ndt
Good article on Wikipedia.Off the top of my head X-ray,ultrasonic,dye penetrant ,all dependent on which part of the aircraft is under inspection.Usually carried out by specialist firm especially X-rays but some testing (after suitable training )carried out by LAMES eg; testing of fan blades on RB211 and IAE V2500 engines.Dont know what qualifications reqd for specialist firms but would imagine quite high educational quals reqd