Mode A or C during aerobatics
Join Date: Mar 2002
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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
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
Join Date: Apr 2004
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Okay Okay....
Simple answer is Yes. Mode C does sometimes cause predicted STCA alerts while Vertical Separation is still maintained. Maybe our Radar is a bit over-cautious - maybe not - that's not really for me to answer. The alerts would not be an everyday or a regular occurence and are not related to aerobatic activity. Our Aerobats don't get close enough to IFR traffic to cause problems. Our IFR / IFR do alert sometimes due to high ROC/ROD while still separated. I've yet to come across a false TCAS RA, and it is possibile that the extra precautions may have contributed to us not having had one.
Without getting too tit for tat .....
1. When the pilot adjusts the altimiter settings and it's checked and indicates airport elevation, that's the "car boot sale" altimiter calibrated. Of course this doesn't check the encoder - thats what we do with verification.
2. If, as you suggest, a pressure altimiter is correct at aerodrome elevation and incorrect at higher altitudes, what will happen? If there is no backup system he'll climb till reaching his desired indicated altitude. ATC will check his alt if it's different from the cleared level and if an error is found, it's the mode C that'll be turned off.
3. Yes, you're correct, Mode C encoders use QNE/1013.2 at all times and the Radar data processors will decode the data & display Alts or FLs as required. Next time in radar, watch a mode C as it passes the Trans Layer.
4. The mode C data is checked when it is verified by the controller, which again, does not mean that an unverified mode C is wrong - it just means that it hasn't been checked yet. If it has been checked and is found to be wrong, it can be turned off and no longer cause confusion. 9 out of 10 unverified mode Cs in uncontrolled airspace are within limits, but just not checked yet. Use it unverified only as an aid to VFR traffic info but not as a method of IFR separation. eg, Unidentified Tfc, 11 O'clock, 2miles, indicates 1200' unverified.
5. Now I think we all agree that mode C should be used if it's available. The majority of our aerobatic activity uses mode C, but some does not. Generally, it's the Gnd-5000' over the airfield that does not, and the Remote Area FL100- FL300 that does. When it's not used, it's because of genuine reasons and extra precautions will have been taken.
And entertaining as it is
, I don't see any need to argue these points any further. I think ATC everywhere uses the same general rules with regard to mode C verification and use.
Without getting too tit for tat .....
1. When the pilot adjusts the altimiter settings and it's checked and indicates airport elevation, that's the "car boot sale" altimiter calibrated. Of course this doesn't check the encoder - thats what we do with verification.
2. If, as you suggest, a pressure altimiter is correct at aerodrome elevation and incorrect at higher altitudes, what will happen? If there is no backup system he'll climb till reaching his desired indicated altitude. ATC will check his alt if it's different from the cleared level and if an error is found, it's the mode C that'll be turned off.
3. Yes, you're correct, Mode C encoders use QNE/1013.2 at all times and the Radar data processors will decode the data & display Alts or FLs as required. Next time in radar, watch a mode C as it passes the Trans Layer.
4. The mode C data is checked when it is verified by the controller, which again, does not mean that an unverified mode C is wrong - it just means that it hasn't been checked yet. If it has been checked and is found to be wrong, it can be turned off and no longer cause confusion. 9 out of 10 unverified mode Cs in uncontrolled airspace are within limits, but just not checked yet. Use it unverified only as an aid to VFR traffic info but not as a method of IFR separation. eg, Unidentified Tfc, 11 O'clock, 2miles, indicates 1200' unverified.
5. Now I think we all agree that mode C should be used if it's available. The majority of our aerobatic activity uses mode C, but some does not. Generally, it's the Gnd-5000' over the airfield that does not, and the Remote Area FL100- FL300 that does. When it's not used, it's because of genuine reasons and extra precautions will have been taken.
And entertaining as it is
, I don't see any need to argue these points any further. I think ATC everywhere uses the same general rules with regard to mode C verification and use.
