Gulfstream V / G500 / G550
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 120; Flight Crew Total 7500; Flight Crew Type 1800
Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Aircraft; Human Factors
Fort Worth Center gave clearance for us to cross CQY vortac at or below 10;000 and to cross ORVLL intersection at 9;000. Both crew members set up proper guidance via VPath to meet these restraints and noticed two minutes out from CQY Vortac that the FMS calculations were wrong and we were going to be non-compliant at the altitude restriction at CQY VOR. Multiple attempts were made to contact Fort Worth Center to let them know we were unable to meet the altitude restriction with no reply. Fort Worth Center contacted us asking our altitude after passing CQY Vortac and we reported our actual altitude of passing 9;400 MSL to maintain 9;000 MSL for our altitude for ORVLL. I believe the cause of the problem is a bug in the Honeywell 6.0 software for the Gulfstream V aircraft which continually causes the Vpath to recalculate its vertical guidance deviating from what was set. As this is just an intermittent problem with the 6.0 software; I am going to discontinue use of VNAV function the Gulfstream aircraft until 6.1 software is installed on the aircraft.
No additional information.
G-V flight crew reports missing a crossing restriction during descent due to what they believe is a flaw in the FMS software.