Narrative:

Upon leaving parking position, I had the student pilot check his brakes, then I checked mine. Both were ok. A second C172 was stopped for run-up for runway 9. As we tried to stop, the student reported no brakes. I applied my brakes, which also didn't work. I then pulled the mixture to shut down the engine. I also steered left to get the propeller away from the other plane. The right wing of our plane hit the vertical stabilizer of the other airplane. Both planes were dented at the place of contact. There were no injuries. The WX was dry cavok. After the accident I taxied the plane back to its parking area and the brakes worked ok. I have no idea why the brakes didn't work in this one instance.

Google
 

Original NASA ASRS Text

Title: A C172 INSTRUCTOR AND STUDENT, TAXIING FOR TKOF AT EGELSBACH (EDFE) GERMANY, EXPERIENCED BRAKE FAILURE, RESULTING IN A COLLISION WITH ANOTHER ACFT.

Narrative: UPON LEAVING PARKING POS, I HAD THE STUDENT PLT CHK HIS BRAKES, THEN I CHKED MINE. BOTH WERE OK. A SECOND C172 WAS STOPPED FOR RUN-UP FOR RWY 9. AS WE TRIED TO STOP, THE STUDENT RPTED NO BRAKES. I APPLIED MY BRAKES, WHICH ALSO DIDN'T WORK. I THEN PULLED THE MIXTURE TO SHUT DOWN THE ENG. I ALSO STEERED L TO GET THE PROP AWAY FROM THE OTHER PLANE. THE R WING OF OUR PLANE HIT THE VERT STABILIZER OF THE OTHER AIRPLANE. BOTH PLANES WERE DENTED AT THE PLACE OF CONTACT. THERE WERE NO INJURIES. THE WX WAS DRY CAVOK. AFTER THE ACCIDENT I TAXIED THE PLANE BACK TO ITS PARKING AREA AND THE BRAKES WORKED OK. I HAVE NO IDEA WHY THE BRAKES DIDN'T WORK IN THIS ONE INSTANCE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.