Tool Control and Calibration under Part-145: 145.A.40 in Practice

A torque wrench three weeks past its label

Night shift at ExampleMRO's line station, 25 September 2026. A B1 engineer draws torque wrench TW-0142 for a brake change. The label reads "Cal due 31 AUG 2026". She hands it back and takes another. The harder question reaches quality next morning: the wrench has been issued several times since 31 August, and nobody can say for which tasks.

Tool control is the system that keeps that wrench out of anyone's hand. Under 145.A.40, a Part-145 organisation holds the tools its approved scope of work needs, uses the tool the manufacturer specifies unless the competent authority agrees an alternative through an exposition procedure, and keeps tools, equipment and particularly test equipment "controlled and calibrated according to an officially recognised standard at a frequency to ensure serviceability and accuracy", with calibration records and traceability to the standard used. The AMC adds a control register (personal tools included), a label that shows the next due date, and intervals from the manufacturer's instructions unless results justify another period.

Key facts

• Tools, equipment and particularly test equipment, as appropriate, are controlled and calibrated to an officially recognised standard, with calibration records and traceability kept (145.A.40(b)).
• Tools needing servicing or calibration control go in a control register, personal tools the organisation agrees can be used included (AMC 145.A.40(a)).
• Labels show when the next inspection, service or calibration is due, and whether the item is unserviceable (AMC 145.A.40(b)).
• Intervals follow the manufacturer's instructions unless results show a different period is appropriate (AMC 145.A.40(b)).
• A change to the MOE procedure for alternative tooling is one of EASA's examples of a change requiring prior approval (GM1 145.A.85(b)).
• Sampled tools missing from the register are EASA's own example of a level 2 finding (GM1 145.B.350(f)).
• Part-CAMO has no tools point. CAOs follow CAO.A.050(b); maintenance outside an approved organisation, M.A.402(d) or ML.A.402(b)(4).

What 145.A.40 says

The maintenance data and performance guide quotes this point beside 145.A.42 and 145.A.45.

Read it as three controls. Point (a)(i) is the right tool: anything else is alternative tooling, agreed by the competent authority through exposition procedures. Point (a)(ii) is availability: a rarely used tool need not be permanently available, but those cases are detailed in an exposition procedure. Point (b) is condition, and "as appropriate" matters: some tools are controlled by inspection or servicing, measuring tools by calibration.

The register, the label and the interval

The working system comes from the AMC (AMC 145.A.40(a), AMC 145.A.40(b)).

In practice: anything that measures dimensions or torque is in the register, including a personal torque wrench the organisation lets people use. Label and register show the same next due date, and an unserviceable tool says so on the tool. The interval starts from the manufacturer's instructions and moves only on results.

"Standard" means two things

EASA's tools user guide for foreign Part-145 approvals (organisations outside the EU that EASA approves directly) explains the word. It is guidance, not rule text.

In a register that becomes two fields: Standard followed, the document the laboratory calibrated to, and Traceability, the reference instrument and certificate chain behind the result. A certificate that gives a reading but names neither is worth a phone call before the tool goes back on the shelf.

Changing or extending a calibration interval

The same user guide covers what results do to an interval.

A torque-tester check between calibrations is evidence for an interval decision, not a calibration. A shorter interval indicated by results is applied at once.

A tool that cannot reach the laboratory in time is a different case. EASA answered it for the COVID-19 crisis in FAQ 116318, last updated on 1 July 2020.

FAQ 116318 — Under the present rules, how can a production or maintenance organisation continue to use tools or equipment even if their calibration/periodical check cannot be carried out before the due date? · EASA FAQ · Continuing Airworthiness, COVID-19 - Continuing Airworthiness

[…] the competent authority may approve a temporary change to the applicable organisation’s procedure to allow an extension of the period at the end of which the calibration/periodical check of the tool or equipment is due.

[…]

The decision of the competent authority on the approval of such a temporary change should be taken based on a risk analysis performed by the organisation.

[…]

Few considerations for the risk analysis may be, but are not limited to the following:

• when the normal calibration/check period is ≤ 12 months the extension of the calibration and/or periodical check can be up to a maximum of 10 % of the normal calibration/check;
• when the calibration/check period is > 12 months the extension of the calibration can be 10 % of the normal calibration/check period up to a maximum of 3 months;

[…]

The tools or equipment with extended calibration or maintenance interval, should be recorded in a dedicated form, allowing tracking the tasks performed. If the tool / equipment fails during next regular calibration / inspection, the completed tasks may require to be verified / performed again.

The extension is a temporary procedure change the competent authority approves on the organisation's risk analysis, not a tolerance an engineer applies at the drawer. The arithmetic is small: 10 % of 12 months is 1.2 months, of 24 months 2.4 months; on 48 months, 10 % would be 4.8, so the 3-month maximum applies.

Alternative tools and the exposition

The AMC outline of an acceptable MOE (AMC1 145.A.70(a)) gives tools their own chapters.

Draft the alternative-tooling procedure carefully the first time: GM1 145.A.85(b) lists changing it as a change requiring prior approval. The MOE guide covers the rest of the document.

What an auditor writes when tool control slips

EASA's guidance to competent authorities on telling a finding from an observation uses 145.A.40(b) as its example (GM1 145.B.350(f)).

Both level 2 examples are register failures, not calibration failures, and the sample starts at the shelf. The findings guide covers the levels themselves.

A tool control system for ExampleMRO

What follows is ExampleMRO's practice; where a step rests on rule text, the quote is on this page.

Identify every controlled tool

Every tool is engraved or tagged with a unique ID before first issue, and each new part number gets a control type. ExampleMRO borrows the three groups in EASA's tools user guide: on condition, service and calibration.

The register template

One row per tool, not per part number: GM1 145.B.350(f) treats a wrong P/N or S/N as a level 2 example.

Recall before the due date

Say the manufacturer's instructions for TW-0142 give 12 months, and ExampleMRO recalls at 30 days because its laboratory turns tools round in about two weeks. Calibrated on 31 August 2025, the wrench is due on 31 August 2026 and joins the weekly recall list on 1 August 2026. Stores sends it on 4 August; it returns on 18 August with a certificate dated 17 August, and register and label move to 17 August 2027. On 25 September it would have been in date. The recall is the control; the label is the backstop.

Found overdue or out of tolerance

Label it unserviceable, put it in the quarantine cage, set its row to Unserviceable, and ask the laboratory for as-found readings before any adjustment. In tolerance as found: record it and return the tool. Out of tolerance: list every task it was issued to since its last good calibration (only possible if the issue log or work card records the tool ID) and let engineering decide what is re-inspected. FAQ 116318 expects the same trail for tools on an extended interval. Then fix whatever let the recall miss.

If it was the only tool in its range, the task waits. A second wrench per range, recalled in a different month, is cheaper.

Lost tools and the shift-end check

Shadow boards and shift-handover tool counts, the foreign object damage (FOD) side of tool control, are practice, not words from 145.A.40. The rule text they serve is 145.A.48(c)(1):

ExampleMRO's lost-tool rule: a missing tool is reported at once, the search is recorded, and the aircraft it was last issued to is not released until the tool is found or the aircraft has been inspected for it.

Tool calibration under Part-CAO, Part-M and Part-ML

Part-CAMO has no point on tools; the tools rules sit with whoever performs the maintenance. A combined airworthiness organisation has CAO.A.050:

Maintenance performed outside an approved organisation falls under M.A.402 or, for Part-ML aircraft, ML.A.402:

The CAO text has no "frequency" clause but keeps records and "the standards used". For an independent certifying engineer, "if necessary" is the test; a personal torque wrench on a task with a specified torque is the obvious case, and the register above works at a scale of one.

Keeping the register in Avioverse

In Registries, the Tool register starter ("Track calibration, location, and availability") is offered while your registries list is empty. It puts Base location and Owner in the header, and gives each row Tool reference, Description, Calibration due and Availability (Available, In use, Unserviceable). Add the other fields from the template in Settings; Availability is a selection list, so you can add an option such as Out for calibration.

The starter's Calibration due is a plain date and shows no due status on its own. To get one:

1. In Settings, Add field and set the type to Calculated.
2. Choose Due and remaining. Under Next due comes from, pick An existing due value, select Calibration due, and set Warn when remaining reaches 30 days.
3. Or add Last calibrated (Date) and Calibration interval (Interval, Calendar — days, weeks, months, years) and pick Last done + interval. A shared interval group such as "Torque wrenches, 12 months, warn at 30 days" updates every linked row when the interval changes.
4. Set Show to Next due, remaining & status, then Save changes.

With a 31 August due date, TW-0142 reads Due soon from 1 August, Due today on 31 August and Overdue from 1 September; on 25 September it shows 25 days overdue. A row with no date reads Unable to assess. Date columns with Show on calendar appear on the Avioverse calendar and its read-only feed; keep it on for one due column only, so each tool appears once. Export gives Export CSV and Registry (PDF). In a Team workspace every member can open and edit the register.

The status is date arithmetic on what you entered. Avioverse does not choose the interval, and Not due is not a serviceability statement. Registries send no reminders, hold no attachments (the certificate stays in your document system), keep no row history or tool issue log, have no import, and offer search, sort and export rather than column filters.

Where to read it yourself

Every rule on this page is from the EASA Easy Access Rules for Continuing Airworthiness (Regulation (EU) No 1321/2014), 2025-09-02 revision. The user-guide passages are from UG.CAO.00132-003, library revision label 2026-05-19; the FAQ is EASA FAQ 116318.