Date: 201507
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dawn
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Training / Qualification
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: Incorrect takeoff weight entered into ACARS Takeoff Performance module.Maintenance was called out to replace the performance computer. Maintenance MEL'd the performance computer and flight pushed late due to required procedures. Dispatch and I agreed I would retrieve takeoff data via ACARS. During briefings I verified with First Officer (FO) we would use the ACARS for in place of the performance computer takeoff data. He entered the ATIS information into the ACARS Takeoff Performance page and we waited for the loadsheet.  The load sheet arrived and weights were entered and takeoff data reviewed; speeds set etc. I then called for the Before Start Check. I verified Zero fuel Weight (ZFW) checked; and takeoff weight crosschecked with the FMC Performance page and the ACARS Takeoff Performance page. Acceleration seemed normal; rotation was noticeably sluggish and I stopped the rotation and let the aircraft fly off which it did at 150 KIAS. I delayed the gear up call; told the FO to apply climb thrust as we were in climb two. This occurred following retracting gear. The remainder of departure was uneventful.  Upon reviewing the ACARS performance module it became apparent the ZFW was entered into the Takeoff Weight (TOW).  All of our data was incorrect.First; neither of us recognized the ZFW was entered into TOW on the ACARS page. Also neither of us had used this procedure before and we haven't discussed it in ground school to my recollection. Third; the habit pattern is to enter ZFW and TOW in the performance computer. Only TOW gets entered into the ACARS Performance page. Finally; I verified the data was correct because I saw 117.1 which was our ZFW and verbalized it. When the FO read TOW on the checklist I saw 150.1 on the FMC/CDU Performance page and verbalized it but did not catch the incorrect entry in the ACARS Performance page. This error has the potential to be catastrophic and needs some exposure in training and operations.


Second narrative: During preflight the performance computer was found to be not functioning properly. Maintenance was called out and was unable to fix the performance computer so it was MEL'd. Now we were late and could not get the loadsheet until a three-way call was completed with Dispatch and Maintenance. When we received the loadsheet; my thought process was that of inputting the Zero Fuel Weight into the box; not the takeoff weight; which was what was required in the data box in the takeoff Performance display in the CDU. This was the error that caused our take off data to be incorrect. I was conditioned to program the CDU and the performance computer with the Zero Fuel Weight. When we completed the Before Taxi Checklist; we had looked up the appropriate pages on the CDU to cross check the data. Due to both of us using this new method; we misread the takeoff weight and the Zero Fuel Weight. While lifting off; the aircraft felt sluggish; so we increased power to max takeoff. The rest of the takeoff and climbout was uneventful. While at cruise; we found our mistake in our takeoff data.I need to slow down and read the boxes in the CDU to make sure I'm inputting what is being asked for! When doing something new; take more time and get it right.


Synopsis: A B737-700 Flight Crew reports departing with an inoperative performance computer by entering weights from the ACARS into the CDU. The First Officer enters the zero fuel weight into the box that requires takeoff weight; resulting in sluggish takeoff performance. Thrust is increased after the gear is retracted.