B737-700
Flight Crew Last 90 Days 171
Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Human Factors
While being vectored to join ILS 27R; the aircraft/crew failed to capture/join the LOC. We then turned back toward the LOC and realized the #2 NAV had the LOC frequency in STBY. The crew opted to break off approach. Crew completed Descent Checklist; re-briefed approach; and flew the ILS 27R. During the next flight; the crew noticed that the #2 NAV would switch from STBY to ACTIVE without depressing the TFR switch. A logbook entry was made noting the discrepancy and a Mechanic was briefed. I am certain we properly briefed the approach prior to flying the procedure. What is not known is if the #2 NAV switched to the STBY frequency or if the crew made a verification error. In the future; I will try to crosscheck the frequency selected while on the base vector.
It is unknown if the localizer frequency was originally selected or remained in STBY the whole time. Double check the frequency. All operations were normal up to that point. There were no extra distractions.
B737-700 flight crew overshoots the LOC course during approach and discovers the #2 NAV has the ILS frequency in the STBY position. A go around is initiated and the second attempt is successful. On a subsequent flight leg it is discovered that the #2 NAV radio could switch from ACTIVE to STBY without depressing the TFR switch.