You have requested our opinion with respect to fully functional aircraft dual controls under 91.109 and 61.45 of the FARs. After further discussion, we have clarified your inquiry as consisting of three questions. The first is whether 91.109(a) requires braking capability for both pilot positions when instruction is being given. The second is whether brakes must be available for both pilot positions for the performance of a practical test under 61.45. The third is whether brakes must be available for the performance of a practical test for a flight instructor certificate also under 61.45.
This is a companion discussion topic for the original entry at https://www.avweb.com/features/toeing-the-line-the-alkalay-memorandum