In this paper we propose a clustering mechanism for improved energy efficiency in aerial based access systems suitable for disaster recovery scenarios and large scale public events. The aerial base station is a low altitude platform (LAP) station that provides access to several terrestrial nodes on the ground over a prescribed coverage area. The terrestrial nodes are battery operated power constrained terminals that have got no base station access except for the LAP. Since the aerial uplink is a high cost energy link we propose a cluster based approach for LAP access. The proposed clustering mechanism is simulated and is compared with the well known clustering technique HEED for energy efficiency. Results show that the proposed clustering technique improves the energy efficiency compared to the non-clustering situation as well as to the HEED clustering technique.