changing squawk
 

if I'm asked to change the transponder code enroute, do I need to select 'standby' while I'm changing it???

Changing squawk
 

I could be wrong in saying this but, you don't have to switch the transponder to standby whilst changing squawk. I.E There's no legal requirement for you to do so.

It is, however, good practice, as it prevents the transmission of an incorrect ident (as you're cycling through the transponder codes) especially, the emergency codes (7500, 7600, 7700).

Aircraft in the FIR squawking 7000, gets an airborne IFR clearance with the squawk 7701 (yes, it can happen). Dials in second '7', gets distracted, doesn't do final '1' quick enough.

The alarms will go off.

Now, having said that, there's no reason why you shouldn't leave it on when you're changing squawk. With new transponders you just push-button the code in anyway. However, be careful when you're doing it for the above reason.

PPRuNe Search 'probably' has the answer :)

There was a discussion about this on here a couple of years ago. I can't remember all the details, but I think that there is now a training edict that you leave it on. If you go to standby you stop the protection of TCAS for those around you.

How much of a big deal are brief false alarms that are easily traced? I had a transponder unilaterally decide to squawk 7700 (I genuinely had 7000 set. Perhaps we should go to an American-style 1200 away from 7000 to avoid this problem). Bournemouth radar let me know so I could recycle, which cleared the problem, but they sounded unfazed by the issue.

Send Clowns
 

The selection of 7700 will cause flashing and label bright-up on all Area control displays at Swanwick and elsewhere. It will inhibit the ability of the system to display genuine emergencies, because it can saturate.....especially on sunny days when the hangar-queens and "company" aircraft get airborne. If the offender happens to be in a busy portion of airspace.....even though all the other traffic is way above.....the 2-dimensional nature of the displayed information means that labels of airways traffic may be blotted out by the spurious 7700. Remember that many aircraft that use 7000 may not necessarily be in communication with anyone; additionally I should add that transponder confidence or validity checks are available via Londion Flight Information if there is no suitable SSR-equipped unit in your area.

ooooh gooody

Been wanting to get this off my chest for some time.

Concur completely with 055166k

PLEASE take more care when changing squawk! If you punch the code in directly then fine, but if you've got the little thumb wheel things then turn it to standby - one missed sweep of a radar does not a TCAS nightmare make. I, the other surveillance people and, I'm sure, D&D are sick to death of chasing up the endless spurious emergency squawks caused by this phenomenon, especially when you set it wrong and then trog all over the country VFR trailing a set of little flashing E's after your radar return - it makes my display all messy!

We were told sometime ago on the Airbus fleet that we should not go to standby when changing squawk as it takes quite a long time for the transponder to start working again when it is switched back, standard practice is now to just the new code with unit still switched on.