Flight Crew Last 90 Days 180; Flight Crew Type 4134
Confusion
ATC Issue All Types
General None Reported / Taken
Procedure
Descending on the ROBUC1 Arrival we were approaching the JOODY intersection. We had previously been given a descend via clearance runway 4R. When we were switched over to approach control; he told us to intercept the localizer; I believe his exact phrase was 'intercept the localizer when able; but comply with the altitude restrictions'. I then went to the legs page on the FMS and brought WINNI intersection to the top and extended the course off of WINNI 036. I selected LNAV after confirming with the Captain before executing anything. I had the captain confirm we were still cleared to 6;000 feet. ATC said yes; we were cleared to 6;000 feet but to comply with altitude restrictions after intercepting the localizer; I started to wonder about what altitude restrictions he was talking about. We were cleared to 6;000 feet; and we were established on the localizer; not the arrival. We were no longer on the arrival; but established on the localizer. The only altitude restrictions were WINNI at 4;000 feet and we were cleared to 6;000 feet. I then thought maybe he wanted us to track the localizer but meet the Arrival altitude restrictions. That's not possible; but I went to the fix page and put SOFEE intersection in the FMC. We were tracking right over the top and were 9;000 feet or above. I confirmed with the Captain that he agreed with what we were doing. He said yes. ATC then switched us to a different frequency. Captain checked in and I believe stated we were on the localizer and descending to 6;000 feet. ATC gave us a acknowledgement of our check in. I don't believe he said anything about complying with altitudes or questioned us about being on the localizer; instead of the arrival Later we were given clearance for 4;000 feet and then given clearance for the ILS to 4R. Performed and normal approach and landing to 4R.  Later looking at the arrival and the approach they are about identical in their track. If they weren't identical then how did ATC expect us to intercept the localizer. The arrival says we will get radar vectors after GOSHI. ATC did not give us anything other than 'intercept localizer';.  He told us that when we were headed to JOODY. The controller should have stated when to intercept; on current heading; after GOSHI or after he gave us radar vectors.
B737 First Officer on the ROBUC1 RNAV arrival to BOS is cleared to 6;000 feet and to intercept the Runway 4R localizer when able but comply with the altitude restrictions. This does not make sense to the reporter and is not clarified prior to landing.