American Airlines will deactivate Shares and fully transition US Airways flights to its Sabre reservation system on Oct. 17,

according to a letter the carrier sent to corporate and agency partners on Friday. It will begin its previously announced three-month transition period on July 18. All tickets sold from July 18 on for flights that depart Oct. 17 or later will be American reservations on the Sabre system. US Airways tickets booked for flights that depart between July 18 and Oct. 16 will remain on the Shares system. US Airways tickets already booked for flights that depart on or after Oct. 17 will move to the Sabre system.