Helicopter
Flight Crew Commercial; Flight Crew Flight Instructor
Flight Crew Last 90 Days 199; Flight Crew Total 1084; Flight Crew Type 980
Other / Unknown
Conflict NMAC
Flight Crew Took Evasive Action
Human Factors
Experimental RV4 flew straight in to S50 making only a single radio call ('Final 34; touch and go; helicopter in pattern say position'). Proceeded to enter the traffic pattern by flying directly over the runway south to north over slower departing traffic; without having the traffic in sight; and turning crosswind in front of that traffic. Since we were able; we slowed and stopped climbing (an airplane would have had to slow below stall speed). After landing; the RV4 took off again; passed downwind traffic at a higher rate of speed and descended in front of them to enter a base turn and land again (once again requiring us to slow to <50 KIAS). S50 is used for flight training by multiple flight schools; and non-standard traffic pattern entries by general aviation traffic puts all pilots here at risk for MAC. This risk is heightened when low-experience instructors; low-time students; or solo students encounter this erratic behavior. Auburn and the area between S50 and BFI are due for a MAC between airplane traffic not using the CTAF; not reporting or coordinating with other traffic; flying at a higher rate of speed than flight training aircraft; and at low altitudes.
Helicopter instructor pilot reports a NMAC with a RV4 that had preformed a touch and go behind the helicopter then over flew the helicopter on the upwind.