THE head of a group representing most global airlines welcomed an international investigation into the forced landing of a Ryanair jetliner in Belarus and said the world must ensure such incidents never happen again. "That sort of behaviour is completely unacceptable and must be strongly condemned. We must have measures to ensure that can't happen again," Willie Walsh, director-general of the International Air Transport Association, told Reuters. The United Nations' International Civil Aviation Organization (ICAO) agreed on Thursday to investigate the forced grounding. Belarus has said it was responding to a bomb threat. Walsh said evidence suggested the threat had…