American Airlines Boeing 767 N330AA flew as flight 201 from New York-JFK (JFK) to Los Angeles (LAX). During a step climb from FL360 to FL380 en route to LAX, the pilots noted that the No. 1 engine was lagging the right engine by about 2 percent. The flight landed at LAX at 09:37. After the passengers had disembarked, the plane was towed to hangar no. 2 and was parked outside. Maintenance personnel were going to conducting a ground run to troubleshoot the reported discrepancy. Several engine runups to maximum power were performed on both engines. Then they did two runups to max power of just the no. 1 engine. When retarding the throttle to idle, the engine experienced an uncontained rupture of the high pressure turbine (HPT) stage 1 disk. Debris punctured the fuselage and fell onto adjacent runway and taxiways. Runway 25R and Taxiways B and C were closed for several hours until the investigation and collection of the debris could be accomplished. The engine caught fire and the plane sustained significant damage to the left wing, fuselage, and tail section. PROBABLE CAUSE: “The HPT stage 1 disk failed from an intergranular fatigue crack because of GE’s inadequate design of the CF6-80 series HPT stage 1 disk. The inadequate design of the disk resulted in a high stress area in the blade slot bottom aft corner that was at or nearly at the material’s capability so that there was no damage tolerance such that a small dent could cause a crack to initiate and propagate to failure. Contributing to the disk’s failure was the FAA’s failure to mandate an accelerated inspection schedule after a previous CF6-80A uncontained HPT stage 1 disk failure had occurred and after other CF6-80A HPT disks had been found during routine overhaul to have cracks in the blade slot bottom aft corners.”