Date: 201704
Local time of day: 0601-1200
Location: HTO.Airport, NY
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class E HTO
ATC / advisory: CTAF HTO
Reporter organization: Corporate
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion
Anomaly: Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was the PIC and Pilot-Flying (PF) on a Part 91 trip with the aircraft owner onboard. The climb; cruise; and descent portions of the flight were routine in VMC conditions. The destination (HTO) was reporting clear skies with unrestricted visibility and winds favoring runway 10; we planned a visual approach (left traffic pattern); but entered the RNAV Z 10 approach into the FMS flight plan and briefed it for situational awareness and advisory glide path information. East Hampton; NY is the shortest runway the company operates to/from with a landing distance of 4255 feet; this fact was forefront in my mind throughout the planning and execution of the flight.As we approached the destination; I asked the Pilot-Not-Flying (PNF) to monitor the CTAF for traffic in the HTO area. Additionally; I asked him to make periodic calls on the CTAF announcing our position and intentions; he did so; stating that the frequency was quiet. I thought it odd there was little traffic on a VFR; Good Friday but was focused on the short field landing; no traffic was noted on TCAS; seeming to confirm the PNF's statements. We entered the left downwind for runway 10; turned left base and final; radio calls were made at each turn. Approximately one mile from touchdown (perhaps a bit less); I saw an opposite-direction high-wing Cessna climbing away from runway 28; this aircraft turned left/south (beginning his crosswind) to avoid our arrival. Seconds later; I noted a low-wing single had side-stepped runway 28 to the north above our altitude; apparently aborting his approach. As we were nearing the runway and no other traffic was observed nor depicted on TCAS; I continued to a normal landing on runway 10. The AWOS still reported south-easterly winds that favored runway 10.As we rolled to the end and exited runway 10; I asked the PNF which frequency he was communicating on; he stated 122.7 which I immediately noted was the UNICOM; NOT the CTAF of 125.22. Exiting the runway I assumed radio communication and made calls on the CTAF as I taxied to parking; the PNF was on the other radio cancelling the IFR flight plan. It was then clear to me the reason we heard no other traffic in the pattern at HTO. The PNF was utilizing the incorrect frequency. As PIC; ultimately I am responsible for the crew's actions; in this case I didn't notice the radio problem as I was concerned about the short runway at a destination I had not been to in a decade (HTO trips are typically handled by a limited number of company pilots).Company SOP dictates the use of Comm Number 2 as the primary radio for ATC communications; Comm Number 1 is used for ATIS; CTAF calls; FBO calls; etc. While inbound to HTO; the PNF used Comm Number 1 to make traffic calls; when Approach Control turned us over to the CTAF; he continued to use Number 1; rather than switching to Number 2; per SOP. As I was then unable to hear his calls; I was forced to ask him which radio he was using and then switch my active Comm to Number 1. On a recent trip with this First Officer to a different non-towered airport; he had the same performance issue; when this was pointed out he acknowledged using the wrong radio. Apparently; remedial training is needed on non-towered airport operations and radio communication. I am also at a loss to explain why an experienced and type-rated First Officer misread the radio frequencies on the approach plate. If HTO were a more familiar airport to me; I would have noticed and corrected the discrepancy prior to arrival in the terminal area. On all future trips to non-towered airports; I will note the active radio frequency and query the other crew member as to its accuracy.




Synopsis: Corporate jet Captain reported they used the incorrect frequency for their arrival and landing at HTO.