B767-300 and 300 ER
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Situational Awareness; Training / Qualification; Workload
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance; Inflight Event / Encounter Other / Unknown
Flight Crew Overcame Equipment Problem
Human Factors; Aircraft; Procedure
Preflight up through takeoff on this flight was normal ops.  I was sitting as the relief pilot with NAME being the PIC and flying pilot and NAME1 being the SIC and pilot monitoring.  During the takeoff roll and at rotation; the flying pilot rotated normally after the 'ROTATE' call and pitched up to approximately 4 to 5 degrees and then stopped rotating any further.  We were very heavy (382;094 TOW).  We had a stop margin of approximately 2;000 feet and the end of the runway was rapidly approaching.  After a moment or two; the flying pilot continued the rotation and we proceeded on normally.  After takeoff and past sterile cockpit; the flying pilot communicated to us that the airplane just didn't seem to want to fly and he held the lower pitch attitude for a moment to allow the aircraft to accelerate a bit and avoid a potential tail strike.  During cruise with my time in the seat; the flying pilot and I discussed the issue a little bit more; determined that we might be heavier than the weight and balance paperwork stated; and agreed to really check the pitch attitude on final approach at the calculated REF speed to see if that was another indication of being heavier than we thought we were.  We did find that some airspeed had to be added to the calculated REF speed to maintain the normal pitch attitude during the final approach.  Upon blocking in; we pulled out the landing REF speed chart in the QRH Inflight Performance section and found that with the additional airspeed we had to add to maintain the normal; fully configured; landing pitch attitude; it was conceivable that we may be UP to 20;000 pounds heavier than what was stated on the paperwork.  We called the Load Master up to the flight deck and he said that flight was loaded at the point of origin in ZZZZ1; he was not involved with the loading process (or maybe more accurately; he wasn't involved in the weighing of the cargo) but was just given the numbers from those that were and that we had around 20;000 LBS of cargo in the lower cargo compartments along with all of the passenger weight. The PIC placed a writeup in the logbook to alert the outbound crew (the airplane continued on to ZZZ1 with the same Passengers and cargo) and we all agreed that we needed to make someone else aware of the issue (I elected to inform the Duty Pilot) and to ensure the outbound crew knew of the situation since we wouldn't see them ourselves.  During the limo ride from ZZZ to ZZZ2; both the PIC and myself made unsuccessful attempts to reach the duty pilot through both Pilot Support and Dispatch.  During the subsequent limo ride and discussing the issue further; the PIC wondered if there was a chance that the ground crew in ZZZZ1 was using KILOS as unit of measure rather than pounds (very possible given the 20;000 LBS of cargo we reportedly had vs what the potential difference in weight we noticed with the landing REF speed).  The PIC was dropped off at the ZZZ2 airport for a commercial flight and the FO (First Officer) and I continued onto the layover hotel.  It was agreed that the PIC would continue to communicate the issue to someone in hopes of alerting the outbound crew of the situation.  I was texted later by the PIC that he did get a hold of the Fleet Captain and discuss the issue.
B767 Captain the ground crew at departure airport possibly calculated GTOW in kilograms and reported that number as pounds; leading to a 20;000 LB mistake in actual Take Off Weight.