Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 3820

1. Introduction and fundamental concepts This Attachment is intended to provide guidance material which Member States may find helpful in providing the degree of facility reliability and availability consistent with their operational requirement. The material in this Attachment is intended for guidance and clarification purposes, and is not to be considered as part of the Standards and Recommended Practices contained in this Annex. 1.1 Definitions acilit availabilit . The ratio of actual operating time to specified operating time. acilit failure. Any unanticipated occurrence which gives rise to an operationally significant period during which a facility does not provide service within the specified tolerances. acilit reliabilit . The probability that the ground installation operates within the specified tolerances. Note.— This definition refers to the probability that the facility will operate for a specified period of time. ean time between failures ( B ). The actual operating time of a facility divided by the total number of failures of the facility during that period of time. Note.— The operating time is in general chosen so as to include at least five, and preferably more, facility failures in order to give a reasonable measure of confidence in the figure derived. Si nal reliabilit . The probability that a signal-in-space of specified characteristics is available to the aircraft. Note.— This definition refers to the probability that the signal is present for a specified period of time. 1.2 Facility reliability 1.2.1 Reliability is achieved by a combination of factors. These factors are variable and may be individually adjusted for an integrated approach that is optimum for, and consistent with, the needs and conditions of a particular environment. For example, one may compensate to some extent for low reliability by providing increased maintenance staffing and/or equipment redundancy. Similarly, low levels of skill among maintenance personnel may be offset by providing equipment of high reliability. ANNEX 10 — VOLUME I ATT F-1 23/11/06 2007/70/II. szám Annex 10 — Aeronautical Communications Volume I 1.2.2 The following formula expresses facility reliability as a percentage: R = 100 e t/m where: R = reliability (probability that the facility will be operative within the specified tolerances for a time t, also referred to as probability of survival, Ps); e = base of natural logarithms; t = time period of interest; m = mean time between facility failures. It may be seen that reliability increases as mean time between failures (MTBF) increases. For a high degree of reliability, and for operationally significant values of t, we must have a large MTBF; thus, MTBF is another more convenient way of expressing reliability. 1.2.3 Experimental evidence indicates that the above formula is true for the majority of electronic equipments where the failures follow a Poisson distribution. It will not be applicable during the early life of an equipment when there is a relatively large number of premature failures of individual components; neither will it be true when the equipment is nearing the end of its useful life. 1.2.4 At many facility types utilizing conventional equipment, MTBF values of 1 000 hours or more have been consistently achieved. To indicate the significance of a 1 000-hour MTBF, the corresponding 24-hour reliability is approximately 97.5 per cent (i.e. the likelihood of facility failure during a 24-hour period is about 2.5 per cent). 1.2.5 Figure F-1 shows the probability of facility survival, Ps, after a time period, t, for various values of MTBF. Note.— It is significant that the probability of surviving a period of time equal to the MTBF is only 0.37 (37 per cent) thus, it is not assumed that the MTBF is a failure-free period. 1.2.6 It may be seen that adjustment of MTBF will produce the desired degree of reliability. Factors which affect MTBF and hence facility reliability are:

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