Embus - enplane - entrain
Avoid these three words - unless you are working in a military context. Entrain was being used as a verb for troops in about 1880. Embus appears to have come into being in the British Army during the First World War. Emplane is first recorded in 1923. All are formed on the analogy of embark, a long-established word meaning 'to get on to a ship'. (Barque, sometimes spelled 'bark', was the name of one type of sailing vessel.)
In traditional British academic circles, embus, enplane and entrain are regarded as ugly and unnecessary coinages. Use the older verbal constructions like 'get on the...', 'board [verb] the ...' and 'climb on board [compound preposition] the ...' instead.
The reverse words debus, deplane and detrain are even uglier, and even more to be avoided. Disembark, being recorded from the sixteenth century and being hallowed by tradition, is more acceptable.