Narrative:

While descending through approximately FL310 and 15 mi south of esl we were cleared to cross 5 miles south of esl at FL250. I advised the PNF (PIC) to tell ATC unable. The controller then cleared us to cross esl at FL250. I again asked the PNF to advise ATC it would be tight due to our high groundspeed. While the PNF was communicating to ATC he was simultaneously programming the FMS with the crossing restriction. For some reason - either input error or FMS error - the FMS sequenced to the next waypoint and the aircraft began turning to the next fix. The controller inquired whether we could comply with the crossing restriction and the PNF stated that we were over the fix and unable to comply with the clearance. At this time the controller stated that we were 12 miles south of esl. While this conversation with ATC was occurring I recognized we were turning south of esl and immediately selected heading mode on the flight guidance panel. Several times in rapid succession I directed the PNF to tell ATC we were experiencing a navigational error and needed either present heading or a vector. The PNF did not call the controller but rather attempted to program the FMS. A few seconds later the controller then gave us a frequency change. The new controller assigned a new altitude without a restriction and I directed the PNF to inform the controller of our nav error. Instead the PNF asked for direct har to which the controller asked 'aren't you going to har?' ATC asked what happened and still the PNF was hesitant to ask for assistance and replied with 'we got a little messed up here.' a vector followed before being cleared direct har.I believe this incident occurred because of task saturation. We were descending at a high rate in an attempt to comply with the crossing restriction. The PNF possibly made an error in FMS programming which increased the task saturation when he directed all attention to the FMS error. As PF when I realized that the PNF was overloaded perhaps I should have assumed control of the radios and told ATC what we needed to do. However; I felt that my sa was greater than the PNF since he was convinced we passed esl. Since we were on ap I focused on descent rate and trying to determine exactly how far from esl we actually were. I feel that if we would have simply communicated our dilemma to ATC it would have relieved some pressure. While on a heading or vector we could have assessed our situation; made sure the aircraft was configured correctly; FMS programmed correctly; and that both crew members were clear on where the aircraft was heading next.

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Original NASA ASRS Text

Title: G280 First Officer described a track deviation when the Captain (pilot monitoring) attempted to program the FMC with a crossing restriction while talking to ATC. Somehow the FMC is sequenced to the next fix and the aircraft turns early. The Captain is unwilling to advise ATC of the FMC issues and request a vector.

Narrative: While descending through approximately FL310 and 15 mi South of ESL we were cleared to cross 5 miles South of ESL at FL250. I advised the PNF (PIC) to tell ATC unable. The controller then cleared us to cross ESL at FL250. I again asked the PNF to advise ATC it would be tight due to our high groundspeed. While the PNF was communicating to ATC he was simultaneously programming the FMS with the crossing restriction. For some reason - either input error or FMS error - the FMS sequenced to the next waypoint and the aircraft began turning to the next fix. The controller inquired whether we could comply with the crossing restriction and the PNF stated that we were over the fix and unable to comply with the clearance. At this time the controller stated that we were 12 miles South of ESL. While this conversation with ATC was occurring I recognized we were turning South of ESL and immediately selected HDG mode on the flight guidance panel. Several times in rapid succession I directed the PNF to tell ATC we were experiencing a navigational error and needed either present heading or a vector. The PNF did not call the controller but rather attempted to program the FMS. A few seconds later the controller then gave us a frequency change. The new controller assigned a new altitude without a restriction and I directed the PNF to inform the controller of our nav error. Instead the PNF asked for direct HAR to which the controller asked 'Aren't you going to HAR?' ATC asked what happened and still the PNF was hesitant to ask for assistance and replied with 'We got a little messed up here.' A vector followed before being cleared direct HAR.I believe this incident occurred because of task saturation. We were descending at a high rate in an attempt to comply with the crossing restriction. The PNF possibly made an error in FMS programming which increased the task saturation when he directed all attention to the FMS error. As PF when I realized that the PNF was overloaded perhaps I should have assumed control of the radios and told ATC what we needed to do. However; I felt that my SA was greater than the PNF since he was convinced we passed ESL. Since we were on AP I focused on descent rate and trying to determine exactly how far from ESL we actually were. I feel that if we would have simply communicated our dilemma to ATC it would have relieved some pressure. While on a heading or vector we could have assessed our situation; made sure the aircraft was configured correctly; FMS programmed correctly; and that both crew members were clear on where the aircraft was heading next.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.