B737NG pilot reported the aircraft navigated off course on its own.

Attributes
ACN	1429464
Time
Date	201703
Local Time Of Day	1801-2400
Place
Locale Reference	ZLA.ARTCC
State Reference	CA
Environment
Light	Night
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Climb
Route In Use	SID BOACH7
Flight Plan	IFR
Person 1
Function	Pilot Not Flying First Officer
Experience	Flight Crew Last 90 Days 204
Person 2
Function	Pilot Flying Captain
Experience	Flight Crew Last 90 Days 255
Events
Anomaly	Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types

Narrative:

After taking off runway 25R; the aircraft was tracking LNAV on course. The aircraft turned to the south on course and ATC assigned us a climb unrestricted to 19000 feet. Aircraft went into heading mode unnoticed. ATC asked us shortly after if we turned early to go direct to boach. We realized the aircraft was in heading mode. ATC said we were the fourth aircraft that night that did the same thing.

Original NASA ASRS Text

Title: B737NG Pilot reported the aircraft navigated off course on its own.

Narrative: After taking off Runway 25R; the aircraft was tracking LNAV on course. The aircraft turned to the south on course and ATC assigned us a climb unrestricted to 19000 feet. Aircraft went into HDG mode unnoticed. ATC asked us shortly after if we turned early to go direct to BOACH. We realized the aircraft was in HDG mode. ATC said we were the fourth aircraft that night that did the same thing.

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.