I’ve found a fair amount of Lower Landing Gear attach bolts that were loose , stretched or broken.
SB 1375A addresses this but I don’t agree that Time Change is the solution.
Current patient had a broken bolt previously.
Had analyzed and failure due to Fretting.
All bolts replaced with AN.
100 hrs later we are finding the nuts loose again.
One is so loose I can spin with fingers but Torque Indicator paint is not broken.
It must be stretched.
Hole measure .250 Bolts .247.
Oddly some old bolts are fine.
The plan is to install 4 new NAS bolts on the bottom.
Some concerns:
NAS 6604-11 comes in both Shear and Tension versions with same p/n.
Is the Torque Spec for NAS bolt the same as for an AN?
Friction Torque + Applied Torque = Desired Torque (Standard 1/4-28 torque)?
Or?
This is not the only aircraft having issues like this.
Many years ago a Pawnee was breaking wheel bolts
Switching to NAS eliminated the problem.
Could this be poor hardware or incorrect torque?
SB 1375A addresses this but I don’t agree that Time Change is the solution.
Current patient had a broken bolt previously.
Had analyzed and failure due to Fretting.
All bolts replaced with AN.
100 hrs later we are finding the nuts loose again.
One is so loose I can spin with fingers but Torque Indicator paint is not broken.
It must be stretched.
Hole measure .250 Bolts .247.
Oddly some old bolts are fine.
The plan is to install 4 new NAS bolts on the bottom.
Some concerns:
NAS 6604-11 comes in both Shear and Tension versions with same p/n.
Is the Torque Spec for NAS bolt the same as for an AN?
Friction Torque + Applied Torque = Desired Torque (Standard 1/4-28 torque)?
Or?
This is not the only aircraft having issues like this.
Many years ago a Pawnee was breaking wheel bolts
Switching to NAS eliminated the problem.
Could this be poor hardware or incorrect torque?
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