I need a backup AI

[201er]

This is already my 3rd vac pump failure in just over a year. First time was a little over a year ago at night enroute to Florida. Ended up continuing 3.5 hours in night VMC with no AI/AP and over 6 hours back home in day VMC. Second time was about a month ago on the ground after landing VMC. Third time was last night on the ground just after start up (less than 20hours/30days since the last one was replaced). What the heck!?

We flew out to Pittsburgh to see a friend and were heading back same evening. We were rushing all day to get back to the airport before 8 when the line service closes to return the car. We ended up running 15 minutes late and were afraid we'd get stuck the night. But it just so happened that the line guy was waiting for a late jet arrival soon so we still made it. He let us drive up to the plane and everything was going great. I fired up and was fiddling with the fuel totalizer and within about two minutes of start up, I notice the 2 vac failure lights and AI keel over. Standby vac that works from differential pressure worked (but this only works effectively in the descent when you throttle back and not useful for takeoff or enroute). It was totally clear VMC. But coming back over some mountains to NYC with an already failed system (plus tiredness and other factors) was not a good idea so we had to stay the night and go back in the morning. The morning departure was rushed because deteriorating ceilings and snow were coming soon.

Are these vac pumps really so defective or is it possible that something is wrong with my plane that breaks them? As far as I can tell, since they suck air and since they are driven by a gear, it's really just the pump failing and everything else is ok. The standby vac that works off differential pressure worked, so that pretty well demonstrates that it's not the result of leaks or problems in the lines. AI worked with the standby so not a problem in the AI either. Anything worth checking or diagnosing before replacing the vac pump for a third time?

I don't want an electric vac pump because I have an electric HSI. So the only vac driven instrument I have is the AI. I figure it's better redundancy and cheaper to just have a backup AI.

Now as to backup electric AIs. Can you use any of them or are there different levels of certification? So far my biggest problem with vac failures (and as probability would have it) was not that they dangerously happened in IMC but that they would keep me on the ground waiting for good day VMC instead of departing when desired. Would having a backup electric AI legally allow me to depart night VMC or any kind of IFR? Or are some of them advisory only, not for exclusive use, or not IFR? How does the type certificate impact departing under the electric backup with the vac system inop?

[201er]

7 minutes ago, bluehighwayflyer said:

Are you putting new pumps in, Mike, or rebuilt?

As best as I can remember, one was rebuilt and one was new. Rapco 215CC. The recent under 20 hour failed one was new.

Edited February 5, 2017 by 201er

[Oldguy]

I switched over to a Tempest vac pump a couple of years ago and have had no problems. But didn't have any with the Rapco it replaced until it died (500+ hrs.).

Contamination a possibility? Does the filter get changed at every annual?

I know there are wet vac pumps versus the typically dry ones most of us run, and the things I read say they are much more likely to make their full life.

While it sounds like a run of bad luck, the fact you are still here and able to work on a solution tends to indicate otherwise.

[cbarry]

You might have someone check your vacuum regulator.  It may be set outside of the normal range.   You might also check your vacuum filter and make sure it's not restricted.  If the system is restricted, someone could have turned up your regulator causing the vacuum pump to work too hard which can lead to premature failure.

[201er]

2 minutes ago, cbarry said:

You might have someone check your vacuum regulator.  It may be set outside of the normal range.   You might also check your vacuum filter and make sure it's not restricted.  If the system is restricted, someone could have turned up your regulator causing the vacuum pump to work too hard which can lead to premature failure.

Thanks. Even in 16 hours since new?

[cbarry]

Some other thoughts:  if the vacuum system still contains some of the graphite components from previous pump failures, then they could be getting ingested into the new pump resulting in premature failure.  Make sure the system is clean before having the new vacuum installed.  Also, make sure you don't have an oil leak on the  flang side of the pump.  This can also cause premature failure.  A throrough review by a eagle eyed  mechanic should be able to trouble shoot this for you. 

[Andy95W]

+1 for the Tempest vacuum pump.

I just installed one a few months ago.  Very well engineered and a very well-thought out oil diverter piece that should help keep oil off the drive gear (one of many things that cause them to shear).

When you get your new one put on, make sure your mechanic replaces the seal that goes in the drive shaft assembly.

https://www.aircraftspruce.com/catalog/eppages/lycomingorings_08-19956.php

[201er]

I'm going to be trying to get a replacement under warranty so that may prevent me from switching to tempest until rapco dies of honest old age.

[Steve Dietrich]

Vacuum pumps can be damaged if the mechanic hits the short outlet with the solvent gun

[thinwing]

I think on the next install,all the lines should be purged and the regulator overhauled ,so many failures indicate contamination of the carbon vanes.Considering how much IFR you apparently fly,I would consider this life or death priority.Do you have space for the new Garmin ?Regardless ,I would restrict yourself from further IFR flight till this is sorted out.

[Danb]

Mike I went through three vacuum pumps in the first 210 hours of my 1988 J, on the dot every 70 hours, I ended up putting on a heat shroud and a thing that lowered the pressure can't think of what is was, 1988'1989, anyway after putting the mods on the forth pump it lasted 700 hours until I sold it for the Bravo. The mechanic was sure the mods would fix it and they did 

[Marauder]

Mike - to answer your backup AI question. If you leave the vacuum AI in and installed an electronic version, you would be essentially be installing a second primary AI. There is no backup requirement for a vacuum AI in our planes. The backup requirement comes into play when you have an Aspen or G500 type system.

I believe your AP uses the vacuum AI for the autopilot. So, I think you may lose that with an electronic version. If you wanted to add more capability to the electronic AI, there are units out there that can support Nav functions as well as airspeed & altimeters.


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[Tommy]

I use a Dynon D2 Pocket Panel as a back up. It can be turned on in flight and only costs you 1k! It will give you extra piece of mind and certainly will address your safety concerns but I am sure not legal concerns. It just doesn't make much a sense to spend 3k+ on something that only needed so rarely especially if you don't fly IMC much. But I think you proably have a systemic problem with your vacuum system as suggested by others. It's hard to pin it down to bad luck when you have so many failures. 

[201er]

3 hours ago, Marauder said:

Mike - to answer your backup AI question. If you leave the vacuum AI in and installed an electronic version, you would be essentially be installing a second primary AI. There is no backup requirement for a vacuum AI in our planes. The backup requirement comes into play when you have an Aspen or G500 type system.

I believe your AP uses the vacuum AI for the autopilot. So, I think you may lose that with an electronic version. If you wanted to add more capability to the electronic AI, there are units out there that can support Nav functions as well as airspeed & altimeters.


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But what requirements does the backup electric ai have to meet in order to be able to legally depart IFR with the vac driven ai failed?

[Marauder]

But what requirements does the backup electric ai have to meet in order to be able to legally depart IFR with the vac driven ai failed?

The G5 from Garmin can replace a vacuum AI. Even if you leave the vacuum AI in, it still is considered a primary AI. There are people out there who have removed their vacuum system and stuck a G5 in to serve as the primary. I don't see why you can't have both installed and still be legal.


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[201er]

32 minutes ago, Marauder said:

 

The G5 from Garmin can replace a vacuum AI. Even if you leave the vacuum AI in, it still is considered a primary AI. There are people out there who have removed their vacuum system and stuck a G5 in to serve as the primary. I don't see why you can't have both installed and still be legal.


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What about a straight electric ai? I'm kinda hoping to snag one cheap from someone jumping on the garmin bandwagon 

[Marauder]

What about a straight electric ai? I'm kinda hoping to snag one cheap from someone jumping on the garmin bandwagon 

I am not sure if the rules are different for mechanical AIs that are powered by electric. I know they can and are used as backups to vacuum AIs. Not sure if you can fly with one exclusively.


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[carusoam]

Mike, 

1) Expect Something is killing off the vac pumps. 

2) Look upstream and downstream to see what is in the lines.  How much to pull out the lines and replace pre-emptively..?

3) check on the cooling of the pump.  Some have cooling fins as part of the case indicating the importance of cooling. Has the cooling disappeared from your current pump?

4) If you go electric AI, look for one with it's own battery. This will protect against some power issues of the main bus.  Low voltage problem...

5) I would also be thinking of what happens when the voltage controller fails, and continuous charge goes on unabated.  High voltage problem...

6) how much voltage can the electric AI take.  Does it protect itself before getting burned out?

7) the current set-up is one electric device (TC) and one vacuum driven device.  An errant VR can't kill both...

8) making two electric units work probably takes two separate busses with digital over voltage protection. Something has to stop the errant VR overvoltage situation.

These are PP ideas specifically for Mike/201er...

1960s technology is so well thought out.  They considered everything over the decades....

Ask a lot of questions like these when talking to your potential suppliers.  There is probably a good answer like the alternator CB opens.

Best regards,

-a-

 

Edited February 6, 2017 by carusoam

[chrisk]

I'd probably install a G5.  Flying a partial panel with no auto pilot in IMC is a tad stressful.

[Guest]

7 hours ago, Marauder said:

 

I am not sure if the rules are different for mechanical AIs that are powered by electric. I know they can and are used as backups to vacuum AIs. Not sure if you can fly with one exclusively.


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I don't think there is a requirement that the AI be vacuum powered.  The Diamond DV20 with a Rotax engine uses an electric AI.

Clarence

[gsxrpilot]

A quick search on aircraft spruce for electric AI's will tell you which model numbers are certified as primary.

[jetdriven]

The G5 cannot replace a AI that has FD bars for an autopilot. Mike do you have the KFC-200?

 

also, that many failures I'd look at instalation practices for the cause. The install booklet is coverred in warnings about no teflon tape on fittings, replacing old hose, no solvents or silicon spray anywhere near the pump. Yet people routinely do all of this when they replace the pump. 

[Marauder]

The G5 cannot replace a AI that has FD bars for an autopilot. Mike do you have the KFC-200?
 
also, that many failures I'd look at instalation practices for the cause. The install booklet is coverred in warnings about no teflon tape on fittings, replacing old hose, no solvents or silicon spray anywhere near the pump. Yet people routinely do all of this when they replace the pump. 

I think he has a Century II or III.


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[Alan Fox]

Just install a precise flight standby system.....

[201er]

38 minutes ago, Alan Fox said:

Just install a precise flight standby system.....

I already said from the start that I have one but it doesn't help my deployment capability when I gotta depart IFR or at night with a broken vac pump.