Which loop resistance tester do the OEMs want you to use?

oem requirements

Identifying the right tool for aircraft OEM (Original Equipment Manufacturer)  bond and loop testing requirements can be complex.

As an MRO, your first point of call should be the AMM (maintenance manual).  However, some OEMs are more prescriptive than others.  And with a broad range of similar tools available on the marketing all claiming to comply with OEM requirements, how do you know for sure which tool is right?

MK’s range of bond testing tools are the BLTU4, BLRT and ExLRT.  These are often mentioned alongside the legacy industry tool, the LRT.  To help differentiate between all the tools, we’ve explained which one is recommended for each original equipment manufacturer:



All loop resistance testing on Airbus aircraft must be carried out at 1KHz, so the BLTU4 is the right tool. Airbus do not require joint testing, only loop and bond. We can support with proving equivalency to Airbus for using the BLTU4 within your operation – get in touch with us for details.



All loop resistance testing on Boeing aircraft must be carried out using 200Hz. In addition to loop resistance testing, Boeing also demand specific joint tests, variance tests and stray current tests – the BLRT is the recommended tool for this.

Both the BLRT and ExLRT are approved for use by Boeing.  What’s the difference between the two?  The ExLRT is certified as Intrinsically Safe and is therefore the best tool for MROs working on fueled aircraft.  However, the BLRT is the tool which has full bond, loop and joint capabilities.

Depending on your requirements and working environment, either of these tools may be suitable for you.  They’re both lighter and smaller than the legacy LRT, and can be operated by a single person.

To learn more about the differences between BLRT and the ExLRT, read this article.


Bombardier are aligned with the Airbus specification of 1000Hz, so we therefore recommend the BLTU4.


COMAC have specified the use of the BLTU4 tool in the AMM for ARJ21 aircraft models.


Embraer follow Boeing in terms of frequency and types of test required, so the BLRT or ExLRT would be the most suitable tools.


Visit the dedicated product pages for BLRT, BLTU4 and ExLRT to learn more about each of our bond and loop testing tools. To learn more about the differences between our tools and the legacy Boeing-approved LRT, visit our blog and filter by ExLRT.


oem requirements  BLTU application 3 - loop resistance and integrity of cable shields and bonding straps