As far as i'm aware, you do need an OCI. This was told to me by the VP OPS of 2 airlines. I've already got a PIO card & when I went to the High Commision of India in my country, the guy there said that airlines in India had been given some sort of directive that NRI's need to be OCI'd. I should be getting mine any day now. I will keep you informed if anything changes.
