Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 195; Flight Crew Type 18000
Situational Awareness
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Weight And Balance
Flight Crew Took Evasive Action
Procedure; Human Factors
I think we have serious safety vulnerability with the current 737-800 Loading Schedule software. The main problem occurs with significant cargo/bag loads and smaller Passenger loads. My latest example was this flight with 80 Passengers and 3600 pounds of cargo/bags. The Agent informed me that she was having the Ramp Agents move all the weight to the front bin. I asked her if she was intending a Zone count. She said no. I asked the Flight Attendants to complete the Zone count for me. The Agent completed the Loading Schedule and put all 79 (later 80) Passengers in Zone 1 (as per Operations procedures). It generated a valid Loading Schedule with 5.5 trim units. I asked her to rerun the software using the Zone count. It came up out-of-limits. We had to move Passengers to make it legal and the Loading Schedule generated 6.4 trim units. The onboard computer increased the computed trim units to 6.9. The FO performing the takeoff reported that it was still heavy nose on rotation. Had we used the initial Loading Schedule of 5.5; or even 5.9 from the onboard computer; the nose would have been excessively heavy; requiring much greater than normal aft yoke travel.I am especially concerned because we have already raised concerns about this and were told that Agents have been instructed to use Zone counts with 120 or fewer Passengers. I have informally polled Agents and discovered that the policy is not clearly disseminated. I fully understand that the current policy/software is deemed legal and approved; but it is questionable on a safety standard. There are cases of short-legged; ample bellied Pilots where aft yoke travel meets belly before takeoff rotation is achieved. The software and policy needs to be changed to require a more even cargo/bag loading and more frequent Zone count so that a larger trim unit setting is generated. In my discussions with respected Agents; they acknowledge this problem and routinely move some of the cargo to the aft bin to solve the problem. My concern is with less informed Agents who doggedly load all cargo in the forward bin and all Passengers in Zone 1. This policy needs to be corrected.
B737-800 Captain described improper weight and balance calculations that can occur with specific cargo and passenger loads when passenger zone counts are not used.