B737-800
Flight Crew Air Transport Pilot (ATP)
Workload; Time Pressure; Confusion
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance
Procedure
We were switched from the OLM Seven to an RNAV arrival right at top of descent; off of a RADAR vector for spacing. We were able to program the last minute change and brief the approach; but time and workload were at a premium at that point; and getting the aircraft back into path was a struggle; we were high and fast. This put us into a full speed brake situation with speed intervention in order to meet the next speed restriction. Next; ATC issued a slow down during this maneuver (250 KTS) which boxed us in even more. Around 10;000; ATC issued a runway change from 34L to 34C. The Captain re-programmed the approach and set me up for 34C; but during this; the FMC caused a reversion to CWS and CWP and I lost any kind of LNAV/VNAV info for a brief period. Automation was soon restored and we continued uneventfully; probably because ATC reverted us to a vector clearance. This practice of issuing speed restrictions and not giving us lower soon enough really messed up our automation and caused too much distraction in my opinion. This could have easily led to a deviation. If we are going to fly RNAV arrivals; we need to be able to fly them as published when they are built to such close tolerance as these new SEA arrivals. We completely negated any kind of fuel savings with all of the speed and altitude changes (lack there of) during the procedure. I think declining these arrivals is the best procedure until everyone is on the same page.
Air Carrier inbound to SEA voiced concern regarding the issuance of speed restrictions on RNAV arrival procedures when ATC fails to issue lower altitudes compatible with FMS capabilities.