BBA Aviation reported a 2.0 per cent rise in half-year revenues to 1.1bn dollars as lower fuel prices were offset by a contribution from acquisitions.Acquisitions contributed $19.5m in revenue, mitigating falling lower fuel prices that reduced reported revenue by $10.8m. The Signature Flight Support arm continued its network expansion including two acquisitions, entry in to Singapore and the addition of a new Signature Select location. The business was awarded a 50-year fixed based operator (FBO) lease with Mineta San Jose International Airport.It agreed to acquire Westchester County Airport operator Jet Systems for $38.5m and purchased a 75% share of Starlink Aviation Inc's FBO in Montréal, Quebec, Canada for $3.0m. Overall group underlying operating profit increased by 6.0% to $94m, in part due to a return to more normal levels of de-icing activity. The underlying operating margin jumped to 8.4% from 8.1% and on a fuel price adjusted basis improved by 20 basis points to 8.4%.Profit before tax came to $63.2m, up from the prior year's $55.4m. Free cash flow rose to $42.9m from $21.8m, as a result of increased profits, a lower working capital outflow and reduced interest payments. Net debt increased to $450.1m from $416.4m, with a net cash outflow of $34.4m including a $50.1m dividend payment as well as the $28.6m cash cost associated with closing out the final remaining cross-currency swaps. Total spend on acquisitions and licences completed during the period amounted to $5.3m.Simon Pryce, Chief Executive Officer, said: "We continue to anticipate making good progress in 2013 with clear upside for our businesses once we enter a period of greater business confidence and accelerated structural growth."Shares fell 3.86% to 2288.90p at 09:36 on Tuesday.