Squawk Idents for Farnborough Radar, why?
 

Being asked to Squawk Ident was pretty rare with Mode C Transponders and now we are flying with Mode S Transponders, rarer still.
Recently, on flights out of Blackbushe with an Eastbound Clearance for Farnborough Zone I have been asked to Squawk Ident, (twice in quick succession on one flight).
Surely, my Unique? Transponder code and Aircraft Registration are shown on the radar screen, so can any Controllers explain why an Ident is needed?

Thanks and regards,

cpl4hire

First a warning, I'm no longer operational and haven't worked with mode S so someone may come along with more current and accurate info.

Squawking ident is nothing to do with mode C. Identing is usually used to confirm that the callsign shown on screen or the radar target is, in fact, the one that the controller thinks it is. Before doing certain things with an aircraft when using radar, the controller must confirm the identification. There are a variety of ways of doing this but getting an ident is often the easiest way assuming both aircraft and radar are suitably equipped. If the ident is transferred from another ATC unit, the pilot does not need to do anything - idents are usually transferred automatically by the radar equipment when aircraft are flying in controlled airspace. So an IFR flight on airways will usually be identified on departure (without the pilot needing to do anything, the controller seeing the aircraft appear in the right place is sufficient), and the ident then transferred in the background by the equipment. There are very limited situations where an aircraft would need to be identified again in that scenario. With mode S, I believe that all that is required is that the crew put the correct callsign in the transponder and for the controller to see this on screen.

In other scenarios a controller may need to ident the aircraft and will commonly do this by requesting an IDENT. As an aside, it doesn't help for the pilot to key the IDENT button on his/her own accord, like coming on to a new frequency, for example, because strictly speaking identification of the radar target requires the IDENT symbol to be seen following a request to select the IDENT feature. Can't tell you why you've been asked to squawk without knowing what the circumstances were but you're not going to be asked for an IDENT unless there's a good reason. BTW, the conversion from mode A to callsign on screen often is still a surprising basic process requiring manual inputs to the radar system for flights which are not conventional flightplanned airways flights.

Cpl4,

We are almost always asked to select ident (on a mode S equipped aircraft) when departing London Heliport, that being so for years.

I thought the primary purpose for IDENT was for the controller to pick out your specific aircraft on a display with many targets. It is not infrequent that I'm asked to IDENT when first calling tower for landing at my base airport or at another local airport. Both have a heavy volume of student training traffic. Two different aircraft - one mode C with UAT ADS-B Out, the other mode S with ES ADS-B Out.

More detail
 

Thanks for the replies so far from Equivocal, ShyTorque and EXDAC
The thing is that on these flights my Aircraft registration was my Callsign and, with Mode S the Controller should already have it displayed on their Radar screen so why ask for an Ident?
The Traffic was light and I don't think Farnborough were giving out a common transponder code for all Aircraft departing Blackbushe because I retained mine until I was handed over to Farnborough Radar West after the Zone Transit.
I am not bothered about having to Ident, (although I have to drill down two menus on the EFIS to do it now, its not simply push a button anymore!), I am just curious as to why the sudden influx of Ident requests on a route I have been flying for years without them.

Regards,
cpl4hire

Irrespective of whether you have Mode S, the controller still has to observe an ident squawk on their radar in response to a request to the pilot; it's the law.

Has the law now changed, to produce the phenomenon that the OP has noted, or is it simply being observed more strictly?

An aircraft may have a mode S transponder but in order for the callsign to show on a radar screen (without any further actions by controller or pilot) the ground equipment has to be suitably equipped. Unfortunately, it is not easy to know how things are set up on the ground unless one actually works with the equipment and has an opportunity to learn how everything is connected up. It's quite rare to find a stand-alone radar - most radar heads are connected to a 'chain' in which all information gathered by the head is put into a pool along with all the other sources in the chain, and the best information available for a particular area to be displayed on screen is used. So, for example, if one radar head is taken out of service for maintenance or whatever, or another head is added to the chain, the procedures that must be used by a controller may change, either temporarily or more permanently.

That's incorrect, unless I've missed an SI at some point to withdraw the Mode S identification criteria...

In my view, the reason why the majority of controllers don't use Mode S identification is the old "we've always done it that way here" reason.

Another possibility, as mentioned above, is that the ground equipment is not suitable for it. Which, if that's the case, is rather disappointing in 2021.

What law is that?

2 s

Conditions for identifying aircraft are laid down for Air Traffic Controllers in the 'Manual of Air Traffic Control'

When I was controlling it was necessary to ask for an 'ident' when the selected squawk had not been verified by the initial unit handling the aircraft. For example, if a squawk had been given to an aircraft departing an airfield that didn't have SSR and couldn't ensure that the transponder was correctly set. It was the only way I could positively identify i was talking to the aircraft I was expecting, and that someone else had not accidentally selected the same squawk.

Thanks, that makes sense
 

Well, that fits what is now happening at Blackbushe.
Originally all Departing Aircraft were given a Transponder code of 7010 with their Farnborough Clearance by Blackbushe AFIS. As soon as you contacted Farnborough Radar they gave you another Squawk (so they wouldn't ask you to Ident).
On the day in question I was given a different Squawk with my Farnborough Clearance by Blackbushe AFIS so Farnborough had to request an Ident on first contact.
I don't know if this new procedure is temporary or permanent, but it does seem to work well, cutting down Transponder code changes at critical times in flight (Arrivals and Departures) so a Squawk Ident is a small price to pay.

Thanks and regards,
cpl4hire

It's definitely not a 'new' procedure. At Fairoaks we always passed the SSR code (obtained in advance by phoning terminal control) along with departure details (with me I passed the code when the aircraft called to taxy) then followed this at the appropriate time with 'take off at your discretion and when airborne contact Farnborough Radar on 134.350' thus cutting down RTF exchanges even more.
I'm now retired but was originally a controller at Farnborough followed by becoming a FISO at Fairoaks after I retired as an ATCO.