SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: Luke Deng
Organization:Aerospace Industry Development Corp.
Date posted: Thu Mar 29 3:26:28 US/Eastern 2001
Subject: Maintenability Index
What's MAINTENABILITY INDEX meanning in physic and mathematic aspect?
Subject: Maintainability Index
Reply Posted by: Ned H. Criscimagna
Organization: Reliability Analysis Center
Date Posted: Thu Mar 29 14:21:09 US/Eastern 2001
The maintainability index is a term used in two different ways.
1. It is used as a measure of the maintainability of software.
> Maintainability Index - a measure of success
- Set of polynomial metrics developed at the University of Idaho
- Uses Halstead’s effort/module and McCabe’s cyclomatic complexity/module, plus other factors
- Validated in the field by HP
- Language independent
- Index is a number between 0 and 100
- Used primarily to determine if modules have a high, medium, or low degree of difficulty to maintain
> HP concluded “modules with a MI less than 65 are considered difficult to maintain”
For more information on MI used in this way, go to http://adaic.org/docs/present/ajpo/pll-cost/html/tsld054.htm or http://www.sei.cmu.edu/str/descriptions/mitmpm.html.
2. It is also used as a measure of the total maintenance effort required to maintain a product in operational status per unit operating time. It is expressed as (from MIL-HDBK-472, dated 24 May, 1986):
MI = (Summation (FRi) Mct Ti + Summation (FO) Mpt Tj)/T
MI = maintenance index
FRi = part failure rates (average part failure rates)
Mct = mean corrective maintenance time
Ti = operating time during calendar time Tj
FO = frequency of occurrences of preventive maintenance tasks
Mpt = mean preventive maintenance time
Tj = calendar time in operating inventory
T = total time
Subject: Maintainability Indices
Reply Posted by: Floyd Kreuze
Date Posted: Tue Apr 3 14:44:30 US/Eastern 2001
Maintainability Index is primarily a mathematical concept. The inquirer should consult the book by Ben Blanchard, "Logistics Engineering and Management", especially Chapter 2 "Measures of Logistics". Maintainability is most often measured using elapsed-time factors such as MMH/MA, MMH/OH, MTTR, Mmax, Mct, Mpt and MDT. These terms are defined in MIL-HDBK-470A (Appendix G) and in Blanchard's book on logistics (see above).
The physics aspects of M Index are a bit remote: (1) Human Engineering, as it deals with things like connector spacings in relation to connector replacement with gloved hands, times to remove and replace mounting screws, etc. (2)Physics of Failure and its impact on MTBF, which in turn influences MTBR, Ao and frequency of maintenance actions.