Suppose you are inside a smooth-flying [no bumps] jet plane moving at constant speed in a straight line across the atlantic ocean. can you detect this motion [i. e., can you tell that you are moving] without directly or indirectly making use of anything outside of your own reference frame? if so, how could you detect this; and if not, why not?

No we cannot perform any experiment that tells us weather we are moving or not at a constant speed.

Explanation:

Motion of any body is relative to other reference bodies. We can perceive motion only if our position with respect to a fixed object changes. This is the fundamental concept of reference frame in classical physics or Newtonian Physics  that motion is always from a reference.

We choose a fixed body as reference and ,measure the distance we cover from this fixed point and also our speed with respect to this fixed point. The choice of frame of reference is completely dependent on the observer.

Since in the given case a reference cannot be established outside the plane thus we cannot detect our motion.

im sorry i dont know