Panel loss above cloud layer VFR

alfadog

Final Approach
Joined
May 3, 2010
Messages
5,057
Location
Miami
Display Name

Display name:
alfadog
Had an interesting flight yesterday. Flew my Arrow II up from KTMB to KVRB for my 1st fly-away with a local pilots' club. I have not been flying the Arrow in the last two months as I have been working on my stick and rudder skills in a friend's 1946 Luscombe Silvaire 8A.

The Arrow has a dated panel and, on return, I departed Vero along a VOR radial that would keep me clear of the Miami Class B airspace and take me to my visual checkpoint for the arrival at Tamiami.

There were a few low scattered and broken layers with rain and I did not want to be bumped around so I started a climb. Pretty soon, maybe 7000', I had no consistent ground reference and I take a look at the artificial horizon. It shows I am in about an 80d bank. Gulp. I knew I wasn't but there is that first instant. Figured I lost my vacuum pump. That fellow at the lunch jinxed me, I thought, with his story of recently losing his.

Cool, thinks I (I only thought about the cost of repair for a moment), partial panel! Great practice for my IR checkride. I look over at the turn coordinator and the little wings are level. Great. Wait, they seem awful still. Try a few turns and discover that the gyro in in the TC seems to have died also. When did that happen? Check breakers. No joy. Even better, I think, partial partial panel. Check compass. That is still working and course is fine.

The Arrow has a secondary vacuum arrangement. I think it bleeds vacuum from the intake manifold. Operated by cable. The cable always looked hinkey and I never pulled it out. Understand we bought this airplane in August, it has been to the shop twice since, and we have an annual coming up. We have not flown it much and are still sorting it out.

I pull it out. Nothing. Of course, I do not have much manifold vacuum. Heck with it, I don't need it, I try to push it back in. The cable refuses to move. I ended up at 10,500 with no ground reference and just using the magnetic compass and VOR to keep me staight. It was a non-issue and as I approached the Bravo, I let down through the breaks to get under the 3000' Bravo shelf and pick up my checkpoint.

Now figure this one out. As I let down, the vacuum instruments came back on line. I can think of a few possibilities. I will probably call the mechanic and get started on the annual a month early as I have a few squawks I want to address before my partner starts his complex in the Arrow next month.

Obviously, this was VFR and no big deal. But it was a fun simulation of real instrument failure. I credit my IR training and the fact that my last almost 40 hours have been in the Luscombe so I am used to looking at the mag compass for the fact that it was fun and a non-event given that I consider myself a low-time pilot.
 
Last edited:
Now figure this one out. As I let down, the vacuum instruments came back on line.

My first thought is the same as yours above... you lost the primary vacuum pump.

As you let down, the vacuum from your standby system came up and drove the instruments. Did you throttle back for the descent? Did you decrease throttle to maintain a MP as you continued to descend?

Seems to me this is the most likely cause. Intake Manifold powered standby vacuum systems don't work at WOT....

-Skip
 
If you have one of those backup vacuum systems that works off of the MP suction, you have to have a differential to the ambient pressure for it to work. So lets say the cable is stuck open when you pulled it. At altitude, you probably needed the power and there was no differential to use for the vacuum system. As you descended, you would have had the power pulled back and there would have been sufficient differential pressure to power your vacuum operated gyros. Just guessing.
 
If you think that mag compass was going to be a good enough source of bank information to keep you oriented in IMC I think you don't realize how lucky you are to have that airplane panel reveal itself during VMC. IMC you would have been spiraling in 6 seconds flat. Go buy a cat cuz you just burned one life Mario.

Is your TC not electric? That is a rather unusual failure to have. electric and vacuum at the same time. Maybe I don't understand your panel layout.

This is further proof that the proposals to open up the market to non-certified installations of avionics are needed badly. Solid state gyros don't quit on ya when you need them. Backup batteries on the things resolve the timing issue enough for an emergency descent out of imc. About time we stopped gambling with life and limb when viable and safer replacements to these horse and buggy technologies exist at an affordable price. Ironic that experimental rigs are actually safer to punch through IFR than my certified warrior, waiting to let me down in the soup one of these days. This is supposed to be fun with a sprinkling of deadly, not deadly with a sprinkling of fun you now...

Glad to hear you're safe and able to fly another day. Tailwinds!
 
Your standby vacuum plumbs the intake manifold to the gyros and cannot provide enough air to run any gyros unless your MP is at least a few inHg lower than ambient. At 10,500 MSL you probably cannot lower the MP far enough to work continuously in level flight but you can close the throttle completely for several seconds every few minutes which should spin the gyros in a pinch. Once you started down your gyros started working because you partially closed the throttle which lowered the MP and as you got lower the ambient pressure went up as well. The system you have sounds like one made by Precise Flight and there should be a supplement in the POH for it explaining all this along with a placard showing the max MP for operation at various altitudes. Technically the plane isn't airworthy without both of those even for VFR unless you placard the system INOP. Also note that there's an AD on the system that should be complied with and given the state of your system I suspect that's needed too. Finally, when the valve is opened your mixture will get slightly leaner.

WRT to the TC, it may be powered by your vacuum pump and if that's the case I strongly recommend that you replace it with an electric version (or better yet an electric AI) before flying the plane in IMC. In any case you really should study the systems on this airplane a bit before flying it again.
 
If you think that mag compass was going to be a good enough source of bank information to keep you oriented in IMC I think you don't realize how lucky you are to have that airplane panel reveal itself during VMC. IMC you would have been spiraling in 6 seconds flat. Go buy a cat cuz you just burned one life Mario.

Is your TC not electric? That is a rather unusual failure to have. electric and vacuum at the same time. Maybe I don't understand your panel layout.

This is further proof that the proposals to open up the market to non-certified installations of avionics are needed badly. Solid state gyros don't quit on ya when you need them. Backup batteries on the things resolve the timing issue enough for an emergency descent out of imc. About time we stopped gambling with life and limb when viable and safer replacements to these horse and buggy technologies exist at an affordable price. Ironic that experimental rigs are actually safer to punch through IFR than my certified warrior, waiting to let me down in the soup one of these days. This is supposed to be fun with a sprinkling of deadly, not deadly with a sprinkling of fun you now...

Glad to hear you're safe and able to fly another day. Tailwinds!

Oh, I think I have all my lives or at least, this certainly did not burn one. I do not fly this airplane in IMC, not the least because I have not yet taken my checkride and I am doing that in a club Cessna. This is an older airplane that we are still sorting out. I think the TC was working when I last flew the airplane but maybe not. Yes, electric but it may have been out on the ride up and I did not notice. Flying the Luscombe has me looking outside a lot more these days.

But I certainly agree that better this stuff crapped out in VMC. As far as whether I would die in IMC as you seem to believe, you will forgive me if I disagree and prefer to survive it :wink2:
 
Last edited:
Your standby vacuum plumbs the intake manifold to the gyros and cannot provide enough air to run any gyros unless your MP is at least a few inHg lower than ambient. At 10,500 MSL you probably cannot lower the MP far enough to work continuously in level flight but you can close the throttle completely for several seconds every few minutes which should spin the gyros in a pinch. Once you started down your gyros started working because you partially closed the throttle which lowered the MP and as you got lower the ambient pressure went up as well. The system you have sounds like one made by Precise Flight and there should be a supplement in the POH for it explaining all this along with a placard showing the max MP for operation at various altitudes. Technically the plane isn't airworthy without both of those even for VFR unless you placard the system INOP. Also note that there's an AD on the system that should be complied with and given the state of your system I suspect that's needed too. Finally, when the valve is opened your mixture will get slightly leaner.

WRT to the TC, it may be powered by your vacuum pump and if that's the case I strongly recommend that you replace it with an electric version (or better yet an electric AI) before flying the plane in IMC. In any case you really should study the systems on this airplane a bit before flying it again.


Good points. I figured the TC was electric but if vacuum, that would certainly explain. Did not think to check it once I came down.

Yes, I figured the bleed would lean the engine and also realized I needed some differential for it to work. Did not think about trying to get it to spin up at altitude by closing the throttle and that is a good tip. I was doing fine and did not need it.

What I am wondering is, given how hinkey the cable was, if it was never closed properly even before I tried to use it and

1. perhaps I haven't had a vacuum pump for while or
2. the pump is fine but is losing vacuum to manifold through the standby valve. I imagine there is some check valve in the system to prevent that but that could have falied.
 
I believe there is an AD on the check valve in those type of systems.

A bad check valve would certainly explain what I experienced and the vacuum pump could be fine. That would be dandy :)
 
Use a battery powered backup system, such as a Garmin 496/696 panel page. Works very well in displaying the basic six. Unless you're real unlucky, some foreign country, probably won't shoot down the eleven satellites it's picking up...........at the same time your panel craps out.
Be aware, that the gps (WAAS) derived altimeter will probably be closer to actual, unless you have a current altimeter pressure setting.

I've used these for years. They really do work.
 
Good reminder to preflight that TC...each and every flight. That's the plan B and when plan A commits suicide you want B to step up and be a hero.
 
It may be worth repeating....


  • Needle: Keep it straight up and down and you are not turning.
  • Ball: Keep it centered.
  • Airspeed: If it's increasing, you're diving. If it's decreasing, you're climbing. Use power to climb/descend, pitch to manage airspeed.
This technique needs to be practiced by VFR pilots as a survival skill and IFR pilots as a backup in case of vacuum loss.

More here.
 
Now figure this one out. As I let down, the vacuum instruments came back on line. I can think of a few possibilities. I will probably call the mechanic and get started on the annual a month early as I have a few squawks I want to address before my partner starts his complex in the Arrow next month.
This is the common behavior of the PRECISE FLITE Standby system. Either descend or REDUCE POWER, or both and you'll get enough vacuum to run the gauges.

My guess... your pump died or there was something else hokey about the shuttle valve to begin with.
 
WRT to the TC, it may be powered by your vacuum pump
The FAA does not permit the AI and TC to be powered by the same nonredundant source for IFR operations. It's not in 91.205(d), but it is in the certification requirements in Part 23 and CAR 3. And the Precise Flight SVS does not count as a redundant power source, since a vacuum leak in the lines will negate the utility of the SVS.

I agree with those who say the combination of high power setting and high altitude neutralized the SVS. As for the TC, I'm virtually certain it is electrically powered, and I suspect it was working better than you thought, but check it out with the shop anyway -- just to be sure.
 
It may be worth repeating....


  • Needle: Keep it straight up and down and you are not turning.
  • Ball: Keep it centered.
  • Airspeed: If it's increasing, you're diving. If it's decreasing, you're climbing. Use power to climb/descend, pitch to manage airspeed.
This technique needs to be practiced by VFR pilots as a survival skill and IFR pilots as a backup in case of vacuum loss.

More here.

Needle - he didn't have one...

Good reminder nonetheless.

I'd be surprised if both the TC and AI were vacuum, I'm 99% sure that's a no-no for IFR airplanes.
 
Oh sorry, are you referring to the compass needle? I thought you were referring to the needle of the T&B or TC (and his TC was inop)

I've never heard of keeping it upright with no gyro at all...
 
The OP said he had a TC, not a T&B. No needle, different system (roll+yaw rate vs pure yaw rate). The problem with a TC is that it can be displaced without actually turning, and you can turn without displacing it.

Can you elaborate. I made at least what I estimate to standard-rate turns left and right and the little airplane did not budge.
 
Can you elaborate. I made at least what I estimate to standard-rate turns left and right and the little airplane did not budge.
You could not do that if it was working. The deceptive readings from TC's are transient, not steady state.
 
(1) You need to verify function of each instrument before you use the runway. DON'T do that again (that be...."sloppy").

(2) With a manifold powered SVS, at 10,000, you would need to close to about 15" MP to have enough "suction" to turn the gyros.....so go to 2550 rpm!
 
Last edited:
(1) You need to verify function of each instrument before you use the runway. DON'T do that again (that be...."sloppy").

(2) With a manifold powered SVS, at 10,000, you would need to close to about 15" MP to have enough "suction" to turn the gyros.....so go to 2550 rpm!

Roger :)

BTW, you forgot the :nono: smiley.

But you are right.
 
Now figure this one out. As I let down, the vacuum instruments came back on line. I can think of a few possibilities. I will probably call the mechanic and get started on the annual a month early as I have a few squawks I want to address before my partner starts his complex in the Arrow next month.

Clogged vacuum inlet filter that had enough moisture in the dust that it froze up and wouldn't flow air?
 
As far as whether I would die in IMC as you seem to believe, you will forgive me if I disagree and prefer to survive it :wink2:

Without a functioning turn coordinator (or T&B ) AND without your vacuum instruments, it is almost assured that you would have died in IMC. Would you care to explain some magical sixth sense that you have that would keep you wings level in such a situation?

Look up the (Itzhak Jacoby) Bonanza accident in NJ in 1999 in which a many-thousand hour ABS instrument instructor crashed into a neighborhood when he lost his pressure system (it turns out his TC had not been working prior to the flight).

Checking the function of the TC should be standard procedure when taxiing out for takeoff (at least prior to an instrument flight).

Wells
 
Last edited:
I believe there is an AD on the check valve in those type of systems.

Yep, it's a pretty old AD. When it came out, I just outright pulled the system from my plane. With the turbocharger the Precise Flight is almost worthless.
 
I believe there is an AD on the check valve in those type of systems.

Another thing I like about my A&P. Called him yesterday and mentioned that the problem I had experienced and how a poster said there was an AD. He comes back with "Yeah, we have to check the logs and see what version you have. The AD applies to versions 2 and 3, most of the installed units are versions 4 and 5." Now that is how I like an A&P to sound :yesnod:
 
Use a battery powered backup system, such as a Garmin 496/696 panel page. Works very well in displaying the basic six. Unless you're real unlucky, some foreign country, probably won't shoot down the eleven satellites it's picking up...........at the same time your panel craps out.
Be aware, that the gps (WAAS) derived altimeter will probably be closer to actual, unless you have a current altimeter pressure setting.

I've used these for years. They really do work.

The panel page will save your bacon..but.... You need to completely ignore the speed dial in that display.. it is ground speed, not airspeed and with a good tailwind you can and will stall the plane...:yesnod::sad: IMHO
 
Without a functioning turn coordinator (or T&B ) AND without your vacuum instruments, it is almost assured that you would have died in IMC. Would you care to explain some magical sixth sense that you have that would keep you wings level in such a situation?

Look up the (Itzhak Jacoby) Bonanza accident in NJ in 1999 in which a many-thousand hour ABS instrument instructor crashed into a neighborhood when he lost his pressure system (it turns out his TC had not been working prior to the flight).

Checking the function of the TC should be standard procedure when taxiing out for takeoff (at least prior to an instrument flight).

Wells
Wow! Kinda creepy that you mentioned this because this is the accident that came to mind as I read this thread. It was the same year I got my private and it freaked me out because he crashed in my town about 5 miles from where I lived . I actually drove down to the crash site and saw the local news crew. A reporter asked a few of us if we witnessed it. I said no but mentioned that I was a pilot (don't know why I did that). She got real interested, I guess she thought I could add something to her reporting but I told her that I'd just got my license and didn't want to speculate!
 
Your statement: I think the TC was working when I last flew the airplane but maybe not. Scared the heck out of me. I do not know everything about flying, am not an instructor and only have 11,400 hours, but your statement indicates to me a very relaxed approach to systems monitoring and safety. Aviation is something you either do right, or don't successfully do for very long.
 
Look up the (Itzhak Jacoby) Bonanza accident in NJ in 1999 in which a many-thousand hour ABS instrument instructor crashed into a neighborhood when he lost his pressure system (it turns out his TC had not been working prior to the flight).
While your point about trying to keep the plane upright with no gyro instruments at all is well-taken, in the accident to which you refer, the pilot was illegally taking an anti-migraine barbituate which is known to cause drowsiness and dizziness, and that was included as a cause.

In any event, one should never start an IFR flight without an instrument ground check including "needle right, ball left, compass card increasing; needle left, ball right, compass card decreasing" during taxi (or whatever equivalent is appropriate to the instruments in your aircraft). And don't forget to check the AI for excessive roll response (five degrees is the recommended limit, but I don't want to see any) while you do that.
 
Last edited:
The panel page will save your bacon..but.... You need to completely ignore the speed dial in that display.. it is ground speed, not airspeed and with a good tailwind you can and will stall the plane...:yesnod::sad: IMHO

Yes. It's GPS groundspeed.
 
Your statement: I think the TC was working when I last flew the airplane but maybe not. Scared the heck out of me. I do not know everything about flying, am not an instructor and only have 11,400 hours, but your statement indicates to me a very relaxed approach to systems monitoring and safety. Aviation is something you either do right, or don't successfully do for very long.

Meh. We bought the plane recently, are still sorting it out, flown very little since purchase. I haven't not flown it in two months, only fly it VFR. TC is not a required instrument for VFR flight. I don't look at it much in VFR flight. It might have been working when I last flew or perhaps it was not.

I am a very relaxed guy, BTW. Took my first skydive last Nov (AFF, never tandemed) and one of the instructors could not quite wrap his head around the fact that I was relaxed and joking on the way up. So yeah, if I am not sure about an IFR instrument in an airplane that I have never flown IFR in, for me, no biggie; not "doinitwrong". For you, something else, your perogative.

But hey, I am still learning, still improving. Working on my IR and perhaps that will ingrain the habit of checking the TC.
 
I don't launch into the soup unless everything is working, including the T&B wing going uppie-downie and the ball going slidie-slidie...

Wait, I thought the T&B had the needle, and the TC has the wing?

Ball's the same for both, and regardless of the instrument, it should show turn both gyroscopically and inertially.
 
Meh. We bought the plane recently, are still sorting it out, flown very little since purchase. I haven't not flown it in two months, only fly it VFR. TC is not a required instrument for VFR flight. I don't look at it much in VFR flight. It might have been working when I last flew or perhaps it was not.

I am a very relaxed guy, BTW. Took my first skydive last Nov (AFF, never tandemed) and one of the instructors could not quite wrap his head around the fact that I was relaxed and joking on the way up. So yeah, if I am not sure about an IFR instrument in an airplane that I have never flown IFR in, for me, no biggie; not "doinitwrong". For you, something else, your perogative.

But hey, I am still learning, still improving. Working on my IR and perhaps that will ingrain the habit of checking the TC.
I'm a relaxed VFR guy too, problem is you cannot take that attitude into the IFR world, it'll kill you.
 
Wait, I thought the T&B had the needle, and the TC has the wing?

Ball's the same for both, and regardless of the instrument, it should show turn both gyroscopically and inertially.

I think you're right,IIRC whenever I was reading the old manuals on needle ball and airspeed technique I'm pretty sure they referenced it as Turn and Bank.
 
Wait, I thought the T&B had the needle, and the TC has the wing?

Ball's the same for both, and regardless of the instrument, it should show turn both gyroscopically and inertially.

Turn & Bank:
10-02138.gif


Turn Coordinator:
10-22510.jpg
 
Back
Top