Sqwing 7700

[727070]

Hello,

I have just been re-reading airlaw to remind me of everything I forgot at the start of my PPL course and came across the reasons for setting 7700 on the transponder.

7700 - to indicate an emergency condition (except that, if the aircraft is already transmitting a code and receiving an air traffic service, that code will normally be retained)

However I have always been told to set 7700 regardless of whether you are with an ATC unit or not. Therefore from an ATCO's perspective would you want me setting 7700 or retaining the squawk I had been given earlier?

Thanks.

[FWA NATCA]

727070

If you are already on a descrete code stay on that code and notify ATC immediately of your problem.

The only time that I could see squawking 7700 when you are on a discrete code is if the controller is extremely busy and you are concerned that you wouldn't be able to break in to announce your emergency, or the situation is of such a dire emergency (rapid decompression, etc) and you are making an emergency descent and you may or may not have time to notify ATC (fly the airplane first).

Regardless what you do, you data tag will stay associated with your target, the difference is that 7700 will set off an alarm and your data tag will flash "EM".

Mike
NATCA FWA

[Spitoon]

Mike's answer is broadly true but there are some variations, certainly in the UK.

What actually appears on the controller's radar display depends on a number of things (including which company built the radar processing software). In most cases the aircraft id, if it was on a discrete code and had been code/callsign converted (i.e. the display showed the callsign rather than the mode A code) in the display software, will remain displayed but some early systems don't do this.

As Mike says, if you are already talking to ATC tell them you have a problem and if there's a good reason to squawk emergency they'll tell you to. In some circumstances the controller will get an aircraft to put up 7700, if it's making an emergency descent for example, so that other controllers know that it may not do what is normally expected (and will try to keep their own aircraft out of the way).

There are lots of other specific situations where 7700 is the best squawk but the controller will know, and tell you, if there is a benefit in changing code. If there is no benefit he/she won't give you something unnecessary to do when you've already got your hands full!

If you're not talking to a controller and ATC might be able to help the best answer is to put 7700 up and speak to the nearest secondary radar equipped ATC unit (or D & D) to declare your emergency.

And I hope you never have to do it. ;)

[jack-oh]

Having dealt with a lot of ac declaring emergencies (Military ATCO);) I always get the ac to squawk 7700 regardless of what squawk has already been allocated. Everyone is left in no doubt what is going on. Other ac will try to get out of your way once they have been told and other ATCOs wont try and co-ordinate with you.

[cb9002]

I was under the impression that 7700 was also useful because it cuts through any height/area filters that other controllers might be using. Is that right?

I guess there isn't much chance of a PPL doing an emergency descent from upper air regions anyway...

[5milesbaby]

In the UK 7700 does indeed break through filters, and also rings an alarm bell in the D&D cell in West Drayton so instantly you are known by all. The alarm in D&D is very useful if you aren't talking to a unit and call on 121.5/243.0 as it gives an immediate ident (subject to altitude) so a great service can be provided from the start.

[Vlad the Impaler]

7700 is also a great attention getter if you are trying to get in on a busy frequency and announce your impending peril/sick pax etc..... I believe airline SOP's do not generally mention 7700 anywhere!!!!!!! it really can help. Everybody can see it A.S.A.P which means easier co-ordination between agencies and therefore a better service for YOU !!!!!!!!

[Scott Voigt]

In the US the 7700 code will go through the filters because we have to have it set up to be seen everywhere. There are also other assets that can see the code in the event you are in an area that may not have normal ATC radar...

regards

Scott

[727070]

Thanks a lot for your replies,

It makes a lot more sence now.

Cheers