Date: 201701
Local time of day: 0601-1200
Location: BNA.Airport, TN
Light: Dawn
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower BNA
Aircraft component: Laptop Computer (performance; planning; etc.)
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Time Pressure
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Weight And Balance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Company Policy; Procedure
Primary problem: Ambiguous

Narrative: During the process of inputting the takeoff data; the battery went dead on the [performance computer]. Being the first flight of the day; we elected to have dispatch run the takeoff data and we were going to let the [performance computer] charge in the cradle. When we got the numbers; we failed to realize that dispatch had used our zero fuel weight as our takeoff weight. I attribute the oversight on our part due to our lack of familiarity to getting our takeoff data in such a manner. We realized our error too late in the takeoff to effectively adapt other than to just rotate slower to accommodate for the slower bugged speeds.


Second narrative: At pushback the [performance computer] lost charge and shut down; making the Before Pushback Checklist undoable. The First Officer (FO) contacted Dispatch with our takeoff information in order to receive takeoff data. This took a while to complete. We already knew that we were going to be late into [our destination] due to strong headwinds. We received the data in an unusual two-transmission format; first receiving a read back of our transmitted input; then another transmission containing our actual settings. All appeared normal; though I had a nagging feeling that the V-Speeds seemed low. I did not voice that concern to my FO (expectation bias - 'the numbers' are always right). During this time; the B Flight Attendant called with a potential Passenger issue that was quickly resolved. (Performance pressures; trying to get back to some degree of on-time performance). Once we taxied; everything up to takeoff rotation was normal.At rotation; the aircraft didn't start flying at a normal pitch attitude. It didn't feel right; so I eased off the pack pressure and let the aircraft to continue to accelerate and delayed my takeoff; holding a takeoff attitude. We broke ground about 15 to 20 knots over computed V2 and slowly climbed out.It was obvious that something was wrong with our takeoff data. Clearing 10;000 feet MSL we reviewed our communications with Dispatch and found the error. Though all weights were transmitted; the weight used for our takeoff weight was in fact our Zero Fuel Weight (ZFW)! Neither of us (Captain or FO) caught this on review. The number we saw was accurate; so we moved on (expectation bias). I began an ACARS conversation with Dispatch; ultimately coordinating a phone call [at our destination]. My Dispatcher apologized profusely for the error; citing a new process using the computer instead of [the performance computer] to calculate the takeoff data; and that she mistakenly used ZFW instead of Takeoff Weight. I emphasized that there were at least three links in this error chain; and none of us broke one.


Synopsis: B737NG flight crew reported receiving incorrect takeoff weights from Dispatch. Flight crew cited a dead battery on the performance computer and having to utilize Dispatch for the weights as contributing factor.