fatigued spar cap angle 1

[taglia]

Suppose during maintenance tasks you find the rear lower spar cap angle with a crack due to fatigue. Is it normal practice to change both, front and rear lower cap angles, or change only the rear damaged angle?.
Thank you

 

[MiketheEngineer]

If I was flying that plane - I would change ALL of them...

 

[FieldTeam]

Why would you replace something that passes your inspection, unless driven by an AD, SB or other technical reference?

Mikes recommendation of changing all of them seams to be precautionary...but at what cost?

 

[rb1957]

rather than changing the front spar lower cap, i'd be more tempted to change the other side rear spar cap ... maybe the fatigue crack is undetectable now, but maybe it'll develop quickly.

what does the manufacturer have to say about this ?

have you crack checked the lower wing skins near the failure ? these would be significantly increased fatigue loading from the failed spar cap.

 

[taglia]

thank you all for your answers.
rb1957: if I do understand correctly, I should change the rear spar cap of both wings, that´s right?, it has sense.
The manufacturer says change the complete spar assembly, where you find damage.
The lower skin shows no damage but the reinforcement union band between the lower spar caps and the wing skin is also cracked, at the same position of the spar cap.
My doubt about changing the front lower spar cap is that nevertheless it shows no damage, I ask myself when will it show the failure, after one hour or after a thousand of flight hours.

 

[rb1957]

the loads on the front spar are often much smaller than the rear spar, depends on the plane (engine and gear loc'ns).

have you talked to the OEM, or are you "just" looking at the SRM ? they'd have a lot of interest in this, maybe some experience too. they'd also be able to tell you if the stress levels (fatigue spectrum) of the front spar are similar to the rear spar (hence the preventative action to change the FS). it Could be that this is an isolated failure (due to something specific to this plane) or it could be due to the general design of the plane; this distinction directs your repair work (if no fatigue failure was expected by design, then crack checking the other side may be sufficient).

sounds like this happened at the outbd spar splice, and you lost the spar and the splice strap ... so you had only 3 effective caps ... that sounds Very lucky to me !

i assume this is a Part23 plane ?

 

[taglia]

The stressed area is close to the rear landing gear fitting and it is "common" to this type of aircraft.
I will try also opinions from the OEM.
We are performing a SB from the manufacturer, but it doesn´t make mention about the other parts or the other side undamaged spar. This lighted on my curiosity.
I cannot give more details because it is government propietary, sorry.

 

[rb1957]

ok, i'd've thought that the SB would have completely spelt out what to do ... inspect, replace if cracked, have a nice day. if this damage is incidental to the SB, then you should call the OEM about it.

i'd still be very careful with the other side (ie inspect it frequently) 'cause it does sound like a design issue (rather than a one-off) and there's no reason that one gear should be significantly more damaging than the other, no?

 

[taglia]

you are right rb1957 about the other side. I was worried about the front rear lower spar cap and didn´t realize about the other hand spar. Thank you very much.