An air starter (10, 210, 410) comprising: a housing (30, 230, 430) defining an interior having a primary inlet (32, 232, 432) and a primary outlet (34, 234, 434) to define a primary air flow path (36, 236, 436) from the primary inlet (32, 232, 432) to the primary outlet (34, 234, 434); a turbine (50, 250, 450) located in the interior and including a rotor (52, 252, 452), with a plurality of circumferentially spaced blades (54, 254, 454), and a drive shaft (70, 270, 470) extending from the rotor (52, 252, 452); a gear box (46, 246, 446) located in the interior and including a gear train (88, 288, 488) and an output shaft (80, 280, 480) coupled to the gear train (88, 288, 488); a spline connection (90, 290, 490), located upstream of the rotor (52, 252, 452) or between the rotor (52, 252, 452) and the gear train (88, 288, 488), and comprising a first spline interface (102, 302, 502) provided on the drive shaft (70, 270, 470) and a second spline interface (106, 306, 506), enmeshed with the first spline interface (102, 302, 502), provided on the output shaft (80, 280, 480); and at least one pilot guide (94, 294a, 294b, 494), axially locating the output shaft relative to the drive shaft, located between the rotor (52, 252, 452) and the gear train (88, 288, 488), and comprising a first pilot element (110, 310a, 310b, 510) provided on the drive shaft (70, 270, 470) and a second pilot element (114, 314a, 314b, 514) provided on an outer surface of the output shaft (80, 280, 480), wherein the first pilot element (110, 310a, 310b, 510) axially overlaps, at least in part, the second pilot element (114, 314a, 314b, 514), wherein the at least one pilot guide (94, 294a, 294b, 494) is axially spaced from the spline connection (90, 290, 490), and wherein the turbine (50, 250, 450) includes a rotor centerline (64, 264, 464) and has a rotor width (58, 258, 458), wherein the spline connection (90, 290, 490) is axially spaced from the rotor centerline (64, 264, 464) a spline distance (92, 292, 492) that is greater than or equal to half of the rotor width (58, 258, 458). a housing (30, 230, 430) defining an interior having a primary inlet (32, 232, 432) and a primary outlet (34, 234, 434) to define a primary air flow path (36, 236, 436) from the primary inlet (32, 232, 432) to the primary outlet (34, 234, 434); a turbine (50, 250, 450) located in the interior and including a rotor (52, 252, 452), with a plurality of circumferentially spaced blades (54, 254, 454), and a drive shaft (70, 270, 470) extending from the rotor (52, 252, 452); a gear box (46, 246, 446) located in the interior and including a gear train (88, 288, 488) and an output shaft (80, 280, 480) coupled to the gear train (88, 288, 488); a spline connection (90, 290, 490), located upstream of the rotor (52, 252, 452) or between the rotor (52, 252, 452) and the gear train (88, 288, 488), and comprising a first spline interface (102, 302, 502) provided on the drive shaft (70, 270, 470) and a second spline interface (106, 306, 506), enmeshed with the first spline interface (102, 302, 502), provided on the output shaft (80, 280, 480); and at least one pilot guide (94, 294a, 294b, 494), axially locating the output shaft relative to the drive shaft, located between the rotor (52, 252, 452) and the gear train (88, 288, 488), and comprising a first pilot element (110, 310a, 310b, 510) provided on the drive shaft (70, 270, 470) and a second pilot element (114, 314a, 314b, 514) provided on an outer surface of the output shaft (80, 280, 480), wherein the first pilot element (110, 310a, 310b, 510) axially overlaps, at least in part, the second pilot element (114, 314a, 314b, 514), wherein the at least one pilot guide (94, 294a, 294b, 494) is axially spaced from the spline connection (90, 290, 490), and wherein the turbine (50, 250, 450) includes a rotor centerline (64, 264, 464) and has a rotor width (58, 258, 458), wherein the spline connection (90, 290, 490) is axially spaced from the rotor centerline (64, 264, 464) a spline distance (92, 292, 492) that is greater than or equal to half of the rotor width (58, 258, 458).