A320
Confusion; Human-Machine Interface; Situational Awareness; Workload
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew FLC Overrode Automation
Aircraft; Human Factors; Procedure; Chart Or Publication
This report is submitted to document the gross errors of the automated FMS in the managed descent mode of the KOHOE ONE RNAV STAR into Denver. All altitude/speed constraints were verified to be correct in the FMS prior to the Descend Via clearance; and all constraints were met by the PF using selected modes because we noticed ahead of time that the FMS was in error. We were at FL360 (ALT CRZ) and were given Descend Via the KOHOE ONE. The pilot flying put 9;000 FT in the Altitude Selector. We also increased the Cost Index to 35 to make sure the descent speed was at least 280 KTS. At this time; the FMS showed a proper Top of Descent (TOD) to meet HMRHD at FL340 and the FMS indicated this. However; the FMS also showed HERNG with a planned altitude of FL340 (with an orange asterisk). KOHOE; SAYGE; and MOKME all also had incorrect high planned altitudes with orange asterisks.We began a managed descent (DES) at the TOD and it went into ALT CST mode at HMRHD at FL340. When this happened; a new TOD appeared but it was past HERNG (which was supposed to be at or below FL320). At this point the PF selected V/S [Vertical Speed mode] to meet the restriction at HERNG. When we crossed HERNG at FL320; the PROG page showed us 2;000 FT below the managed/planned glide path. Throughout the arrival we continued to meet the constraints in V/S mode even though the managed/planned glide path and altitudes still indicated high (with orange asterisks). We remained in managed speed at 280 KTS; until approximately 2 NM prior to KOHOE when the FMS speed changed to 250 KTS; so the pilot flying went into selected speed at 280 KTS (per the arrival). Nearly every constraint on this arrival was calculated incorrectly in Managed Descent mode; except the 'hard' constraint at DOGGG. Inbound from SAYGE it looked like managed DES (with selected speed) would work; so the PF managed DES. However; the FMS still planned FL173 at MOKME (even after we pushed the correct altimeter setting). The pilot flying selected V/S again to meet the restriction yet when we crossed MOKME at exactly 17;000 the PROG page showed that we were 350 FT below the managed/planned glide path. Lastly; several miles prior to DOGGG when the FMS should have reduced managed speed to 210 KTS (per the arrival); it actually went into Approach mode and reduced to green dot. This arrival would have caused violations of altitude and/or speed at almost every waypoint had we not been closely watching its every move.The FMS needs to be tested and corrected on this (and all) of the arrivals to ensure it is working properly. I have had the same problems (to a lesser extent) on the EAGUL FIVE RNAV ARRIVAL (landing east) into PHX; where the FMS will do an ALT CST at TINIZ (at FL330 even though the restriction is 'At or below FL330'); and then begin a descent too late to meet the restriction at PAYSO. Also; on the JAGGR arrival (DEN); the FMS 'dives' to FL270 at LYNKN even though this constraint is 'At or above FL270'; then shallows into a very shallow descent to CLPTN. This is not needed and not efficient. When the constraint at LYNKN is deleted it calculates a much better crossing altitude of FL302 with a THR IDLE descent all the way down. The FMS seems to work correctly when there is a hard altitude/speed constraint. But something is not working properly in the FMS when it calculates these descent profiles when there is an 'At or above/below' or a 'Between' constraint.
A-320 fails to comply with the complex altitude and airspeed restrictions on the KOHOE RNAV STAR to DEN. The reporter believes the problems to be systemic to the A-320 autoflight systems and backs that opinion up by citing previous similar problems when attempting to comply with similar RNAV STAR arrivals at PHX and DEN.