I think
You should assume some things. For example You can assume that relationship Flight->Equipment becomes unidirectional and for every flight in the system, this flight is services by exactly one plane(equipment).
Or You can try and change BDOM (there are success stories of
SCEA's who did that), or You can do anything else... just be sure to document it and be confident about Your assumptions and design.
Good luck
SCJP 1.4, SCWCD 1.4, SCBCD 5, SCEA