# Component Removal Rate, MTBUR and NFF Cost Calculator

> Source: https://netray.co/tools/component-removal-rate-mtbur-and-nff-cost-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Compute MTBUR, MTBF, removal rate per 1,000 hours and the annual cost of no-fault-found removals from fleet hours and removal counts.

## Category

maintenance

## Industry

Aerospace MRO

## Audience

- Reliability engineer
- Component planner
- Technical records

## Tool

**Kind:** calculator

**Currency:** $

**Inputs:**

#### Aircraft in fleet

**Key:** fleet

**Type:** number

**Default:** 24

**Min:** 1

**Step:** 1

**Unit:** aircraft

#### Flight hours per aircraft per year

**Key:** fh_year

**Type:** number

**Default:** 3200

**Min:** 1

**Step:** 100

**Unit:** FH

#### Units installed per aircraft

**Key:** installed

**Type:** number

**Default:** 2

**Min:** 1

**Step:** 1

**Unit:** units

#### Unscheduled removals in the year

**Key:** removals

**Type:** number

**Default:** 38

**Min:** 1

**Step:** 1

**Unit:** removals

#### Removals with no fault found

**Key:** nff_pct

**Type:** slider

**Default:** 35

**Min:** 0

**Max:** 90

**Step:** 1

**Unit:** %

**Help:** Share of removals where the shop could not confirm a failure.

#### Cost of one NFF removal

**Key:** nff_cost

**Type:** number

**Default:** 4500

**Min:** 0

**Step:** 100

**Unit:** $

**Help:** Labor, test fee, freight, pool charge and aircraft downtime effects.

**Outputs:**

#### Fleet unit hours

**Key:** unit_hours

**Expr:** fleet * fh_year * installed

**Format:** integer

#### MTBUR

**Key:** mtbur

**Expr:** unit_hours / removals

**Format:** integer

**Primary:** true

**Description:** Unit hours per unscheduled removal.

#### Removals per 1,000 unit hours

**Key:** rate_1000

**Expr:** removals / unit_hours * 1000

**Format:** decimal

#### Confirmed failures

**Key:** confirmed

**Expr:** removals * (1 - nff_pct / 100)

**Format:** decimal

#### MTBF from confirmed failures

**Key:** mtbf

**Expr:** unit_hours / confirmed

**Format:** integer

**Description:** Higher than MTBUR whenever NFF removals exist.

#### NFF removals per year

**Key:** nff_count

**Expr:** removals * nff_pct / 100

**Format:** decimal

#### Annual cost of NFF removals

**Key:** nff_annual

**Expr:** nff_count * nff_cost

**Format:** currency

**Primary:** true

**Chart:**

#### Annual NFF cost vs NFF share

**Type:** line

**X:** nff_pct

**From:** 0

**To:** 80

**Steps:** 20

**Series:**

- nff_annual

**Disclaimer:** 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.

## Content

**Intro:** 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.

**Sections:**

#### How to use the calculator

**Body:** 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

**Body:** 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.

**Bullets:**

- 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

**Body:** 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

**Body:** 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.

**Cta:** 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.

**Faq:**

#### Is MTBUR the same as MTBF?

**Answer:** 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?

**Answer:** 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?

**Answer:** 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?

**Answer:** 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.

## Search terms

MTBUR calculator, mean time between unscheduled removals, no fault found cost calculator, component removal rate, MTBF aircraft component, NFF rate aviation, removals per 1000 flight hours, reliability program calculator

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