B767 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 188; Flight Crew Total 3894; Flight Crew Type 432
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition
Aircraft
Climbing out of 10;000 ft. as we started to accelerate; I noticed that on the airspeed indicator that VMO was 260 kts. and the Minimum Maneuvering speed (Amber bar) was at 243 kts. After discussing this and making sure all cockpit instruments were in the correct position we thought it could be a flap sensor failure of some type so we cycled the flaps even though the flaps were indicating up and all indications were zero; every indication remained the same and all airspeed indicators were the same on the First Officer and Captain's side still 260 kts. VMO and 243 kts. Amber bar. We got in touch with [Maintenance Control] as there were no lights or indications of a problem there were no checklists to be run. We [advised ATC] and thought we might be able to dump some fuel. The center tanks were already approaching zero so we had no way of dumping fuel. We requested vectors back to ZZZ and we were about 35;000 lbs over max landing weight. We notified Dispatch of our intent to return to ZZZ. The aircraft was handling normally so we figured it was an indicating error not a control error so I elected to burn off some fuel enroute back to ZZZ so we could land at a lower gross weight; ATC was very helpful using vectors and letting us go slow as I wanted to extend the flaps before doing an approach to see if they would extend and if we would have any controllability symptoms before we got into the landing phase. The approach and landing were normal but we landed at 340;000 lbs about 20;000 lbs. over landing weight; it was a smooth soft landing. As we taxied to the gate we had high brake temperatures due to the landing weight but they seemed to cool normally. After the jetway was on the airplane the flight crew discussed the event and what we did right and wrong per the checklist and we determined that our return was a success with good crew coordination. After the flight deck door was opened a maintenance personnel came up to the cockpit and told us that they had found the issue it was a switch in the E&E compartment that was in the wrong position and it keeps VMO below gear speed. When the switch was put into the correct position VMO went to a higher position about 330 kts. All items were written up in the logbook that pertained to this event.
Flight Crew reported the airspeed indicators displayed lower-than-normal Vmo and Minimum Maneuvering speeds resulted in a diversion.