Date: 201811
Local time of day: 0601-1200
Location: ZMP.ARTCC, MN
Flight conditions: VMC
Weather elements / visibility: Turbulence
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZMP
ATC / advisory: Center ZMP
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Human factors: Confusion; Communication Breakdown
Second reporter function: Pilot Flying; Captain
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: I checked on with Minneapolis Center. After being on the frequency for about 5-10 minutes; our ride started to deteriorate. The Captain (CA) got on the radio and told the controller that our ride was light turbulence at FL370 and asked about rides up ahead. The controller responded that he did not have anybody at FL370. The CA then requested FL350. The controller cleared us to descend and maintain FL350; so that is what was selected and the CA initiated the descent. When we were descending through FL355 the controller asked us why we had not started our descent. I said [callsign] is in the descent to FL350. The controller then said he told [another company callsign] to descend to FL 350 and we needed to return to FL370.  I said we are at FL352 and you want us to climb back to FL370? He did not answer this question and instead this same controller that cleared us to FL350 then asked what our flight number was and where are you? The CA got on the radio and said we are [callsign]; we are 80 miles south of DSM and we were the ones that asked about the rides and requested FL350 and you cleared us to FL350. The controller's immediate response was to have us switch frequencies to Minneapolis Center. I checked in on the frequency and stressed we were at FL350. Upon initial contact; the controller switched us to Kansas City Center. Upon checking in on Kansas Center frequency and stressing the FL350; this controller said we descended to FL350 with no clearance and that nobody was talking to us while this happened. The CA then said on the frequency that we were cleared down to FL 350 by a previous controller and were continuously in communication with ATC at all times. The KC center controller asked who cleared us and we said it was the guy on frequency. We stayed at FL350 and did not hear anything more from ATC about what happened. Not scheduling similar sounding flight numbers around the same time of day would help in preventing confusion. We used and heard our [callsign] throughout the entire conversation with ATC. At no point where we ever told of [company flight with similar callsign] until the controller said he was telling [company flight with similar callsign] to descend. I think the similar sounding call signs were confusing for ATC because from my perspective [company flight with similar callsign] was not on the same frequency because I never heard them on frequency (and we were not told of similar sounding call signs).


Second narrative: During the Flight at FL370 started to experience continuous light turbulence. Talking to ATC on frequency 119.72. I believe it was Denver Center; we asked what the lower altitudes were for turbulence and reported our conditions. ATC said the ride was better at FL350 so we requested FL350. He gave us the lower altitude and we read back our call sign and the Altitude and descended to the lower altitude. As we were leveling off at FL350 which was a good ride we heard Center ask [company flight with similar callsign] are you leaving FL370? There was no answer so when he asked again we said are you asking for [our callsign]? And we said we left FL370 and were leveling off at FL350. ATC said we need to still be at FL370. We said do you want us to go back to FL370? He replied that he had no idea who we were. At this time the First officer was talking on the radio; so I keyed my mike and said we were the ones that just talked to you about the rides at FL370 and you cleared us to FL350. He asked our position and said we shouldn't be with him we should be on 118.82. We had checked on previous and were with him for a while before any of this happened. We went to frequency 118.82 and checked in. She asked our position and sent us to 113.72. When we checked on she said they all were looking for us and nobody knew where we were and nobody was talking to us. They all assumed we were still supposed to be at FL370; and were aggravated that we were at FL350. We said we were cleared to FL350 and were then asked what frequency cleared us to FL350. We were never cleared to go back to FL 370 by any of the ATC controllers. The ATC center that talked to us about turbulence never tried to hand us off previously and we hadn't been on the frequency more than about 10 minutes. I feel that he may have lost us on radar or forgot about us. He thought he was talking to a different flight but the flight number he was looking for [company flight with similar callsign]. We never heard [company flight with similar callsign] answer even though he called for them at least 2 times. He obviously was confused about who was in his sector. We were never out of radio communication with ATC even though they didn't have any idea who we were. We were alert at all times and don't feel like we missed any radio calls or didn't check in when handed off to a different ATC freq.


Synopsis: Air Carrier flight crew reported confusion and miscommunication with ATC due to a similar callsign situation.