The excerpt “There is substantial anecdotal evidence to suggest that language miscommunication has been a contributing factor in several airplane crashes, and in even more near-misses.” (lines 2-5) means that
it has been proved that unclear language has triggered most aircraft accidents and near collisions.
it has been undeniable that inadequate communication is the major source of accidents and near accidents in aviation.
it has been difficult to attest that language mistakes have been responsible for a large number of airplane accidents and near crashes.
there has been a slight suspicion that most airplane accidents and near accidents have been caused by the ineffective communication.
there have been strong indications that linguistic misunderstandings have played a significant role in aviation accidents and narrowly avoided collisions.