starship-design: MTBF

["L. Parker" <lparker@cacaphony.net>]

Timothy,

I forgot to mention something important. The definition of what MTBF is 
varies depending upon who you ask, for instance some manufacturers exclude 
components older than the designed lifetime from testing. In other words, 
if they test 1,000 components for five years all of which have a designed 
lifetime of four years, any components that become older than four years 
during the course of the test are removed from testing and replaced with 
new components!
In addition, in a sample real life test of components rated for 1,000,000 
hours MTBF and a designed lifetime of five years, 11 percent failed in one 
year. Hardly what you would expect from components with a rated 1,000,000 
hours MTBF! MTBF is a guideline, not a guarantee. As a matter of fact it 
says so in the fine print at the bottom of the page...
Lee
                                                          (o o)
------------------------------------------------------oOO--(_)--OOo-----  
----
Up the airy mountain,
Down the rushy glen,
We daren't go a-hunting
For fear of little men;

William Allingham, Ireland, 1850