Split S The Split S is an air combat maneuver mostly used to disengage from combat . To execute a Split S , the pilot half - rolls his aircraft inverted and executes a descending half - loop , resulting in level flight in the exact opposite direction at a lower altitude . The Split S is taught to be used in dogfight ing when the pilot has the opportunity to withdraw from battle . Contrary to popular belief , this manoeuvre is almost never used to evade target - locked air - to - air missile s . However , it can be an effective tactic to prevent an enemy behind ( between eight o ' clock and four o ' clock positions ) from gaining a missile lock - on while one is disengaging from a fight . The Split S manoeuvre is contrasted with the Immelmann turn , which is an ascending half - loop that finishes with a half - roll out , resulting in level flight in the exact opposite direction at a higher altitude . The Split S is also called a reversed Immelmann turn , or can be listed with a hyphen Split - S . In basic terms , they are very similar manoeuvre , both accomplishing the same goal , but the Split S exchanges altitude to gain speed , while the Immelmann turn exchanges speed to gain altitude . The Split S , being a descending manoeuvre , means that the pilot must always ensure that he / she is starting high enough to complete the half - loop ; the exact altitude needed depends on factors like the aircraft ' s speed , weight and manoeuvrability , likewise the terrain below the plane . Misjudgements can arise from a lack of situational awareness or from an error in reading instruments . The reason for starting the Split S manoeuvre from the inverted position is " If you are flying straight and level and push the nose of the plane down , you will experience your weight lessening . The harder you push the nose down , the more " weightless " you will feel ; you are experiencing negative Gs . These negative Gs result in blood rushing up into the head , which is the opposite of positive Gs where blood rushes to the lower extremities . However , while the body can stand up to 9 positive Gs without severe consequences , blood vessels in the eyes would start to rupture when already applying 2 up to 3 negative Gs . This is the redout effect . A pilot who pushes too many negative Gs will be seeing the world through bloodshot eyes . " However , the Split S " without " a beginning half - roll was frequently used in early WWII by German pilots seeking to evade British fighters . The Merlin engine used in British fighters was carburetted , and the float valves would malfunction under negative g - force leading to reduced power or a stalled engine ( The German fighters were not subject to this problem since they used fuel injection ) . This could be prevented by quarter - rolling the aircraft before starting the dive , but doing so took up enough time to give the German pilots an excellent chance of escaping . The beginnings of a solution was provided by " Miss Shilling ' s orifice " , a fuel - flow restriction device , and was finally solved by changing from the original S . U . carburetters to Bendix - Stromberg pressure carburettors , and later to S . U . injection carburettors .