Calibration, flight inspection and performance assurance of VOR/DME/VORTAC facilities

The Federal Aviation Agency has performance assurance programs, for the VOR/DME/VORTAC short-distance navigation system, designed to provide the highest practicable availability of service to the users consistent with economic constraints, and always within established standards of technical performance. During the calendar year 1963, the national average of facility availability was 98.7 per cent, Each facility is composed of high-quality equipment designed for 24-hour continuous operation. Each station is carefully calibrated through measurements of the signal characteristics made on the ground and confirmed by in-flight measurements, and is maintained by competent technicians. Continued performance is reported in a manner capable of analysis by statistical methods. A semiautomatic flight inspection system (SAFI) provides, on a continuing basis, an in-flight check of each station's performance. A recent study disclosed that certain preventive maintenance was contributing to increased outages and increased cost of maintaining the stations. The availability or service from the VOR and TACAN stations has shown that providing a standby transmitter with automatic changeover dues not in itself assure full availability of service to the users. Dual-transmitter VOR stations provide only about 23 hours per year additional time over single-transmitter stations. For the TACAN facilities the gain is of the order of 80 hours. Redundancy studies indicate that standby transmitters are not justified for all locations. Redundancy must be judiciously applied after careful consideration of the service availability requirements and appropriate cost benefit studies. The nonavailability of any station is compensated for by alternate routings to provide an overall system of navigation of very high dependability.