B737-800
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 200; Flight Crew Total 25000; Flight Crew Type 250
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert
Procedure; Human Factors; Chart Or Publication
[We were] conducting the TRUPS ONE arrival. ATC had taken us off of and back on the arrival a few times for spacing. We were then cleared direct TRUPS Intersection and resume the arrival. After passing TRUPS Intersection we continued the descent to cross FRDMM at 8;000 FT. As we were passing 10;400 FT Controller intervened and advised that we had not been given a new altitude and then cleared us to 9;000 FT. No conflict was noted by the flight crew or indicated by the Controller. I suggest when giving a clearance to resume an RNAV STAR that the Controller verbalize either a maintain altitude or give the clearance to descend via the arrival to avoid any miscommunication.
The reporter confirmed that they had; indeed; originally been cleared 'via' the STAR and then vectored off. He was uncertain; but believed that when they were vectored they had also been cleared to descend to 11;000; which is also the crossing restriction at TRUPS. When ATC cleared them 'direct to TRUPS' and to 'resume the STAR' they interpreted that 'resume' meant they were; again; cleared 'via' the STAR and--lacking a new cleared altitude--could descend 'via' the balance of the arrival as they would have had they not been vectored off it.He also advised their aircraft was a -800 model B737; equipped with fully functional FMS VNAV capability including autothrottles. When allowed to fly even the most complex STARs in their entirety the system routinely performs perfectly and it is only when it is necessary for ATC to interrupt the arrival that errors such as this occur.
After they were vectored off the TRUPS RNAV STAR to DCA for spacing the flight crew of a B737-800 assumed that a clearance 'direct to TRUPS; resume the STAR' included the clearance to resume descent on the arrival. ATC disagreed; believing they should have maintained their last assigned altitude independent of the STAR restrictions.