Page 555 - IRSEM_Main Book

3.0 Examples of RAMS Parameters for Railways

3.1 Reliability Parameters:

Failure Rate λ(t )

Mean Up Time MUT

Mean Operating Time To Failure (for non-repairable items) MTTF
Mean Operating Time Between Failures(for repairable items) MTBF

Reliability R(t)

Failure probabilityR(t) F(t)

3.2 Maintainability Parameters:

Mean Down Time MDT

Mean Operating Time Between Maintenance MTBM

MTBM (Corrective or Preventive) MTBM(C), MTBM(P)

Mean Time To Maintain MTTM

MTTM (Corrective or Preventive) MTTM(C), MTTM(P)

Mean Time to Restore MTTR

3.3 Availability Parameters:

Availability A

Inherent Ai
Operational Ao

Ai = MTTF/(MTTF+MTTR) for non-repairable items
Ai = MTBF/(MTBF+MTTR) for repairable items

Ao = MUT/(MUT+MDT)

3.4 Safety Parameters:

Hazard Rate h(t)

Probability of Wrong Side Failure PWSF

Tolerable Hazard Rate THR

Annexure:G1: Reliability, Availability, Maintainability & Safety (RAMS) Page 498 of 535