The "Five Whys"

You may be aware of a technique called The Five Whys.  This technique is often used in Root Cause Analysis and in Six Sigma.

The gist of the technique is to ask “why” five times and that (supposedly) leads you to a Failure Mode that is written at just the right level so that an appropriate Failure Management Strategy can be developed.

Recall from our module on Failure Modes that a Failure Mode is like a road. Properly written Failure Modes allow us to reach our “destination” (aka technically appropriate maintenance tasks and intervals and Default Strategies).

Back to The Five Whys.

Here’s what my mentor John Moubray had to say about The Five Whys.  (I remember like it was yesterday. During my RCM Practitioner training, John stood in his stocking feet and taught us that The Five Whys is “a bunch of rubbish.”)  Here’s how he explained it to us.

Let’s start with the Failure Mode "Bearing Seizes.”  Obviously “Bearing Seizes” is written at too high a level for us to formulate any meaningful solutions.  So, let’s ask “why” five times.

Ask "Why" Five Times

1. Why did the bearing seize?

- Because there was excessive wear on the raceways and rolling elements.

2. Why was there excessive wear on the raceways and rolling elements?

- Because the bearing had insufficient lubrication.


3. Why did the bearing have insufficient lubrication?

- Because the technician didn’t lubricate the bearing properly.


4. Why didn’t the technician lubricate the bearing properly?

- Because he was hung over and wasn’t paying attention during the lubrication task.


5. Why was the technician hung over?

- Because he had a fight with his wife and went out to the pub the night before with his buddies.

"A Bunch of Rubbish"

Hopefully you get the point.  It’s our job to make sure our Failure Modes are written at the right level.

Our goals drive how detailed our Failure Modes should be. When you’re writing Failure Modes, if you keep your goal in mind AND you use your common sense, it should be relatively easy to properly write your Failure Modes.