Large Transport
Situational Awareness; Human-Machine Interface; Confusion
ATC Issue All Types; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action; Flight Crew Returned To Clearance; Flight Crew FLC Overrode Automation; Flight Crew Became Reoriented
Aircraft; Chart Or Publication; Procedure
I am submitting this report to document the SILCN 1 Arrival and the problems with the descent profile. We were prepared for the descent issue from the notice on the departure weather packet in the originating station. ATC gave us the clearance to fly the filed route which had the SILCN 1 arrival into SJC. After the initial descent; ATC gave us descend and maintain FL200. The SILCN fix has an altitude of FL200A. We closed the route on the FMC prior to our descent and were wondering what the descent profile would be if we made the altitude at SILCN a hard altitude of FL200. The descent profile went from on the flight path to over 4;000 feet high.We were NOT given a clearance to descend via on the arrival; so I elected to slow down to 250 knots at SILCN because I was concerned about being too high on profile. In retrospect; I should have asked ATC if we needed to observe that restriction.After we passed SILCN; we accelerated up to almost 320 knots to get back onto the descent profile. When checking the altitude and airspeed at the KLIDE fix; we also removed the ABOVE part of the altitude restriction which put us over 2;000 feet high again. Having flown this approach almost 100 times in my career; I know that the current altitude fix and speed (230 knots) is a comfortable descent profile. In summary; please adjust the SILCN 1 for a proper descent profile so that crews do not need to be vectored off the arrival to get onto an acceptable profile.
The reporter stated that the ILS 30 transition is at GILRO intersection; even though KLIDE is the common Waypoint for the SILCN 1 to ILS 30; so the FMS will fly back to GILRO to begin the approach. That extra leg; KLIDE; GILRO; KLIDE; adds the additional altitude to have the aircraft arrive a second time over KLIDE at 4;000 feet.
A Large Transport Aircraft was high on the SILCN 1 arrival profile because the ILS 30 transition point is GILRO which occurs after the common SILCN 1 to ILS 30 transition point KLIDE. Therefore the FMC will fly from KLIDE to GILRO to KLIDE which requires the additional altitude.