** Oil major Shell slumps nearly 4% to 22.4 pounds as a profit beat was dampened by co flagging global economic slowdown
** Q3 profit of $4.8 bln topped estimates of $3.91 bln
** "Weak macroeconomic conditions" and "challenging outlook" create uncertainty about co's buyback time frame – CEO Ben van Beurden says
** If losses hold, Shell to turn negative for the year vs. the FTSE 100's +8% YTD
** By 1110 GMT, Shell shares made up for nearly half of the FTSE 100's fall
** Shell results come just days after BP disappointed markets with a profit plunge amid weak oil prices
** BP shares also down 1.4% on the day
(Reporting by Safia Infant)