Repost: To Castle and Back

“Cessna 69N, 20 miles south of Atwater, say intentions?” asked  NORCAL Approach.
“Request ILS 31 approach into Atwater”  responded I.
“Descend and maintain 5000, fly heading  310”

“Roger” said I and eased back the throttle to  2000rpm to start a slow descent from the 8000ft we were flying on our way to Atwater and turned to a heading of 310.

Nothing happened!

The VSI still stayed at zero. The tachometer read 2000 rpm.

What was going on?

Continue to read here.