Flight Crew Air Transport Pilot (ATP)
Training / Qualification; Situational Awareness; Human-Machine Interface
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types
Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Aircraft
En route MIA approximately 40 SM south of DFW at FL370 experienced 25 degree roll to right. Aircraft was engaged in LNAV and was observed switching to APP mode without pilot input (FMC changed lateral modes on its own). Both Captain and First Officer VHF radios tuned to 111.75 departing. DFW ILS 17L/35R has same frequency of 111.75. Minimal heading deviation occurred before corrective action taken.
A B737-NG overflying DFW 40 SM south at FL370 had 111.75 selected on the VHF radio heads and the APP MODE engaged causing a twenty five degree roll right. DFW ILS 17L/35R frequency is 111.75.