Two Mechanics report preforming a high power runup on an ATR42 with the parking brake set and chocks in front of all wheels. At 80% torque the aircraft begans to slide resulting in damage to the ground power receptacle and a main gear door before the aircraft was stopped.
Synopsis
Two Mechanics report preforming a high power runup on an ATR42 with the parking brake set and chocks in front of all wheels. At 80% torque the aircraft begans to slide resulting in damage to the ground power receptacle and a main gear door before the aircraft was stopped.
Narrative
The crew had informed me of a write-up about a #1 torque problem. The write-up was as follows: #1 torque reduces to 60% when bleed is turned on after takeoff. The needed power lever correction results in a power lever split. Another Mechanic and I had decided to run the aircraft to confirm the problem. We moved all of the cones around the aircraft and set them aside. We then performed a quick walk-around of the aircraft to ensure the aircraft was ready for a run and determined ramp was good to run at high power settings. I noticed my partner making sure the chocks were tightly against the tires; and I went around again and kicked the chocks tightly against the tires to make sure. Once [the] aircraft was prepped and ready for an engine run; we climbed into the cockpit shutting the main cargo door behind us. My partner took the left seat while I took the right seat. I had informed him that he would monitor the gauges and be in control of the aircraft while I watched to make sure we would not slide and verify the problem the crew had informed me about with the torque. After engines stabilized; we brought the condition levers to max and then the power levers to 80%. After about 5 seconds of the plane being at 80% torque; I started yelling 'STOP; STOP; STOP!' as I noticed the plane starting to move. My partner immediately brought the power levers to reverse to stop the aircraft. Once the aircraft was stopped; we shut the aircraft down as per the checklist and went to assess the damage. Found DC power receptacle to be bent and the receptacle pins to be strong. No cracking was found around the receptacle. Also found right main gear door to be broken off. Did inspection of prop blades and found no evidence of a prop strike with either the GPU or GPU cord. [We] secured aircraft and contacted Maintenance Control. It has been determined by our assessment that we did everything possible to avoid this situation. NOTE: 4;500 LBS fuel on board. Aircraft sliding distance 55.7 FT. Suggest sanding the ramp; pulling GPU when running engines at high power.
Second reporter narrative
After performing the after-start portion of our engine-run checklist I then brought the engines out of feather; after all engine parameters stabilized I proceeded to bring engines up to 80% max power. After engines were stabilized my partner was about to perform the bleed and pack test to see if we could identify the torque drop and the throttle split. Before bleeds and packs could be turned on the aircraft started to move. When the aircraft started to move I put both engines in full reverse to stop the aircraft. After getting the aircraft stopped I shut down the engines and went to assess the possible damage to the aircraft and to see what could have caused this to happen. We determined that the aircraft jumped the nose chock and the proceeded to drag both main tires. Upon further inspection of the aircraft we identified that the external power receptacle was bent out of position even though the receptacle is bent there is no indication of cracking or any loose rivets holding the receptacle in place. Also the GPU power cord had ripped off the upper hinge portion of the aircraft right hand main landing gear door. We inspected the propeller; GPU; and the GPU power cord to ensure there was no prop strike. After everything that has occurred our assessment of the situation is that we took every step possible to prevent a situation like this from happening. Note: Aircraft had 4;00 LBS of fuel on board for run. Rubber noted on concrete from both main tires dragging on concrete.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.