I believe the US methodology is for the Crewman to have aircraft engineering background training, and as 'Crew Chief' when his/her aircraft undergoes deep maintenance, so the 'Crewman' contributes & oversees the work.
In the UK, Crewmen are Aircrew with only sufficient engineering knowledge to undergo turn round servicing as indeed so do the pilots. They have no involvement in offline servicing and are neither constituted crews nor aircraft supervisors. The U.K. crewman is expected to be able to deliver a briefing to their base groundcrew concise and accurate enough for a deploying ground crew party to know exactly what problem they face when deployed to a downed-bird situation brought on by technical failure.
There would be little benefit for a gunship aircrew undertaking flying training with rear crew and I assume that their flying training path is basic trainer > Apache direct.