B737-300
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 210; Flight Crew Type 12000
Other / Unknown
Aircraft Equipment Problem Less Severe
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Procedure; Aircraft; Human Factors
This is the third time in several months I have flown a -300 late at night to STL; following the KAYLA RNAV Arrival.  Each time; the aircraft was correctly following the VNAV PATH and then abruptly disconnected and reverted to VNAV SPD.  I think this is due to a faulty design of the arrival.  Here's why:  The arrival has KAYLA point at 11;000 feet MSL; followed 5.0 miles later by GIBEE at 280/11;000 feet-15;000 feet MSL; followed 12.6 miles later by OZZEE at 11;000 feet-10;000 feet MSL; followed 9.2 miles later by SNYDER at 9;000 feet-8000 feet MSL. As near as I can reconstruct; we passed KAYLA at about 17;000 feet MSL; GIBEE at about 15;000 feet MSL or slightly lower; at which point VNAV PATH reverted to VNAV SPD and showed us several thousand feet high on path.  Since I had experienced this before; I had alerted the other pilot to watch for this to happen; so as soon as it did; we reverted to a lower level of automation and reset the altitude window to 10;000 feet; pulled out the speedbrake; and used Vertical Speed to begin to correct the path to make the crossing altitude for the next point OZZEE.  We barely made the crossing restrictions for the next three points; using everything we had available to increase descent rates and try to keep airspeeds at those specified for the arrival.  If I remember correctly; on at least two of the three arrivals where this happened; there was a thirty-plus knot tailwind from the west.  Even with the winds programmed on the Descent page; the VNAV system could not maintain the correct PATH.  My recommendation is simple:  Make KAYLA a hard altitude of either 11;000 MSL or 12;000 MSL; to force the VNAV system to bring the aircraft lower before passing GIBEE and disconnecting.  GIBEE should also be a hard altitude of 10;000 MSL or 11;000 MSL to ensure the next mandatory altitude window of 8000 MSL at OZZEE is attainable.
B737-300 Captain reports difficulties flying the KAYLA1 RNAV to STL on several occasions. On each occasion with 30 knot tailwinds; the FMC reverts to VNAV speed crossing GIBEE and requires speed brakes to make the next three restrictions.