Example of FMEA worksheet Failure mode and effects analysis

1 example of fmea worksheet

1.1 probability (p)
1.2 severity (s)
1.3 detection (d)
1.4 dormancy or latency period
1.5 indication
1.6 risk level (p*s) , (d)

example of fmea worksheet

probability (p)

it necessary @ cause of failure mode , likelihood of occurrence. can done analysis, calculations / fem, looking @ similar items or processes , failure modes have been documented them in past. failure cause looked upon design weakness. potential causes failure mode should identified , documented. should in technical terms. examples of causes are: human errors in handling, manufacturing induced faults, fatigue, creep, abrasive wear, erroneous algorithms, excessive voltage or improper operating conditions or use (depending on used ground rules). failure mode given probability ranking.

severity (s)

determine severity worst-case scenario adverse end effect (state). convenient write these effects down in terms of user might see or experience in terms of functional failures. examples of these end effects are: full loss of function x, degraded performance, functions in reversed mode, late functioning, erratic functioning, etc. each end effect given severity number (s) from, say, (no effect) v (catastrophic), based on cost and/or loss of life or quality of life. these numbers prioritize failure modes (together probability , detectability). below typical classification given. other classifications possible. see hazard analysis.

detection (d)

the means or method failure detected, isolated operator and/or maintainer , time may take. important maintainability control (availability of system) , important multiple failure scenarios. may involve dormant failure modes (e.g. no direct system effect, while redundant system / item automatic takes on or when failure problematic during specific mission or system states) or latent failures (e.g. deterioration failure mechanisms, metal growing crack, not critical length). should made clear how failure mode or cause can discovered operator under normal system operation or if can discovered maintenance crew diagnostic action or automatic built in system test. dormancy and/or latency period may entered.

dormancy or latency period

the average time failure mode may undetected may entered if known. example:

seconds, auto detected maintenance computer
8 hours, detected turn-around inspection
2 months, detected scheduled maintenance block x
2 years, detected overhaul task x

indication

if undetected failure allows system remain in safe / working state, second failure situation should explored determine whether or not indication evident operators , corrective action may or should take.

indications operator should described follows:

normal. indication evident operator when system or equipment operating normally.
abnormal. indication evident operator when system has malfunctioned or failed.
incorrect. erroneous indication operator due malfunction or failure of indicator (i.e., instruments, sensing devices, visual or audible warning devices, etc.).

perform detection coverage analysis test processes , monitoring (from arp4761 standard):

this type of analysis useful determine how effective various test processes @ detection of latent , dormant faults. method used accomplish involves examination of applicable failure modes determine whether or not effects detected, , determine percentage of failure rate applicable failure modes detected. possibility detection means may fail latent should accounted in coverage analysis limiting factor (i.e., coverage cannot more reliable detection means availability). inclusion of detection coverage in fmea can lead each individual failure have been 1 effect category being separate effect category due detection coverage possibilities. way include detection coverage fta conservatively assume no holes in coverage due latent failure in detection method affect detection of failures assigned failure effect category of concern. fmea can revised if necessary cases conservative assumption not allow top event probability requirements met.

after these 3 basic steps risk level may provided.

risk level (p*s) , (d)

risk combination of end effect probability , severity probability , severity includes effect on non-detectability (dormancy time). may influence end effect probability of failure or worst case effect severity. exact calculation may not easy in cases, such multiple scenarios (with multiple events) possible , detectability / dormancy plays crucial role (as redundant systems). in case fault tree analysis and/or event trees may needed determine exact probability , risk levels.

preliminary risk levels can selected based on risk matrix shown below, based on mil. std. 882. higher risk level, more justification , mitigation needed provide evidence , lower risk acceptable level. high risk should indicated higher level management, responsible final decision-making.

after step fmea has become fmeca.




^ mil-std-882 e system safety . www.everyspec.com. retrieved 2017-01-04.