Date: 201905
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Taxi
Airspace: Class G ZZZ
ATC / advisory: UNICOM ZZZ
Second aircraft: Bell Helicopter Textron Undifferentiated or Other Model
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Commercial
Human factors: Situational Awareness; Communication Breakdown
Anomaly: Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Taxi
Contributing factors: Human Factors; Aircraft
Primary problem: Human Factors

Narrative: Winds reported on the local AWOS varied from 100 to 140 degrees at 3-12 knots while I preflighted the plane and taxied from the hangar; sky was clear with several scattered layers above 5;000 feet; visibility well over the AWOS-reported ten miles. Local glider ops were using Runway XX. As I proceeded to Runway XX via taxiway; listening on CTAF and AWOS; I saw a glider in the pattern and then on final for XX; and clearly heard its calls for landing on XX. I also heard but did not understand another radio call (about which more later). This call was much quieter and less distinct than the glider call; and unintelligible; being stepped on by the AWOS broadcast. Because it was much quieter than the glider call; I assumed it was an airborne aircraft either inbound to ZZZ or calling another facility in the area. I reported taxiing across Runway Y and continued past the runway hold line. At the instant I entered Y; a helicopter flew directly overhead and continued north-easterly along a path above Runway Y. As I continued taxiing; and while performing my pre-takeoff checklist; I heard additional relatively quiet calls that were difficult to understand; but it eventually became apparent the helo was operated by [name removed] and it remained in a left closed pattern for Y. I continued to hear its position reports in the pattern as I took off from Runway XX and departed the airport area to the north-east for a short practice flight. I could hear reports from the helo for the duration of my half hour flight including immediately after I called inbound from 8 miles north-east. I also heard a call from a glider on approach to XX. When I called downwind for XX the helo was on the number for Runway Y but called and announced its departure from Runway Y and the airport area; which it subsequently did before I turned base for XX. I might have seen the helicopter as I taxied toward Runway Y if I had looked in that direction at the right time; so I will for sure be doing that in the future. However; the helo might not have been visible if it was already airborne and above my wing. The position/action radio call from the helo might have been more audible if I hadn't been listening to the AWOS at a time and location when hearing position/action reports was clearly more important; so that's another important take-away. Finally -- and beyond my control -- louder and more distinct radio calls from the helo might have helped avoid this situation.




Synopsis: Cessna 172 pilot reported being overflown by a helicopter while taxiing to the runway.