A little google searching told me they are top ranking aeroplane mechanics, they would now the the mechanics inside out, so basically they build aeroplanes..


Leading Aircraftman (LAC) (or Leading Aircraftwoman (LACW)) is a rank in the Royal Air Force, ranking between Aircraftman and Senior Aircraftman and having a NATO rank code of OR-2. The rank badge is a horizontal two-bladed propeller. The rank was introduced on the formation of the RAF in 1918, replacing the Royal Flying Corps rank of Air Mechanic 1st Class (which wore the same badge). It was only a trade classification until 1 January 1951, when it became a rank, although it is non-supervisory.