PMTOW and PMRTW

[Jkotows2]

I see that PMTOW can be way less than PMRTW. Why is that? Is PMTOW based off of aircraft limitations where PMRTW is the max weight with given environmentals that an aircraft can takeoff on a specific runway?

Thanks

[Goldenrivett]

Hi Jkotows2
Yes. RTOW is a theoretical weight (mass) which could be lifted with a calculated engine thrust and the aircraft structure from that particular runway and environment conditions and meet the required performance criteria.

[AerocatS2A]

We still use paper RTOW charts with corrections for environmental conditions. For example, a low QNH requires a reduction in weight and having ice protection on requires a reduction in weight. By allowing the software to provide RTOWs that are higher than the MTOW you can apply corrections and still go at MTOW. If the RTOW was capped at MTOW then any performance decreasing adjustments would result in an RTOW that was below MTOW even though it didn't need to be.