Is it just me, but sand does not erode. What would it erode to? SMALLER pieces of sand? Sand shifts, beaches erode.
No, but sand is made up of pebbles not rocks and sand pebbles move when driven by moving water. Plane crashes into water, settles to the sandy bottom and currents move sand over the plane, sand collects on and covers plane. The ocean currents shifted in this area and caused some washing away of sand that had covered the plane over the years.
Also, small sand pebbles do erode over long periods of time because they are pushed against other pebbles and eventually they become fine dust in the ocean. Sand didn’t start as sand, it started as large rocks that erode and continue to erode regardless of size.