Basis for Calibration Method and Intervals (Frequency) - FAA approved repair station

[turbines]

We operate an FAA approved repair station and have been performing in house calibration of torque wrenches and pressure gauges for many years. Out procedures basically compare our MTE to masters that are sent out to a calibration lab on regular intervals. We perform no repairs or adjustments and equipment that fails is sent out for repair or replaced. Recently we decided to add micrometer calibration to our procedures and in the process of having the new procedures accepted by the FAA they are reviewing the entire procedures manual and have asked us to provide answers to the following per FAA Advisory Cirular 145-9 (4-12).

What is the basis for the test intervals (manufacturer, standard industry practice, etc.)?

Is the calibration technique recommended by the manufacturer or standard industry practice?

The FAA wants us to reference documentation relating to standard industry practices with regard to methods of calibration and intervals when no specific recommendations have been provided by the manufacturer. We are having trouble finding documentation the FAA will accept. NIST, for instance, provides nothing on the calibration standards for torque wrenches. Where are the resources that might help us on this documentation for all types of MTE?

[BradM]

Originally Posted by turbines

We operate an FAA approved repair station and have been performing in house calibration of torque wrenches and pressure gauges for many years. Out procedures basically compare our MTE to masters that are sent out to a calibration lab on regular intervals. We perform no repairs or adjustments and equipment that fails is sent out for repair or replaced. Recently we decided to add micrometer calibration to our procedures and in the process of having the new procedures accepted by the FAA they are reviewing the entire procedures manual and have asked us to provide answers to the following per FAA Advisory Cirular 145-9 (4-12).

What is the basis for the test intervals (manufacturer, standard industry practice, etc.)?

Is the calibration technique recommended by the manufacturer or standard industry practice?

The FAA wants us to reference documentation relating to standard industry practices with regard to methods of calibration and intervals when no specific recommendations have been provided by the manufacturer. We are having trouble finding documentation the FAA will accept. NIST, for instance, provides nothing on the calibration standards for torque wrenches. Where are the resources that might help us on this documentation for all types of MTE?

Good question. In my experience, it will be significantly easier to find recommended calibration procedures than for calibration frequency. First, since you work with government contracts, you should be able to get access to GIDEP. They should be able to provide you some industry standards for calibrating the devices. Also, many times you can purchase a calibration procedure from the MFG. If I understand their query, the FAA inspector wants to see upon what basis you have developed your calibration procedures (where did they come from, BTW?).

As far as calibration interval, they would seem to be more of a policy dictated by history. If you have been calibrating annually with no issues, then that interval should be sufficient. If you are having failures, then your recall schedule should be shortened. Also, there is an element of risk analysis that may be in order. Saying, if you have a critical process/ measurement, you may not want such a long interval, should a problem occur. I have battled a long-standing culture/accepted "law" that instruments should be calibrated every six months.

Also, there is establishing a correct program for your standards, their interval, competent labs, etc. Also, hopefully you develop a lattice approach, where you perform cross-checks of your standards, redundant equipment, etc., to minimize exposure should one of your standards be found out of tolerance.

[turbines]

Thanks Brad for the info. Unfortunately we do not do any contract work and aren't eligible for memebership in GIDEP. Can you suggest any other alternative sources?

[errhine]

When I send out the micrometers and Torque wrenches from our repair station, I normally get a calibration certification that is good for one year. We verify torque wrenches every 90 days (in house) and they must be checked out every day prior to use. We have been able to keep the micrometers on a one year cycle without any problems. Both our PMI and all of our customers so far are comfortable with this practice.

Unfortunately I do not think that this practice has a basis in anything stronger then 'Tribal Knowledge'.

[turbines]

We have used the same intervals for years without problems but now the FAA wants the documented evidence that the interval and the calibration procedures have been established in accordance with a standard from an accredited or otherwise recognized organization such as NIST, ASTM, SAE, ISO. Trying to comply with the FAA request seems to be easier said than done.

[andygr]

Easy item first.
Based on calibration history ( actuals) you should be able to justify the interval based on documented drift as seen durring calibration. This is clearly addressed as acceptable practice in the calibration standards. 4-12 c and 4-12 (2)of the AC clearly states that you set the interval unless you use pass/fail or state that you deligate this to the manfacture.

On to the issue the PI is pushing on procedures.
The AC is not requiring that you use procedures from these sources it is asking for the basis of the procedures you are using in house. 4-12 2 h has the word "could" not "shall" when refering to manufacturer or standard procedures. The AC clearly states that the items you quoted are guides in helping develop and not requirements.
Look at the calibration requirements as stated in the ANSI or ISO standards and show how your procedure addresses these.

Ultimatly you have to educate the PI and get him to approve your manual. If they are unflexable you can always try to get them to "educate" you on where in the AC is this clearly a requirement and hope they learn something themself.

[BradM]

Originally Posted by andygr

Easy item first.
Based on calibration history ( actuals) you should be able to justify the interval based on documented drift as seen durring calibration. This is clearly addressed as acceptable practice in the calibration standards. 4-12 c and 4-12 (2)of the AC clearly states that you set the interval unless you use pass/fail or state that you delegate this to the manfacture.

Exactly. Thanks for the section citations. That should help the OP.

Originally Posted by andygr

On to the issue the PI is pushing on procedures.
The AC is not requiring that you use procedures from these sources it is asking for the basis of the procedures you are using in house. 4-12 2 h has the word "could" not "shall" when refering to manufacturer or standard procedures. The AC clearly states that the items you quoted are guides in helping develop and not requirements.
Look at the calibration requirements as stated in the ANSI or ISO standards and show how your procedure addresses these.

Ultimately you have to educate the PI and get him to approve your manual. If they are unflexable you can always try to get them to "educate" you on where in the AC is this clearly a requirement and hope they learn something themself.

Again, superb advice. I second our requests-do you know where your existing procedures came from? They may be fine; they may not. As Andy suggested here, if you are confident that the procedures you have are adequate, then talking with the PI about them is a good idea. If you don't know where your procedures came from, or if they are any good, then you might want to revisit your practices.

[turbines]

The PI has advised me that the FAA acceptance criteria is now changed per a new FAA Order dated 1-08-2008. I have not been able to review a copy but from what he is telling me it mandates certain things that aren't addressed in the AC. I am anxious to get a copy of that new order. I can't find anything new on the FAA website but it just may not be posted there yet. Since he hasn't furnished a copy of the order I wonder if he's actually reviewed it or just heard about it.