ADS-B is of course not mandatory in Europe and nor are all aircraft covered by the Enhanced Mode S mandate, so some aircraft will indeed not transmit their magnetic heading. For those who must have it, then there is no choice but to have the capability to transmit magnetic heading.
Indeed, ADS-B is not mandatory yet and not all aircraft are subject to the Mode S mandate. But there are some things changing in the next 4 years.
From December 2017 all general air transport aircraft with an MTOM > 5700 kg or a maximum cruising speed > 250 KTAS flying in Europe must have the following:
Mode S ELS (Elementary Surveillance)
- 24 bit address
- Mode A code
- pressure altitude
- ground/airborne indication
- aircraft identification (flight id/call sign)
- special position indicator ("ident")
- emergency status
- TCAS RA activity (if TCAS II equipped)
EHS (Enhanced Surveillance)(for fixed wing aircraft)
:
- selected altitude
- roll angle
- true track angle
- ground speed
- magnetic heading
- indicated airspeed
- vertical rate (baro or baro-inertial)
- barometric pressure setting
- track angle rate (or true airspeed if track angle rate is not available)
ADS-B (Automatic Dependent Surveillance Broadcast)
- 24 bit address
- aircraft identification
- Mode A code
- Special Position Indicator
- Emergency Status
- ADS-B Emitter Category
- Horizontal position (WGS 84)
- Pressure altitude
- Geometric altitude
- Ground speed vector
- Quality indicators for position, geometric altitude and velocity
- vertical rate (baro, baro inertial or GNSS)
- selected altitude
- barometric pressure setting
- TCAS RA activity (if TCAS II equipped)
- ADS-B version 2