Avionics Etc.

Fluke 77 or Equivalent

By Marijan Jozic

We are trained to measure different things: voltages, frequency, power, current, etc. A few years ago someone decided that technicians had to prove they are using the right equipment for measuring. Let me explain.

In the component maintenance manual (CMM) the manufacturer provides the list of equipment required to do the test. After the line replaceable unit (LRU) is designed, the engineer at the factory writes the test for the unit. The unit must be tested at the test bench to demonstrate it is working as specified. The test equipment available at that moment is used. If the company is rich, it would have a lot of fancy and expensive equipment, otherwise old test equipment is used. The CMM is supposed to list the necessary equipment. That is when the trouble starts. To please his customers, the manufacturer does not just specify one piece of equipment, but gives the choice by saying "or equivalent."

For decades, avionics shop technicians were evaluating the test procedures for the LRU's. They were checking tolerances and instead of using the meters specified in the CMM's they were saving money and using meters available in their shops. Thus, the technician issues the company test procedure and specifies the equivalent meter. Many years ago the authorities were willing to accept sound judgment. Actually by introducing the LRU in the avionics shop the equivalency was established and for years nobody questioned it.

Then one smart guy at the authorities decided to force the whole industry into serious costs. He was in a position to ask and enforce. He asked: are you using the equivalent? He enforced: prove for all equipment you are using that it is allowed to be used. He didn't care that we are trained to measure. He just wanted to satisfy the paper, which became more important than common sense.

Now after many years the authorities decided to force avionics shops to start a gigantic project and exercise every CMM and issue a determination report for every test. The report must provide the statement that the CMM final test is reviewed and a certain alternative equipment may be used to accomplish it. If the avionics shop is big, it takes some time to check all CMM's and to issue the reports. If the airline had smart technicians who designed a lot of equipment and adjusted the test procedures to use the equipment available in house, they would save a lot of money for the airlines.

All that saving is going down the drain at the moment because the airlines have to pay somebody to evaluate the CMM test procedures and write determination reports. For a small size shop (200 technicians) they have to evaluate 3,000 to 4,000 CMM's.

Assuming that a good technician can check 4 CMM's per day and write a report, it will take 1,000 days to finish the job. That is a lot of money. Four CMM's per day is fast. It is easy when you deal with new equipment or test setups which use the CMM prescribed equipment. Just check it and copy the statement. No deviation. The equipment used in the text is the same as the CMM.

But the difficulty comes when the test equipment in the CMM is made by a company that does not exist any more, or the company name has changed and is unknown. Since there is no data about the original equipment, and no specification kept, there are two possibilities: to spend days searching for data on the Internet or to scrap it all and delete the capabilities.

Some CMM tests are not used as manual tests at all. They are rewritten in Atlas (programming language) and executed on ATEC's or other automatic test equipment.

Well, after 1,000 days the paper requirement is satisfied. Now we are in a strange situation. The determination report is finished and the authorities are happy. The technician is doing the test and he discovered that the Fluke 77 is in the calibration lab for recalibration. He has to finish a job and decides to use Fluke 78 (which is even more accurate). Wrong! Although he is right and he is using good equipment (and he is also using his brain) his QA inspector (who is not using his brain but a piece of paper) will disapprove it because Fluke 78 was not mentioned in the determination report as equivalent.

ARINC spec 668 is issued to help airlines. It is written to provide guidelines for determination of equivalency. If 668 was not written, the QA guys would require airlines to create even more paperwork, for example: OEM statements, OEM approval of equivalency or NTO (no technical objection). Worldwide, millions of determination reports are issued and millions of dollars were spent. Is sound judgement worth nothing? Did this exercise make the world a safer place?