Squawk code WITH mode s?

[PaulJahn]

Dear guys,
this may be a stupid question, but I didn't find a good answer on google.

So I am speaking especially about commercial airliners: So I know that each airplane has a unique mode S Hex code which basically never changes. If you are beginning a flight, you will enter your flight number (or atc call sign) in your FMS. So with your hex code and your FMS callsign, the tower should get all he wants, right? Why will he give you a 4 letter squawk code? Does this have any benefit?
I am curious about the answers =).

[The Fat Controller]

Even though the majority of ground radars are Mode S, not all ATC systems use this to display the callsign on the controller's display.

The 4 digit SSR code allocated is paired with the flight plan database and THIS is used in some places to provide the required information on the radar display.

Therefore, both are still needed for now.

When I retired from Prestwick Centre 18 months ago, the sectors below FL255 used the SSR Code and database, the high level sectors used the Mode S on their newer system.

The low level sectors were able, using a mouse click, to look at the Mode S information, which was quite useful when a "7000" popped up in the FIR when we were providing services outside CAS.

A lot of them on the West Coast of Scotland were regulars who were listening out and we just called them and asked their intentions, which meant we could agree separation if necessary.

PS. It is not unknown for the pilot to input the callsign incorrectly, such as BA1471 instead on BAW1471 !

[PaulJahn]

alright so I guess one can say it is more or less a ground equipment issue (receiver issue).. in other words, if worldwide all radars would be mode s capable, no need for squawk anymore?!
It just seems to me much more easy to allocate the callsign/flight # with the atc flight plan instead of having to create a squawk every time..
but thx for the answer =)

[DaveReidUK]

See also

PPRuNe: Squawk 1000 (https://www.pprune.org/atc-issues/484742-squawk-1000-a.html)

One of the drawback is that crews don't always enter the correct callsign.

Most days you will see a few LHR movements, for example, where the Mode S ACID hasn't been entered correctly. It will often be rectified at the FIR boundary once Eurocontrol detect it.

[Pringle_]

One of the drawback is that crews don't always enter the correct callsign. <-- the same could be said for entering the correct SSR code, both are easily changeable as far as I'm aware.

My understanding is that ORCAM codes are still issued because not every ATCU uses mode-s as the primary means of identification. It also helps if an aircraft is squawking a discrete unit code a service is being provided outside of controlled airspace as the controller knows which unit to get traffic information/coordination from.

[Talkdownman]

Crews occasionally don't even check the callsign input. I have seen some interesting 'sabotage' entered by engineers...

[chevvron]

One of the drawback is that crews don't always enter the correct callsign. <-- the same could be said for entering the correct SSR code, both are easily changeable as far as I'm aware.

My understanding is that ORCAM codes are still issued because not every ATCU uses mode-s as the primary means of identification. It also helps if an aircraft is squawking a discrete unit code a service is being provided outside of controlled airspace as the controller knows which unit to get traffic information/coordination from.

This is correct. Just because aircraft are fitted with these snazzy modern bits of kit it doesn't mean every radar unit with a jobsworth watching the purse strings has the facility to display the information.

[ChickenHouse]

Dear guys,
this may be a stupid question, but I didn't find a good answer on google.

So I am speaking especially about commercial airliners: So I know that each airplane has a unique mode S Hex code which basically never changes. If you are beginning a flight, you will enter your flight number (or atc call sign) in your FMS. So with your hex code and your FMS callsign, the tower should get all he wants, right? Why will he give you a 4 letter squawk code? Does this have any benefit?
I am curious about the answers =).

Quite easy. Mode-S Hex will tell the aircrafts identity, squawk will tell its intention.

ATC does use filtering techniques to separate which aircraft they want to see at a certain workplace. Think of it like "controller A is today looking over all westbound flights" and to achieve the filter in one-click the traffic westbound gets squawks starting with a certain number, say 5xxx. The categories may vary from day to day, from ATC to ATC, from shift to shift and cannot be done easy by using the Hex code identities. Don't assume the ATC equipment is comparable to the error-prone blinky-blinky smartphone world, it is old and proven equipment.

[zonoma]

It is even more complicated than suggestions so far! The UK radars (as in the ground based things that spin around) are mostly now upgraded and can receive Mode S, however the equipment in London Area Centre can only display certain elements of the Mode S, and callsign is not one of them!! In the enroute sectors the system can even cross check the level entered into the ATC system against that selected in the cockpit using the Mode S data, and will alert the controller if there is any mismatch. But still we can only see Mode A to identify a track, or just a primary return otherwise.

[chevvron]

In any case, what if you 'need' to select a 'special purpose' code for any of the main reasons?

[ChickenHouse]

It is even more complicated than suggestions so far! The UK radars (as in the ground based things that spin around) are mostly now upgraded and can receive Mode S, however the equipment in London Area Centre can only display certain elements of the Mode S, and callsign is not one of them!! In the enroute sectors the system can even cross check the level entered into the ATC system against that selected in the cockpit using the Mode S data, and will alert the controller if there is any mismatch. But still we can only see Mode A to identify a track, or just a primary return otherwise.

Not to forget that the systems don't have an online link to all flight plans ...

[Juggler25]

It is even more complicated than suggestions so far! The UK radars (as in the ground based things that spin around) are mostly now upgraded and can receive Mode S, however the equipment in London Area Centre can only display certain elements of the Mode S, and callsign is not one of them!! In the enroute sectors the system can even cross check the level entered into the ATC system against that selected in the cockpit using the Mode S data, and will alert the controller if there is any mismatch. But still we can only see Mode A to identify a track, or just a primary return otherwise.

This is nothing to do with the Mode S London AC has but the flight data system. NAS is from the 60's! When it's (eventually) replaced with iTec the Hex ID will become the norm. Mode A will still be required though, for the countries that don't have Mode S.