ATR FOS
jolibee,
I am no expert but this is my understanding;
The FOS weight is the approved MTOW, it would appear that you have 22.5t. The 22.8t is a mod that you get from ATR by paying the right amount.
MTOW 22.5t equates to MZFW of 20.5t, MTOW 22.8t equates to MZFW 20.8t. This means that the ATR can carry fuel of 2.0t on every occassion without impacting load so long as FOS allows a Non-limiting take-off or 22.5t MTOW.
Using your example for Laoag, with a fuel load of 1.6t the MTOW weight would be MZFW + Fuel = 22.1t.
The ATR has 4 weight limits, if MTOW 22,500 then, Max Ramp 22,670, MZFW 20,500 and Max Landing 22,350. If any of these limits are breached then you can't go. I.e total take off weight can not be greater than 22.5t; MZFW + fuel is the limit if less than 22.5t; Trip fuel + Max Ldg the limit if less than 22.5t. If the FOS Max is less than the three possible limits then it is the limiting factor. Make sense???
Our FOS makes the temp correction (-5to+37C) and the QNH correction for 10mb block from 1013hpa to 993hpa. QNH below or above we further correct. Below subtract 24kg per hpa, above add 8kg per hpa to the 22.5 limit. We don't ever use the Max Ramp figure.
Hope this helps, feel free to point out errors.
Cheers
