B737-700
Flight Crew Last 90 Days 189; Flight Crew Type 6400
Communication Breakdown; Human-Machine Interface; Situational Awareness
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance
Procedure; Aircraft
We were given 50 NM out from CSN at FL 270 very late and were unable to make it down. ATC agreed that they had given it to us late and said descend to FL 270 then cross CSN at FL 190. After reaching FL 270 in Level Change; I started a descent to FL 190 in VNAV PATH and confirmed that VNAV PATH was engaged. As we were descending; I was crosschecking the arrival altitudes on the chart with the altitudes in the CDU. Then we were given a frequency switch from Washington Center to Potomac that was the wrong frequency. The Captain discovered that we were high at CSN and we quickly continued our descent to FL 190. Then the Captain got the correct frequency and checked in with Potomac. Neither controller spoke to us about being high at CSN.
A B737-700 flight crew was cleared to cross 50 NM from CSN at FL270 too late to do so.  The subsequent clearance with an open descent to FL270; thence cross CSN at FL190 was programmed but the FMS failed to comply.  Attention diverted by a temporary loss of comm and; perhaps; an inappropriate VNAV mode selection resulted in a failure to comply with the CSN crossing.  ATC made no comment about the failure to comply.