B737-300
Flight Crew Last 90 Days 227
Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Procedure; Human Factors
On the KEPEC 3 into LAS cruising at FL250.  LA Center issued PD descent to FL240 and then issued next frequency.  Next Controller stated; 'After MISEN; cross CLARR at 250 knots and one three thousand feet.'  At no time were we given a crossing clearance for MISEN.  The chart shows to expext MISEN at FL240.  Captain and I discussed the clearance and agreed we could disregard the MISEN expect crossing and I set 13;000 in the alt preselector.  We descended below FL240 prior to MISEN.  ATC asked us what we were doing and told us to maintain FL210.  PM and ATC attempted to clarify issue.  ATC seemed to be under the assumption that we were in violation of the MISEN FL240 crossing.  Proceeded normally from this point on. ATC sould have issued the MISEN crossing.  We should have clarified clearance with ATC.
B737-300 First Officer reports descending below FL240 at MISEN on the KEPEC 3 arrival to LAS due to lack of a specific instruction from ATC to comply with the RNAV procedure. Only the speed and altitude at CLARR is issued.