THE PLT RPRTD THAT WHILE AT 100 TO 150 FT AGL ON AN APCH TO LAND, THE ENG LOST PWR AS THOUGH IT HAD FLAMED OUT. HE ENTERED AN AUTOROTATION, BUT WAS UNABLE TO REACH THE HELIPAD. SUBSEQUENTLY, THE HELICOPTER LANDED IN TREES & WAS BADLY DMGD. DRG THE INVESTIGATION, THE ENG WAS REMOVED FM THE AIRFRAME & OPERATIONALLY CHECKED, BUT NO REASON WAS FOUND FOR THE PWR LOSS. DISASSEMBLY OF THE ENG REVEALED SVRL DISCREPANCIES, BUT NONE OF WHICH WOULD HAVE SINGULARLY RESULTED IN A FLAME-OUT. AN EXAM OF THE ENG'S INTERNAL COMBUSTION LINER REVEALED AN OVERTEMP BLISTER, CRACKS ON THE FLANGE & NON- APPROVED WELDS; A REQD MOD OF THE LINER WASN'T COMPLETED. THE IGNITER & FUEL NOZZLE MOUNTING PAD ON THE OUTER COMBUSTIONLINER WAS SLIGHTLY DISPLACED (.009' FM PERPENDICULAR), RESULTING IN A SLIGHT DISPLACEMENT OF THE FLAME PATTERN INSIDE THE INNER LINER. THE #1 PWR TURBINE NOZZLE WAS BURNED, CRACKED & ERODED. THERE WAS EVIDENCE THE ENG HAD EXPERIENCED 1 OR MORE OVERTEMP CONDS, POSSIBLY FM HOT STARTS, HI PWR LVLS OR LACK OF COOLING BFR ENG SHUTDOWNS.