Tolerances in automatic landing: an analysis of the effect of equipment tolerances, changes in aircraft configuration and variations in wind conditions

To ensure that production systems will perform an automatic landing with consistent accuracy, it is necessary to analyse the variations that may be expected in the landing performance. The system discussed is the B.L.E.U. single channel automatic landing system which utilizes ground-based radio aids to provide aircraft position information to the autopilot. The critical landing parameters are discussed, together with the factors which contribute to variations in these parameters. The methods used to determine the errors are analysed and the criteria needed to assess whether or not the errors are acceptable are established. It is found that variations in wind conditions make a significant contribution to the total errorsand that changes in the aircraft configuration also add to the overall variation. The effect of equipment tolerances varies widely with the landing parameter under consideration so that it is not necessarily possible to improve performance significantly by tightening equipment specifications. Should it be necessary to reduce the probability of an unacceptable performance, restrictions on the allowable wind conditions and on the aircraft weight and centre of gravity position must be considered.