Small Aircraft
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 30; Flight Crew Total 3350; Flight Crew Type 600
Communication Breakdown; Situational Awareness
Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Excursion Runway; Ground Incursion Runway
Flight Crew Took Evasive Action
Human Factors; Procedure
I was on a cross country flight. While inflight I elected to make a fuel stop at Twin Bridges airport in Montana. A quick look online showed no NOTAMs for the airport. 10 miles out I announced on the UNICOM my position and intentions. While monitoring the UNICOM frequency I heard a lot of chatter. It appeared to be a group of 10 planes organizing something. I ask and was told they were departing momentarily for 'some fun'. I assumed they were a lunch group heading out on a group flight to another airport. When I was about two miles out the planes started to take off in sequence. I extended my downwind to allow them to depart. When the last plane started to roll I turned inbound. On short final I noticed a laggard member of the group sitting on the cross runway. An uneventful landing and taxi to the end of the runway toward the fuel pumps. I was surprised to find the ramp to be full of people blocking the ramp. I announced my intentions to back taxi on the UNICOM. I turned around to back taxi only to find the laggard plane taking off while I was still on the runway. I quickly pulled into the tall grass along the runway to allow the departing plane to pass me. As I continued to back taxi I was again surprised to find a plane on short final; I quickly exited onto the cross runway to avoid the landing aircraft. My real surprise was to learn that 10 planes had lined up to drop bowling balls on the spot I had just been on! I cannot make this stuff up! No NOTAM; no announcements other than 'having fun'. Not sure how I would do things differently in the future. Assume less is all I can think of. I will never assume that my fellow pilots are going to communicate their intentions. My assumption was that when they said they were departing I thought they meant to another airport not departing the ground with a return trip to drop 10 bowling balls onto the runway I announced I was landing on. I do know the organizers of events like this would be well served issuing a NOTAM; having an air boss on the radio and over-communicating to other pilots in the vicinity of their impromptu air show.
GA pilot reported runway excursion to avoid departing traffic. No NOTAM was available for airport event.