Can aeroplane cause placental abruption ?

Not unless it crashe: There is no evidence that air travel causes placental abruption. Trauma can cause placental abruption, but most cases are related to hypertension/preeclampsia or are idiopathic (unknown cause).

If bumpy ride: Abruption is a bleed from the placenta; a disruption of either the mother or baby's blood supply. Many causes: trauma, high blood pressure, drugs (cocaine), preterm labor, polyhydramnios. Can be very large or very small, so even US can miss a diagnosis. Symptoms: usually preterm contractions, sometimes vaginal bleed. Fetal monitoring is necessary. Wait, watch; abruption can self-heal sometimes.