We're talking all about the vacuum system this week on BTP. That's why we say... this show SUCKS!
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00:01
Behind the Prop Intro
Clear prop S73 Cherokee number two following twin traffic three mile final one trolley bravo makesford in Runway two five going four mile.
00:10
Nick Alan
This is behind the prop with United Flight Systems owner and licensed pilot Bobby Doss and his co host, major airline captain and designated pilot examiner Wally Mulhern. Now let's go behind the prop.
00:24
Bobby Doss
What's up Wally?
00:26
Wally Mulhern
Hey Bobby, how are you?
00:27
Bobby Doss
I am fantastic as always. We are revisiting a system today and we did Pitot static system a couple weeks ago and seemed very popular. Lots of downloads and listens to that show. So we are going to complement that today with the vacuum system and really we are going to talk gyroscopic instruments that are driven by the vacuum system along with we are going to throw in the turn coordinator to try and make this a more teaching or lesson oriented type podcast to hopefully help all of you perform better on your check rides and really just understand the systems and hopefully do better in case you ever have a failure. Wally, have you ever had a vacuum system failure? Any part of it?
01:14
Wally Mulhern
Well, before we even start, I'm going to say this because when we came up with the idea of this show, I came up the idea of saying what I'm about to say and I wanted to say it. So this show is really going to suck.
01:26
Bobby Doss
There you go. Maybe we should make that the title of the show.
01:31
Wally Mulhern
No Getting back to vacuum pump failures. As were prepping for the show, I was asking Bobby how many hours they get out of a vacuum pump before I got my instrument rating. This was a long time ago, but before I took my checkride I had three vacuum pump failures. So I became a believer, very much a believer in partial panel training and in fact probably my instrument students, we probably had the vacuum instruments covered up for sure more than half the time. But I'd say 60 to 70% of the time that went out and flew it was partial panel just because I had it happen three different times. Three different airplanes by the way, in.
02:24
Bobby Doss
IMC or VMC or.
02:26
Wally Mulhern
Oh no, no. It was all vmc. It was all vmc. You know, I wasn't instrument rated at the time. But the vacuum pump failure or a vacuum system. Well, basically every vacuum failure, every vacuum system failure I've had has been because of a vacuum pump failure. It's, it's hard to recognize. It's, you don't get a flag that says inoperative. Some airplanes you may have get an enunciation that says vacuum. But you know, the vacuum gauge or the suction gauge, as some manufacturers call it, is probably something that's not in our scan, and I don't know, it probably ought to be. I've always thought that kind of the worst scenario would be a VFR night flight with no moon or anything. No visit, you know. You know, no prominent horizon, and having a vacuum pump failure.
03:33
Wally Mulhern
Because what happens is as these gyros and these instruments begin to spin down, they don't come to a screeching halt. They spin down. So these instruments go from being, you know, call it a hundred % accurate to 99%, 98, 97, 96. And if that attitude indicator begins to tilt and you're following it, you could put yourself in a very bad situation.
04:06
Bobby Doss
No doubt, the degradation of these instruments, no matter how or what they're doing, to fail, it could be a scary proposition. And that's why I'm a little biased because I just got back from redbird migration. But that's why a sim is so valuable to this type of training, right? You're in the clouds. You can be completely in the clouds. You can simulate that at night, no visual reference to the ground and degregate the pump or fail the system in some way. And the attitude indicator is not just going to fall off the map. It's going to, as you say, become a three degree pitch. And as you try to correct that, then your heading is going to start moving and your headings going to start moving a lot, maybe even start spinning.
04:51
Bobby Doss
If that heading indicator started spinning and that attitude indicator started showing a turn opposite of that spinning heading indicator, it's going to be hard for any of us to keep those wings level. Thank goodness most planes now have a turn coordinator, which is why we're talking about it, that is driven by something different than the vacuum pump. That gives us kind of an out.
05:13
Wally Mulhern
Right, right. And, you know, I was talking to a young man this morning about it, and were talking about vacuum pump failures. And I, I used the analogy. I don't know, I hope it wasn't too out of line. But I said a vacuum pump failure is like dying of cancer as opposed to a heart attack where it's, you know, boom. It's usually pretty quick. This is a long, slow process to see the, you know, see the instruments fail and, you know, just recognizing it. And I suggested to this guy that he has a couple of, you know, like the instrument covers that your instructors may use to cover up the instruments to practice. Partial panel.
06:06
Wally Mulhern
I think all pilots ought to carry those in their bag simply because if you do have a failure of this system and you're continuing the flight, it's probably a lot easier to put a suction cup cover over those instruments than to have it staring you right in your face. Because we've been trained our whole piloting career to, you know, watch the instruments, follow the instruments, believe the instruments. Now we're saying, just kidding, these two in the middle that are right smack dab in the middle aren't any good anymore. So it's hard, it's hard to quit following that.
06:48
Bobby Doss
So I think it's almost impossible. Right. So I'm a big believer in carrying those. I carry a couple suction cups that I could use to cover them up in a steam gauge aircraft and then plenty of post its. If it was ever in the G1000 that I was concerned about an instrument giving me bad information just to get it off my scan. Because you're inevitably going to make a reaction based on what you're seeing. If you've flown 500, a thousand hours trusting that instrument, it's gonna be very hard to ignore it for sure. So let's kind of give an overview of how the entire system works. A little easier on video sometimes, but I think the podcast works well to talk through it. And this is in the Pilot Handbook of aeronautical knowledge, chapter 10, all kinds of sources on the Internet.
07:36
Bobby Doss
But you can get the Pilot Handbook of Aeronautical Knowledge from the FAA as a free download if you want that. We'll try and put that in the show notes as well. But there's a vacuum input inbound filter somewhere in your aircraft. It's probably in these Cessnas and Pipers somewhere in the cabin. So that we're actually starting with clean air from somewhere and sucking that air in. As Wally said, this show really sucks. But the air is going to get sucked in through that filter and then it goes through the instruments through the suction gauge. The instruments that are driven by this vacuum pressure or the attitude indicator and heading indicator. In most aircraft, sometimes the turn coordinator could also be vacuum air driven.
08:29
Bobby Doss
Once they go through the instruments to spin the gyros that are making those instruments stay erect or work through precession, they go through a vacuum relief valve which is keeping them kind of constant at different power settings. Spinning a vacuum pump that's engine driven could be spinning at different RPMs. So that this vacuum relief valve is really what kind of keeps them all Spinning at the same rate. And then outside of that vacuum pump, there's a vent that lets the extra air leak leave the system. And I asked this question quite a bit because it seems common sense, but new pilots don't know these things. And I remember being a new pilot, is the vacuum pump pushing air through it or is it pulling air through it? And the name gives it away because it's a vacuum pump.
09:21
Bobby Doss
But I was taught primacy lives here, that it's not a push system, because it could become very dangerous pushing that. That air through those systems and blowing those gyros up or having that relieved on the other side of those instruments. Whether that's true or not, I don't know. But I think the vacuum relief valve and the vacuum pump is what's helping regulate some of that pressure, causing that. Because it's being pulled through those instruments. Not something that's going to happen and cause problems in those instruments.
09:57
Wally Mulhern
Yeah. And, you know, when you. If you happen to be in an airplane where you can actually open the cowling and see inside, you know, you can. There's all kinds of stuff in that engine compartment. And a typical vacuum pump is about the size and shape of a coffee mug, if you will. So, you know, it might be something, if you ever happen to see an engine on cal, to go up to the mechanic and. And just say to him, hey, where's the vacuum pump? And just go take a look at it with that mind, you know, I asked Bobby, you know, and this was a very informal survey. I. I've again, I told you I had three before I got my instrument rating. And then I had. I've had two since then.
10:46
Wally Mulhern
One was not too long ago in my Saratoga, which the vacuum system does nothing but power standby instruments. So it was not that big a deal. But I looked over there and, you know, yeah, sure enough, that attitude indicator and the attitude indicator over on the right side weren't working. And lo and behold, guess what? We had zero vacuum pressure. So, you know, I had to have that. That pump replaced. But it seems to me that you get about 1500 hours, 2000 hours out of a vacuum pump, and it's probably more years driven than ours.
11:34
Bobby Doss
I think for us, again, not scientific here, everybody, but for me or for this flight school, it's the number of hot and cold seasons that we go through. So in a year where, if you're not from Texas, you may not believe this, but we might have summer, winter, spring, winter, summer, winter, spring, winter, summer, all in the span of about five months because it can go from freezing cold in November to 85, 90 degrees with 100% humidity again in late November to really cold in December. I've worn shorts on Christmas more than I can count to freezing in January, to warm in January, to ice in February.
12:21
Bobby Doss
And I think all that up and down in temperature changes the things that are in the actual instruments themselves, which is a lot of that ceramic and that I guess contraction and expansion and contraction and expansion because of the hot and cold just kind of wears those instruments out and wears those gyros out. And the less fluctuation in temperature we have, the longer those instruments and that vacuum system seem to operate correctly.
12:53
Wally Mulhern
Okay, well, that's a good thought. So chances are, you know, if you fly enough, you're going to see this at some point. Now, a lot of the newer airplanes don't have vacuum systems and a lot of the older airplanes, people choose to take the vacuum system out. It's, it's an economic decision. Probably doesn't make a whole lot of economic sense to do that, but some people choose to do it nonetheless.
13:25
Bobby Doss
Yeah, we've done it in a few aircraft and thinking about doing it more, but it is, it's a $10,000 quote unquote upgrade versus a thousand dollar keep it as is and fight through each instrument at a time. Right. That's assuming you're changing one instrument or one vacuum pump in a little bit of work. It's a super reliable system until it breaks. Right. And that's the beauty of it. I think that there's all kinds of reasons why you don't want that to happen in imc, but in vmc it's not that big of a deal if as long as you can navigate. We, we talked about this with instrument approaches and using an electronic flight bag. Would you use for flight to navigate if that was your last choice? And I think the answer we would all say is heck yeah, we're going to use it.
14:18
Bobby Doss
And I've always been kind of in the same boat that if I lost my vacuum system, I'm going to use my stratus and the heads up display on foreflight to give me my synthetic vision and kind of what I'm doing. I'm going to use everything I got to stay upright. And I think that would work really well. In the experimental world you can make this pretty economical, but in a typed aircraft that's used for type training or training, then you're not gonna. It's not that inexpensive. These FAA tickets and stickers and certificates cost a lot of money.
14:56
Wally Mulhern
Yeah. Yeah. And I think getting back to actually flying the airplane, when you have that, this is a reason to keep the scan going. You know, you don't want to get fixated on that attitude indicator. All things being equal, if everything's working just fine, I mean, I guess you could just. As long as you're keeping the wings level and the pitch where it needs to be, you're not going to climb, you're not going to descend, you're not going to turn. But that's the reason for the scan. I had an instructor one time that would always say, eyes moving fast, hands moving slow. Eyes moving fast, hands moving slow. And I've used that many, many times over the years. So you want to, you know, you're. You're basically evaluating everything. You're looking over at that airspeed indicator. Okay. Does it make sense?
15:52
Wally Mulhern
Attitude, altimeter, vsi, heading turn coordinator. Are they all jiving? And once you get one that's doesn't seem to be playing nicely with the other five, it's time to kind of back things off and evaluate, try to figure out what's happened. You know, have I lost my attitude indicator or have I lost my vacuum system? Well, we have a vacuum gauge, so. Or a suction gauge. So that's. That's kind of easy. If you, if you think the attitude indicator is not. Is. Is. Has failed. Take a look at the suction gauge. If the suction gauge is at zero. Well, yeah, it certainly has failed. And, and that DG is going to fail, or it probably already has.
16:44
Bobby Doss
Yeah. And I have seen. It's probably far less common, but I have actually seen a suction gauge that was stuck at zero, and that. That could be pretty disorienting to someone. I definitely wouldn't fly in a. Into IMC with that, but again, you wouldn't really know what was causing that if. Unless you could open that up and diagnose that suction gauge was wrong. Because the outcomes of that being at zero or the vacuum system having no pressure would be pretty daunting for sure in that environment. Normally, what we see at the flyschool is something that's tumbling, and when it's tumbling, it's normally the instrument itself. Right. So an attitude indicator or heading indicator that just won't. Won't stay erect is normally that actual device itself, the system still working.
17:38
Bobby Doss
The vacuum pump, the relief valve, and the suction gauge, all that's working, it's normally just an instrument. Why do you think the turn coordinator is electronic, Wally?
17:53
Wally Mulhern
Well, for diversification, for another word for it. You know, if we have a, a vacuum powered turn coordinator and we lose the vacuum, then we've lost all kinds of ability to tell if the airplane is turning, if we, we're in IMC conditions or there's nothing visible outside. So for the most part, and you know, if you go into your airplane or your airplane that you rent, if you look at the instruments themselves, it probably says on the turn coordinate coordinator, most of them say DC Elec and that means DC electric. So that would tell you that it's electric. The heading indicator, the DG and the attitude indicator probably say vacuum on them or suction. The airplane I was in this morning, I believe one said suction and one said vacuum. But the answer is right there.
19:03
Wally Mulhern
You know, I asked these questions on all private commercial and certainly instrument checkrides, we discuss all this. And all you got to look do is look at the instrument. The answer is right there.
19:19
Bobby Doss
And if they were all ran on electric, then you have a single source of failure if you have an electric failure. And again, I think it's ingenious how we've gotten to where we're at. And unfortunately, probably a lot of people suffered their demise because of how we got to where we're at. But having systems that are diversified, as you said, running on different pieces of technology, vacuum or electronic systems, then we have some backups there that will help keep us safe and keep us flying along the way.
19:51
Wally Mulhern
Yeah, and I think what's very important that we need to be aware of is if you are in an airplane that has been either upgraded or never had a vacuum system, or I think it's, you have to understand the backup behind your primary attitude indicator, most of them will have basically a standby battery. And those batteries are supposed to be good for about five or six hours in most cases. But that's something that we need to include in our pre flight because if we do have an electrical failure, and everybody knows that electrical failures are near and dear to my heart, if we do have an electrical failure and we don't have that backup battery, we're going to lose our ability to keep the wings level. And that's a big deal.
20:50
Wally Mulhern
So I think maybe a lot of us jump in a new airplane, say, oh gee, this has a, let's say a Garmin G5. It's got two G5s in it. And maybe we just don't understand that they might or they might not. I know I had put something in my 172 and it was an option to get the backup battery, which I did, but you didn't have to get it.
21:22
Bobby Doss
Better know what you got in something like that for sure.
21:25
Wally Mulhern
Yeah, absolutely.
21:29
Bobby Doss
So what's driving the G5S if it doesn't have a. Are the, do those have gyros? I don't even know that I know the answer to that, to be honest. Do those. Are those gyro driven or they're driven by something else?
21:42
Wally Mulhern
I, I don't know if there's an Ahars. I, I don't know. I, I really don't know. I, I don't.
21:48
Bobby Doss
That's where I was taking. It's down to the Ahars route. Right. So with a system, if an aircraft doesn't have vacuum Systems like a G1000 or most, I would call them glass cockpits. Today they have an AHAR system and the AHAR system stands for Air Data Attitude Heading Reference System. And it's a computer, for no better intent, that is electronically calculating all those flight parameters. And you would be very wise to have a backup battery, a standby battery of sorts. And the one question that I can almost stump everybody on, but you won't be stumped if you're a behind the prop listener, is what's. What's required from the backup battery or from the systems in the handbook, the pilot, the poh, for a system that has a backup battery, like a standby battery in a G1000.
22:40
Bobby Doss
And many people look up and think and wonder, well, surely it's required equipment. So they normally say in VMC it's not required, but in imc, yeah, it is required. And the reality is that it's not required equipment in the United States for IMC or vmc. Shockingly now Bobby's personal minimums say I'm never going to fly an all electric aircraft without a standby battery. That's the test. Like it's working well, but it's only required in Europe, from what I understand to be required for flight into IMC. But there's no way I'd fly a G1000 aircraft without a standby battery that was operational in IMC for sure.
23:27
Wally Mulhern
Yeah, absolutely.
23:30
Bobby Doss
So what kind of things? We're going to a checkride quiz here a little bit, right. Other than just how these instruments Work which I'm assuming you ask applicants what is it that you reference or relate to on these three instruments for private pilot check rides? What are you asking about them? Is it pretty mundane, low level questions? Are you diving pretty deep into how the systems work?
23:58
Wally Mulhern
Yeah, no, it's, it's, I like to think of it as operational. I will, I will say what would be the result of a failed vacuum pump.
24:10
Bobby Doss
Okay.
24:11
Wally Mulhern
And, and in general, applicants are pretty darn good on it.
24:18
Bobby Doss
My dome light would quit working. Is that true? My dome light could quit working?
24:24
Wally Mulhern
I think, I think the dome light would work. I think it'd be just fine. And of course, on an instrument check ride, we will actually fly an approach with the loss of the primary flight instruments. Now, in a vacuum pump airplane, it's easy. I, you know, I cover up the two instruments that are vacuum powered. I had one this morning and it's really pretty easy. And again it's with, with the big stickers or suction cups or whatever on top of the instruments. It's, it's really fairly easy to, well, to recognize it. And maybe not so easy to fly the airplane. But one thing that I have been very successful in is being able to do time turns, you know, and being able to do math in my head.
25:22
Wally Mulhern
I know if I'm heading 240 and ATC wants me to turn left heading 180, I know that's a 60 degree turn and I know it's going to take me 20 seconds. So I put the airplane into turn for 20 seconds, roll it out, check my compass and make small adjustments. I know a 10 degree turn is going to take about 3 seconds and so forth. So those skills come into play very much so in, you know, in a, especially if you've lost your heading indicator or your, you know, your primary flight display, bottom line is, you know, if you've lost your attitude indicator, if you're not climbing and descending and your airspeed is staying constant and you're not turning, you ought to be in good shape. And again, that's assuming a constant power. Now it comes into play when we have to start descending.
26:23
Wally Mulhern
So, you know, being able to descend at whatever rate per minute is your typical approach descent profile is something that hopefully you've done a lot with your instructor. I'm talking about for an instrument rating. But you know, just, you know, you may think, well, this is kind of boring and dumb to be descending at 500ft a minute. But you know, that Might be what you're stuck with. You know, you, you may need to do that.
26:57
Bobby Doss
Well, that might save your life too, right? I was thinking probably a less of an angle than that. If it's me flying an imc, I'm gonna, well, probably declare an emergency, but I'm definitely gonna tell them that I need to start descending way before I need to make sure that I'm not making massive big adjustments because that's what's going to really start confusing your body for sure.
27:22
Wally Mulhern
Yeah, yeah. And I was thinking flying a three degree glide slope, you know, flying an approach.
27:29
Bobby Doss
So, so what else? Do you go any deeper on CFI check rides? Is there any other than knowing operational and kind of common failures of the system? Anything that applicants need to be thinking about as they prepare for checkrides?
27:50
Wally Mulhern
Not, not really. You know, on the more advanced airplanes you're different, knowing your different options. I mean, can we take that screen that's right in front of you and put it over on the right, the information that's on that screen that's right in front of you and move it over to the right screen, you know, and that might be real easy to do and you just, you know, instead of looking straight ahead, you're looking a little bit to the right. But I still think it's very important to be able to use the standby, the traditional standby instruments, which again might be a vacuum system, but it may be an electric G5 over in the corner. That's about a tenth of this. Well, maybe not a tenth, but about an eighth of the size of which we're used to looking at.
28:44
Wally Mulhern
So I mean, I know on a triple seven where we've got a very small standby attitude indicator, but you know, we have three others. So we're in a world of hurt if we're down to that.
28:59
Bobby Doss
Yeah, that's a scary proposition for sure. Well, I remember when I was first a young rookie pilot, young pilot, that these systems seem very complicated. I think the experience of owning a fly school and replacing them on the fleet of 20 that we have has taught me a lot about how the systems work. But it really is just a few pages in the pilot Handbook of Aeronautical Knowledge, a couple videos you can watch. Listening to this show hopefully will help you. But we want you to be a safe pilot and know what's going on in that system.
29:34
Bobby Doss
If the system's failing and, or if the system's working, just know the systems read your POH we have a plane that has two vacuum pumps, and I would bet in the grand scheme of things, very few people know that's got a dual vacuum pump system and that's just for redundancy. Right. And I would feel pretty confident in that aircraft no matter where I was at, because there's the redundancy. So.
29:57
Wally Mulhern
Right. Right.
29:58
Bobby Doss
It, it makes it safe. You be safe, fly safely, and stay behind the prop.
30:05
Nick Alan
Thanks for checking out the behind the Prop podcast. Be sure to click subscribe and check us out online at behind the Prop.com behind the Prop is recorded in Houston, Texas. Creator and host is Bobby Doss. Co host is Wally Mulhern. The show is for entertainment purposes only and is not meant to replace actual flight instruction. Thanks for listening. And remember, fly safe.