Date: 202006
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Rain; Thunderstorm
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: FADEC / TCC
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Workload
Second reporter function: Other / Unknown
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Aircraft was actually [Tail Number X]; not [Tail Number Y]. It was grounded for more than 72 hours prior to our flight. Experienced significant delay (about 3.5 hours) due to thunder storm in terminal area. On pushback we got the EEC ALTN lights. Prior to taxi; with parking brake set CA (Captain) called [Dispatch] for patch to [Maintenance Control] ENG. Spoke to [Maintenance] about problem. Noted CA reset EECs; with ALTN extinguished. Inquired if there was any issue with continuing. Maintenance inquired about CDS flags or other cautions. None observed; OK to continue per [Maintenance]. Normal taxi out and initial takeoff. A/T disengaged almost simultaneously with the airspeed on FO (First Officer) reaching 100 knots (about 60 knots on CA display who was PF [Pilot Flying]). After startle; then quick cross check FO called out 100 knots and that there was a problem with airspeed indications ... noting his were normal. Transfer of PF duties prior to V1 ... normal rotation and takeoff by FO. Flew out on departure and got the aircraft cleaned up and safely away from the ground. Continued climb out to get out of MOD TURB in area due to TS to allow for troubleshooting. Informed ATC of the problem and asked to stop at FL200. Overspeed clacker started and we elected to stop the climb and initiate descent to 10;000 feet to continue troubleshooting. CA as PNF (Pilot Not Flying) was distracted by the EEC issue and slow to realize the Airspeed Unreliable situation. FO and [the jumpseater] did great job in keeping ACFT in safe envelope. Turbulence and distractions from warnings and annunciations contributed to PNF not completing all QRH checklists. Hand flown ILS to VIS runway XXL after speaking with flight attendants; passengers; and ACARS message to [Dispatch] of return and EMERG. Uneventful; safe; under max weight landing on RWY XXL. Taxi to gate followed by crash and fire. CA spoke to [Operations Management] on cell at gate after completion of parking checklist. ELB entry made. Spoke to local [Maintenance] in cockpit to try to assist in troubleshooting prior to aircraft swap to next gate for continuation of flight.CA supported by a superb FO yesterday (and [the jumpseater] who we brought into help). Good CRM and communication between crew. CA needs to do a better job separating PF / PNF to allow for more focused approach to identification of the problem and completion of all appropriate checklists. Spoke to [Union] member who noted that it seemed to be a good opportunity for learning; and I agree.


Second narrative: I was sitting in the jumpseat of Aircraft X on this particular day. ZZZ was experiencing very bad thunderstorms that morning. It was a [morning] scheduled departure that finally pushed back about [afternoon] local time. As we pushed back and started both engines I observed the crew doing their after start check. Running through their flow they received a Master Caution and it was in reference to the EEC's; both were lit Amber (Fault). The Captain reached up and reset them and the lights went out. He then called dispatch and [Maintenance Control] since we were off of the gate. He explained to [Maintenance Control] what happened and what he did. I looked at the FO (First Officer) and I was not quite sure if he was ok with that or not. [Maintenance Control] seemed to agree with the fix and we started to taxi out. Everything went well on the taxi out. We lined up on runway XYL received the takeoff clearance and then off we went. It was the Capt's leg. The next set of events I was a little unsure for a few seconds of what was taking place because both pilots had on Bose headsets so I could not hear their conversation clearly as their voices were not loud enough for me. This is a guess; but somewhere around 100kts I witnessed a transfer of controls and I saw a Master Caution light up. I looked straight up and I saw the EEC's both amber again. I then looked back at the flight controls and I figured out why they exchanged flight controls; I saw the IAS Disagree on the FO PFD. Going back to the 100kts; I am guessing it was around that speed because we were on the runway for a while before the V1 and Rotate call. Once airborne both pilots performed the PF and PNF (Pilot Flying and Pilot Not Flying) duties according to procedures. When I saw there was a break I asked the Capt to please hand me his QRH so I can at least help them get started on the problem. I looked up IAS Disagree and that led me to the Airspeed Unreliable checklist in the QRH. I turned to the table of content pages for Airpeed Unreliable 737-800 and handed the book to the Capt. Honestly I did not realize that was not the beginning of that checklist; I saw 737-800 under Airspeed Unreliable and I just went to 737-800 Airspeed Unreliable. It led me to the climb charts for the non-normal. I handed the QRH to the Capt. and he looked through the checklist. He read the tables and then decided to run the EEC checklist. Again he reached up and reset the EEC's I then stated and the FO backed me up; the EEC's are not your problem right now it's your Airspeed. He kept insisting that the EEC's needed to be handled first.During this time the FO was hand flying and getting bumped around pretty bad by the weather. We were still climbing out and then the Capt decided to [advise ATC] and return back to ZZZ. I believe we were at 13;500 climbing to 16;000. I then noticed on the FO PFD Altitude Disagree amber message. I was then fixated on assisting the FO with any airspeed deviations and altitude issues. I did see the FO had a really good handle on cross checking his PFD with the STBY PFD. He was doing an excellent job with everything. As we started a descent back down to 10;000 ft the Capt. Airspeed was doing like 330kts plus giving us a clacker and I think stick shaker. It was because of the erroneous info coming from the Capt side. Between 12;000 and 10;000 ft the IAS Disagree went away and the Altitude Disagree went away. Once we leveled off at 10;000 ft the Capt set the airplane up for arrival back into ZZZ and did the whole briefing for the FO; contacted OPS. During this time I [advise] the FA's (Flight Attendants) and spoke to the passengers. At this time in my mind I was wondering why there was no memory item in the checklist. However I later realized during debrief with the FO when I went to 737-800 that was not at the beginning of the checklist. We then started our descent and headed back for ZZZ and the IAS Disagree came back. As the FO asked to be configuredthe Capt. Airspeed went to 45kts again giving him the clacker and the shaker then I remember the airplane said either 'Too Low' or 'Airspeed' I can't remember which one. Again I couldn't hear all communications between the pilots because they had the BOSE headsets but I did hear the FO say something about running the QRC. The Capt. hesitated for a second but then ran through the Airspeed Unreliable QRC. He read through it and I couldn't see it clearly to back him up. As the clacker was going off the Capt turned his attention back to the PF. Then finally I said; 'Flight Director's need to be off then on to flying pilot' at the same time the Capt was reaching up on the MCP to turn them off I assume. Once that happened and the Master was back on the FO side then things calmed down. The FO landed the aircraft on XXL; again doing a superb job; and the Capt took the aircraft about 100kts and barked orders to tell the Fire Trucks no assistance needed and to tell the tower what gate they were going to. Then he asked me to tell the Pax 'Remain Seated Remain Seated' as we pulled off of the runway. We got to the gate and we did a small debrief but then the Capt contacted the {Operations Management]. The FO thought he forgot something on his initial walk around so he went back out for a postflight walk around just to double check. Fire Dept came to the Aircraft to check on the crew and then I exited. Once we swapped airplanes and was on our way. Overhearing what I could of the crews conversation; they were continuing the debrief they had on the last airplane after I walked away. To me it sounded as if the FO was questioning the Capt of why they did not abort the takeoff as they were both referencing the FOM and what constitutes an Abort. The Capt stated he only had a split second to make a decision of a highspeed abort and felt that the situation was under control so it was better to take the aircraft airborne because highspeed aborts can be dangerous. The FO was not too happy with that answer and they discussed this more. The FO then reviewed the EEC checklist and in the checklist it makes mention of messages on the Control Display Panel. The FO says that alone should have stopped him from running that checklist. The Capt did not think there were any messages on the Control Display and then I backed the FO up and said well you did have IAS Disagree and Altitude Disagree messages. The Capt said that he did not see the Altitude Disagree message. In the end the Capt did accept responsibility and said that once the plane was under control and the FO was flying that he should have disconnected and managed the situation better and read the checklist more careful. Instead he admitted that he was more concern of the aircraft being flown. They seem to agree on that and the Capt. did say he learned a lesson and will reflect on it. They both discussed about writing the [report] and then we continued on our way uneventful. There are a lot of lessons to be learned here; I am just not sure if the Capt had trust in the FO. Not saying this particular FO but just FO's in general. This could have been handled a lot better had the PNF taken input better and took his time.


Synopsis: B-737 flight crew; including jumpseat pilot; reported an uneventful emergency air return due to a malfunctioning EEC on takeoff.