Nibog,
Have you experience of aircraft doing aeros with mode C on causing problems? i.e. Military flights or similar that may be operating in airspace below which your flights are operating?
We reguluarly pass close to large military danger areas which are within controlled airspace. If flights within those segrated areas were told to switch off mode C we would have serious safety concerns because it has happened that flights have exited the airspace both vertically and laterally and without mode C, the ACAS system and your STCA has no way of drawing our attention to a possible collision.
I don't think it very wise to fly through (or allow an aircraft to fly through) an area of (Controlled) Airspace that has aerobatics in progress
I agree that it is unwise for a pilot to fly through and area where a pilot is performing aerobatics. However, in general that is a pilot decision and the chosen separation by a VFR flight against another VFR flight is up to the pilot.
It's nothing to do with equipment calibration.
Altimiters are calibrated on every flight prior to departure - what does the pilot do with the QNH?
As you are no doubt aware the encoder that provides the level information to the transponder is permanently set to 1013.2. Setting QNH in the aircraft makes no difference to the level information transmitted by the transponder. Your supervisor or engineers have to imput your QNH into your system so that the computers can work out and display altitudes when appropriate.
Setting QNH on the altimeter pre-flight and checking the indication against the elevation of the apron / threshold / airfield ensures that the aircraft's pressure altimeter is correct at that level. It does not in any way check the encoder which supplies information to the transponder.
Just because the altimeter indicates the correct airfield elevation with QNH set does not guarantee that the altimeter will indicate 5000ft when the aircraft reaches 5000ft even if it is ISA.
Regards,
DFC