ATC question
 

Greetings, just a quick question regarding transponder emergency codes 75,76, and 7700... with ads-b, if you insert one of these codes into your transponder, will atc see this distinct code or will they only see a nonspecific code where in you will have to verbally tell them what your actual emergency is? If the answer is the latter, it would be difficult if you've inserted 7600. Thanks to all in advance for offering your many insights.

fly safe,

Good question, you mean outside the SSR radar coverage, right?

ADS-B Out transmits the same squawk code as set on the transponder. There is no "non-specific" code.

Mode S transponders with ADS-B Out use the code directly in their extended squitter. UAT ADS-B Out typically captures the code by receiving the transponder signal and decoding the squawk code.

ATC can't see any code other than the one you set.

You might confuse SSR A codes and Mode S selective address codes . . As EXDAC said, ADS-B out will transmit the A codes set in the transponder . , Now the display of that code on the controller may vary from system to system , some will show the actual code ,most modern systems will automatically translate A7700 as " EMER" , "EMERGENCY" or some eye catchy symbol . As to your question regarding 7600, obviously you can't transmit the reason , but it does not really matter ,the procedures to follow is fixed for the controller to follow for each code . Remember that in n some real emergency cases , there is also no communications for a while until the event is over or under control , It's Aviate well before Communicate .

As a very new pilot I had a radio failure in the Birmingham zone. Setting 7700 to declare a Mayday before setting 7600 for radio failure and then landing didn’t save me from receiving a very threatening letter from the CAA for not knowing the radio failure procedure for Birmingham.

From the difficulty they had trying to get the signal lamp out of the door I concluded that it had been a very long time since someone had landed at Birmingham with radio failure.

In answer to Slim75’s question - it may be dependent on the ATC unit’s equipment - squawking an emergency code will flash red and highlight your aircraft data block on the screens we use, but we will still see your original details (eg callsign converted if you were on an airways squawk, or original squawk code if not).

In response to the second poster’s comments on the lack of use of an Aldis lamp during radio fail at Birmingham - the unit does not physically have one to use.. and has not had one for many years. It would be interesting to see if many modern towers have one available- my suspicion is larger modern units won’t have, unless specifically mentioned in the AIP?

In UK the following will apply.

Setting 7500 will result in a discrete enquiry from ATC “(Callsign) confirm you are squawking assigned code (code assigned by ATC that it would otherwise be squawking).”

Setting 7600 will merely indicate a comms loss with the expectation that you will will follow any published comms loss procedure.

Setting 7700 will require verbal explanation of the nature of the emergency and any resultant requests/intents.

Thanks to all for your insights. I was able to get this question in with Los Angeles Center last week while airborne. The controller told me that regardless of the emergency code entered into the transponder (ads-b), his screen will only see the aircraft's callsign and a nondistinct code other than what was originally assigned but not anything specific. He further stated that operators need to verbally tell the controller the nature of the actual emergency since their ground systems can not distinguish the specific code entered into the transponder. i guess i'll go with that. thanks again.

stay safe,

Quick one for those who look after us in the tower:
Delivery tells me to squawk 7502 in my clearance.
My transponder is set 1000.
If I start from left to right, my transponder will very shortly read 7500 (until I change the last 0 to a 2).

Does ATC see this pop up (7500) whilst I'm setting 7502?

I was told to always set the transponder from right to left.

Always used to select STBY before changing squawk.
I've been out of it since 2012 so maybe things have changed with ADSB.

Unless your transponder automatically does so, we were always taught to set to standby when changing codes, in order to inadvertently select one of the special use codes while changing.

Thanks for the input but the question reads like an ATPL question. You have to really read the question.

Will ATC be able to see the 7500 code whilst I'm turning the knobs of the transponder?

From personal experience, have seen it happen.

No , normally not, you may but in very exceptional circumstances , i.e you will have to pause significantly while passing through this exact number , and the radar antenna has to be hitting you right at that moment , but remember the rpm of a typical en route radar is 12 Rpm. so hitting you for a nanoseconds every 5 seconds . so you will have to be extremely unlucky to have this ,I personally never seen it in my whole career ,
In addition , quite a few ATM systems have a filter that needs at least 2 returns to confirm an anomaly , especially on the mode C ., to avoid garbling and false alerts , in this case no chance for ATC to see your "intermediate " codes.

@Dixi188 : Shows your age :E, a bad habit today as most ATC systems run on SSR only and you will then briefly disappear from view, it will also delay TCAS reactions . ,and on the ground, multilateratuion protections from vehicles depends on having your transponder on at all times..( for those airports equipped)