How much maintenance backlog is healthy, and how should you measure it?

Why the count is worthless

Two hundred lightbulbs and two hundred compressor rebuilds are the same number. They are not remotely the same problem, and a metric that cannot tell them apart is not measuring anything.

Crew-weeks measures the work: how many weeks of your actual crew’s actual capacity is sitting in the queue. That is the number that tells you whether the queue is survivable.

Total, and ready

Two numbers, and they answer different questions — one asks whether the queue is survivable, the other whether your crew can actually start work this morning:

• Total backlog: 4–6 crew-weeks is the convention. Below that and you are probably over-staffed or under-inspecting; well above it and the queue is no longer a queue, it is a list of things that will not happen.
• Ready backlog: 2–4 crew-weeks. Planned, scoped, parts on the shelf, permits in hand — work a technician can start today. A backlog with no ready work in it means your crew waits while jobs get planned around them.
• Age cap: ninety days. An item nobody has done in three months is not a backlog item. It is a decision nobody has made — either do it, or close it, but stop pretending it is queued.

What a growing backlog is telling you

One of two things, and it is worth finding out which. Either the team is understaffed for the asset base, or the PM programme has generated more work than the asset base actually needs — over-frequent schedules, PMs on assets that do not warrant them.

Both are entirely fixable. But the trend is the signal, and it precedes the failures by months. That is the whole value of measuring it: a backlog is the only maintenance metric that warns you about next quarter rather than reporting on last one.