i am currently doing diploma in fabrication tech and erection engineering will i be eligible for BE in aeronautical engineering

Yes you can do but you will have to start afresh.

akheel...for B.E ,,minimum requirement is 12th with PCM subjects.....and if you got diploma in fab. & erection....then its good for ur course...B.E in aeron. eng. is a very good field by job prospects point if view. so dont worry go for it.