Date: 201403
Local time of day: 0601-1200
Location: S56.TRACON, UT
Flight conditions: VMC
Weather elements / visibility: 50
Light: Daylight
Aircraft: IAI1125 (Astra)
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Descent
Airspace: Class B SLC
ATC / advisory: TRACON S56
Reporter organization: Corporate
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Human-Machine Interface; Confusion
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Aircraft Automation Overrode Flight Crew; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors
Primary problem: Ambiguous

Narrative: On descent into SLC we were told to cross JAMMN at 17;000 FT MSL. I initiated the VNAV to descend 17;000 FT MSL and the VNAV captured JAMMN at 17;000 FT MSL. We were then given the DELTA 3 arrival and to cross DRAPR at 14;000 FT MSL then descend via the DELTA 3. The arrival was programmed into the FMS and the VNAV was activated. The descent was started. The procedure on the FMS VNAV is to set the Altitude Alert [and] capture at the lowest arrival altitude on the arrival and the VNAV will capture each altitude and descend automatically. The co-pilot set the altitude to 11;000 FT MSL as required and we confirmed that all altitudes were entered correctly. We were descending to cross DRAPR at 14;000 FT MSL and upon reaching 14;000 FT MSL at DRAPR the VNAV captured and the plane leveled out at 14;000 FT MSL. At this time for some unknown reason the VNAV did not continue to descend to the next fix SPIEK at 13;000 FT MSL. I noticed that it was not responding as expected so I questioned my co-pilot [and] asked for him to check on it. We both noticed that in the window of the FMS where the [vertical speed] required to [make the next restriction] is shown; that the [vertical speed] required to descent correctly was 500 FPM and that it started to increase rapidly up to 1;000 FT MSL then to 2;000 FT up to as high as 3;000 FT per minute. The co-pilot was trying to put in a descent altitude and I would hit the VNAV capture each time but the [vertical speed] showing what was needed to descend was increasing faster than he could put it in. I decided to manually control the VNAV and selected 500 FT per min descent and started to descend. We both were focused on trying to get the VNAV to work but continuing to program altitudes and then selecting the VNAV button to try to get it to work. During one of the times I was pushing the VNAV button; the VNAV captured and started a rapid descent at 2;500 FT per minute. I didn't realize that it had captured at first and by the time I did; we had descended through the SPIEK crossing altitude of 13;000 FT MSL. It had captured the restriction at DRAPR of 14;000 FT MSL because we had pre selected 14;000 FT MSL in the preselect altitude window. It did not capture the VNAV altitude at 13;000 FT MSL at SPIEK for unknown reasons but it would have stopped at 11;000 FT MSL because that is what we had selected in the preselect altitude window. We had descended down through 12;000 FT MSL when I noticed the error and just about the same time as the Controller also noticed. He gave us an altitude alert and instructions to climb back to 13;000 FT MSL. I turned off the autopilot and I immediately started a climb back to 13;000 FT MSL and leveled out. The conditions at the time were VFR and weather was very clear. My attention was both inside and outside of the cockpit and I knew where we were. At no time did we get a TCAS alert; Terrain alert; or Radar Altitude alert. There was no evasive action needed either; however I did initiate an immediate climb to 13;000 FT MSL. After leveling at 13;000 FT MSL I assume during multiple attempts to push and arm the VNAV that I inadvertently selected HDG mode during one of those many attempts. I thought that I had activated the autopilot but must have inadvertently pushed the heading button instead of NAV. Hitting the heading button instead of NAV caused me to drift off course a little [and] I was asked by the Controller to fly a heading [and] intercept the arrival. I intercepted the arrival [and] continued on the approach and landed without further problems. We have flown this arrival many times and have never had any problem with VNAV not capturing the profile.Other factors I feel I need to comment on are that we had just completed a major inspection at our maintenance facility and this was our first flight after this major maintenance inspection. One of the squawks for Maintenance was that we were having problems with our GPS approaches where when crossing the initial approach fix all of our waypoints would disappear. During one of the FMS test [and] diagnostic sessions I was able to sit in the cockpit with the Avionics Technician to duplicate the problem. We were able to duplicate the problem but not able to determine what the problem was. The Avionics Technician was reprogramming and configuring the FMS and the vertical navigation VNAV system trying to see if the system was set up correctly. Being that he was in the configuration part of the FMS; VNAV part; I don't know if something was accidentally changed or that he forgot to change it back out of some configure mode he had input. That being said he was not sure what was causing the problem. He has contacted the Avionics Rep Technician to help fix the problem. They have told him the FMS [and] VNAV are capable of doing the GPS approaches coupled with VNAV without dropping the waypoints. Both our Avionics Technician [and] Avionics Rep Technician are continuing to troubleshoot the problem and fix it. I will say that the waypoints will not drop off if I program in each waypoint individually.Because of this event we have changed company policy to set each altitude on the approach to the waypoints individually instead of setting it to the lowest step down altitude. This will give us more control over capturing the altitude. We will further monitor the VNAV on all upcoming flights to determine if this is a problem with the VNAV; configuration of the FMS/VNAV. I have always taken command of the aircraft when there is an issue like this in the cockpit and flown the aircraft first as the main priority and have always given my co-pilot the job of figuring out the problem. For some reason; perhaps because it was such a clear beautiful day and we were repositioning the airplane without any passengers I let myself become involved trying to fix the problem. I will also keep myself focused on flying the airplane and not try [and] troubleshoot a problem at the same time. My co-pilot is very capable of evaluating [and] fixing the problem and I should have not tried to help visually just verbally. In my 42 years of flying I have never deviated an altitude. I take my job flying very seriously and I read and study these NASA reports and other articles to try and make my flying the safest as I can possibly do; still I see more ways in which I can improve.


Second narrative: ATC cleared us via the DELTA Three arrival to SLC. As the pilot not flying/SIC I confirmed that all fixes and step down altitude requirements of the RNAV arrival were programmed into the #1 FMS and cross filled into the #2 FMS. We were cleared direct to JAMMN intersection on the DELTA Three and told to cross JAMMN at 17;000 FT. I set the Altitude Alert to 17;000 FT and programmed the vertical Nav (VNAV) to a 2;500 FPM descent and armed it for crossing JAMMN at 17;000 FT. I felt the VNAV take over as I was running a Descent Checklist and contacting the FBO on the #2 radio. The aircraft was being flown on the autopilot and descended to 17;000 FT as commanded by the PIC. ATC then cleared us to descend via the DELTA 3 arrival into SLC. The company procedure is to set the lowest altitude on the arrival into the altitude alert window. This was 11;000 FT which was a required altitude to cross both PITTT and MAGNE. To perform this maneuver properly the aircraft MUST capture the vertical Nav through the FMS while on the autopilot or an altitude deviation could occur. The PIC armed the vertical Nav to capture the flight director. It commanded about a 500 FPM descent rate to cross the next fix DRAPR at 14;000 FT. The aircraft started to descend though I can't confirm I saw that the autopilot captured the VNAV on his Primary Flight Display (I'm not saying it wasn't; I'm saying I didn't confirm it and I should have). The next thing that occurred was that the PIC indicated he was having a hard time capturing the VNAV. I noticed as he did that the rate of descent required to cross the next fix was increasing on the #1 FMS telling both of us that the aircraft was not going down fast enough to meet the crossing requirements. The way to correct this irregularity is to increase the FPM descent number in the FMS just above the required rate to meet the requirements of the next fix and rearm the VNAV for the flight director to command the autopilot. The PIC made several attempts and then I took over increasing the FPM number to get the autopilot to capture the proper mode. The number I was programming in his FMS was beyond 2;000 FPM after 2-4 attempts. The altitude deviation occurred somewhere in a 45 second to 90 second window. It is noted that I was only focused on the FMS and not comparing where we were on the arrival on the center PFD display vs. the altitude requirement during that segment. This has worked ok for many flights in SLC as long as the VNAV capture was achieved. So ATC notified us that we needed to check our altitude. We were at 11;400 FT and the PIC initiated a climb back up to 13;000 FT immediately and this occurred by SPIEK intersection. Obviously my feeling was that a serious event had occurred and worry overtook me though the aircraft was in VMC and never in any danger. Also noted was that ATC gave us a heading that was left about 10 degrees and asked if we were on the arrival still. I checked and saw that the #1 flight director was in heading mode and that button is just below the VNAV mode. I assume in the multiple attempts to push and arm the VNAV that the PIC inadvertently selected HDG mode during one of those many attempts. This still does not explain why the #1 FMS was commanding such a high rate of descent to cross SPIEK at 13;000 FT when it was only a 1;000 FT difference from the altitude we were at prior. Frankly after discussing this on 3 different occasions in the last 24 hours; we are unclear why the FMS was commanding a steeper rate of descent during the step down. I question which fix the FMS was taking its information from to give us such a high rate of descent. We know that with 11;000 FT in the altitude alert window that the aircraft is going to go to that altitude if not coupled to the flight director and VNAV to stop at the programmed step downs. It happened very fast. I will strongly confirm again that the FMS box was properly loaded as it is a pet peeve of mine that pilots will load the FMS and not confirm all the waypoints. I believe it should be noted that this flight was the first flight requiring VNAV after a major aircraft inspection. The FMS and VNAV were being tested; checked; and configured at Maintenance Center during this inspection last week for a separate waypoint/VNAV issue. The PIC sat in on that test and configuration due to an aircraft specific problem that the Avionics Technician could confirm. As we sit discussing this issue we know we will need to monitor the FMS for several more flights to determine if the FMS is acting properly. As I understand it; and this gets complicated. It was determined by the technician that our aircraft is hardwired for coupled VNAV GPS approaches but that the autopilot; the flight director; or the EFIS is NOT allowing the aircraft to capture VNAV in the GPS NAV approach mode. This is believed to be causing all the fixes to disappear when nearing a segment on the final approach fix on all types of approaches. It is a separate issue but this is suspect because the technician was entering/configuring the FMS approach and VNAV modes to fix that separate issue. He went and looked at another Astra SP aircraft on the field and that experienced pilot told him he was having the same issue in losing fixes. I would assume he made some type of report about that. In summation I believe this occurred because of a combination of pilot responses and FMS computer programming and the lack of backing up the computer with situation awareness. We will know more as we monitor the displays for several flights. Regardless of that; this issue can and will be avoided again. Corrective Action: The new company procedure is going to be to set the altitude alert to each step down fix altitude going forward. It will eliminate any further low altitude occurrences. It should be noted that I am 56 years old; have been flying IFR for 30 years and have never had an altitude deviation. I and the PIC/Chief Pilot take our jobs very seriously and approach aviation in a cautious manner. Our communication inside and out of the aircraft is good. Still we see ways in which we can improve on that.


Synopsis: IAI1125 flight crew experiences an altitude and track deviation while attempting to comply with the DELTA 3 RNAV arrival to SLC. Software issues and pilot error may have been factors in the deviations.