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Lost Vacuum under hood...wow


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So I’m working on my PPL in a 172 while my M20 is in pieces all over the country for various reasons. This Sunday was the first practice under the hood. I have previously flown in IMC with an IIFR certified instructor in the right seat and so this wasn’t the first time under instrument. I did fine that time, however, this Sunday was a different experience. 

Under the hood I was really struggling to hold the heading. If I put the wings level in the AI the DG would show me turning one way. Then I would fix it. Wings level. Then it would say I was turning the other way. I commented to the instructor that I suck this time and I don’t know why. It started to mess with me. What my body felt, what my senses told me, what logic was telling me, didn’t match what I was seeing. Then the AI started telling me I was rolling to the left and I started to correct it, but it didn’t add up. I told him “something’s wrong, I don’t like this” and panicked a little even though it was VFR with the instructor in the right seat. I lifted the hood briefly and saw I was still wings level. 1 Mississippi, 2 Mississippi...,5 Mississippi and the Instructor says “wow, look at your vacuum gage”. IT was reading zero and the AI was a tumbled sideways and down (basically the opposite of what I would have done to try and save it)

There are some valuable lesson here as with many things that happen to go wrong that don’t kill you....I don’t think I would have survived that in real IMC, especially if alone. But now I’ve seen exactly what a vacuum pump failure looks like. It’s subtle at first as the gyros spin down. They will kinda work, the errors will get worse...then they fall apart like a top running out of spin.

I tried flying partial panel a little bit after and boy that would be tricky with just a T&B and compass for wings level. Survivable in a straight line until I’m clear of clouds but that’s about it at my current skill level. So this further enforced for me the fact that I’m not going IFR until I have an electric AI as a primary or backup. I want a way to quickly double check that the primary is correct...not just for when the first one fails because once you realize that it failed, it might be too late. 

This trip was my first time flying with only a Whiskey compass...what a terrible instrument! I now see I need to focus more on learning how to use it better or I need a vertical card.  Dreadful thing.  I have a lot more respect for our flying ancestors and understand better how Amelia probably vanished.

I also learned that I hate vacuum gages. I would much rather have the idiot light like my 66’ E. That light would have warned me to not trust the gage and this AI didn’t have any flags which would have also worked. 

My take-aways, in summary:

1.  Don’t fly IFR if your AI doesn’t have a vacuum loss flag or your panel only has a vacuum gage  

2.  Vacuum pumps fail...a lot apparently, don’t bet your life on it not.  Have a damn good plan B and a clear way of knowing when to take it.  

3.  If the gages don’t add up, maybe fall back on the secondary while you judge if the primary is safe to follow, don’t let them fly you into the ground if multiple sources aren’t agreeing.  I did decide it was wrong this, but panic boiled up. It wouldn’t have ended well. (I’m pretty sure this type of guidance is in IFR training?)  This also directly conflicts with the idea of trusting your gages in IMC.  Having this doubt in your mind might be really bad actually.

BTW, before you beat me up, I only have about 25hrs of VFR training with interruptions as my Mooney failed on me again and again. This was my first time under the hood...I’m still a noob. 

Comments on what else I should take away are welcome but don’t try to talk me out of hating a mag compass. Lmao. 

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Honestly, this sounds like an experience that more people should have.

In a safe environment, VMC with an instructor, you've seen first-hand what happens when an instrument fails. And you're starting to think seriously about personal minimums (including about minimum equipment for instrument flight). 

I suspect there are quite a few instrument rated pilots flying around in IMC who have never experienced a real equipment failure, and have an inadequate appreciation for how quickly things can go to hell. 

Doing the debrief in your head, with your instructor, and with others on MS or elsewhere is the right way to go. But don't be too hard on yourself. You'll be a better pilot for having seen this first-hand. 

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Now you know the value of a backup attitude indicator. I’d never fly IMC without a backup. You had the luxury of looking at the horizon that day. Imagine if that wasn’t an option. An invaluable experience that can’t be taught. Training partial panel has its limits. The element of surprise is absent. When your instructor blocks an instrument you know what’s going on. When the bad info from the panel creeps in slowly you have to figure the situation out. Nice catch! Live to fly another day! 

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I had 3 vacuum loss in Mooney, two in IMC, annunciation in panel comes handy for low vacuum pressure and electric AI backup sitting nearby does confirm it, I am still trying to convince two pilots in my partnership to remove whole vacuum system and switch to 2*G5 standalone units, also you will find out that servicing vacuum AI & HSI as one-off costs as much as two G5...the funny thing is that most people think it is a good idea to rely on vacuum systems as primary :blink:, I personally find them misleading and they have wired failure modes (it takes 30min from getting low vacuum to getting the AI to tilt 45deg and get stuck when you are sure it is dead not working) vs electric & electronic standalone units (e.g. G5) which have very clean failure modes as far as I am concerned, although full glass integrated cockpits need a good read...

Not that I would treat an AI failure lightly, I had it twice both were emergencies where I did cloud break and continued VFR, but once you are aware it is not working and you put a paper on it, then slow down on speed and throttle back on power, surviving in IMC with partial panel should be non-event, but doing precision approach or navigation on partial panel to unfamiliar places in tight weather will be tough, how tough? anything procedural or vectors in busy ATC places will eat all your mental capacity, unless it is “non-gyro” PAR/SAR cloudbreak or instrument approach you will be under the rug in ATC system...

Also, limiting your IMC time (20min? 30min?) should do the job until you get two electric backups and decent AP that hooks to them at least in wing leveller mode, if you are flying serious weather you are better flying with gyros attached kittens than relying on old vacuum systems for primary attitude for a 4h hand flying flight :lol:

Glad you experience it and manage it, it is all about the slow surprise element that is what you should watch for, a fast spinning vacuum AI is better than one that tilts 1deg/1min...

A tip: if you want to know how YOUR vacuum AI behaves in loss of vacuum, stay in the aircraft when you stop the engine while parking on a level surface after a flight you will see the whole picture from start to end ;) in theory, the real behaviour may differ depending on variation errors from accumulated acceleration, earth rotation and transport wander but I am sure you can ignore these on a 30min “no gyro” flight !

 

Edited by Ibra
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IMC airplanes really should have three ADIs,,,you need a tie breaker....I have two G5's and feel just okay about it...but I do have an AHARS in the GTX345 that displays on the panel mounted iPAD.

The step further it really needs is to have a comparator that  looks at the primary G5 ADI and the behind the scenes ADI in the HSI G5...Garmin says there is none....There really should be..

Vacuum pumps fail a lot for various reasons.....toss the vacuum ADI

Also as a technique go with sky pointers....its what is in most if not all corporate jets and airliners....makes life easy when the crap hits the fan...the arrow is always pointing to the sky....its all what you are used to but you mind as well get used to the stuff the pros use....

 

image.png.9f47156be3614bc74e283fd14c9ae212.png

 

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10 hours ago, Nukemzzz said:

So I’m working on my PPL in a 172 while my M20 is in pieces all over the country for various reasons. This Sunday was the first practice under the hood. I have previously flown in IMC with an IIFR certified instructor in the right seat and so this wasn’t the first time under instrument. I did fine that time, however, this Sunday was a different experience. 

Under the hood I was really struggling to hold the heading. If I put the wings level in the AI the DG would show me turning one way. Then I would fix it. Wings level. Then it would say I was turning the other way. I commented to the instructor that I suck this time and I don’t know why. It started to mess with me. What my body felt, what my senses told me, what logic was telling me, didn’t match what I was seeing. Then the AI started telling me I was rolling to the left and I started to correct it, but it didn’t add up. I told him “something’s wrong, I don’t like this” and panicked a little even though it was VFR with the instructor in the right seat. I lifted the hood briefly and saw I was still wings level. 1 Mississippi, 2 Mississippi...,5 Mississippi and the Instructor says “wow, look at your vacuum gage”. IT was reading zero and the AI was a tumbled sideways and down (basically the opposite of what I would have done to try and save it)

There are some valuable lesson here as with many things that happen to go wrong that don’t kill you....I don’t think I would have survived that in real IMC, especially if alone. But now I’ve seen exactly what a vacuum pump failure looks like. It’s subtle at first as the gyros spin down. They will kinda work, the errors will get worse...then they fall apart like a top running out of spin.

I tried flying partial panel a little bit after and boy that would be tricky with just a T&B and compass for wings level. Survivable in a straight line until I’m clear of clouds but that’s about it at my current skill level. So this further enforced for me the fact that I’m not going IFR until I have an electric AI as a primary or backup. I want a way to quickly double check that the primary is correct...not just for when the first one fails because once you realize that it failed, it might be too late. 

This trip was my first time flying with only a Whiskey compass...what a terrible instrument! I now see I need to focus more on learning how to use it better or I need a vertical card.  Dreadful thing.  I have a lot more respect for our flying ancestors and understand better how Amelia probably vanished.

I also learned that I hate vacuum gages. I would much rather have the idiot light like my 66’ E. That light would have warned me to not trust the gage and this AI didn’t have any flags which would have also worked. 

My take-aways, in summary:

1.  Don’t fly IFR if your AI doesn’t have a vacuum loss flag or your panel only has a vacuum gage  

2.  Vacuum pumps fail...a lot apparently, don’t bet your life on it not.  Have a damn good plan B and a clear way of knowing when to take it.  

3.  If the gages don’t add up, maybe fall back on the secondary while you judge if the primary is safe to follow, don’t let them fly you into the ground if multiple sources aren’t agreeing.  I did decide it was wrong this, but panic boiled up. It wouldn’t have ended well. (I’m pretty sure this type of guidance is in IFR training?)  This also directly conflicts with the idea of trusting your gages in IMC.  Having this doubt in your mind might be really bad actually.

BTW, before you beat me up, I only have about 25hrs of VFR training with interruptions as my Mooney failed on me again and again. This was my first time under the hood...I’m still a noob. 

Comments on what else I should take away are welcome but don’t try to talk me out of hating a mag compass. Lmao. 

Did your instructor follow up this failure with a practice no-gyro approach with ATC?  Thats a great get out of jail free-ish card that it seems like many IFR students arent taught (although sometimes location dictates ability).  Get him to show you next time. 

I carry a few hundred dollar Dynon D3 digital attitude indicator https://www.dynonavionics.com/pocket-panel.php  

Now I have my default vacuum system, backup manifold vacuum, gtx345 to ipad AHRS, and d3 pocket panel.  One thing I like about the ipad connected AHRS is that I can split the screen and have AHRS on one side and my approach plate on the other.  When I take my eyes off of the panel to look down at the plates I have a tendency to induce a roll.  This lets me see it immediately as I switch my vision back and forth between the panel and the ipad. 

Also PSA - change your dang vacuum pumps at the recommended TBO (time or hours).  I teach some for APOA and it seems like every accident video they produce is about some guy with a 15 year old vacuum pump and 10000 hours on it who loses suction in IMC.  Pretty sure Mike Busch says the only two things he changes on TBO are magnetos and vacuum pumps. 

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I ever get to do the IR thing (keep funning out of ca$h) the Mooney is getting a standby vacuum or a couple G5's.  I wouldn't go into the soup without some sort of backup.  I've seen youtube videos of guys with more ratings, time, and skill than me totally loose it partial panel.

Also, the iPad panel is likely to be useless if you don't practice it.  An emergency (which is what loss of vacuum in IMC is) is a crappy time to try things out for the first time.

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7 minutes ago, steingar said:

 the Mooney is getting a standby vacuum or a couple G5's. 

Two G5's adds a lot more value to the airplane than the standby vac.  Plus they are a lot safer and do more....Let me spend your money

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Just now, Jim Peace said:

Two G5's adds a lot more value to the airplane than the standby vac.  Plus they are a lot safer and do more....Let me spend your money

I would do it right now had I the ca$h.  Actually, I'd do the IR had I the AMUs.  But I don't, so all I can do is dream.

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Great shared experience, Nuke!

Two things that are a challenge to practice...

1) Vac pump failure...

  • recognizing it is a challenge... (Pilot experience helps recognize bad data, not thinking it is a bad pilot)
  • Doing something about it is a challenge.... (Find the failed instrument, then use what’s left)
  • Not reverting back to the dead instrument is a challenge... (post its and other instrument covers)

2) Failed turbo systems...

  • There is no switch for these things either...

 

PP thoughts only, not a CFI...

Best regards,

-a-

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If you vacuum pump fails you should catch the failure early on.  That is the reason to include the vacuum gauge in your scan.  if the pump has failed, cover up your vacuum powered instruments with a piece of paper or cardboard.  It is near impossible to ignore a misbehaving instrument, a distraction you will not need even if VFR.

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1 hour ago, David Lloyd said:

If you vacuum pump fails you should catch the failure early on.  That is the reason to include the vacuum gauge in your scan.  if the pump has failed, cover up your vacuum powered instruments with a piece of paper or cardboard.  It is near impossible to ignore a misbehaving instrument, a distraction you will not need even if VFR.

I’m still not a fan of the vacuum gage. 99.99% of the time it will be fine so when it isn’t, you’ll see what you expect and not notice. I think you really need a flag or light. Something to snap you out of the “normal” scan. 

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13 minutes ago, Nukemzzz said:

I’m still not a fan of the vacuum gage. 99.99% of the time it will be fine so when it isn’t, you’ll see what you expect and not notice. I think you really need a flag or light. Something to snap you out of the “normal” scan. 

You can add on a separate annunciator pretty inexpensively.. something like this

https://www.aircraftspruce.com/catalog/inpages/vacuumwarning.php

(I have no experience with that particular product, so ymmv - just an example.)

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18 hours ago, Nukemzzz said:

I’m still not a fan of the vacuum gage. 99.99% of the time it will be fine so when it isn’t, you’ll see what you expect and not notice. I think you really need a flag or light. Something to snap you out of the “normal” scan. 

I'm equally suspicious of other indicators. The gauge you can continuously monitor and see that it is working.  I would much rather have both a gauge and a light indicator.  Naa.  I would much prefer to get rid of the vacuum and go with all electric with a backup battery. Just waiting for approval from the home office.

 

Just checked my POH to be sure.  The 1975 C did not have a gauge, just an annunciator.  Guess my gauge was added later.  The 1976 models had a gauge but no annunciator.  Glad mine has both.

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4 hours ago, David Lloyd said:

I'm equally suspicious of other indicators. The gauge you can continuously monitor and see that it is working.  I would much rather have both a gauge and a light indicator.  Naa.  I would much prefer to get rid of the vacuum and go with all electric with a backup battery. Just waiting for approval from the home office.

+1

My attitude indicator has an orange flag that drops when vacuum fails.  I also have a vacuum gauge.

When I had a vacuum pump failure (in VMC) the first thing I noticed was the flag, then I confirmed with the gauge, so I definitely agree with David.

I should say "used to have".  My home office recently approved the upgrade.  The day the G5s arrived, my vacuum system got removed.  I should have the new stuff installed in the next month or so.  Thanks to @bradp for answering questions and posting his thread:

 

 

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