Originally Posted by
Loose rivets
What made me take an initial look was the Rosemont vane builds and rebuilds. In short, I'm starting to be spooked on the macro scale.
Well, have a look at the Emergency AD that the FAA issued on April 18 to ground all Cirrus SF50 light jets.
http://rgl.faa.gov/Regulatory_and_Gu..._Emergency.pdf
Cirrus and Aerosonic (manufacturer of the technical standard order AOA sensor) have identified the probable root cause as an AOA sensor malfunction due to a quality escape in the assembly of the AOA sensor at Aerosonic. Two set screws that secure the potentiometer shaft to the AOA vane shaft may have improper torqueing and no application of thread locker (Loctite) to secure the two set screws. The AOA sensor with this quality escape is labeled with part number 4677-03
Not the first time that a shaft set screw backing off has caused an AoA sensor to fail.
http://www.smartcockpit.com/docs/Boe...On_Takeoff.pdf
Examination of the main gear revealed that the set screw that secured it to the shaft was not fully tightened: the overhaul manual specifies an assembly torque of 4.0 - 4.5 inch-pounds for this item. This was established as the reason for the random readings of the resolver outputs with respect to vane displacement, which thus resulted in the right ADC receiving erroneous angle of attack data.
Maybe not the best design choice? I've pretty much never seen a set screw installed in a self-locking threadform, they typically rely on anaerobic sealants to prevent them from loosening. A more permanent type of fastener might be a better choice.