Date: 201912
Local time of day: 0001-0600
Location: ZAN.ARTCC, AK
Weather elements / visibility: Windshear
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZAN
Aircraft component: Communication Systems
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Regained Aircraft Control
Contributing factors: Procedure; Weather; Aircraft
Primary problem: Ambiguous

Narrative: We were flying from ZZZ to ANC and we were CPDLC. We had been step climbing as our optimum altitude increased and had been at FL380 for probably about 20 or 30 minutes. We had been mostly smooth at that altitude with just a few occasional bumps. Just about 60 to 80 miles south of PADQ we received an ATC message to contact Center.At almost the same exact time we entered into an atmospheric wave and our airspeed began fluctuating. I was the PF (Pilot Flying) and the CA (Captain) was the PM (Pilot Monitoring). The CA switched to the given frequency and attempted to make contact with Center. At this time we received another message from CPDLC saying that communication with them had ended. After multiple tries and unable to reach Center the CA tried using guard. There was still no reply.At this point our airspeed fluctuations had increased to going between almost barber pole and almost low speed yellow band. I had disconnected the auto throttles in an attempt to not over speed. Our route of flight at this point was not on a published route and we saw no one on TCAS so the CA said (and I agreed) that we should descend. We descended down to FL360. This altitude was much smoother. During the descent we continued to try and contact Center and were trying to look up a different frequency. The CA was about to send Dispatch a message when a Company flight answered us on guard and gave us the frequency that they were on; but that still didn't work. Finally Company asked Center what frequency we should be on and passed it on to us. It was close to but not the same frequency as what CPDLC had given us; leading us to conclude they had given us the wrong frequency.Once in contact with Center we told them what had happened. They told us we could maintain FL360. We gave them a pilot report of moderate to severe atmospheric wave with +/- 15 to 20 kts. The flight proceeded without further incident. After landing the CA called Dispatch and informed them of what had happened.I believe we acted appropriately for the given situation. The CA used his [PIC] authority the aircraft flying safely and to keep from exceeding any airspeed limits.The lapse in communication seems to be due to being given the wrong frequency as well as being unable to reach Center on guard while simultaneously being disconnected from CPDLC.




Synopsis: Air carrier flight crew encountered an atmospheric wave which caused large fluctuations in airspeed and necessitated a descent.