Droop Cam Jack Shaft
In 1992 UH-1-92 ASAM-13 was issued that later became TB1-1520-210-19 one time & recurring inspection of the droop compensator jackshaft.
At that time the messages were issued first. Sometimes there were questions or corrections. Then later the Tech Bulletin would be issued which was the final version.
The text of this message seems to be lost to history.
Just the other day I came on to an example of what the message was about and thought I would pass this along.
You were to inspect the arm on the end of the droop cam jackshaft on the engine side of the forward firewall.
You then cleaned of a small area of paint from the arm facing you. You then tested it to determine if it was aluminum or magnesium.
To test it you could use vinegar if it was magnesium there would be a fizzing / bubbling action & if it was aluminum there would be no notable reaction.
You would clean of any vinegar from the shafts and etch an M on the magnesium arm and repaint the aluminum arm and continue use.
The magnesium arms required recurring inspections. You were required to replace the magnesium arm & shaft when they became available.
The arms and shaft are riveted together. The Magnesium arms were known to corrode and fail.
Again the intervals and max time are lost to history.