Date: 201807
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: MD-11
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Speed (Rate Sensing)
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: At FL350; M0.82; received Flap Disagree Level 2 Alert. The throttles then immediately went to idle thrust and the upper and lower foot on the CA (Captain) PFD (Primary Flight Display) came together. The flaps were indicating 0/ret on both the handle and the configuration page. Hydraulics were normal. All three airspeed indicators were indicating the same airspeed. All of these alerts were occurring intermittently but frequently and at a fast pace. Although I had disengaged the autothrottles to prevent them from going to idle; when the alerts occurred the autothrottles would re-engage as though the airplane was trying to go into High Speed Protection with no aural alerts. Because none of the checklists led us down the proper path; and we could not ascertain which pilot's side was the problem. We decided to return to ZZZ.We [advised ATC] and coordinated the return. The flight back was uneventful with the alerts occurring two more times. Things considered were the availability other airports enroute; the loss of a CADC (Central Air Data Computer) in RVSM airspace; and that it was a night oceanic flight. Maintenance is not sure. No faults were recorded. They did a precautionary replacement of CADC 1 and replaced FCC (Flight Control Computer) 2.


Second narrative: Cruise @ FL350; night VMC; approximately 1 hour after departing ZZZ. Airplane showed FLAP DISAG; and CA's (Captain) airspeed erroneously showed lower and upper feet meeting together on speed tape. Airspeed still correctly showed M0.82 on CA; FO (First Officer); and standby instruments. Airplane thought it had a speed problem due to CA's side airspeed; and autothrottles came to idle to correct that problem. We clicked off the autothrottles and pushed the power back up. After a few minutes; all errors disappeared. We started to run the FLAP DISAG checklist; but the erroneous indications disappeared before we finished that QRH checklist. Errors noted above continued to pop back up; then resolve on their own. We did not have erratic airspeed at any point; but the airplane transiently presented bad stall data on the CA's side. Crew elected to [advise ATC] and return to ZZZ. During the return; the same transient errors would reappear at irregular intervals. Once on final and configured to land; no errors reappeared. Approach and landing were uneventful.Exact cause unknown. Maintenance was unable to duplicate the errors. We left the aircraft after they had swapped a CADC (Central Air Data Computer) and were proceeding with checking the flap system due to the FLAP DISAG.


Synopsis: MD-11 flight crew reported experiencing intermittent airspeed related malfunction alerts.