allowable takeoff and landing weights for particular  aircraft/engine configurations for a specific airport, runway,  and range of temperatures. The computations also consider  flap settings, various aircraft characteristics, runway  conditions, obstacle clearance, and weather conditions.  Obstacle data also is available from these service providers  for operators who desire to perform their own analysis  using the OEI climb performance and flight path data  furnished in the Airplane Flight Manual or when using an  aircraft electronic performance program supplied by the  manufacturer or other service provider.  Airport/runway analysis is typically based on the  assumption that the pilot will fly a straight-out departure  following an engine failure on takeoff. However, when a  straight-out departure is not practical or recommended,  a special OEI turn procedure can be developed for each  applicable runway. This OEI turn procedure may follow  the path of a published IFR departure procedure or it  may follow an independent path designed to avoid  to determine a lateral path that is usable by a wide variety  of aircraft types, and establishes a clearance plane that  aircraft must be able to stay above to fly the procedure. A  Part 25 transport category and Part 23 commuter category  aircraft’s OEI takeoff flight path is established by or on  behalf of the operator for a particular aircraft type and then  limit weights are determined that assure clearance of any  obstacles under that flight path (or within the prescribed  lateral distance from the flight path centerline).  It may be necessary for pilots and operators of these  categories of aircraft to use the services of an aircraft  performance engineer or airport/runway analysis service  provider as means of compliance with the requirements  of Part 121 subpart I, or Part 135 subpart I concerning  OEI net takeoff flight obstacle clearance and takeoff field  length requirements. [Figure 1-20] Airport/runway analysis  involves the complex, usually computerized, computations  of aircraft performance, using extensive airport/obstacle  databases and terrain information. This yields maximum  Figure 1-21. Graphic ODP/booklet front matter.  1-22 