Widebody; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 8177
Distraction; Human-Machine Interface; Workload
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Clearance
Procedure
Crew planned for DOOBI2 arrival into IAH expecting runway 26L.  On descent prior to approach ATC changed arrival to ZEEKK1 with runway 26R transition.  Next; while inside AEX on the arrival approach ATC changed transition to runway 27.  Each change required changes in the FMC which caused the FMC to become confused creating a serious distraction to both crew members.  This required switching to heading select while making sure the crew had the correct flight path and fixes.  By the time the FMC figured out the descent path the aircraft was well above the path necessitating speed brakes to get back on path.  Meanwhile; a check of the FMAs revealed that the aircraft was still in HDG mode which was quickly changed back to LNAV.  Lastly; each runway transition on the ZEEKK1 arrival into IAH has a different bottom altitude and ATC changes induce the opportunity to forget to set the proper altitude once ATC has changed the transition.  Altogether; this unnecessary chain of events created by ATC must be immediately rectified by terminating the descend via clearance until the FMC has been properly programmed and the crew is relieved of having to comply with step down fix restrictions that cannot be verified while the FMC is confused.  ATC needs to know about these frustrating and potentially dangerous complications that occur when changes are made after a descent has begun on a descend via clearance.
Air carrier Captain reported multiple changes to the IAH arrival clearance drastically increased the workload and vulnerability to error.