R46 married pair 6216+6218 out of service because of a horrible flat wheel on 6216. Set is being towed to Coney Island Yard. It's also missing an end rollsign box, which makes me come up with this theory based on other married pairs' past situations:
Pitkin Yard may be using the married pairs for spare parts whenever they're not in active service. Then, they could send them to Coney Island Yard (or 207th Street Yard?) to receive more parts.