Medium Large Transport
Flight Crew Air Transport Pilot (ATP)
Distraction; Confusion; Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Human Factors
Descending on the WEEDA 2 arrival into DTW we were cleared to 12;000. When reaching the selected altitude the Captain notified me that he was going to make a passenger announcement and I was to monitor the radios. I was the pilot flying. As soon as he switched off I received instruction from ATC to slow to 200 knots. I found this to be an odd instruction for how far out we were; but I repeated the instruction and heard no correction or objection from ATC. I started to slow the aircraft. The captain finished his passenger announcement and was back on the radio. I notified him of the change and as we were reaching about 230 indicated the same controller came back on and questioned why I was slowing. The captain asked if she instructed us to slow and she said 'No; speed back up.' The captain told the controller we were speeding back up and it was left at that. We increased our speed. We also had a jump seat onboard this flight and he also recalled hearing a call to slow to 200 knots.After that we heard another instruction from the same controller who told us to descend to 5000. The Captain read it back and I began a descent. As we were about through 10;000 the controller came on again and instructed us to maintain 11000. We immediately stopped the descent and started to climb again. As we started to climb the controller came on again before reaching the assigned altitude and told us to descend to 9000. The Captain now got on the radio and questioned the controller as to what her intentions were and as he was doing that we received another altitude assignment of 7000 again from the same controller. The Captain called her and wanted her to clarify that she was talking to us because at this point it became rather confusing. She told us that yes; it was for us; and handed us off to the next controller and the rest of the flight was smooth.
Air carrier First officer reported confusion with ATC reference speed control and altitude descent.