What happened
On July 7, 2001, a Yak-52, registration LY-ANS, was performing a VFR flight from Skien Airport Geiteryggen to Gullknapp Aerodrome. During the landing on runway 23, the pilot executed a three-point landing at approximately 120 km/t and immediately applied heavy, pulsating brakes. Shortly after the application of brakes, the braking effectiveness vanished due to fading. The pilot attempted to steer the aircraft toward the gravel shoulder to increase friction using the rudder; however, the aircraft left the paved surface at approximately 30 km/t. The aircraft continued onto a gravel shoulder and struck a stone-filled embankment, causing it to overturn on its back. The pilot escaped the wreckage without injury, though the aircraft sustained extensive structural damage to the propeller, nose gear, canopy, tail fin, and left wingtip.
The investigation
The investigation examined the landing technique, the aircraft's braking system, and environmental conditions. Analysis of amateur video footage confirmed that the aircraft landed in a three-point attitude rather than a standard two-point attitude, and showed blue smoke emanating from the main wheels, indicating significant tire rubber burning due to intense friction. The investigation also reviewed the aircraft's maintenance and operational manuals, noting that the braking system utilized compressed air, a design common in Russian-built aircraft like the Yak-52. The investigators calculated that the landing speed was approximately 12 km/t higher than the recommended approach speed for the aircraft's weight. Additionally, the ambient temperature of 25 °C (10 °C above standard) was noted as a factor that increases both ground speed and brake heating.
Findings
- The primary cause of the accident was brake failure caused by overheating due to heavy braking.
- The pilot utilized an incorrect landing technique for a short runway, opting for a three-point landing at an excessive speed of 120 km/t instead of a controlled approach speed of approximately 108 km/t.
- The use of "pulsating" braking (pumping the brakes) at high speeds contributed to rapid heat buildup in the drum brakes, leading to brake fading.
- High ambient temperatures increased the kinetic energy that the brakes were required to absorb and further exacerbated the overheating.