Six Nines

Six Nines (99.9999%) Reliability …

On May 5, 1983, as an Eastern Airlines L-1011 began its descent into Nassau following a 47 minute flight from Miami, the No. 2 engine was shut down because of low oil pressure. After turning to head for Eastern’s maintenance base in Miami, the No. 3 engine failed, followed shortly by the No. 1 engine. The L-1011 had experienced a triple engine failure!

That’s how I began a paper I wrote for the ASME. Was this the exceedingly unlikely occurrence of an extremely rare event, or was its rarity grossly underestimated?

In your practice your clients may confront risk, and the ability to measure and quantify it could make – or break – your circumstance. There may be other situations when you should call me: We can asses the probability of future product failures, with or without corrective action, using Weibull and Lognormal Analyses of your field data augmented by RFC models to evaluate differing “what-if” scenarios.  We use Bayesian methods to evaluate ex post facto risk in light of new evidence.  Maybe all you require is an articulate expert to explain important technicalities to a jury.

Oh, yes, and what of that L-1011 triple engine failure? Engine No. 2 was restarted at an altitude of 3,500 feet and the plane made a successful emergency landing in Miami. You can find out what happened and why, along with a discussion of misapplied rules of probability and resulting conflicting estimates of risk, in my paper – but that’s not the point:

You and your client may find yourselves in circumstances where success or failure depends on knowing the true risk of a situation. Please Bookmark this Website now, so you can call me then.


Annis, Charles “Estimating the Probability of Early Failure in Engineering Structures,” AD-Vol. 28, Reliability Technology, American Society of Mechanical Engineers, 1992