I have been finding corrosion inside the flap torque tubes of 320/360s despite all of them living in a low humidity part of the country.  I first noticed this on my own 360 some 14+ years ago.

The plating on the inside of the torque tube does not adhere very well.  Since the tubes are capped in the center there is no cross ventilation.  Any moisture or water that get into the tube cannot easily escape.  This combination makes the tubes prime candidates to corrosion.

The biggest concern is the weld at the very end of the tube.  The greatest load on this part occurs at full flaps.  The most likely failure mode would be one flap suddenly retracting during a landing approach.

Inspecting the interior of this tube should be on everyone's annual condition
inspection checklist.

A few mitigation steps are possible if corrosion is found or suspected.

1.  Wiping the interior with a corrosion inhibitor such as LPS3 or ACF50 during every annual.  This can be done with a rag or towel secured to a long rod. 

2.  Coating the interior with a white (white for easy inspection) epoxy paint.  A rotary wire brush on the end of a long rod will help remove all of the loose plating and corrosion prior to painting.

Also, drilling the end-plates to form a through hole will enable cross ventilation to remove rain or other moisture that finds its way into the tube.

be safe out there,

Chris Zavatson

N91CZ

360std

www.N91CZ.net