I have no idea what the operating rules are today for DC traction units in an MU'ed consist with AC traction units. When the BN purchased all those SD70MAC units, back in the early 1990s, they first had a policy of not mixing the two different types within an MU consist. A bit later, the "policy" was modified that should DC and AC units be mixed in an MU consist, the DC units MUST be in the lead.
After the merger with the AT&SF and the BN, all such "mixing policies" went out the window! Naturally, it didn't take long for an AC & DC MU consist to be assembled with the AC unit/units in the lead, and again it didn't take long for them to burn the traction motors out of the DC unit! Naturally, the Engineer got the blame! So much for proper training of operating crews and motive dispatchers.
