ATC reported that air carrier crews on the RDU RASKL 1 RNAV were descending to 4;000 FT after NEDIE when the depicted clearance is NEDIE at or about 6;000 FT with no required descent until cleared by ATC after NEDIE. The RDU 5R ILS depicts PECIT at 4;000 FT but it is not mandatory.

Narrative

We were flying the RASKL 1 into RDU. We had been cleared to descend via the arrival. We set 6;000 FT in the altitude selector and were descending in VNAV Path. During the descent; ATC asked us what altitude we were planning on descending to. We responded 6;000 FT as the last altitude depicted on the arrival was NEDIC 6;000 FT. He said that two Company aircraft had descended to 4;000 FT after NEDIC that day and wanted to know if we saw any reason that they might have done so. There seems to be a problem with the way crews understand this arrival. When the RASKL arrival and ILS 5R are loaded in the FMC; there is no disconnect in the route. PECIT is the last fix on the arrival and the first fix on the approach. PECIT is loaded in the FMC with a 4;000 FT crossing altitude. I don't know whether these crews thought they had been cleared for the approach or made a mistake in understanding the descend via clearance. Since PECIT is on both the arrival and the approach; crews may think they are cleared to descend to 4;000 at PECIT with the descend via clearance. I think this is a new STAR and there seems to be a problem with crews understanding the clearance limit.