  We prove that the equation ${ (x - y)^4 + x^4 + (x + y)^4 = z^n }$ has no
integer solutions ${ x, y, z}$ with ${ \gcd(x, y) = 1 }$ for all integers ${ n
> 1 }$. We mainly use a modular approach with two Frey ${ \mathbb{Q} }$-curves
defined over the field ${ \mathbb{Q}( \sqrt{30} ) }$.
