Citation Excel (C560XL)
Flight Crew Air Transport Pilot (ATP)
Training / Qualification; Human-Machine Interface
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Human Factors
We departed SNA on the MUSEL 7 departure. We were initially cleared to 3000'.  The MUSEL 7 states that; upon reaching 1.0 DME from ISNA to turn left to 177 degrees for vectors to MUSEL.   Before 1.0 DME I armed the 'nav' mode to follow the flight director which was following FMS instructions.  Both pilots had checked the FMS prior to flight and confirmed correct data for the departure and flight.  At approximately 2000' I armed the autopilot and ATC instructed us to climb to 5000'.  At 1.0 DME; the fligt director commanded a left turn and stopped on 177 degrees for a few seconds; as it was supposed to.  The flight director then initiated a turn toward MUSEL.  The autopilot remained on.  At approximately 4000' ATC inquired if we were on the MUSEL 7 departure. We said 'Yes.'  They instructed that we were supposed to remain on 177 degrees and wait for them to vector us.  ATC gave us a new heading; and we complied.    While the FMS initially displayed the correct departure procedure. the flight director initiated  a left turn to MUSEL prior to the point desired by ATC. The SID chart should say 'EXPECT' vectors; like it does in the enroute portion of SIDs; to draw attention to the fact that this heading needs to be maintained until instructed to do otherwise.  Also; I believe Honeywell should check the autopilot/FMS performance for this approach [departure].
Having briefed and understood the departure we departed climbed to 3000 on 196 hdg then the 177 hdg.  Upon reaching MUSEL we turned towards TEYKI on the TRM transition.
C560XL crew experience a track deviation while departing SNA on the MUSEL7 departure which is detected by SCT. The reportes believe the FMC malfunctioned taking the aircraft direct to MUSEL instead of maintaining a 177 degree heading for vectors.