Narrative:

During a training flight with a student in an L-39 the aircraft overrun runway 27 by approximately 80 ft. We conducted a normal start; taxi; and runup; testing both the normal and emergency brakes in the front seat. After ten landings we planned a full stop. The student (who is rated in the L-39) landed on speed and in the first 1;000 ft of the runway. We then aero-braked the aircraft until 3;000 ft were remaining. He lowered the nose; applied full forward stick to make sure the weight on wheels switch was open and would allow the normal brakes to operate. My student applied normal brakes and got no response. I checked the brake pressure indicator in the back which showed pressure (in the L-39 this is system brake pressure; it can still be interrupted by the anti-skid system). I called for more brakes; and then took the aircraft and applied full main brakes in the back with no response. I then applied emergency brakes slowly to prevent locking the main wheels (emergency brakes have no anti-skid); and when I got no response applied more emergency brake in the back; eventually getting to full e-brake. When that did not work I instructed my student to apply e-brakes in the front; which he did; but not before the aircraft departed the runway surface. I do not know if the emergency brake in the front worked; the ground was soft and the aircraft overran the runway by approximately 80 ft with no damage to the aircraft or runway lights. The rear seat emergency brake had not been tested in a few months; which I will not do before every flight. The combination of the failure of the rear seat e-brake along with the lack of anti-skid on the brake; necessitating a slow application; caused us to run out of time to try all four braking options on the aircraft before runway departure.

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Original NASA ASRS Text

Title: An L-39 instructor reported both the normal and emergency brakes failed on landing so the aircraft departed the runway end without sustaining damage or causing injury.

Narrative: During a training flight with a student in an L-39 the aircraft overrun Runway 27 by approximately 80 FT. We conducted a normal start; taxi; and runup; testing both the normal and emergency brakes in the front seat. After ten landings we planned a full stop. The student (who is rated in the L-39) landed on speed and in the first 1;000 FT of the runway. We then aero-braked the aircraft until 3;000 FT were remaining. He lowered the nose; applied full forward stick to make sure the weight on wheels switch was open and would allow the normal brakes to operate. My student applied normal brakes and got no response. I checked the brake pressure indicator in the back which showed pressure (in the L-39 this is system brake pressure; it can still be interrupted by the anti-skid system). I called for more brakes; and then took the aircraft and applied full main brakes in the back with no response. I then applied emergency brakes slowly to prevent locking the main wheels (emergency brakes have no anti-skid); and when I got no response applied more emergency brake in the back; eventually getting to full e-brake. When that did not work I instructed my student to apply e-brakes in the front; which he did; but not before the aircraft departed the runway surface. I do not know if the emergency brake in the front worked; the ground was soft and the aircraft overran the runway by approximately 80 FT with no damage to the aircraft or runway lights. The rear seat emergency brake had not been tested in a few months; which I will not do before every flight. The combination of the failure of the rear seat e-brake along with the lack of anti-skid on the brake; necessitating a slow application; caused us to run out of time to try all four braking options on the aircraft before runway departure.

Data retrieved from NASA's ASRS site as of July 2013 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.