EMB ERJ 190/195 ER/LR
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Procedure; Human Factors
Coming into BOS on the KRANN 2 RNAV arrival BOS Approach first told us to cross KRANN at 11;000 FT. then while descending they told us to descend VIA the KRANN 2 Runway 22L transition. So we set 5;000 FT in the alt. selector. After reaching and leveling off at 11;000 FT I thought BOS Approach said continue down to 9;000 FT so I set 9;000 in the MCDU at CRADL and hit DES now. After reaching 9;000 FT and hitting the TOD for the rest of the arrival the aircraft started to descend to 5;000 FT. At approximately 8;700 FT; BOS Approach told us to immediately climb back to 9;000 FT and turn left to I think 030. After we stabilized at 9;000 FT BOS said we were told to maintain 9;000 FT and asked us to call after landing; which I did. The Approach Supervisor asked me what happened and I told him again that we understood that we were cleared via the 22L transition and that approach just wanted us at 9;000 FT early so we just continued via VNAV to 9;000 and never changed the bottom of 5;000 FT. He said that; no we were told to maintain 9;000 FT which deleted the rest. I told him again I did not remember being told to maintain 9;000 and that I thought they just wanted us at 9;000 early because; had they not said anything we would not have started down so early. [We were confused] being given different clearances in close succession without making clear that the previous clearance no longer applied. I think ATC should say that they do not want you to continue via a profile descent after they have already cleared you to do so; instead of saying that the new clearance implies that the previous clearance is deleted.
On the KRANN 2 arrival we were cleared to cross KRANN at 11;000. Then we were cleared to descend via the 22L transition. 5;000 FT was selected as the bottom altitude. Later we were told after KRANN to maintain 9;000. I thought it was just for the next arrival segment. Descending below 9;000 ATC told us to turn left and to climb back to 9;000. So we did. ATC informed us to call after landing. ATC clearing us to an unpublished altitude after being cleared to a 'descend via procedure' without making clear that the 'descend via procedure' no longer applied. ATC should state very clearly 'Cancel descend via'; and that will trigger in the pilots that the bottom altitude is no longer what should be set in the ALT selector.
EMB190 flight crew reports misunderstanding an ATC altitude clearance after beig initially assigned to descend via the KRANN 2 arrival.