Find the aircraft your fleet average is hiding
Fleet averages hide the aircraft that carries a problem, and that aircraft costs more than defects: in one operator's data, an aircraft with recurring bleed and air-conditioning defects also burned 3% more fuel than its sisters for years. Drop in your technical log to see which aircraft carries more than its share of defects in each ATA chapter, and which faults keep coming back.
Drop your technical log here
Excel (.xlsx, .xls) or CSV, exported from your maintenance system.
Check the columns
Results
Each aircraft against its sisters
Defects per 30 days in the log. The vertical line is the fleet median.
Hot spots
One aircraft carrying far more than its share of one chapter. Only differences too large to be chance are listed.
Repetitive defects
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All hot spots
All repetitive defects
Where the defects are
Chapters ranked by share of all defects.
Monthly load
Defects recorded per month across the fleet.
This is a screening aid. It does not replace your approved reliability programme and it is not a basis for any airworthiness decision on its own.
Three columns are enough
- Aircraft — registration, tail number or any fleet number
- Date the defect was raised
- ATA chapter — 21, 21-51 or 2151 all work
- Defect text, if you have it: repeats are then matched on wording, not just chapter
- Reported by, if you have it: shows how much comes from crew
A year of data gives the clearest picture. Fewer than 30 usable rows is too little to say anything.
The method, in plain terms
Hot spots
For each chapter, each aircraft is expected to carry a share of the defects equal to its share of the fleet's days in the log. An aircraft is flagged when it has at least five defects in the chapter, at least 1.6 times its expected number, and the gap is too large to be chance. The chance test is a Poisson test, tightened for the number of aircraft and chapters checked at once so that looking at many combinations doesn't produce false alarms.
Repetitive defects
The same fault on the same aircraft, returning within 30 days of the previous report, on three or more separate days. With defect text, "the same fault" means the same chapter and closely matching wording, and position numbers must agree: brake 3 and brake 4 are different units. Without text it falls back to the ATA reference.
What it doesn't do
It doesn't know flight hours or cycles, so it compares per calendar day. It doesn't judge severity, MEL category or cost. It reads the ATA chapter you recorded and can't correct a wrong one.