After a B737 landing gear was selected down both green and red indicator lights were on and when too...

Narrative:

While on final to runway xxl and descending toward 1;500 [feet] I called 'gear down; flaps 15; landing checklist.' both my first officer and I heard a momentary gear warning horn. Looking at the gear lights we noticed three red gear lights along with the normal three green lights. Looking at the overhead paned we saw three green lights. We both commented that the gear was down and safe. We continued the approach considering that maybe the lights may go out with further configuration changes. The lights remained on and at 500 feet AGL we got a 'too low gear' audio warning. I called for a missed approach. The red lights went out with the gear retraction. We ran the 'gear disagree' checklist. Since the lights were out at that time I elected to leave the GPWS circuit breaker; the final item on the checklist; in. We planned that during the next approach we would extend the gear early and if the same lights illuminated we would be able to finish the final item; if necessary; for a safe landing. We returned for another approach; the red lights never came on and the approach and landing were normal and eventful.

Original NASA ASRS Text

Title: After a B737 landing gear was selected down both GREEN and RED indicator lights were ON and when TOO LOW GEAR warning sounded at 500 feet a go-around was executed. Upon returning for a second approach all indications were normal.

Narrative: While on final to Runway XXL and descending toward 1;500 [feet] I called 'gear down; flaps 15; landing checklist.' Both my First Officer and I heard a momentary gear warning horn. Looking at the gear lights we noticed three red gear lights along with the normal three green lights. Looking at the overhead paned we saw three green lights. We both commented that the gear was down and safe. We continued the approach considering that maybe the lights may go out with further configuration changes. The lights remained on and at 500 feet AGL we got a 'too low gear' audio warning. I called for a missed approach. The red lights went out with the gear retraction. We ran the 'Gear Disagree' checklist. Since the lights were out at that time I elected to leave the GPWS circuit breaker; the final item on the checklist; in. We planned that during the next approach we would extend the gear early and if the same lights illuminated we would be able to finish the final item; if necessary; for a safe landing. We returned for another approach; the red lights never came on and the approach and landing were normal and eventful.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1088765
Time
Date	201305
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Plan	IFR
Component
Aircraft Component	Landing Gear Indicating System
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 14000
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

After a B737 landing gear was selected down both green and red indicator lights were on and when too low gear warning sounded at 500 feet a go-around was executed. Upon returning for a second approach all indications were normal.