Date: 201311
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: Mixed
Weather elements / visibility: 7
Light: Night
Aircraft: B737-300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Indicating and Warning - Landing Gear
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Training / Qualification; Confusion; Distraction
Second reporter function: Pilot Not Flying; Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Chart Or Publication; Aircraft; Manuals
Primary problem: Aircraft

Narrative: On visual approach; after landing gear was put down and Flaps 15 called; an intermittent warning horn sounded with only a red light for the nose gear. Gear felt and sounded like they were down. Called for go-around; told Tower; and he switched us over to Departure. Ran Gear Disagree Checklist; but it did not help our problem. Then found gear CB popped. After reset; had normal gear indications. Approach and landing normal. Conferred with Maintenance at gate who called MOC. Since this was a first time occurrence; an info writeup was put in the log.Possibly could have saved time if check the gear circuit breakers was in the checklist. I know it is in the manual to check them for problems; but a night go-around caused by an unsafe gear indication with a lot of traffic; a little reminder is appreciated.


Second narrative: During descent I noticed when the throttle was at idle; the only Gear Disagree light that was illuminated was the nose gear. The Captain and I talked about that and said; 'That is strange.' Neither of us had ever seen that before. We were on the [ILS] and told to fly 170 knots until final. At the initial approach fix I called for gear down and Flaps 15. At that time the Configuration Warning horn sounded. We initiated a go-around and I called for landing gear up and Flaps 5. The gear wouldn't come up but when we went to Flaps 5; the horn silenced. We then tried to find the correct checklist for our problem. We decided the Gear Disagree was the closet to our problem. The checklist called to manually extend the gear which we believed to already be down. At that time the Captain looked to see if there were any circuit breakers out and found a breaker tripped. He then reset the CB and we then had all three green lights illuminated. We then proceeded to an uneventful landing.


Synopsis: During descent with the thrust lever at idle only a B737-300's nose gear red disagree light illuminated; then during approach the Configuration Warning alerted with the gear extended; flaps greater than 5. The landing gear circuit breaker was discovered tripped; and the system returned to normal with its reset.