A decision in this regard was taken at a cabinet meeting chaired by Chief Minister Pinarayi Vijayan here.
They have been asked to submit their report within nine months, an official release said here.
It would be the responsibility of the consultant to complete necessary steps for getting clearance from different central agencies for the airport to be constructed on the 2,263 acre Cheruvally estate, about 48 km from the Sabarimala Lord Ayyappa Temple.
The temple is situated in the mountain ranges of the Western Ghats in Pathanamthitta district.
The number of pilgrims visiting the temple has gone up in recent years and an airport is considered as an alternative to reducing the traffic congestion during the festival season.
The state government had in February 2016 accorded in-principle sanction to construct the greenfield airport.