ERTMS/ETCS RAMS Requirements Specification Chapter 2 - RAM

EEIG ERTMS Users Group2.3.2.1.3 Minor FailuresThis requirement is not related to the ERTMS/ETCS Operational Availability inthat it does not influence service by definition.Anyway an appropriate availability requirement has to be defined also for thiscategory of failures in order to avoid an excessive request of logistic support fornot service critical subsystems.The following requirement is therefore defined:® The minimum tolerable availability, related to hardware MINOR failures, shallbe 0.995® the corresponding mean downtime per year due to MINOR failures shall beDT HW,M = (1 - A HW,M ) . 8760 h = 43 hour 48 minutes2.3.2.2 Transmission Errors ContributionAs transmission error is intended the event that, in absence of any kind of faultoccurred to the transmission equipment, a message is not received, is received inwrong way or is not received within the allowed time delay causing a system failure.The contribution to the system unavailabilities due to transmission errors is stated asthe 10%.As a consequence the transmission errors contribution A TX to the quantifiableportion of the operational availability A OP is established on the basis of the followingformula:ATX=TopTop+ Tfault=[( 1 − Pds)Tdn + PdsTdnd][( ) ]1− P T + P T + 01 . ⋅ 0. 6 ⋅ P ⋅ 0.9 ⋅ Tds dn ds dnd ds dy=90== 0.99998490 + 01 . ⋅ 0. 6 ⋅ 0. 0027 ⋅ 0.9 ⋅10® The ERTMS/ETCS quantifiable contribution to operational availability, due totransmission errors, shall be not less than 0.999984.Doc. Ref.: 02s1266- page 42/83