You do not need to select the three CMD buttons. Only one needs to be ON. Once the ILS is captured and you are about 5 - 7 nm from the runway threshold, all three CMD buttons turn ON and the AUTOLAND 3 light comes on.

Put simply. One CMD button MUST be ON, the others come on AUTOMATICALLY. You don't need to do anything except press the LOC and APP buttons at the appropriate times to capture the ILS and G/S.

Hope this helps.

Mark