On May 18, 3:19 pm, terry wrote:

Would love to know what your sources are on that information MX. in
all the aircraft I have flown both the AI and DI were powered from the
same vacuum pump and the pump is the most common cause of failure of
gyroscopic instruments. How do I know that? not from any books I have
read, and I have many on aviation, but from first hand advice from
several flying instructors, and actually had a vacuum pump failure in
a Warrior on one of my PPL flight tests ( and you are not allowed to
ask why I had more than one test :) )

We have no vacuum pump failures anymore. Just gyro failures.
Cessna now requires a pump replacement every 500 hours, or a pump with
an inspection port that can be replaced when the vanes wear to certain
point, which takes around 1100 hours on a Lyc, less on a Continental
because of the higher rotational spped of the pump on the Cont. It's
almost always vanes worn beyond limits that cause pump failure, or
rotten and breaking-up vac hoses that release junk into the pump and
lunch it. Cessan wants those hoses replaced every 10 years. Now you
know why.
Of course, so many owners and mechanics ignore the
manufacturer's requirements that pump failures will continue to be a
major problem.

Dan