UAL Corp. (UAUA, news, chart, volatility) and the other airlines are set to finish the week on a high note. The AMEX Airline Index (.XAL) is up for a fourth consecutive trading session with help from falling crude oil prices. Crude is down another $2.00 to $41.67. XAL is up almost 20 percent since Monday and at three-week highs heading into the close. Options activity is picking up in the sector, with approximately 47,000 calls and 11,000 puts traded on the major airlines Friday. UAL calls are among the most actives, with 12,000 contracts traded or roughly four times the number of put options. Sentiment based on the flow is directionally bullish (70 percent), as investors are actively buying December 20 calls with strike prices ranging from 12.5 and 17.5. January 17.5 calls are also being bought Friday.