B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Deviation - Speed All Types
Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; Flight Crew Returned To Gate; Flight Crew Diverted; General Flight Cancelled / Delayed
Aircraft
Red eye flight. The first event was a pushback and engine start. After the engines were started; a Master Caution illuminated with ENG on the Recall panel and EEC ALT lights. We talked to Maintenance and returned to the gate. Maintenance did engine runs with no return of EEC ALT lights. So; we were signed off; reboarded; and taxied back out for takeoff. Around 80 knots my First Officer and I noticed that the First Officer's airspeed indicator dropped suddenly and we had an IAS Disagree message. Then it seemed to recover somewhat; but now we were above 100 knots. My First Officer's indicator was still lower than mine. After looking at our three IAS indicators and remaining runway; I called V1 and rotate at what I thought was close. On climbout our airspeed differences were inconsistent. Then as we climbed they became greater and stayed between 10 and 15 knots different; with mine slower. The standby IAS was closer to my First Officer's; but the First Officer's indicator seemed more erratic than mine. The standby IAS was about 3 knots less than my First Officer's.We stopped our climb at FL320 instead of FL350; and told Approach that we didn't want to leave radar and VHF without solving this. I called Maintenance; with little help. They just said that their computers were slow; so I did a VHF phone patch with Dispatch and a 3-way call to Maintenance but that was taking too long and we were leaving VHF coverage; so I tried a HF phone patch; but Dispatch and Maintenance were unreadable. I received a free text message that said Captain's discretion; so we decided that we didn't want to cross the ocean in the middle of the night not knowing what our airspeed was. We wouldn't know how much margin from Barber Pole to minimum speed we had; and we had nowhere close to divert. We returned to our departure airport; and we did a smooth; overweight landing with no problems. Maintenance blew out the pitot static system and did a test and we continued or flight later that morning.
Late in the takeoff roll we got an IAS DISAGREE display and decided to continue. The display with differing airspeeds between the Captain and First Officer was from 5-15 knots and intermittent. After cleaning up the airplane and running the after takeoff checklists; I took the radios and had the airplane while the Captain ran the checklist. The checklist did not give much guidance to our situation. As we continued climbing and continuing on the flight; the Captain contacted Maintenance and also ZZZ on VHF and HF. The unreliable airspeed indication throughout the climbout became constant and consistently an 8-17 knot difference. We decided that the safest course of action was to return to [our departure airport] and not continue on an ETOPS flight in the middle of the night with an unreliable airspeed indication. We diverted back to [departure airport] and landed over weight without incident.
This Boeing 737 crew received EEC ENG and EEC ALT Master Caution warnings after engine start and returned to the gate for maintenance attention. After Maintenance sign-off; the flight again departed; and during takeoff and climb they now noticed airspeed indicator discrepancies and received an IAS Disagree message; and returned to their departure airport.