(Ref. from Flight Crew Operating Manual Vol. 1 7-11-1)

1. GO messages have approved MMEL dispatch alleviation and the associated MMEL rules do not require procedures that require return to ramp for action. However, the aircraft MMEL must still be consulted to understand and invoke associated flight and/or system limitations.
2. NO GO messages do not have dispatch alleviation and the flight must be canceled until maintenance can be effected.
3. RETURN TO RAMP messages have approved MMEL dispatch alleviation, however, if the affected annunciation occurs following aircraft push-back but before take-off, it is recommended that the aircraft return to the ramp as the procedures associated with pre-dispatch are too lengthy or complicated without ramp facilities available.
4. AS REQUIRED messages have approved MMEL dispatch alleviation, however, there are restrictions associated with the dispatch that may be weather related, or may require additional maintenance procedures depending upon a failure mode (e.g.: valve fail OPEN vs. fail CLOSED).