ANSWER 1: “On June 11, 1958, RL201 lands with the left gear only partially deployed. The final turn and extension is incomplete, leaving the tandem wheels at an angle to the direction of travel. Jan Zurakowski is unaware of this condition, since the chase plane landed earlier due to lack of fuel.” “Likely cause of incomplete main gear extension – A chain assembly pulls the inner shaft of the main gear up and while shortening the overall leg rotates it through some 36 degrees. On deploying the gear, drag and gravity forces reversed this sequence. Early on in the program, Avro felt a chain dust cover was needed at the top end of the gear to ensure that nothing got into the inner shaft area which might block its decent. Apparently, Dowty did not agree but carried out the required modification. Because of this change, early accident investigation was centered on this modification as a probable cause. More in-depth work revealed that this particular gear was sluggish in its operation right from the start. Tracing its manufacture through various steps, it was discovered that, rust inhibiting cadmium plating of the ultra high tensile steel inner shaft varied in thickness and was properly ground to be within tolerance. During the plating operation, hydrogen migrates into the steel and slowly bakes it way out. With the cadmium plating in place the hydrogen on leaving the steel swelled the cadmium changing its thickness…in RL201’s case so much that the gear stuck. The solution – Plating was needed for rust protection. Hydrogen migration with plating is a fact of life. How do you get rid of the hydrogen, or at least keep it in place? The normal routine is to bake the metal at high temperature so that it bubbles out. This is not possible with the gear because the much needed heat treat would be lost. The solution was to coat the steel with a flash plating of inert gold and then plate over it with the cadmium. The gold stopped the hydrogen from getting out.”

Source:

Arrow Countdown,

pg. 36, 38-39 (Zuuring)