CHI87FA153

Drg arr at the Milwaukee/lawrence j timmerman arpt, the plt made 2 atmts to use the localizer 15L apch. After the 2nd missed apch, he elected to divert to Milwaukee/general mitchell fld (mke). At that time, he was adzd the mke wx was 300' ovc, 1/4 mi vis with fog, RVR 3500'. The plt was continually adzd of the RVR at mke. Initially, the RVR was vrbl btn abt 6000 & 3500 ft. after being clrd for the apch, the plt acknowledged clnc to twr freq, but delayed freq chg untilreminded. When he finally contacted the twr, he was clrd to land. He was adzd the RVR had dropped to 2000', then about 1 min later, was told it was 1800', but the plt did not reply. After about another min, an ELT signal was heard for about 2 sec & radio contact was lost with the acft. The aircraft had hit a treetop, crashed & burned about 1/4 mi fm the apch end of rwy 7. No preimpact part failure or malfunction was fnd. Ten min after the acdnt, mke wx was in part: 100' obscured, 1/4 mi with fog. Mins for the apch were 200' ceiling & 1/2 mi vis or 2400' RVR.