Why on earth try to solve a differential equation whilst flying an aeroplane?
What is it you need to know? The time it'll take to turn through a given number of degrees at a given TAS and AOB?
In which case if you want to turn through n deg, the time taken will be n x (2pi x TAS x 60)/( 360 x g x tan AoB) seconds.
At 240 TAS and 25 deg AoB, that simplifies to roughly n/2 seconds...or 0.4712 n if you prefer.
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