Bell Helicopter Textron Inc., Fort Worth, Texas, is being awarded a $581,113,421 modification to definitize a previously awarded advance acquisition contract (N00019-13-C-0023) for the manufacture and delivery of 15 Lot 12 UH-1Y, 19 Lot 12 AH-1Z, one Lot 13 UH-1Y and 21 auxiliary fuel kits for the Marine Corps and government of Pakistan.  The aircraft contract line items on this modification are fixed-price-incentive and the auxiliary fuel kit contract line items are firm-fixed-price.  Work will be performed in Fort Worth, Texas (60 percent); and Amarillo, Texas (40 percent), and is expected to be completed in August 2018.  Fiscal 2014 and 2015 aircraft procurement (Navy) and foreign military sales funds in the amount of $581,113,421 will be obligated at time of award, none of which will expire at the end of the current fiscal year.  This contract combines purchases for the Navy ($523,193,712; 90 percent) and the government of Pakistan ($57,919,709; 10 percent) under the Foreign Military Sales program.  The Naval Air Systems Command, Patuxent River, Maryland, is the contracting activity.