Component Removal Rate, MTBUR and NFF Cost Calculator
Mean time between unscheduled removals (MTBUR) tells you how often a component leaves the aircraft for a fault, confirmed or not. This calculator turns fleet hours and removal counts into MTBUR, MTBF and the money lost to no-fault-found removals.
Your numbers
Share of removals where the shop could not confirm a failure.
Labor, test fee, freight, pool charge and aircraft downtime effects.
Your results
Single year, single part number view. Use a longer window for low-volume parts and combine with your authority-accepted reliability program methodology where one applies.
Annual NFF cost vs NFF share
Sweeps Removals with no fault found from 0 to 80, holding your other inputs fixed.
Reliability dashboard from your ERP
Optional: we can review how removal and shop finding data could feed MTBUR automatically.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the fleet size, annual flight hours per aircraft and how many units of the part are installed on each. Add the unscheduled removals you recorded in the year, the share the shop returned as no fault found and the cost of one such event. You get MTBUR, the removal rate per 1,000 unit hours, MTBF based on confirmed failures and the yearly NFF bill.
Definitions
MTBUR counts every unscheduled removal, while MTBF counts only confirmed failures. The gap between them is the NFF population, which is often a troubleshooting and fault isolation problem more than a component problem. Both use unit hours, meaning aircraft hours multiplied by the number of installed units.
- Unit hours = aircraft x hours per aircraft x units installed
- MTBUR = unit hours / unscheduled removals
- MTBF = unit hours / confirmed failures
- NFF cost = NFF removals x cost per NFF event
Reading the result
With the defaults, 153,600 unit hours and 38 removals give an MTBUR near 4,040 hours, but only about 25 removals were real failures so MTBF is about 6,200. Roughly 13 NFF events cost about 60,000 dollars a year. Cutting NFF through better fault isolation is usually cheaper than buying a more reliable unit.
Common mistakes
Mixing scheduled and unscheduled removals, counting hours for the wrong population or comparing MTBUR across fleets with different operating environments leads to bad conclusions. Also treat NFF carefully, since a unit that passes the bench may still fail intermittently in service, and repeated NFF on the same serial number deserves its own review.
Frequently Asked Questions
Is MTBUR the same as MTBF?
No. MTBUR counts unscheduled removals regardless of whether a fault was found, while MTBF should use confirmed failures only. MTBUR is the figure that drives spares and logistics, MTBF the one that describes the hardware.
How many removals do I need for a meaningful number?
Very small counts swing widely. With fewer than about ten events, use a longer period or pool similar fleets before drawing conclusions or changing a provisioning level.
Should hours be flight hours or operating hours?
Use whatever basis your reliability program and the part's life use. Many avionics units run on power-on hours while others follow flight hours. Be consistent across the whole calculation.
What is a high NFF rate?
It depends on the system. Avionics and electrical units often show higher NFF than mechanical parts. Trend your own rate by part number and look for outliers instead of using a universal threshold.
Netray can build a read-only agent that pulls removal and shop findings data from your ERP and records system and calculates MTBUR by part number, tail and vendor.
Related Tools
MRO Repair vs Exchange Breakeven Calculator
Compare repairing a rotable with exchanging it, adjusting for loaner cost, turn time, beyond-economic-repair probability and remaining life, and find the breakeven repair price.
Aerospace & DefenseMRO Component Repair Quote Comparison Worksheet
Compare vendor repair quotes on total landed cost including freight and downtime, with cost per warranty day and approval status, then export to Excel.
Aerospace & DefenseLLP Remaining Life and Pro-Rata Value Calculator
Calculate remaining cycles, life consumed, pro-rata value and the date to order a replacement for a life-limited part, with a chart over utilization.
Maintenance & ReliabilityMaintenance Check Interval Escalation Savings Calculator
Estimate annual and multi-year savings from extending a base check interval: checks avoided, direct cost saved and aircraft days regained.
More Maintenance & Reliability tools
See all- MRO Hangar Check Capacity Calculator
- MTBF and MTTR Worksheet
- TPM Autonomous Maintenance CIL Standard Template
- TPM Autonomous Maintenance Standard Template
- TPM Pillars and Autonomous Maintenance 7 Steps Reference
- Preventive Maintenance Schedule Template
- Maintenance Work Order Template
- Inherent vs Operational Availability Calculator (MTBF, MTTR)
- Spare Parts Criticality Scoring Worksheet