Pertaining to the A320 family.
Let's assume a situation in which you had performed the landing gear gravity extension, (let's say due to hydraulic problem) and possibly with a Slats / Flaps locked situation. For some further freak occurrence you had to Go-Around at your destination and had to proceed to your alternate with the gear down and the slats and / or flaps out (as mentioned in a HYD G + Y SYS LO
PR summary for example).
In the manuals it is stated (FCOM 3.02.10 P8) that your fuel consumption will be be penalized by a multiplying factor of 1.6 (Slats extended), 1.8 (Flaps extended) or 2 (Slats and Flaps extended).
Somwhere else in the books it is stated that fuel consumption must be multiplied by 2.8 for flight with gear down.
So my question is... Should I add the 2.8 to the 1.6 (for expl.), should I multiply one by the other or just assume a penalty of 2.8 as my total fuel consumption increase?
Couldn't find any guidelines for this calculation anywhere in the manuals, although they do acknowledge that this situation (flight with gear down and slats / flaps out) is possible...
Any light shed, as usual, would be much appreciated.