The pilot and the flight instructor were departing for an instructional flight, and before beginning their taxi, had tested their airplane’s brakes and noted no anomalies. The subsequent taxi was normal, and as they approached the run-up area, the pilot attempted to apply the right brake but it was ineffective. The flight instructor also attempted to apply the right brake, but during his attempt the pedal went completely to the floor. The airplane’s left wing subsequently struck the empennage of another airplane that was stationary and operating in the runup area, resulting in substantial damage to the fuselage and empennage of that airplane. The pilot and the flight instructor’s airplane incurred minor damage. Postaccident examination of the airplane’s brakes by the operator’s maintenance personnel found no evidence of any preaccident mechanical malfunctions or failures.