Date: 202004
Local time of day: 1801-2400
Flight conditions: IMC
Weather elements / visibility: 5
Light: Dusk
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise; Landing
ATC / advisory: Center ZZZ
Aircraft component: Flight Dynamics Navigation and Safety
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew FLC Overrode Automation; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: First Officer's leg. Just after rotation the Captain's PFD instruments were erratic. The indicated airspeed increased rapidly and the Overspeed warning sounded followed shortly thereafter by a Windshear warning. Airspeed increased to the max and then slowly started to reduce. First Officer's instruments were stable and as the flying pilot I continued to fly. Captain selected the Alternate ADC as we continued the climb out. Sporadic Mach/Speed trim and Rudder Ratio EICAS messages displayed. The First Officer's flight director had some momentary erroneous indications but settled down. When everything had stabilized sufficiently for a period of time and we were passing 8;000 ft.; I called for the autopilot and the Captain selected the right autopilot to command. The airplane flew well for about 5 minutes and then the 'Autopilot' EICAS message appeared. I disconnected the autopilot and we tried the Center autopilot but it was not operating with sufficient stability. We were assigned and cleared to FL370 but leveled at FL270 to remain below RVSM airspace as directed by the QRH. The remainder of the flight was flown in manual flight. I had an intermittent Speed LIM warning on my PFD which lasted only a short time. We continued to receive occasional intermittent EICAS messages as well as status messages (Flap/Slap Electric). Shortly after we leveled off we received a [message] to change our destination to ZZZ for company operational needs. After referring to checklists and discussing issues at hand we contacted Flight Control via JetComm. We relayed our status to Flight Control and [Maintenance]. ZZZ weather was 1;000 ft. broken and ZZZ1 was 4;500 ft. broken and we agreed with Flight Control that ZZZ1 was the better option. We ran the airspeed unreliable checklist which drove us to a flaps 20 landing. We [advised ATC] due to the abnormal flaps 20 landing and single ADC operation. We asked ATC to pass along a request for [Crash Fire Rescue] at ZZZ1 and the reason for our declaration. We briefly switched flying duties during the flight for duty convenience and to provide a brief break. We discussed best options for the approach and landing. I continued to fly as Pilot Flying. We briefed that the Captain would continuously crosscheck Captain and First Officer instruments with the standby attitude instrument indications. If there was any major discrepancy; he would take the airplane if the standby indications were more reliable. I briefed the approach and potential go around including pitch and power settings. We asked for and received an alternate straight out missed approach procedure. The approach was uneventful; I configured early and landed without incident. All indications were normal and stable during the approach.




Synopsis: B757-200 First Officer reported that an ADC malfunction resulted in a diversion.