Reporting altitude in Shannon
 

Hi all,

I had a puzzling exchange with ATC last week that I hope someone can help me with. I was transiting the Shannon class C in a light single VFR and was at 3000. Approach advised there was traffic in the circuit and other traffic inbound and handed me to tower. Tower requested descend and report 2000 to cross the centreline so began a descent. He then called me back with traffic and other update. I ack'd and as I was talking passed 2000 so I added "and now at 2000". He replied "yeah well that's not what my information says why don't you call me back when established level 2000".

I had no idea how to respond so mumbled something about being there now. Did he really not trust my report? Is there not a known delay in the secondary / mode C response? Shoudl I have delayed my report until his screen had updated (however long that is)?

TIA for any insight. :confused:

As far as I'm concerned (as an approach controller) when you say you're level at 2000, you're level. Now if your Mode C readout says something radically different then I would query it with you. There is a slight delay and even then we use that data with a tolerance of +/- 200ft.

An unreasonable response from a controller having a bad day I expect. Don't worry about it and move on.

I would have responded with "Callsign - Maintaining 2000" if that's what you were doing... But I'm not sure exactly what you've said even here in writing... So were you level or still on descent? Maybe this was the problem, he wanted you at 2000 but you descended lower? But as gc4 said we use +/- 200ft on your Mode C if your transponder read out is outside that tolerance we'd ask you to Squawk mode A only.

Thanks for the insight. I was literally levelling off as I spoke the words. I thought I would save the trouble of making another radio call but it looks like I shouldn't have taken that short cut. I don't know the update frequency of the mode C but +200 ft could be possible.