Date: 201910
Local time of day: 0001-0600
Flight conditions: Marginal
Weather elements / visibility: Haze / Smoke
Aircraft: MD-11
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Climb
Aircraft component: Air Data Computer
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Workload; Troubleshooting; Human-Machine Interface
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: First Officer was hand flying while climbing off of Runway XXR on the SID while departing ZZZZ. I noticed the airspeed decreasing while the airplane was increasing pitch. This was prior to flap retraction; so it was less than 3;000 ft. I verbalized to the First Officer 'watch your airspeed.' When I said this; the First Officer looked at his Indicated Airspeed and then at mine; while I was doing the same. We realized that one of the airspeed indicators was incorrect. We were able to determine that it was most likely the First Officer's airspeed that was incorrect based on the standby altimeter and airspeed indicator that was matching mine. I took control of the airplane and was hand flying the airplane while the First Officer pulled out the QRH. We also started receiving multiple level-two alerts and noticed the autopilot and auto throttles were inoperative. The Flight Director failed [and] the FCP (Flight Control Panel) had dashed lines in the windows. During the climb the First Officer was converting meters to feet to be used. The FCP was not working at all. Airspeed; heading; altitude; and climbs were all determined and complied with without automation. No airspeed bugs; no altitude bugs; no heading bugs were usable. I tried to fly the departure via the magenta navigation line while constantly increasing/decreasing the map range to ensure terrain and aircraft separation.While we were trying to sort through the alerts to determine what checklist to perform we continued to climb when instructed up to 2;100 meters and finally 6;300 meters. Sometime early in the climb; The CAWS (Caution and Warning System) 'overspeed' was annunciating due to the First Officer's false airspeed. It was indicating it was exceeding the top foot. We realized that the proper checklist was the Airspeed Unreliable checklist. The CAWS 'overspeed' call lasted throughout the event making it extremely difficult to communicate with ZZZZ and the complete the checklist. The language barrier with the Controllers was equally challenging.In the climb we were also asked to speed up for traffic flow. While we were sorting out the problem I attempted to keep the airspeed around 280 kts to ensure we weren't exceeding any limitations; but giving us enough airspeed for performance. Shortly after this request as I leveled at 20;700 ft. (6;300 meters); we were queried about our altitude. My altimeter was indicating 20;700 ft. and my First Officer's altimeter was 1;000 ft. above and the Controller said we were showing 300 meters high. This was close to the time we were able to [advise ATC]. We [requested priority handling] to return back to ZZZZ. We were issued a left turn to 090 and started our descent. We were vectored back to Runway XXR and landed uneventfully.The language challenges; dealing with the constant 'overspeed' CAWS; multiple alerts in conjunction with a lack of automation made this event extremely challenging.When we were debriefing the event after blocking in; we determined the altitude deviation was due to the #2 transponder being selected but indicating [inaccurate] information. The First Officer did a great job managing the radios and performing the checklists. Maintenance at ZZZZ found an ADC #2 fault.


Second narrative: Early on climb out; before even cleaned up; First Officer's airspeed started increasing inappropriately. Pitch command from flight director became unexpectedly high even for the SID. Captain; who was Pilot Monitoring at the time; said something to the effect of watch your airspeed. Captain's airspeed was 10 kts. above the foot and mine was approaching slat retract speed. A very rough estimate of altitude would be 1;500 ft. I gave him the jet and he continued on the SID. We determined the standby system agreed with Captain's instruments. Adherence to the SID was maintained. After cleaning up flaps and slats; the airspeed differential continued to become worse. All the symptoms documented in the QRH become present; (FADEC; elevator feel; airspeed and altitude comparator; over speed warning). Additionally; the flight director; autothrottles; autopilot; and entire FCP (Flight Control Panel) became inoperative. The 'meters' value in the altimeters also disappeared. Eventually we reached a level off of 6300m (20;700 ft.). I was struggling to keep the Captain fed with all the altitude conversions. At 6;300 m.; ATC queried our altitude and made some comment about being off altitude. I don't recall the specifics. When this happened; we noted the First Officer's altitude was 1;000 ft. higher than the Captain's. Captain's altitude was 20;700 ft. +/- 50 ft. I do not recall the specific order of events; but it was at this time we [requested priority handling] and expressed a desire to return to ZZZZ. We by now had determined the unreliable airspeed checklist was appropriate. We were also being queried about fuel; people; dangerous goods; required assistance; landing weight and intentions all with the inherent language barrier. ATC was not out of line; but all; the questions; along with incessant CAWS over speed clacker and warning made communication very difficult. In addition the first vector was the long way around (270 deg) to a 090; on a metric altitude that had to be converted manually. ATC was also asking for our altitude; which I was trying to convert back to meters; and I'm not confident the translations were very successful. We saw the QRH note about certain tail numbers with the additional CADC (Central Air Data Computer) but elected not to accomplish because of proximity to landing and an anticipated unfamiliarity with the switch location. The First Officer's static switch was moved to Alternate and returned to Normal because nothing changed. At this point we were approaching final; with lots of ATC instructions and no approach built. So I elected to build the approach; communicated an abbreviated brief and get the approach and before landing checklists accomplished. The runaway came into sight at about 4 miles and and approximately 3;000 ft. At this point I felt it better to forgo any more checklist items and continue to land. The Captain seemed in concurrence. Landing was uneventful. After parking; we noticed the transponder in 2; which was the likely cause of ATCs altitude concern. It was probably reporting 1;000 ft. high.Maintenance deferred ADC 2.I don't feel this was unpreventable. We were not extremely fast to start the unreliable airspeed checklist; because of all the all the other associated warnings; but eventually got there. ATC is likely and rightly to be concerned about altitude. I believe the transponder reporting was wrong; but am confident we did not violate any altitude restrictions.


Synopsis: MD-11 flight crew reported Air Data Computer malfunction resulted in multiple instrumentation and system failures during climbout and required a return to land.