As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT NOT GROUNDED: PILOT REPORTS IN ROUTE VNAV DEFAULTED TO ALT HOLD AND SPEED MODE AND WOULD NOT RE-ENGAGE. IN ENGAGING VNAV, AIRPLANE WOULD PITCH DOWN. CONTINUED FLT IN ALT HOLD AND SPEED MODES. VNAV CRUISE AND ECON VNAV DECENT PAGES NORMAL. MAINTENANCE REMOVED AND REPLACED THE AUTOFLIGHT MODE CONTROL PANEL IAW AMM 22-11-02 PERFORMED ALL REQUIRED TEST.