MHT Controller described a go around event required because of the spacing provided by A90 with two arrival aircraft to intersecting runways; the reporter questioning A90's separation procedures.

Narrative

An A300 [was] cleared to land on Runway 24 while approach cleared a B737 for a visual approach to Runway 17; the intersecting runway. No separation applied prior to shipping both aircraft to the Tower. By Letter Of Agreement between A90 the RADAR facility and MHT Tower; MHT does not have control of arriving aircraft and is not responsible for successive arrival separation. The B737 was advised to continue the approach and expect landing clearance short final and be prepared to go around. Weather was VMC and the B737 had the A300 in sight. Event occurred at night. The aircraft tied at the intersection and the B737 was sent around to avoid collision. The A300 inquired as to what type of separation was being provided and was advised to contact the Tower Supervisor. A90 is interpreting the handbook as stating that as long as simultaneous visual approaches are being conducted and are advertised on the ATIS; then standard separation is; aircraft don't hit at the intersection. A90 Management is aware of this problem and believes their interpretation is correct. Someone from Headquarters needs to look into this innovative interpretation.