Talking for the A320 family: The fuel penalty factors in the QRH are conservative. It's important that your flight plan is properly sequenced to get an accurate consumption estimation.
If you have gears stuck, it would be certainly after airbone or during approach so most probably you won't go anywhere else unless it's one of those days and you took off below landing minima.
In that case, personally I would not use the QRH fuel penalty table. It's faster and more accurate to look at the fuel flow with gears down at green dot speed than trying to sequence your flight plan and make some potentially ''confusing'' calculations at low altitude. Since you would probably not fly faster than green dot unless you want to burn more fuel, whatever is displayed on the fuel flow is a good estimation of how much time you have.
on the A 320, with gears down at green dot speed, it will be roughly 4000kg/h fuel burnt. That's what I observed during my last sim. In a glitch of an eye you have a good idea of your endurance.
Last edited by pineteam; 19th May 2018 at 06:39.
Reason: Typo