just googled a bit. I appear to be correct in those switches being three way with the top position being momentary:

https://www.youtube.com/watch?v=9YEeX1hl_ns

Yep, it also appears to be Mode C.

http://www.rexsystems.com/Images/APX-72/apx-72%20brochure.pdf
http://radiosets.tpub.com/TM-11-5841-268-25/TM-11-5841-268-250012.htm

And for some more info:

http://radiosets.tpub.com/TM-11-5841-268-25/index.htm