A320
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface; 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 New Clearance; Flight Crew Requested ATC Assistance / Clarification
Aircraft; Chart Or Publication; Human Factors; Procedure
We were cleared to 'descend via' Kohoe One Arrival EXCEPT to maintain 270 KTS till SLMON. Captain typed 270 KTS in PERF page (DES) of MCDU. We crossed HERNG at FL320 and 270 KTS in managed descent. The aircraft started a slow descent after HERNG and barely made KOHOE at FL280 (270 KTS). To compound the situation (and we believe this to be the determining factor to the issue); ATC slowed us to 230 KTS. The aircraft performance was unable to lose 6;000 FT between KOHOE and SAYGE (only 15 DME) with max drag (spoilers) and a change in automation to OPEN DES (because managed descent had us leveled off trying to slow to 230 KTS). We advised ATC unable to cross SAYGE below FL220; then advised unable to cross MOKME below 17;000 FT. ATC then gave clearance to maintain 250 KTS and descend to 14;000 FT.We believe trying to slow the aircraft started a chain of events that would not allow the aircraft performance to cross at or below the crossing restrictions. The Captain was using good CRM the entire time and was aware immediately that we would not be able to cross SAYGE below FL220 and MOKME below 17;000 FT. With the experience; I would notify ATC (on future flights) that we could either give them the speed or altitudes; but not both.
Three things. ATC should not expect to give additional speed constraints without possible difficulties in flying profile descents. The software on this approach needs to be re-evaluated for possible errors. Finally; ATC should acknowledge that the deviation in altitude was not a concern. ...we checked and crosschecked each point on this arrival and flew the arrival as trained. We did not change any constraints and if not for intervening and notifying ATC we would have zipped right through one of the programmed constraints built into this arrival. I suggest taking a close look at the programming of this arrival.
When cleared to 'descend via' the KOHOE RNAV STAR to DEN 'except maintain 270 KTS' the flight crew of an A320 was unable to comply with subsequent altitude crossing restrictions at SAYGE. The reporters cited the initial 270 KTS and subsequent 230 KTS ATC restrictions as primary contributing factors.