** Support services firm's shares down 5.6 pct,poised for biggest one-day drop since early Nov in relativelystrong volume
** Says increased start-up costs & operational difficultiesat Heathrow to impact H1 2015 results; posts 39 pct drop in FYpretax profit
** Co, whose interests are split between aviation servicesbusiness & print distribution business, says 2015 results willbe weighted towards H2
** Shares in co had fallen to more than 4-yr low of 385pence in Nov when it warned FY aviation unit profit would bebelow expectations (venkateshasoumithri.mamidipudi.thomsonreuters.com@reuters.net)
