Air-start assembly and method

An air-start assembly for an aircraft gas turbine engine having a fan powered by a low pressure turbine through a first shaft, and a compressor powered by a high pressure turbine through a second shaft disposed coaxially around said first shaft comprising;

• a gear train selectively operatively joined between said first and second shafts by a selectively engageable first clutch for transmitting torque through said first clutch only in one direction from said first shaft to said second when said fan is windmilling for driving said second shaft to allow an air-start of the gas turbine engine during flight;
• and
• a second clutch operatively joined to said gear train and selectively engageable at speeds of said second shaft below a predetermined release speed, and disengageable at said release speed and above;
• wherein said gear train has a speed ratio greater than 1.0 from said first shaft to said second shaft;
• wherein said gear train comprises;
• a first gear having a hub operatively joined coaxially to said first shaft, and further having gear teeth;
• a second gear having a hub operatively joined to an idle shaft and having teeth joined in engagement with said first gear teeth for transmitting torque therebetween;
• a third gear having a hub operatively joined to said idle shaft, and further having gear teeth;
• a fourth gear having a hub operatively joined to a starter shaft, and further having gear teeth joined in engagement with said third gear teeth;
• a fifth gear having a hub operatively joined to said starter shaft, and further having gear teeth;
• and
• a sixth gear having a hub operatively joined to said second shaft, and further having gear teeth joined in engagement with said fifth gear teeth;
• wherein said second clutch is operatively joined between said idle shaft and said third gear hub for selectively allowing torque transmission from said idle shaft through said second clutch to said third gear below said release speed of said second shaft, and for preventing torque transmission from said third gear to said idle shaft at and above said release speed.