Date: 201811
Local time of day: 0601-1200
Location: ORD.Airport, IL
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class B ORD
ATC / advisory: TRACON C90
Aircraft component: Autopilot
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Human-Machine Interface; Situational Awareness; Workload
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew FLC Overrode Automation; Flight Crew Returned To Clearance
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: While on WATSN arrival at FL250 and expecting to cross HULLS at 120 [heading]; we were issued a descent to cross PRISE intersection at 12;000 [feet]. Aircraft was level flight; VNAV / LNAV engaged with autopilot on; utilizing good CRM. At approximately 35 miles from PRISE; Pilot Monitoring noticed we should have begun our descent (3 miles per 1;000 feet at normal descent speeds); but verified the path at our increased speed (310 KIAS) that we still had a few miles of level flight remaining. Pilot Monitoring made PA to cabin and upon return ATC asked whether we would make our crossing restriction at PRISE. At that point; both Pilot Flying and Pilot Monitoring realized we were no longer in VNAV and Pilot Flying selected LVL CHG and we began a high speed descent in accord with ATC instructions to maintain 310 or greater. Pilot Flying increased airspeed to 320 and extended speed brakes to make the crossing at 12;000 [feet].When within 5 kts of barber pole; both pilots expected the autopilot to slowly pitch up when there was a sudden increase in airspeed due to unexpected turbulence and the high speed alert sounded and we exceed Vmo by 15-20 kias. Both pilots announced upset and Pilot Flying disengaged autopilot and slowly made the upset recovery to desirable state. We flew the rest of the arrival and landed in ORD without incident. We made a MX entry and talked to maintenance personnel upon arrival at gate.


Second narrative: On descent into ORD on WATSN3 star ATC issued descent from 26 to 25k. Pilot Flying initiated DES NOW on DES page executing VVM with Pilot Monitoring. Aircraft descended from 26 to 25k on autopilot B with LNAV/VNAV engaged. ATC issued cleared us direct PRISE and to cross PRISE at 12;000 [feet] while maintaining speed of 310. After approximately 1 minute; autopilot was flying when ATC called and asked if we would be able to make PRISE at 12k. Both Pilot Flying and Pilot Monitoring simultaneously noticed VNAV was disengaged. Pilot Flying immediately reached up and engaged LVL CHG mode; extended speed brake and verbally stated the change. Pilot Monitoring acknowledged and aircraft began uneventful descent. Both Pilot Flying and Pilot Monitoring stated that it was coming down nicely and making PRISE at 12;000 [feet] shouldn't be an issue. Pilot Flying selected 320 in the IAS window which was approx. 20 kias below the barber pole. Pilot Flying also verbalized that he wanted to maintain plenty of buffer below VMO to which the Pilot Monitoring concurred. Passing thru approximately 17;000 [feet]; the aircraft pitched slightly over and approached VMO. Thinking the autopilot would raise the pitch angle to catch the speed increase; the Pilot Flying paused to allow it to catch up. As it exceeded VMO; both pilot knew it was at an undesirable aircraft state. Pilot Flying then took hand control of aircraft and initiated upset recovery procedure. I am not sure if prior to doing this if the autopilot was still engaged; but no audible warning was noted. Aircraft exceeded VMO by approx. 15 KIAS. Aircraft was hand flown back to desirable state making PRISE AT 12;000 [feet]. Approach and recovery flown uneventfully.


Synopsis: B737 flight crew reported an overspeed situation while on descent to ORD.