Narrative:

We were conducting a visual inspection of a pipeline right-of-way (row) from the class B surface area into [a] class D environment. After establishing communications with tower and being cleared on our transition through the airspace; my right-seat observer requested we circle to re-capture data in our computer-based patrol software at the southernmost extent of the class D. I informed tower I needed to circle to evaluate a sighting; and this was approved. We made a single circle; captured the data we needed; and continued on our way; roughly due north. As we approached the field (our pipeline route is inside the airport fence for a short distance) tower advised us to let him know when we were back northbound due to inbound traffic. Realizing that he was not expecting us to be close to the field; I stated we were already northbound; began a climb and asked tower if we needed to circle. At this time the controller called helicopter traffic close to us about the same time as our traffic advisory system alerted us to the traffic. As we were already in a climb; we had between 200-300 feet vertical separation and the traffic advised tower they had us in sight. The tower advised the helicopter to maintain visual separation. We never got closer than 4-500 feet horizontally before passing the traffic but it was obvious that both I and the controller had misunderstood each other's intentions and ended up with a traffic conflict. The helicopter pilot was obviously vigilant and had us in sight before we saw him. We continued our patrol without further conflict or incident. Upon reflection; I should have been clear with the controller and stated that we needed to make a single circle and then would continue our patrol. This would have allowed him to plan for the inbound rotorcraft and avoided the conflict altogether.

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Original NASA ASRS Text

Title: C172 pilot reported an NMAC with a helicopter during his pipeline patrol.

Narrative: We were conducting a visual inspection of a pipeline Right-of-Way (ROW) from the Class B surface area into [a] Class D environment. After establishing communications with Tower and being cleared on our transition through the airspace; my right-seat observer requested we circle to re-capture data in our computer-based patrol software at the southernmost extent of the Class D. I informed Tower I needed to circle to evaluate a sighting; and this was approved. We made a single circle; captured the data we needed; and continued on our way; roughly due north. As we approached the field (our pipeline route is inside the airport fence for a short distance) Tower advised us to let him know when we were back northbound due to inbound traffic. Realizing that he was not expecting us to be close to the field; I stated we were already northbound; began a climb and asked Tower if we needed to circle. At this time the Controller called helicopter traffic close to us about the same time as our traffic advisory system alerted us to the traffic. As we were already in a climb; we had between 200-300 feet vertical separation and the traffic advised Tower they had us in sight. The Tower advised the helicopter to maintain visual separation. We never got closer than 4-500 feet horizontally before passing the traffic but it was obvious that both I and the Controller had misunderstood each other's intentions and ended up with a traffic conflict. The helicopter pilot was obviously vigilant and had us in sight before we saw him. We continued our patrol without further conflict or incident. Upon reflection; I should have been clear with the Controller and stated that we needed to make a single circle and then would continue our patrol. This would have allowed him to plan for the inbound rotorcraft and avoided the conflict altogether.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.