metaphorical aboard = on board with

[Mark A. Mandel]

In today's NY Times:
  >>>
Justices Say E.P.A. Has Power to Act on Harmful Gases
http://www.nytimes.com/2007/04/03/washington/03scotus.html

This was the issue on which the coalition’s lawsuit had appeared most 
vulnerable, given that in recent years the Supreme Court has steadily raised 
the barrier to standing, especially in environmental cases. Justice Scalia 
has long been a leader in that effort, and Chief Justice Roberts made clear 
that, as his statements and actions in his pre-judicial career indicated, he 
is fully **aboard** Justice Scalia’s project.
  <<<

I hadn't seen "aboard" used this way; I would expect "on board with". 
Neither Merriam-Webster nor OED have this sense on line, and OED doesn't 
have it for "on board" either:

m-w.com:

aboard

2 a : on, onto, or within a vehicle (as a car or ship) b : in or into a 
group, association, or organization <her second promotion since coming 
aboard>


under "board":

- on board

1 : ABOARD

2 : in support of a particular objective <needed to get more senators on 
board for the bill to pass>




OED Online, under "board":
12.
     c. on board: on one side, close alongside (of a ship or shore); also as 
prep., short for on board of.

14. a. on board (beside the technical sense in 12c) has now, in common use, 
the meaning: On or in a ship, boat, etc.; into or on to a ship.


m a m