On April 14, 2006, at 1830 eastern daylight time, a Dassault Aviation Falcon 2000, N722JB, received substantial damage when the left engine cowl separated from the engine and impacted the horizontal stabilizer during cruise at flight level 250 near Stilesville, Indiana. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 flight was operating on an instrument rules flight plan. The pilot and copilot were uninjured. The flight originated from Abraham Lincoln Capital Airport (SPI), Springfield, Illinois, at 1700 central daylight time and was en route to James M. Cox Dayton International Airport, Dayton, Ohio. The flight diverted to SPI where it landed without incident. Prior to the flight the right engine starter was replaced. According to the Federal Aviation Administration Inspector, the copilot reported that he performed a walk around inspection of the airplane prior to the flight. The pilot stated about 30-50 miles west of Indianapolis, Indiana, a loud noise was heard and it felt like something hit the airplane. All the engine and electrical systems seemed normal. There was a slight difference in airplane sound. The flightcrew diverted to SPI and the flightcrew reported that the landing was normal, except for a slight noise and airflow difference and a slight increase in drag for a given power setting based upon an indicated airspeed that was slightly lower for a given power setting. Examination of the airplane by the Federal Aviation Administration revealed that the lower spar of the left horizontal stabilizer was damaged. The left engine primary fuel line was dented through half its 1 1/2 inch diameter. A trajectory analysis of the cowling was performed by the National Transportation Safety Board's Vehicle Performance Division and an area or footprint was created where the cowling may be located. This area, about 2 miles northwest of Rockville, Indiana, is bounded by the following coordinates: N39.80458 degrees, W87.26732 degrees N39.81214 degrees, W87.24437 degrees N39.77137 degrees, W87.26978 degrees N39.7736396 degrees, W87.2366407 degrees Local law enforcement was notified and a search conducted, but at the time that this report was created, the cowling remains missing. A European Aviation Safety Agency Airworthiness Directive (AD) No. 2007-0016, Engine Cowling Latching Improvement to Prevent In-Flight Cowling Separation was subsequently issued and became effective on January 26, 2007. The airplane manufacturer, "strongly recommends that all F2000 operators comply with the above referenced Airworthiness Directive in the country of registration of their aircraft."