Citation X (C750)
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Human-Machine Interface; Distraction; Confusion; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Aircraft; Human Factors
Flying into SLC on the DELTA THREE RNAV arrival (DELTA.DELTA3). Somewhere prior to MLF; we were told to descend via the arrival and delete speed restrictions. We already were descending in VNAV to JAMMN at 17;000 FT so we selected 11;000 FT (lowest crossing altitude). We had thoroughly briefed the descent/arrival and approach prior to top of descent. We were monitoring the descent at each point and the aircraft was doing a crossing JAMMN at 17;000 FT; DRAPR at 4;000 FT; SPIEK at 13;000 FT; next was HEIRY at 12;000 FT and the aircraft was set up perfectly; after HEIRY I realized we were not going to make PITTT at 11;000 FT. I immediately initiated a non-VNAV descent and missed the altitude by a few hundred feet. 11;000 FT was set in the FMS at PITTT and also at MAGNE; 11;000 FT was set in the preselect and VNAV was armed the whole time with the VGP centered. This event really bothered me and I spent the next few hours thinking about it. I was involved in a similar situation before and caught it at about the same time. I also know there have been multiple instances of this type in recent months and I think I know why this may be happening as both events I have now been involved with share ONE very similar characteristic. On this occurrence PITTT was supposed to be crossed at 11;000 FT. 'AT 11;000' the next waypoint 7.1 miles following PITTT was MAGNE and also had a hard altitude 'AT 11;000'. The FMS tried to cross MAGNE at 11;000 FT and ignored the crossing restriction of 11;000 at PITTT. The other situation I was in was on the JAIKE THREE RNAV ARRIVAL (JAIKE.JAIKE3) into TEB. I crossed JAIKE Intersection high (supposed to be 13;000) while descending in VNAV per ATC instructions and the arrival (VNAV engaged bottom altitude of 7;000 set and all altitudes verified in the FMS). I realized the aircraft was descending to cross the following fix; ILENE at 13;000 FT and ignored JAIKE at 13;000. The commonality between both of the arrivals is that there were two consecutive FIXES with common crossing Altitudes. I truly believe there is a problem with the FMS on arrivals like this and VNAV can not be trusted or possibly the second restricting altitude need be deleted to capture the first restriction. By no means is this an excuse; I; in both cases; should have caught these earlier. In the future; until I am completely confident that I know what I did wrong or the FMS did wrong I will plan on descending on a conservative path in VS to assure these restrictions are met.
The Reporter stated that his aircraft is equipped with a Honeywell 5000 (Primus 2000) FMS which is standard equipment on the Citation 10. This is the not first time this type anomaly has been seen and because other pilots are also discussing the issue; his Company has published guidelines stating that the automation should be used with caution. He was not certain if the manufacturer is involved in the investigation of this type altitude deviation. While the altitude constraint was only missed by about 200 FT the Reporter thought it was important to get the word out that because this may be a larger issue than just the two events he has witnessed.
A CE750 Captain noted that his aircraft's FMS was high crossing the first in a series of RNAV waypoints which had the same altitude constraint; but correctly crossed the second waypoint. This behavior had been seen previously on other RNAV arrivals.