Findo
If they cross the airway at the base flight level then they are not technically WITHIN Class A airspace. So whether the service is being provided by an autonomous radar unit matters not a jot. RAS or RIS would be the appropriate service.
Being as a lot of bases give at least 500' separation from the lowest whole level within the airway, then the answer is to provide essential traffic information and if necessary take the appropriate remedial action if requested by the pilot.
If you look at the bases they are (or would have been in the mists of ancient time) decided so that a pilot crossing at right angles would have 500' separation from traffic inside under the Quadrantal Rule. Hence why the same rule of crossing does not apply when the base of the Airway is defined as an altitude.
Feel free to scour the AIP and find one that doesn't and prove me wrong
