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Time based communications (TBC) involves the use of an active data channel for time transfer [1]. In 2002, testing was conducted with the Air Force Research Lab (AFRL) at Wright Patterson Air Force Base to demonstrate a TBC implementation from the ground to an airborne platform using standard communications channels and equipment. Algorithms to perform Dynamic Two-Way Time Transfer (DTWTT) were developed and demonstrated to correct raw time transfer data for platform motion and measurement effects. Flight tests were conducted in November 2002 to demonstrate the algorithms and determine the level of performance that can be expected from dynamic two-way time transfer. Tests were conducted using Satellite Relay links and line-of-sight (LOS) links between the ground and the aircraft. The results from the Satellite Relay case were presented in a PTTI 2002 paper entitled "Two-Way Time Transfer to Airborne Platforms Using Commercial Satellite Modems". The LOS results are presented here. This paper begins with a review of Dynamic Two-Way Time Transfer for the line-of-sight communications link case. The flight experiment is presented with a description of the data collection hardware as well as a detailed presentation of the flight data. Conclusions on the use of DTWTT are drawn based on the results of the flight tests.

Abstract-LORAN-C is being examined as a viable backup to GPS for timing and navigation. Accuracy from the LORAN-C network has always been limited by variations in

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