At the end of S02E06 of NuWho, The Age of Steel, the Tenth Doctor and his companions are clinging to John Lumic's Zeppelin via a rope ladder as they escape from the Cyberman Factory.
Moments before, Mickey had disabled all of Lumic's Cybermen's emotional inhibitors, causing (most of) them to self-combust as they became overwhelmed by their emotions.
A surviving Cyberman manages to climb onto the rope ladder and starts to climb it, before the Doctor throws his sonic screwdriver to Pete Tyler and tells him to use it to melt the rope below him, causing the Cyberman to lose its footing and fall to its death.
Because this Cyberman's emotional inhibitor had been disabled, it's likely that it had reverted to being a human being in a Cyberman's suit, with all of its previous memories and experiences, just like Sally Phelan earlier in the episode. This seems evidenced by the Cyberman's very human-like screams as it falls.
Because of this reversion to its harmless human state, it's likely that this Cyberman meant no harm to the Doctor and his companions, and was simply trying to climb aboard to safety just as they were.
Did the Doctor knowingly kill an innocent human being?