Airborne_Again wrote:
For IFR it is simple. Mode S is required by EU regulation.
I have no problem taking your word for it, especially since it aligns with what I found last year when composing a table about equipment requirements, but I have not found it “simple” to find the exact reference in the EU regulation where it is stated. I believe you have to look up several cross-references to make sense of the regulation in question. And then some exceptions are mentioned, going until 2025 it seems, I am not sure.
You are also right about enforcement, I have heard of none in Denmark. But also, absolutely no trace of information from the Authority about transponder requirements have been detected, and I do not think mode S requirement is mentioned anywhere in AIP or AIC.
@ibra: Beautiful airplanes and pictures!
Maybe I am an over-cautious old fart, but I always discourage formation flying as a means of solving equipment requirements
Indeed it’s hard to maintain a loose formation than a tight one, in controlled airspace and weather it’s probably more complicated, but under SERA.3135, formation flights have to be less than 0.5nm laterally & 100ft vertically in controlled airspace, under 100% eye contact, or one has to manage requests to join-up and breakaway
It’s fun to fly formation in CAS but it will need way more planning, once in formation we got transit of Luton who surprisinly arranged a handover to Heathrow Radar then Farbrough, we got clearance to overfly London City airport while overead Luton airport, the flight was VFR and none of the aircrafts had TXP but ATS service we got that day was far better than when flying IFR with TXP in UK !
huv wrote:
Somewhat embarrassing I am still not sure about the current requirement for mode S in Denmark. I
For IFR it is simple. Mode S is required by EU regulation. Whether this is actually enforced in Denmark is a different question.
According to the Danish VFR AIP, mode C suffices for VFR.
Somewhat embarrassing I am still not sure about the current requirement for mode S in Denmark. I cannot even tell whether EU Reg 2020/587 from last December made any difference. All I can say is that the wisest and most well-informed people I know have differing opinions. Asking our Authority might appear obvious, but then we should feel comfortable that the answer we get is correct, and unfortunately, from experience, we are not quite there.
8.33 requirements are more straightforward. For VFR it is only required in parts of Copenhagen Area, IFR needs it everywhere.
But, so far very few ground stations are 8.33, and there is generally no way for ATS/ATC to detect whether you use the old 25kHz frequencies instead of the corresponding 8.33 channel.
Maybe I am an over-cautious old fart, but I always discourage formation flying as a means of solving equipment requirements, being it 8.33 or transponder. For pilots trained to fly formation, or at least interested in the art and taking it seriously, fine. But the way this is sometimes suggested as a solution, many pilots are lead to believe there is not much to it, in neither preparation, attention nor skill. And many non-formation-proficient pilots wrongly believe that a loose formation with some distance is much easier and safer than flying tight. There may not be frequent accidents out there to support my view, but I do not have the nerves to form up with someone without proper planning and knowing they are serious about it.
Formation under IMC & CAS, PIC & ATC will say no thanks 
VFR yes, who needs a TXP? a friend of mine flew vintages UK to Saudi, indeed he had a funny formation flying in Egypt, they rented a local C172 to “help delivery” a non-TXP vintage T6G, the C172 was mandatory to file the flight plan but did not make it past the border
Sebastian_G wrote:
I have never done this and do not know the legal details but the best idea might be to fly in formation with another aircraft? Then you are only supposed to turn on one of the transponders and only one plane does the radio.
This is a good suggestion. I also have not done it myself, but fly with a group of antique pilots (and aircraft 
) that do this a lot. Sebastian is correct on the transponder and radio work. The other aircraft are in listening mode, and if radio installations allow they can talk privately on an air-air frequency. Also, it should be done on a flight plan and only one flight plan should be filed regardless of number of aircraft in formation (2, 3, 4, …). The FPL is filed for the lead aircraft with transponder/radio and the other registrations should be listed in the FPL remarks area with of course in indication of the number in the formation. All radio calls are done “Call-sign FORMATION”. There must be some instructions on this somewhere, but I don’t know where.
In Germany you need 8.33khz. I have never done this and do not know the legal details but the best idea might be to fly in formation with another aircraft? Then you are only supposed to turn on one of the transponders and only one plane does the radio.
For the Netherlands, best to call the Operational Helpdesk of the LVNL for that. +31 (0)20-406 2201
I suspect the answer will be no, but you might be able to convince them if it’s for a one-off to a location where your mode-S is going to be fitted.
Assuming the 8.33khz and IFR GPS box is ticked, might ATC allow a ferry flight in CAS IFR with just Mode C?
