Airline shares fell Monday on fears that new security restrictions swiftly implemented following a botched attempt to blow up an airliner could curtail business travel on lucrative international routes Delta Airlines slid 48 cents, or 41 percent, to $1129, American Airlines parent AMR Corp fell 39 cents, or 48 percent, to $775 and United Airlines parent UAL dipped 45 cents, or 34 percent, to $1264 Market reaction may be accentuated this week by low trading volume between the Christmas and New Year's Day holidays, said Jeff Straebler, an RBS Securities Inc analyst The Bloomberg US Airlines Index of 13 carriers traded last week at its highest since January on signs that travel demand is improving The index fell 29 percent Monday