Narrative:

During a training flight of takeoff and landings; we had made three touch and go landings. The fourth was planned for a full stop. As the main wheel touched down with no problem; as the aircraft was slowing down and the tail made contact with the runway; we started going left and right and left of the centerline of the runway about 10 degrees of runway heading. That's when I called for 'I have the controls'.the aircraft was going straight down the runway and we were about 500 feet from [the taxiway] where I plan to exit the runway. At that point the aircraft started going to the left and I applied right brake and it went to the stop. I applied right brake again and it went to the stop again. So I started applying left engine to get it straight; but the engine did not come up in RPM quick enough to stop the turn to the left. The aircraft exited the runway about 75 feet before [the taxiway] on a heading of 240 degrees. The aircraft did ground loop to the left and stopped pointing the runway at heading of about 010 degrees.I locked the tail wheel and taxied to [the taxiway] which was 50 feet away. Tower asked if the aircraft exited the runway early which I said yes and told tower that there was a brake failure. While taxing I got the right brake back to working; but heard a metal to metal sound. I told tower that we did not need assistance; but taxi back to parking. Completed after landing check and taxied back to parking.the flap had contacted a runway light on the exiting of the runway early which had bent the trailing edge of the left flap at the second bay outboard from the inboard of the flap. The right brake a piece of metal at the brake disc and caliper. The airport was told that a runway light was possibly had been hit. Wind was out of the south at estimated 6 to 8 knots.

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Original NASA ASRS Text

Title: Beech 18 instructor reported they experienced a brake failure during landing rollout resulting in a runway excursion.

Narrative: During a training flight of takeoff and landings; we had made three touch and go landings. The fourth was planned for a full stop. As the main wheel touched down with no problem; as the aircraft was slowing down and the tail made contact with the runway; we started going left and right and left of the centerline of the runway about 10 degrees of runway heading. That's when I called for 'I have the controls'.The aircraft was going straight down the runway and we were about 500 feet from [the taxiway] where I plan to exit the runway. At that point the aircraft started going to the left and I applied right brake and it went to the stop. I applied right brake again and it went to the stop again. So I started applying left engine to get it straight; but the engine did not come up in RPM quick enough to stop the turn to the left. The aircraft exited the runway about 75 feet before [the taxiway] on a heading of 240 degrees. The aircraft did ground loop to the left and stopped pointing the runway at heading of about 010 degrees.I locked the tail wheel and taxied to [the taxiway] which was 50 feet away. Tower asked if the aircraft exited the runway early which I said yes and told Tower that there was a brake failure. While taxing I got the right brake back to working; but heard a metal to metal sound. I told tower that we did not need assistance; but taxi back to parking. Completed after landing check and taxied back to parking.The flap had contacted a runway light on the exiting of the runway early which had bent the trailing edge of the left flap at the second bay outboard from the inboard of the flap. The right brake a piece of metal at the brake disc and caliper. The airport was told that a runway light was possibly had been hit. Wind was out of the south at estimated 6 to 8 knots.

Data retrieved from NASA's ASRS site 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.