Unmanned aviation systems (UAS) acquired for US Navy for military roles are developed in the context of NAVAIR's rigorous and well-established policies, procedures and processes employed in the acquisition and development of manned aircraft. A key process is the preparation and approval of interim flight clearances (IFC) prior to flight test to ensure the aircraft is airworthy and thus safe to operate. Due to the perceived risks of UAS experimental flight test, the use of this process has been mandated for all Navy organizations, including use of commercially available UAS in research projects. This policy has proved to be a challenge, impeding and discouraging the use of UAS in research and experimental projects. Currently, the cost of compliance is unaffordable and IFC preparation and approval time are inconsistent with research cycle time expectations. The research reported here investigated the difficulties and advocates solutions devised through the application of systems engineering. In particular, a hazard and risk analysis tool exploiting Bayesian belief networks was developed and demonstrated in support of the interim flight clearance process for the the JACKAL VTOL UAS platform being developed for use in Naval Research Laboratory research flight testing.