B737-700
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 349; Flight Crew Type 11000
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Flight Crew Took Evasive Action
Aircraft; Company Policy; Procedure
This is a general complaint about performance software. In ZZZ we were IFR at night; with -FZDZ falling. Used performance software for takeoff with full aircraft and alternate with 15;000 pounds of fuel. Deiced with Type 1 and Type 4 fluid. On takeoff roll performance software set power at 83.4% N1. We had a very long takeoff roll and clawed our way into the sky. This takeoff felt very bad and the aircraft was extremely sluggish until I called for full climb power at 1;000 feet. I believe this power setting was too low for the IFR/ Deiced conditions. The problem is there is no middle ground with [the] performance software. I could have over-written the reduction (assumed temperature was 59 degrees) but then I would have been guessing at the trim setting. I also could have; and will next time; use max power whenever using Type 4 anti-ice. Performance software is setting takeoff power too low on most takeoff conditions. On a later flight this same day; with 20 knots of crosswind; but no LLWS being called; the same low power was used for takeoff. We were lighter and the sky was clear. But still a big gust or airspeed drop at liftoff could have been a problem. We have very little power margin with 83% N1 on takeoff. Performance software has us setting takeoff power too low on most takeoffs. We; as pilots must return to a safer place; when determining the power setting for the actual weather conditions. After deicing and having low weather at night; we should not allow [the] performance system to set static power conditions which are not appropriate for safe flight; just to save on maintenance [costs] and engine wear tables. Performance system needs a button that returns a minimum of 90% N1 reduction in certain conditions (or something in the middle). Two settings; max or put-put slow are not good aviation.
B737-700 Captain reported concerns with takeoff data settings being too low.