On April 11, 1995, at 1130 hours Pacific daylight time, a Cessna 170A, N1276D, ground looped while landing on runway 36 at Watts-Woodland Airport, Woodland, California. The pilot was completing a visual flight rules personal flight. The airplane, registered to and operated by Grass Valley Aviation, Inc., Grass Valley, California, sustained substantial damage. Neither the certificated private pilot nor the two passengers were injured. Visual meteorological conditions prevailed. The flight originated at Nevada County Airpark, Grass Valley, California, at 1030 hours. National Transportation Safety Board investigators conducted a telephone interview with the pilot on April 13, 1995. The pilot said that the approach was normal. On touchdown, the airplane bounced. The pilot arrested the bounce, but the airplane began to drift to the left. She said that she applied right rudder to arrest the drift. However, the right wheel locked and the airplane ground looped and exited the runway. When the airplane exited the runway, the tailwheel stuck in the soft terrain causing the AFT fuselage section to fold. The pilot repeated her telephone statement in the National Transportation Safety Board Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2; however, the pilot did not show in the accident report that the airplane experienced any preimpact mechanical malfunctions or failures. A Federal Aviation Administration (FAA) airworthiness inspector from the Sacramento (California) Flight Standards District Office conducted the on-scene investigation. The inspector reported that the pilot told him the " . . . right brake locked up causing the aircraft to ground loop . . . ." The inspector said that his examination of the airplane brake system revealed that the brakes and tires were in good condition; the tires did not display any abnormal scuff or wear marks. He also said that the flight controls operated normally. The inspector did not examine the airplane crosswind landing gear system. A line worker for a fixed-base operator at the airport told the inspector that the airplane made a normal approach to the runway. When the airplane tail touched the ground, the airplane began a porpoise and then ground looped. The line worker said that the pilot told him " . . . she had messed up the landing . . . ." The Safety Board retained a mechanic from Sierra Mountain Aviation, Grass Valley Airport, to inspect the airplane crosswind landing gear system. The mechanic reported that he found that the landing gears detent stop groove and snubber pin were worn. He said that the findings resulted in the "brake-out" force of the left gear to be half of the force required for the right landing gear. The left main gear was able to unlock (kick-in) prematurely and without warning. This condition allowed the airplane to rotate to the right.