Challenger 300
Flight Crew Air Transport Pilot (ATP)
Confusion; Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance; General Maintenance Action
Aircraft; Human Factors
Quick repo flight to RDU. We picked up the aircraft from Maintenance. Our departure clearance was 'radar vectors to LWOOD then as filed.' We plugged it in the FMS and verified the route. In flight; after departure; a few minutes into the flight; the controller assigns us 'direct to LWOOD'. As I am trying to hit DIRECT; the FMS doesn't pull up LWOOD anymore. We assume it dropped out so we manually plugged it back in and hit DIRECT and NAV and the aircraft turned to LWOOD. A few moments later the controller; fairly alarmed asked us where we were navigating towards and that we needed to make an immediate 180 degree turn to LWOOD. At this moment we realized our MFDs were showing a DR icon. We confirmed the spelling of LWOOD and that that's where we were navigating to; but asked him for vectors to RDU. He assigned us to intercept the 082 from [departure airport] which we did in green needles. The FMS needles were showing opposite directions and nowhere near [our location]. So we stayed in green needles until we landed in Raleigh. On the ground we called Maintenance and reset the FMS; and re initialized our position. Eventually it all went back to normal. We flew two more legs without further issues. We relied too much on the box to be correct that we didn't realize our GPS was not working correctly. Keeping situational awareness at all times will avoid situations like that. I am glad the controller noticed right at the same time we did; so we could correct that error.
We were assigned runway heading with expectation of vectors to first fix. At approximately 3;000 MSL in IMC we were given clearance direct LWOOD intersection. LWOOD seemed to have sequenced out of the box so we reentered and executed the fix. We turned to the heading indicated by the box. Almost simultaneously the FMS posted a GPS dead reckoning for more than five minutes and ATC indicated that we were not proceeding direct to LWOOD. I asked ATC for a heading and stated that our FMS did not appear to have an accurate GPS fix and that we needed a vector and or a clearance with a ground based navigation fix. On green needles we established our position and track and proceeded to RDU. The status pages indicated that we were not in dead reckoning mode but that the GPS receivers both had a good and identical fix. The FMS position did not reflect the GPS position; nor did it switch to DME/DME or VOR position sensing.Once on the ground at RDU it took a hard reboot and several tries to get the FMS position to agree with the GPS position. Following flights were uneventful.I was surprised that we did not get any flags or other indications on the ground prior to departure. Our departure procedure was a vector so I did not notice the position error on the MFD as I was not expecting to see a procedure or track displayed. The airport itself should have displayed but I did not catch this. I could or should have compared the FMS lat long to the GPS LAT LONG displayed on POS INIT page two in the FMS more carefully. It is not unusual to see small differences in those indications while sitting at the ramp with the GPS receivers settling on an accurate fix. In this case the LAT LONG numbers seemed close but were not identical. Ultimately our FMS position ended up being about 135 miles off of true in spite of having entered the GPS fix. When we landed at RDU the MFD screen showed us in the vicinity of Norfolk VA. Working with maintenance the box continued to fail to accept pos init using GPS; airport; runway end or gate updates. We rebooted the airplane and it took two or three more attempts before the box finally accepted the correct position data.I have not seen this before. My takeaway is to be certain the box accepts the GPS position exactly; including the numbers to the far right of the decimal. Further; while I did anticipate the right turn after takeoff; it should have been a 30 or 40 degree turn; not a 90 to 120 degree turn. It was humbling to experience just how much confusion on the MFD track displays affects situational and positional awareness. I was initially concerned that both track AND heading information could be suspect; but a quick check of the mag compass and a confirmation with ATC showed it was FMS position error only. Naturally this happened in the only IMC departure we have done in the last six months.
A CL300 pilot experienced a track deviation after departure when cleared direct to LWOOD. It was noticed too late that the FMS was in DR mode due to the GPS not operating correctly. ATC issued a vector and the crew navigated to RDU in Green Needles. Maintenance reset the FMS; and re-initialized the position after several attempts.