On November 18, 1993, at 1107 hours Pacific standard time, a Cessna 172RG, N9620B, was struck by a Cessna 172P, N97766, while on taxiway K while awaiting departure clearance at John Wayne Airport (SNA), Santa Ana, California. The pilots aboard both airplanes were beginning a local visual flight rules instructional flight. N9620B, operated by Lenair Aviation, SNA, sustained substantial damage; N97766, operated by American Flyers, SNA, sustained minor damage. Neither the certificated commercial pilot/flight instructor (CFI) nor the certificated private pilot/dual student aboard N9620B was injured. Neither the CFI nor the noncertificated student pilot aboard N97766 was injured. Visual meteorological conditions prevailed.

The Orange County Sheriff's Department, Airport Division, conducted the initial investigation immediately following the accident.


Both pilots aboard N9620B told the investigating deputy that they were holding short (facing west) of runway 19L as instructed by the ground controller. Neither pilot saw the approaching Cessna 172 (N97766) while it was taxiing north on taxiway C.


The student pilot told the investigating deputy that the airplane began to veer toward N9620B. She tried to correct with the rudder (the rudder also controls the nose gear while on the ground), but got no response. She attempted to steer the airplane like a car using the ailerons, but without success. She then informed the instructor that they were going to hit the parked aircraft.

The CFI told the investigating deputy that he was instructing the student and noticed she was in trouble. He attempted to turn the airplane "...using slight rudder to the right...," but got no response. He then applied full right rudder and full braking and "...leaned the throttle [mixture] in the attempts to avoid the collision...."

The CFI submitted a Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2. He said in the report that as the airplane was approaching taxiway "K" the student retarded the throttle. He then instructed the student to apply the brakes while he was simultaneously applying the brakes.

As the airplane veered to the left toward the standing airplane (N9620B), the CFI applied right rudder and more right brake, but without success; the airplane did not stop or arrest the left turn. The CFI pulled the mixture control before the collision.

The CFI also reported that there were two other incidents where the right brake failed; one in Florida, and the other in New York. Both involved the Cessna 172 airplane.

The dual student submitted a written statement to the Federal Aviation Administration (FAA), Long Beach Flight Standards District Office. The student confirmed her previous statement to the Orange County deputy and added that she thought the airplane was taxiing too fast and she fully retarded the throttle. She didn't notice any difference in the airplane's speed and she informed her instructor. He instructed her to "...brake a little...", which she did.

The mechanic who repaired the airplane in Florida told National Transportation Safety Board investigators that the right brake failure was caused by a faulty "O" ring seal in the master cylinder. Safety Board investigators were unable to contact the mechanic who repaired the New York incident airplane.

A Cessna Aircraft Company representative was interviewed by telephone on June 7, 1994. He told Safety Board investigators that he has no knowledge of a brake failure without a known faulty mechanism involving the accident airplane make and model. Safety Board investigators examined the brake system of N97766 on December 3, 1993. Investigators visually examined the brake linings. The brake linings did not appear excessively worn. A functional test of both brakes appeared normal.

The investigators disassembled the brakes and both master cylinders. The investigators found that the right brake lining was worn to the height of the rivet heads, between 1/16 of an inch to 3/32 of an inch. The Cessna 172 maintenance manual requires replacement of the brake lining when it is worn to 3/32nd of an inch.

Investigators found no discrepancies in either brake master cylinder. Examination of N97766's airframe logbooks showed that the operator was maintaining the airplane according to an "Approved Aircraft Inspection Program " (AAIP). This program requires inspection events every 75 flight hours. The operator did the last inspection, the number two (2) event, 36.7 hours before the accident. The number two (2) event did not include inspection of the brakes. The airplane had accrued 111.7 hours since the number one (1) event, which included the brake inspection.

The mechanic who repaired the airplane told Safety Board investigators that he operated the right brake master cylinders for two hours after it was reassembled. The master cylinder operated normally throughout the functional test.

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