Date: 201703
Local time of day: 1201-1800
Location: ZZZ.Tower, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: PA-31 Navajo/Chieftan/Mojave/T1040
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Main Gear
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Part 91 flight with a pilot-rated-passenger. Normal start; with a normal hydraulic system check.During descent; gear were lowered per the checklist. I observed that the left main landing gear indicator did not illuminate. I cycled the gear up and then back down. The same landing gear indicator did not illuminate; and this time also received a red 'gear unsafe' light; and the landing gear handle did not 'snap' back into its recess. Tried one more time with the same result. Asked Tower if we could circle over the field while we ran a checklist and they approved our request.Asked the passenger to find and read the 'Emergency Gear Extension Checklist.' We followed the checklist prior to using the emergency gear extension. This included aggressive pitching; rolling; and yawing the aircraft; as well as steep turns to attempt to get the gear to lock in place. Still only had two greens. I asked the pilot-rated-passenger to pump the gear down per the checklist. Checklist called for approximately 60 pumps. Passenger pumped to well beyond 60; with no change in gear indication. Tried pulling the throttles to idle and did receive a gear warning horn; indicating that the gear were not down and locked.At this point we called our maintenance department on the company frequency to see if they had any ideas. Their suggestions had already completed per the checklist. Asked the company to activate the Emergency Response Plan. I asked the passenger to secure any loose items in the aircraft.We [advised ATC]. During a low approach; Tower reported that it appeared that the gear were all down. A nearby helicopter heard our call and offered to come make a visual inspection. We agreed; and they flew up next to us. They observed that all the gear were down but that the left main did not appear to be locked in place as it was swinging when we turned.We decided to circle for a while to burn fuel. While circling; Tower said that Approach had offered [a nearby large airport] to us. After a brief discussion; we opted to use [that airport] for the larger runways and more advanced fire/rescue equipment. We continued to circle while talking to [Approach] until the fuel was as low as we were comfortable letting it go.We told [Approach] that we were ready to land and they handed us over to Tower. Tower cleared us to land and confirmed that emergency equipment was standing by. They said that they could see gear and gear doors.




Synopsis: PA-31 pilot reported landing with the main landing gear indicating not down and locked. Maintenance found the left main gear over center cam had failed to lock.