on board vs. a board


Could someone tell me whether there is any difference between on board and a board(both meaning getting on a ship,plane,train)?

Can they be interchangeably used in all occasions?

Thank you

Yes they can. On board, and aboard mean the same same.

Dear Mr Kitostad,
‘on board’ and ‘aboard’ is not always the same,
and definitely not same same.
‘aboard’ has more than one meaning, depending upon sequence or circumstance.
‘aboard’ = on board, overboard, to throw sth. overboard; (Dictionary).
Hence the famous phrase: “Man overboard!” when someone has fallen from the ship into the water.