Narrative:

The problem arose upon taxiing from the FBO to the active runway for departure.we were cleared to taxi and hold short of runway 25L; then cleared to cross runway 25L and line up and wait on runway 25R. We had previously briefed the departure takeoff speeds and verified the fixes and restrictions for the karvr 4 departure mzb transition. While taxiing to runway 25R I noticed that the FMS had deselected the takeoff speeds on my pfd. I prompted the first officer (I was flying the airplane) to reinstall the speeds; which in this case; needed to be done by reinserting the runway for departure. This all happened whilst we received a clearance for takeoff from runway 25R and were advised that there was traffic on short final.I performed the takeoff as per standard SOP but the auto throttle system failed to engage while on the takeoff run; I continued the takeoff and flew the initial 251 heading and climb towards our top altitude of 5000 on an LNAV and flch mode. When we switched to socal departure at approximately 2000 MSL; the controller instructed us to turn immediately 190 heading and climb to and maintain 13000. They later informed us of a possible pilot deviation and gave us number to call.upon calling said number; I was informed that the radar showed us on a right turn on initial climb out; so we were directed to turn to the south to avoid conflict.contributive factors were fatigue; high workload (auto throttle fail on takeoff roll) and high traffic environment on an unfamiliar procedure at night.probable cause of the deviation was either an unconfirmed FMS reprogramming and/or a heading miscompare event.

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Original NASA ASRS Text

Title: EMB550 Captain reported FMC anomalies during takeoff that disabled autothrust or LNAV; resulting in a track deviation.

Narrative: The problem arose upon taxiing from the FBO to the active runway for departure.We were cleared to taxi and hold short of runway 25L; then cleared to cross runway 25L and line up and wait on RWY 25R. We had previously briefed the departure takeoff speeds and verified the fixes and restrictions for the KARVR 4 departure MZB transition. While taxiing to runway 25R I noticed that the FMS had deselected the takeoff speeds on my PFD. I prompted the First Officer (I was flying the airplane) to reinstall the speeds; which in this case; needed to be done by reinserting the RWY for departure. This all happened whilst we received a clearance for takeoff from RWY 25R and were advised that there was traffic on short final.I performed the takeoff as per standard SOP but the auto throttle system failed to engage while on the takeoff run; I continued the takeoff and flew the initial 251 heading and climb towards our top altitude of 5000 on an LNAV and FLCH mode. When we switched to Socal departure at approximately 2000 MSL; the controller instructed us to turn immediately 190 heading and climb to and maintain 13000. They later informed us of a possible pilot deviation and gave us number to call.Upon calling said number; I was informed that the radar showed us on a right turn on initial climb out; so we were directed to turn to the south to avoid conflict.Contributive factors were fatigue; high workload (auto throttle fail on takeoff roll) and high traffic environment on an unfamiliar procedure at night.Probable cause of the deviation was either an unconfirmed FMS reprogramming and/or a heading miscompare event.

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.