[rikur_]

I was taught not to switch-on transponder (from standby) until lining up because of TCAS alerts .... but was then subsequently told this was out of date, and nowadays switch it on with the radio ....I haven't had anyone object, except an instructor on a revalidation flight, who reasserted what I was originally taught.

[T67M]

I was taught not to switch-on transponder (from standby) until lining up because of TCAS alerts .... but was then subsequently told this was out of date, and nowadays switch it on with the radio ....I haven't had anyone object, except an instructor on a revalidation flight, who reasserted what I was originally taught.

Wouldn't it be nice to have a single, definitive source of consistent, up to date information? Like a sort of Skyway Code. Sadly CAP1535S merely tells us to use "Mode C at all times", which is ambiguous about use on the ground, and includes a picture of a transponder with no control labelled "Mode C" but a very clear "ON" switch.

[Crash one]

I note that 93% voted option 1.
Did anyone expect anything different on an aviation forum that discusses safety on a regular basis?
This is like asking a police convention if any of them use a mobile phone while driving.
Point 2. Shirley pilots should know how their equipment works and what the various switch positions do?

[Melanie Moxon]

Always goes to ALT, its part of the lined up checks.

[Crash one]

I think there should be an AD mod directive that all transponders in current use should have their switch positions modified to:- Off, Code, On.
On. would be Alt.
Or they should be hard wired into the radio/avionics switch and squat switches fitted if possible and a big warning light saying, TSPDR off!!!

[Cub]

I thought this was dealt with via quite a lot of comms a few years ago? Transponder use should be from startup to shutdown. There are very few, if any circumstances where emission on the ground is an issue, these days.

[Full Metal Jackass]

That check list could get me a blocking at certain airports I fly from - in particular where heavy metal is landing. If you switch on your transponder to ALT whilst parallel to the runway doing your run-up checks and a TCAS equipped jet is landing, you will cause a TCAS alert to be given which means paperwork....

For that reason they demand, especially if CAT is on final, that the transponder is only switched ON / ALT when you line up on the runway.

I'm not sure this is correct.

TCAS II inhibits any RAs below 1000ft AGL, 'Descend' RAs below 1100ft, and 'Increase Descent Rate' RAs below 1550ft. It should also filter out any transponder returns that are at 0ft AGL.

Well obviously something went wrong that day. I was parallel to the Runway at EDDG having just completed my engine checks and had switched on my transponder, was switched over to Tower where an incoming pilot was talking about 'receiving an alert' and the tower then asked me if I had mine on - which obviously I did and told him so.

His response was that I should never turn on my transponder until I'm lined up and cleared for takeoff because it gives issues for other aircraft and since then, I turn on my transponder just before synching the DG.

[Dave W]

There are very few, if any circumstances where emission on the ground is an issue, these days.

My old mate Onan begs to differ.

[Paul_Sengupta]

[Full Metal Jackass]

That check list could get me a blocking at certain airports I fly from - in particular where heavy metal is landing. If you switch on your transponder to ALT whilst parallel to the runway doing your run-up checks and a TCAS equipped jet is landing, you will cause a TCAS alert to be given which means paperwork....

For that reason they demand, especially if CAT is on final, that the transponder is only switched ON / ALT when you line up on the runway.

Name the airports because the TCAS assertion is absolute tosh. Many 'heavy metal' airports I fly from won't even let you push off stand if the transponder is off/sby.

As I said, EDDG. That was where I was told the Transponder needs to be switched OFF until lining up.

[Dave Phillips]

Worth a read.

https://www.eurocontrol.int/sites/defau ... -guide.pdf

[Full Metal Jackass]

Worth a read.

https://www.eurocontrol.int/sites/defau ... -guide.pdf

Very interesting, thanks.

FYI: Until 2012 it was standard practice to leave the transponder switched off until lining up because

'with older radar systems, transponder operation on the ground could cause interference and multiple targets on the radar display. Modern digital systems can filter out transponders close to the antenna.'

[SteveC]

Always used it. Its fully automatic as its linked to the GNS so I would have to make a conscious decision to turn it off.

This assumes that the automatics work. My transponder is automatic, but one group member said it always failed for them. On investigation it transpired that the sequence you turn on other bits of kit could inhibit the auto-ALT function. I now always check at around 500' just after the flaps have come up.

Get it fixed then.......

[James Chan]

FYI: Until 2012 it was standard practice to leave the transponder switched off until lining up

I too, was back in the day, taught to set mine to OFF or GND for the same reason.

Then around 2012 someone from our aero club asked someone from NATS who said setting to OFF/GND was no longer necessary.

[Dave Phillips]

FYI: Until 2012 it was standard practice to leave the transponder switched off until lining up because

'with older radar systems, transponder operation on the ground could cause interference and multiple targets on the radar display. Modern digital systems can filter out transponders close to the antenna.'

FYI, we're in the second half of 2017. There was an AIC about half a decade back.