Date: 201201
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 12
Light: Daylight
Aircraft: PC-12
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Landing
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Personal
Reporter function: Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Human factors: Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Executed Go Around / Missed Approach; General Maintenance Action; General Declared Emergency
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: I; with the pilot owner of the aircraft; and 2:20 hours of fuel on board departed after receiving Maintenance. The Maintenance included a 100 Hour Inspection; Prop Overhaul; wingtip replacement and GNS 750 and GNS 650 Garmin Touch screen GPS installation. The aircraft was in maintenance for about 3 weeks. We conducted a test flight with an A&P Tech on board with no issues. We dropped the Tech off and departed VFR with no issues. After doing an extended downwind we then turned about a 5-6 mile final. The Landing Gear was selected down with all three red transit indicators illuminated but when gear operation was complete the left main and right main gear received no 'Green' gear down and locked indication. Immediately executed go around and departed pattern to the north to troubleshoot. The Emergency checklist was completed and included 2 gear cycles and 1 manual emergency gear extension. No change in gear indication was seen. At the time I believed it was a bulb issue as I could hear the hydraulic pump complete the cycle and feel the landing gear lock in place but because of the unknown gear light and lack of confirmation of gear position we decided to confirm gear position with Tower and declare emergency. In the PC-12 the landing and taxi light are mounted on the landing gear. Those lights will only be illuminated when the gear is down and locked the Tower confirmed the landing and taxi lights were on. This reinforced my feeling that we had a bulb issue. Yet because of the unknown quantity; per checklist; we then executed the emergency landing with main gear unlocked checklist. The landing was flawless and uneventful. I taxied off the high speed; shut down on the taxiway and called for the tug. Maintenance was on hand and bulbs were on the field. They replaced the bulb within 20 minutes and we were then receiving 3 green indications on the ground. I believe the cause of the problem was the aircraft coming out of maintenance with extensive avionics work. The gear selector and indicators are very close to the avionics and could have been damaged. The owner and I were very calm and considered every action. We took our time completing each checklist and discussed each decision before it was done.

Callback: After this incident all of the landing gear indicating light bulbs were changed; thinking that the bulbs may have been handled during maintenance and that oils from human hands may have shortened the life of the bulbs. No further bulb failures have been experienced.



Synopsis: PC12 pilot experiences landing gear indicator light failure during approach and goes around. After ensuring the gear is in fact down a normal landing ensues.