For the Netherlands, from the Dutch AIP:
4.1 Elementary surveillance
Aircraft shall be equipped with a mode S transponder with elementary surveillance (ELS) functionality. The equipment must be in accordance with the technical specifications laid down in ICAO Annex 10, volume IV, amendment 77.
Activation of mode A/C transponders is prohibited in the Amsterdam FIR.
Exempted from the mandatory carriage of a mode S transponder are:
motorised VFR flights in class G airspace below 1200 ft AMSL (excluding the North Sea area Amsterdam, see ENR 2.2).
non-motorised aircraft (gliders, hanggliders, parasailers or balloons) outside the transponder mandatory zones (TMZ, see ENR 2.2).
Carriage of a mode S transponder is strongly recommended in the UK North Sea area V, this recommendation is published in the UK AIP and regulation.
4 .2.3 EHS non-capable aircraft
Exemption from the EHS requirements may be granted to non-mode S EHS capable aircraft and non-mode S EHS compliant delivery and maintenance flights with a first certificate of airworthiness issued prior to 31 March 2005 that conduct IFR/GAT flights in notified mode S airspace in the Amsterdam FIR. In these instances the aircraft must, as a minimum, be mode S elementary surveillance (ELS) compliant.
A standard form for the mode S EHS exemption request is published on the website:
Inspectie Leefomgeving en Transport (ILT) - Formulieren luchtvaart.
------------------
The same for Belgium if you plan on flying in any controlled airspace requiring use of a transponder (Brussels TMA/crossing CTR) and generally above FL50 if I remember correctly.
A standard form for the mode S EHS exemption is contained in AIC 02/2009.
Exemption requests should be addressed to:
Mail:
Belgian CAA
Commercial Aviation Department
Fax:+32 (0) 2 277 42 52
Email:
[email protected]
The request must reach the administration 15 working days before the first flight using the exemption arrangements.