Date: 201410
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Weather elements / visibility: Rain
Aircraft: B737-400
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked; Takeoff / Launch
ATC / advisory: Tower ZZZ
Aircraft component: ACARS
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Aircraft; Company Policy; Human Factors
Primary problem: Ambiguous

Narrative: We were called to re-crew a flight that had previously done a gate return that resulted in an aircraft swap for a mechanical issue. The new aircraft had been pre-boarded and power was initiated by a mechanic prior to our arrival. The preflight was normal until we tried to initialize the flight data on the ACARS. The Auto Init prompt continued to appear after several initialization attempts and even after the flight data was ultimately loaded manually. No Takeoff Performance Report was included in the flight paperwork packet even though it was requested and printed 20 minutes prior to departure. We did receive the load close-out but had to enter it manually into the FMC. Takeoff data was requested thru ACARS but we received an error message 'Takeoff Plan Not Found'. We finally had dispatch send us takeoff data which was verified accurate; manually loaded; and briefed per standard operating procedures. We taxied out in moderate rain in a long line for takeoff. After approximately 20 minutes we were cleared for takeoff. The takeoff was ops normal until around 80 knots when we both felt the acceleration to be lower than normal. I rechecked that the N1 was set to the FMC programmed bug; which was indicating 84%. This seemed low to me for the takeoff weight but I did not have access to the printed; dispatch generated; takeoff values previously briefed in order to verify. Also; due to the long takeoff delay I could not remember the briefed N1 value. Lastly; with the standing water on the runway I could justify the slower acceleration rate. As we neared V1 we both agreed that a continued takeoff was safe. The First Officer rotated normally and began the climb out but only at a sustained 1000 feet FPM. At 1000 feet AGL I checked the N1 limit page in the FMC and manually increased the power to climb N1 of approximately 92%. The climb out proceeded normally. There was no further issues for the duration of the flight.I can only speculate what caused this problem. Obviously there was an ACARS data transfer glitch disallowing the request to initiate specific flight data. We found an ACARS message in the cockpit from a previous flight stating 'aircraft XXX is listed out of service contact dispatch before push'. We don't know if this is evidence that the ACARS was having issues prior to our event; however. We received an ACARS message during numerous initialization attempts stating 'Error Message. No Takeoff Plan Found'. We mentioned this message to dispatch with no answer to its meaning. Lastly; the previous flight had a much lighter takeoff weight (approx 100;000 lbs) which required an N1 close to the setting generated on our takeoff. Could the old data somehow populate itself into the FMC?




Synopsis: B737-400 Captain detects very sluggish takeoff performance and suspects that the takeoff data they received did not reflect the actual aircraft load.