Date: 201901
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Initial Approach
ATC / advisory: TRACON ZZZ
Aircraft component: Air Data Computer
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Troubleshooting; Workload
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: With the Captain as Pilot Flying (PF) and on heading 090 at 4000 ft we were cleared to turn heading 030 and join the 36L LOC. In the turn to intercept the LOC the PF airspeed and altitude tapes began to increase rapidly. This caused the autopilot to disengage; the Auto Throttle to disengage; the L and R ENG EEC to indicate off; the TERRAIN SYS OVRD to FAIL and the L transponder to fail. In addition; there were comparator indications on the PFD and the overspeed warning sounded. The altitude and airspeed tapes did not freeze or slowly indicate a difference. It was rapid and continuous. The comparator indications were present but due to the complexity of the situation I do not recall each comparator that was displayed. Once all the above occurred while in the turn the PF did his best to quickly cross check and determine which flight instruments were providing good information and which were providing bad information. We were able to determine the right avionics and standby avionics information was good and the left air data information was bad. This was all occurring while hand flying and trying to maintain the LOC course and assigned altitude. Due to the loss of the left transponder ATC approach was not receiving an altitude input from us and asked to verify altitude. The Captain as PF when the failure occurred transferred controls to the First Officer once the airplane was stable and the determination was made that the First Officer (FO) avionics information was accurate. The First Officer became the PF and the Captain became the Pilot Monitoring (PM). The Captain assumed radio communication and advised ATC that we have an avionics malfunction. The PM then reported to ATC our current altitude and deviation from the LOC as we worked to center the LOC guidance. With the airplane stable at 4000 ft and on the 36L LOC the PM told ATC that we would like a vector away from the immediate airport area to reference our checklist and would like to stay within 20 miles of the airport. Due to the busyness of [the situation] the PM requested that ATC provide holding type vectors and that we could not accept a holding pattern. This was to prevent either pilot from being heads down setting up the FMS. Once on a heading out of the immediate approach traffic area and stable at 4000 ft the PM referenced the QRH. There were approximately 5 Amber CAS messages displayed associated with the failures. The L ENG EEC and R ENG EEC messages were referenced in the QRH. This guidance did not apply to the root of the problem based on the air data system failures and we discussed that we should focus on the Airspeed Unreliable checklist. We followed the Airspeed Unreliable non-normal QRH procedure. The PM completed the checklist and the PF monitored the airplane. Following the checklist guidance; we reengaged the autopilot to help with workload management. Once the checklist was complete and we were holding on the deferred items the PM (Captain) brought to the PF's attention that as an additional tool we could radio Dispatch and have them communicate with Maintenance to determine if there were any further actions we could take with their guidance. At the time we had approximately 13;000 lbs of gas and both agreed we had time to get additional guidance. The PF took over ATC communications and the PM communicated with Dispatch. We contacted Dispatch and relayed all our indications to them and they communicated with Maintenance. Maintenance's response was they felt the L ADC was bad and to use the R ADC information; just as the checklist guidance provided. After finishing communication with Dispatch the PM summarized our situation and asked if the PF had any input or questions prior to continuing. We both agreed we were on the 'same page' and setup and briefed the approach. We advised ATC we were ready for the approach and told them we would like to join the ILS 36L outside of ZZZZZ1 at 4;000 ft. ATC provided vectors and then switched us to final Approach Controller. On the approach frequency the controller changed our landing runway to 36C. The PM setup the XXC ILS and briefed the PF on the changes. We joined the LOC XXC approximately 10-15 miles outside of ZZZZZ at 4;000 ft. I told the Approach Controller we would be in a non-normal approach configuration and our airspeed would be higher than normal. I also told the controller not to put anyone in front of us to reduce the likeliness of a go-around. On the final approach course the Approach Controller asked us to slow twice and to descend. The first airspeed reduction was not an issue and we slowed. He asked us to descend to 3;000 ft and I told him we would like to stay at 4;000 ft and follow the GS guidance down on the approach. He approved this and then asked us to slow again. I told him 'you are not making this easy; we are [a priority] aircraft'. I told him this because we were [a priority] aircraft and our plans were to be stable and configured on the ILS no later than 10 miles out to reduce our possibilities of becoming unstable on the approach. We continued the ILS XXC Approach with the FO as PF and the Captain as PM. The approach and landing were normal. Per our plan and brief; the PF (FO) brought the airplane to a stop on the runway and then transferred the controls to the Captain to taxi. Once clear of Runway XXC we cancelled the emergency and taxied to the gate. Unreliable Airspeed due to ADC failure


Second narrative: [Report narrative contained no additional information.]


Synopsis: An air carrier flight crew reported experiencing an ADC #1 failure; failure of the Captain's Airspeed and altitude. The crew performed the QRH checklist and landed without incident.