Metrics of voice communications between pilots and air traffic control provide important indices of NAS system performance. They help to characterize current operations, define requirements for future systems, and establish baselines against which performance of new systems can be compared. This article presents a review of studies of communication metrics in actual operations. It summarizes what is objectively known about various aspects of communication performance, including: the number of controller transmissions per minute, the characteristics of pilot responses, communication error rates, and the time required to transmit a message. Gaps in performance data are identified, empirical links between communication performance and other measures of system safety are explored, and the implications for system specification and evaluation are discussed.

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The self-induced exchange of tritium with the dihalogenated aromatic compounds o-and m-chloroiodobenzene, o-chlorobromobenzene, and o-bromoiodobenzene was studied as a function of the amount of T2 present and exposure time. A smooth correlation exists between the rate with which chlorine, iodine, bromine, and hydrogen were exchanged and the bond energies involved. A mechanism involving organic radicals is proposed to explain the results. Since the incoming tritium atom occupies the same position as the replaced halogen, preferentially the weaker bonded atom, the method can be used to prepare specifically labeled products of high specific T activity.