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I was torque checking pitot tubes with a click type wrench for 4 years and never caught it | Avionics Technicians - nhfree.com

parkerh38•1mo ago

I was torque checking pitot tubes with a click type wrench for 4 years and never caught it

For 4 years I used a click type torque wrench on every pitot tube install and never once got a failed leak check after. Then about 2 months ago I was doing a swap on a G450 in Wichita and a guy from the next hangar watched me finish, then asked if I had ever checked the wrench itself. I said why would I, it clicks when it hits the number. He grabbed his beam wrench and we ran the pitot bolts on a scrap mount to compare, and my wrench was pulling about 9 in-lbs low at 35. Click type wrenches go out of spec slowly enough that you never feel it, especially if you drop them or leave them set at a number in your box instead of backing them off to zero. The leak checks were passing because pitot tubes seal fine even a little loose, but the manual gives a min and max for a reason and I was quietly sitting under it. Now I break out the beam wrench every 6 months and check it against a known good one before the task. Is there a cheaper way to verify a small torque wrench in the shop without sending it out for cal, or do you guys just run beam wrenches on pitots full time?

1 comments

1 Comment

dakotacraig27d ago

Check the spec on that torque wrench before you trust it as a "known good" reference, because most click type wrenches in the sizes we use on pitots are only rated plus or minus 4 percent accuracy, and that is at full scale. At 35 in-lbs on a wrench that tops out at 150 or 200, you are down near the bottom of the scale where the error gets even bigger, so checking yours against it does not really prove much. What you actually found is that his beam wrench read different, not that yours was 9 low. To know which one is right you need a real standard, like a torque tester or a calibrated deadweight setup. So running beam wrenches full time does not fix it either, beams drift too and they are a pain to read at an angle. The cheap shop answer is a small dial or digital torque tester, and if the budget is not there, at least send one wrench out for cal and use it only as your shop reference, never as a working tool. Pitots sealing a little loose is exactly why this bites people, the leak check gives you a false sense of good when the real issue is a fastener that is not at the torque the manual calls for.