50 degrees lean of peak doesn't exist in turbine engines, the condition is either fuel on or off. FADEC should monitor the parameters of the engine and adjust as necessary or shut it down before exceeding limits. Whereas non-FADEC engines require a trained mammal to watch temps, pressures, rpms and to intervene before failure occurs.
50 degrees lean of peak isn’t a thing, but the fuel is metered so that the stoichiometry is correct in the burner can. Turbines don’t have “mixture” but to say that it’s either “off or on” is misleading.
Also, some turbine powered airplanes have different min fuel conditions.
Yeah it was critical on the mid series of models since they had gained a lot of excess weight from the original skinny light short range day attack plane variants.
As they gained more and more empty weight bring back loads aboard ship became more reliant on using it as part of fuel planning. The newest Pegasus variants have put a lot of the power margin back along with lighter more capable systems/weapons to accomplish the same tasks (Brimstone instead of older bigger Maverick, 1 LGB/JDAM instead of a couple dumb bombs for example). Now the water is more a ballast but it still gets used in a pinch.
Many older turbine engines had fuel trim selectors that would increase or decrease the fuel flow separately of the throttles.
(usually geared turboprops)
In a way, you could consider this a mixture adjustment.
Turbines always run lean with the excess air contributing to cooling in one form or another.
So if your trim settings were wrong on startup, you could easily smoke the engine if you weren't paying attention.
Same goes to takeoff power.
Select Water injection (which SHOULD start automatically)
Set Takeoff trim
Power levers to maximum
Confirm water injection
Set Trim to predetermined temperature.