B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Diverted; General Maintenance Action; General Declared Emergency
Aircraft
On approach; flaps indicator showed flaps 2 with flaps extended to a greater flap setting.  Unable to land due to a flaps 2 indication [runway length]. Declared an emergency; contacted Dispatch via ACARS that we were an emergency aircraft and were diverting.  Ran the QRH procedure and landed with flaps 15 using alternate flap extensions. Landed without incident.
On approach flaps would not indicate past 2 degrees. Go around executed. Emergency declared. Divert to ZZZ. I ran the QRH procedure and alternately extended flaps until indicator showed 15 degrees. Contacted company via ACARS. Captain had normal landing in ZZZ. Was told Maintenance found indicator box not working properly.
B737-800 flight crew experiences a flap disagreement between the selected setting and the indicated setting during approach and goes around. Crew elects to divert to a longer runway and lands with flaps indicating 15 using the alternate extension system.