More recently, the iFly project[26] defined a new concept of operations of self-separation in higher density airspace, based on the works described above, and evaluated it quantitatively using advanced stochastic simulation methods.[27] The results obtained from these studies indicate that self-separation can be safely used in an airspace with thrice the density of European en-route airspace as of in the year of 2005, if the ADS-B dependability level improves by a factor of five or if the TCAS dependability improves by the same factor.