Date: 201208
Local time of day: 0601-1200
Location: ACK.Airport, MA
Aircraft: Cessna 402/402C/B379 Businessliner/Utiliner
Operator: Air Taxi
Operating under: Part 135
Flight plan: VFR
Flight phase: Descent
Airspace: Class E ZBW
ATC / advisory: Center ZBW
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Confusion; Communication Breakdown; Workload
Anomaly: Conflict NMAC
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Airspace Structure; Weather; Human Factors; Procedure
Primary problem: Human Factors

Narrative: We still owned Cape Approach's airspace; and were giving multiple departure and approach clearances; as well as holding aircraft and working a few overflights. The weather was approximately OVC020 at ACK; and all over the Cape Cod area. The normal air-to-air frequencies are used as Clearance Delivery frequencies; as well as air-to-air frequencies when Cape Approach and the airport Towers are closed. We had airplanes calling on the frequency requesting departure clearances every couple of minutes; and they were starting to get testy that we were making them wait; as we have a one-in-one-out rule. A C402 checked in; at first we thought he was on the ground looking for a clearance; and then we realized he was in the air; but thought he was looking for an IFR clearance; and then eventually he made it clear he wanted VFR advisories to ACK; but he was already in the descent to the airport. The RADAR Controller gave him a beacon code and RADAR identified him; but did not tell him about the other aircraft that was inbound on the ILS; approximately 2-3 miles away; also descending into ACK. I prodded the RADAR Controller a couple of times; and he finally called the traffic to one of the aircraft; I can't remember which; but not to the other; and was fairly vague about what the plane was doing. He is normally very thorough; so I can only guess that it was the complexity of the traffic situation with all the departures trying to get clearances and giving others holding instructions that diverted his attention from calling the traffic alert. I was lax in not being forceful enough about his making sure they were both aware of the other traffic. After the data blocks separated; the IFR called up to cancel his flight plan; and asked if we were talking to a VFR airplane in the vicinity. The RADAR Controller responded in the affirmative; and the pilot said; 'He almost hit us;' and that the other airplane was flying around in the clouds. The RADAR Controller apologized and continued working the rest of the airplanes without incident. He tried to reach the VFR aircraft; but was unsuccessful. When Cape Approach called to open; I told them there was a VFR; and the call sign that we never got a hold of; and were not sure if he landed; and the Approach Controller said he would inform the Tower when they opened. The situation was made complex due to the sheer number of aircraft looking for departure/approach clearances and not understanding why they were being told they had to wait. If there was a separate Clearance Delivery frequency from the normal air-to-air frequency; I could have been talking to the planes on the ground while the RADAR Controller was working the planes in the air. This is only an issue once or twice a week; in the summertime; but it could have potentially life-threatening consequences.




Synopsis: ZBW Controller described a conflict event between a VFR and an IFR inbound to ACK. The situation was complicated by a number of aircraft requesting IFR clearances.