N81589 WAS FLWG A BOEING 727 ON ILS APCH IN IFR CONDS. APRX 2.5 MI FM RWY, N81589 SUDDENLY DEVIATED LEFT NRLY 90 DEG. 39 SEC LATER, PLT RPRTD HE ENCTRD SVR TURBC, THEN SAID HE WAS TRYING TO CLB. N81589 SUBSEQUENTLY FLEW THRU TREE TOPS ON RISING TRRN FOR APRX 2 CITY BLKS, THEN HIT PWR LNS & A POLE & CRASHED AGAINST A TREE. NO EVIDENCE OF TURBC DUE TO WX AT/NR APCH ALT. INV SHOWED 4.7 MI SEPN BTN ACFT WHEN THE 727 PASSED THE POINT OF DVN (POD). AT POD, THE 727 WAS ON THE ILS GLIDE SLOPE AT 850'; N81589'S ALT WAS NOT DETERMINED. WND WAS FM 120 DEG AT 3 TO 6 KTS, SHIFTING MORE SOUTHERLY WITHALT. PREVAILING VIS WAS 1/2 MI; RVR FOR RWY 12L WAS 6000'; LGT RIME ICG WAS RPRTD. WITNESSES HEARD PWR INTERUPTION OF 1 ENG AT POD; BUT THERE WAS NO INDCN OF PWR LOSS WHERE ACFT HIT TREES. RADAR DATA SHOWED ACFT SLOWED TO 80 KTS AT POD, ACCELERATED TO 100 KTS DRG DVN, SLOWED TO 70 KTS BFR IMPACT; VMCA WAS 74 KTS. SAFETY BOARD BELIEVES THE PLT MOST LIKELY LOST CONTROL DUE TO SLOW SPD & LGT AIRFRAME ICG; POSSIBLY ENCTRD WAKE TURBC. NO REASON FND FOR LOSS OF ENG PWR.