changing calibration intervals

Aviation calibration testing ensures that measuring tools and equipment are working correctly. When an instrument continually passes testing without fail, and did not require any adjustment, many wonder if the next step should be lengthening the calibration due date. On the other hand, if equipment constantly requires repair or frequently fails testing, should the calibration interval decrease? There are multiple factors to consider, especially for MROs and FBOs that must observe FAA mandates. Answer the questions below to determine if changing calibration intervals is the best choice.

What is the Manufacturer Recommendation?

The best place to start is checking the calibration interval suggested by the manufacturer. Most manufacturers will have a suggested calibration interval listed inside the equipment manual. This will normally be listed under a calibration, testing, or maintenance section in an equipment manual. Custom equipment may not have any documented recommendations for calibration testing, the best course of action is to ask the fabricator.

What are the Testing Results for the Past 3 Years?

You must ask, “What does past performance show?” Previous testing will clearly show the reliability of an instrument. A minimum of three years for equipment records should be used to determine results. The maximum calibration cycle for the majority of equipment is one year. Three years of historical results will provide information for at least three test results.

For example, take a pressure gauge with a nine month calibration interval. If the pressure gauge calibration process has never required adjustment and shown passing results, you could consider extending the calibration interval. The past performance demonstrates that this instrument is a good candidate for a longer cycle.

ItemID Type Status Ref DueDate PrevDueDate
3338 5,000 psi pressure gauge Pass N/A 12/1/2014 3/1/2014
3338 5,000 psi pressure gauge Pass N/A 9/1/2015 12/1/2014
3338 5,000 psi pressure gauge Pass N/A 6/1/2016 9/1/2015
3338 5,000 psi pressure gauge Pass N/A 3/1/2017 6/1/2016


If the instrument regularly is found out of calibration or fails testing, it may require a shorter calibration interval. For example, contemplate a dial caliper with an annual calibration cycle. In the example here, the dial caliper has failed testing, required repair, and been adjusted. When researching the problem, we find that this dial caliper is often used outside of the hangar. This instrument is more likely to incur exposure to the elements or be dropped during transit. In this case, changing the calibration interval to a shorter cycle may be recommended.

ItemID Type Status Ref DueDate PrevDueDate
7558 dial caliper Fail N/A 6/1/2015 6/1/2014
7558 dial caliper Pass Repaired 6/1/2016 6/1/2015
7558 dial caliper Pass Adjust 6/1/2017 6/1/2016


Does the Equipment Have Known Issues?

Once equipment has been in service for a few years, AMTs and calibration labs will begin to notice if any common issues occur. In the instance of a mass flow controller, debris or a collapsed tube are known issues. Many times a calibration technician will clean out or repair any problems noted during calibration testing. AMTs may benefit by having these instruments tested more often.

Are Calibration Intervals Specified in Any Contract Agreements?

If your company has a contract with customers, check if there are any stipulations regarding calibration intervals. A customer may include requirements for maintaining the manufacturer recommended calibration interval or another interval of their choosing. An example would be that all navigation equipment must be tested annually. If the calibration interval is part of a documented agreement, be prepared to justify your reasoning for requesting the change.

Does Changing Calibration Intervals Contradict FAA Mandates or Internal Quality Guidelines?

Meeting or exceeding FAA guidelines is of the utmost importance to MROs and FBOs. Luckily, FAA guidelines aren’t as intimidating as they appear. The bulk of the regulations focus on following manufacturer recommendations and the calibration procedures that are outlined in the Quality Control Manual or other related documentation. In most cases, there aren’t any restrictions on decreasing calibration intervals. Lengthening calibration intervals is where you need to be careful. Refer back to the manufacturer recommendations for the calibration interval. Changing calibration intervals will not create any problems as long it does not surpass the manufacturer interval.

Next Steps

Quality Control Manual documentation should be updated when changing calibration intervals. This is extremely important to remember, especially for audit purposes. As soon as you decide to change the interval, update the manual right away. Make sure to replace any printed documentation to reflect the change.

Communicate with everyone effected by the aviation tooling calibration process. Make sure that everyone is aware of the change so that the calibration due date is not missed. If applicable, update the calibration interval change in any aviation asset management software or calibration certificate software.

Make sure that you keep the above points in mind if you are considering changing calibration intervals. If you have any questions about changing calibration intervals, contact e2b calibration (an ISO/IEC 17025 accredited calibration laboratory).