Date: 201511
Local time of day: 1801-2400
Location: PIE.Airport, FL
Flight conditions: VMC
Weather elements / visibility: 5
Light: Dusk
Aircraft: Widebody; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Initial Approach
Airspace: Class B TPA
ATC / advisory: TRACON TPA
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation - Altitude Excursion From Assigned Altitude
Detector: Automation Aircraft RA; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: The flight was the second leg of the day and the Captain was the flying pilot. It was a route that this Captain and I had flown together three other times in the last week. I was well rested and the Captain appeared to be also. We worked well together and had no conflicts in or out of the cockpit. The flight was a short leg to St. Petersburg-Clearwater (PIE). It was VFR; nearly dusk; and we were being vectored for the ILS 36R.  We were on a left base on a heading of about 110 and Tampa instructed us to descend to 2000 ft. I read back the clearance and we descended to and leveled at 2000 ft. The Captain was trying to acquire the airport visually when I realized the frequency had been unusually quiet for some time. I was just about to mention that to the Captain when we received a 'Traffic' call from our TCAS followed almost immediately by an RA 'Climb climb.' When we received the traffic call I immediately looked at our TCAS and saw a yellow number on the display below our aircraft symbol just slightly to the right and in front of us. I did not see what the altitude separation was. The Captain climbed 300 feet in response to the command to climb and then the TCAS showed no conflict. Neither of us remember hearing and other statements from the TCAS. I called on the frequency that we had been using and was told by Tampa that we were on the wrong frequency and that they had been trying to call us. The frequency was 118.5. I do not recall what frequency they said we should have been on. We contacted PIE tower and landed without further incident. During taxi in to the gate ground control instructed us to call Tampa approach and gave us the phone number. The Captain and I spoke with the Supervisor together on speaker phone and he requested details of the event from our perspective. He indicated that we had passed within 300 feet of the other aircraft. He said that he would listen to the tape of the event in an effort to try and discover how we had ended up on the wrong Tampa frequency. He called back a few minutes later and did not have a definitive answer as to why he thought we ended up on the wrong frequency. The captain then asked why they did not try to contact us on 121.5 (which we were actively monitoring) and he did not have an answer because he said he was not our controller at the time. He then stated that he would not file a deviation because we could not conclude how the communication was disrupted.


Second narrative: [Report narrative contained no additional information.]


Synopsis: While on approach to PIE; flight crew discovered that they were not on the correct ATC frequency due to radio silence. Just as they began to investigate; they received a CLIMB TCAS RA. Crew spoke with the ATC Supervisor via telephone after the flight and confirmed that they had been on the wrong frequency and that ATC had been attempting to contact them; but not on 121.5 guard frequency.