Proactive vacuum pump replacement

TMetzinger said:
I don't understand this at all. How does a climb or descent affect the indication of your bank attitude on an AI? That's what the pointer at the top of the instrument is for, isn't it? I dunno, maybe your AI looks different than what I'm used to.
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Might be different from yours, or maybe the location in the panel. Not sitting at the airplane right at this moment to try and figure out "why". However, we found the top pointer to be unusable while bouncing around in turbulence on our IPCs and were trying to reference from the "wings" (which is fine as long as you're not climbing/descending).
 
One of the nice things about at least the restart Cessnas is that they have dual vacuum pumps standard. I've had two or three of them go out on me, and the only way I knew it was the annunciator, since either one is sufficient to provide the necessary suction. So in the restart Cessnas, the answer is easy; replace the vacuum pump when it fails. For Scott's situation, I'd concur with his decision to replace it proactively for the reasons that Bill and others have said. Not just to make it easier to fly when it goes out in flight, but to prevent being stuck away from home needing an unexpected repair. You don't know what the opportunity cost will be on something like that!
 
I know a lot of folks who keep the vac pump they just removed in the plane incase of a failure away from home. Many also swear that having a spare ensures that the installed pump never fails.:rofl:
 
Why your vac pump keeps working is less important than the fact that it does!
 
It's surprising how many pilots fly around with an intake manifold pressure based backup vacuum system while having no idea how it works.

Nor do they understand that the power limitation means you must remain BELOW that power setting, not above it. The vast majority of owners I've flown with trust they have one but would have been screwed had they actually used it. It's a topic I cover when I spot one of these systems during flight training.
 
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My Mooney had an electrically driven vacuum pump in the tail as a standby - that worked very well when tested.. but the times I was partial-panel in that airplane was do to the AI failing, not a vacuum problem.
 
I've heard a few people here say they replace their vac pumps at around 500 hours. What's the basis for this?
 
This is a very common cost benefit reliability decision. It almost doesn't matter what the part is. The question is Replacement "on condition" vs replacement "on time."

It depends what the cost and frequency of failure events are to the operation.

If it's not possible to make MTBR or MTBF calculations, why?
(Mean Time before removal, mean time before failure)

Sounds like there is a quality/reliability problem with some of these units to begin with.

One of the reasons for high quality control in manufacture or overhaul is to achieve predictable performance.

If somebody's overhauling parts that don't last, I'd suspect the practices their shop uses are faulty. Maybe consider parts that are backed by a warranty, if possible.

If your operation could incur unacceptably large financial impact when a failure occurs, perhaps owing to a guarantee you make to your customers, use a reliable part and replace it on time. This is more expensive maintenance, but makes your business plan work.

If your business plan can tolerate the occasional adjustments in operating schedule that occur when failure occurs, replace on condition or at failure.

There is a difference too. Sometimes waiting until failure drives your repair costs up.
 
Hmm...not sure if that addressed my question...but currently I have about 1400 hours on my dry vac pump and its still working well. Can't imaging replacing it "just in case," especially after my previous failures in IMC. FWIW, I was hoping some people here have actually looked at the expected service life put out by the manufacturer...it's a surprising number of hours...
 
jesse said:
It's surprising how many pilots fly around with an intake manifold pressure based backup vacuum system while having no idea how it works.

Nor do they understand that the power limitation means you must remain BELOW that power setting, not above it. The vast majority of owners I've flown with trust they have one but would have been screwed had they actually used it. It's a topic I cover when I spot one of these systems during flight training.
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That's exactly why I ripped the Precise Flight out of my (turbocharged) plane.
 
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