the doua of fear is: "la ilah illa allah" (no god but allah) this is what written in sahih bukhari and sahih moslim
but u always should say the doua "سبحان الذي سخر لنا هذا وما كنا له مقرنين وإنا إلى ربنا لمنقلبون"
"subhan al-ladhee sakhara lana hadha wa ma konna laho moqreneen wa enna ila...