Guest Forum User asked 17 years ago

Is there a formula to calculate the MTBCF from typical MTBF/FITs data. Please help.

Thanks

4 Answers
RMQSI Technical Staff Member Staff answered 17 years ago

The definition for MTBCF is the mean time between critical failure. This value has to be determined through the modeling of the unit or system so that one can determine which part failures cause mission loss. The only formula that would work as is, is if the loss of all parts cause mission loss then you could apply a one to one ratio. For modeling guidance, I would suggest that you review our reliability toolkit or MIL HDBK-338 Reliability Design Handbook.

anup hegde answered 8 years ago

Is there a formula to calculate the MTBCF from typical MTBF/FITs data. Please help.

Thanks

Can anyone plz let me know the exact difference between MTBF & MTBCF(theoretically & also practically)

anup hegde answered 8 years ago

Can anyone plz let me know the exact difference between MTBF & MTBCF(theoretically & also practically)

John Reade Staff answered 8 years ago

Mean Time Between Failure (MTBF) is a basic measure of reliability, where all failures that occur over an operating period are counted. It is sometimes referred to as logistics reliability because it determines the number of spares that you will need to replace items (e.g., parts, assemblies, etc.) that fail.

Mean Time Between Critical Failure (MTBCF) is sometimes referred to as “mission reliability” and is a subset of MTBF because it only counts those failures that result in a mission abort or mission failure. The reliability analyst needs to be able to distinguish between those failures that are critical to the mission versus those that are not (failures that are not critical to the mission will still need to be fixed and counted as part of the MTBF calculation).

This is a very high-level view of the difference. The calculation of MTBCF is very specific to the type of equipment and type of mission that is being conducted, and depends on how “critical failure” is defined for that equipment/mission. A failure may be catastrophic (total mission failure) or represent some pre-defined level of performance degradation.