This bulletin provides information advising flight crews to avoid engaging an autopilot after capturing the localizer B/CRS mode provided recommendations in the event the autopilot were inadvertently engaged after B/CRS capture.
The -105 Flight Control Computer (FCC) has an anomaly when flying a backcourse approach using the flight director and subsequently engaging an autopilot. If an autopilot is engaged after flight director localizer B/CRS capture, B/CRS may disengage and, depending upon course error, one of the following would occur: for course errors less than 60 degrees, the FCCs revert to HDG HOLD and LOC mode arms; for course errors 60 degrees or greater, the FCCs revert to LOC mode and command a 30 degree bank turn to capture the localizer front course resulting in turning away from the backcourse localizer centerline.
The -106 FCC installed by Boeing Service Bulletin 767-22-0026 or production equivalent configuration (PRR B11723) corrects this anomaly.
If the autopilot is to be used for a localizer backcourse, engage the autopilot prior to localizer B/CRS capture. In the event the autopilot is not engaged prior to B/CRS capture, the autopilot and both Flight Directors must be switched off. The autopilot may then be re-engaged if desired, prior to reselecting B/CRS. Operation of the flight director for backcourse localizer is not affected if the autopilot is not engaged.
This Operations Manual Bulletin will be canceled after Boeing is notified that all affected airplanes in the operators fleet have been modified by Boeing Service Bulletin 767-22-0026..