Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Descending into ZZZ my First Officer (FO) and I noticed there was an unusual sound but we couldn't tell where it was coming from; I called the flight attendant and asked her if she could hear anything and she said no everything sounded normal to her in the back. We then pulled up the engine page and looked at the engine system followed by checking the electrical page but we couldn't see anything abnormal. We continued our descent and started our approach; it was visual conditions so we were on a visual approach to Runway XX; we had already canceled IFR. I called for flaps 12 and the FO put flaps 12 in; we noticed that the sound had changed a little so we again went through the engine instruments and everything still seemed normal. As we continued to add flaps we noticed the sound would get a little louder each time and when we went flaps 32 we could feel a small vibration coming through our feet. We checked the hydraulic page and everything looked fine; we then checked the flight control page and everything still looked normal. I was hand flying and did not notice any change to the handling of the aircraft; the only thing we noticed was the sound and then the small vibration. We continued to land with no issues; just a normal landing. After parking the aircraft and deplaning; I asked my First Officer to take a little extra time with his post flight to see if he could see anything that would have made the noise and vibration on the approach. After his postflight he came in and said he couldn't see anything unusual outside. I finished up my tasks and then decided to walk around the aircraft myself. When I got to the left side I noticed something sticking up on top of the wing maybe a foot or two from the fuselage. I grabbed a ladder and climbed up to look at it; I found that the trailing edge of the flap was cracked right next to the fuselage and then again about a foot or two away there was another crack. The top trailing edge of the flap had a piece that had come off and was sticking up. I took pictures and called the mechanic on call. I sent him the pictures and he called me back with a plan to send a mechanic down on a different aircraft that night. I went off duty at that point and when I got back to the airport the next morning my aircraft had been swapped out with a different aircraft for us to continue our day.
Captain reported finding cracks in the trailing edge flap assembly on post flight inspection following detection of excessive noise on descent to landing.