Transport stocks were the worst performing stocks on Tuesday with airlines hit by negative newsflow and postal group Royal Mail under pressure after cautious comments from Credit Suisse.Airlines such as British Airways owner IAG, Easyjet and Ryanair were reeling in afternoon trade on rumours that Russian authorities are exploring the possibility of imposing a ban on European carriers' ability to fly over Siberia. According to a report in Russian business daily Vedomosti, that measure could cost European airlines about €1bn over three months as a result of longer flights, higher fuel use and other costs. Meanwhile, reports that RAF jets had to escort a passenger plane to Manchester Airport due to a possible device on board could also have been a factor behind the weakness in the transport sector. The incident, involving a Qatar Airways Airbus A330 plane, prompted the temporary suspension of flights in and out of the airport.IAG's shares were down nearly 4%, Easyjet was 2.4% lower, while Ryanair dipped 0.1%.Aviation support and aftermarket services firm BBA Aviation was unwanted with shares declining 1.9% after the company underwhelmed with a 1% rise in interim profit before tax to $79.2m. The company said the business "delivered as anticipated in the first half".Elsewhere in the transport sector, Royal Mail's stock was dented by Credit Suisse, which said it sees "no near-term positive catalysts" for the postal company.The bank slashed its target price for the shares from 460p to 360p as it kept an 'underperform' recommendation, saying that margin targets this year "will be difficult to achieve". The stock was down 3%.Top performing sectors so far todayAutomobiles & Parts 8,159.85 +1.22%Food Producers & Processors 7,499.25 +1.10%Health Care Equipment & Services 5,952.17 +1.01%Tobacco 39,073.61 +0.99%Food & Drug Retailers 3,339.19 +0.79%Bottom performing sectors so far todayIndustrial Transportation 2,638.07 -2.32%Industrial Metals & Mining 1,198.02 -1.75%Aerospace and Defence 4,784.47 -1.46%Construction & Materials 3,864.22 -0.64%Travel & Leisure 6,850.97 -0.58%BC