Instrument Failure Modes

[Jaybird180]

I need a better way to visualize what happens to instrumentation when failures occur, for my learning purposes.

For example: what conditions pitot-static instruments will show when iced over in flight (comes to mind). I don't quite get that particular failure mode of using them as baro indicators considering that I have only experienced an Attitude Indicator failure, which I picked up in a new to me airplane.

Although I know this is tested during the Instrument written, is this also typically part of the Instrument Interpretation portion of a CFII curriculum and best covered and drilled there?

What can I do to resolve this deficiency and also to drill on other instrument interpretation skills?

 

[akpilot907]

I need a better way to visualize what happens to instrumentation when failures occur, for my learning purposes.

For example: what conditions pitot-static instruments will show when iced over in flight (comes to mind). I don't quite get that particular failure mode of using them as baro indicators considering that I have only experienced an Attitude Indicator failure, which I picked up in a new to me airplane.

Although I know this is tested during the Instrument written, is this also typically part of the Instrument Interpretation portion of a CFII curriculum and best covered and drilled there?

What can I do to resolve this deficiency and also to drill on other instrument interpretation skills?

Get one of the Gliem's Instrument practical test books. They have a section dedicated to recognizing instrument failures... (Climbs, turns, Descents, gyro failures, static port iced over, etc...) Hope this helps

 

[murphey]

Understand the vacuum and pitot-static systems. Understand the systems, you will understand the failures.

 

[StevieTimes]

I like to plan a local flight in fsx in bad weather. I will set the pitot or vacuum to fail at some random time. then you get that slow attitude failure that's harder to catch than your instructor slapping a sticky note on.

then I'll try to fly the entire approach, go missed, hold, then another approach all partial-panel... all compass, no gps.

there are a lot of failures you can program to happen @ random times.

 

[Ted]

Well, I've actually had a lot of these things happen.

Whenever a pitot tube has iced over in my experience, airspeed starts to decay and eventually hits 0. I've never seen it act as an altimeter and hold pressure the way the book says. You notice your airspeed is slowing vs. what it should be. The cross check is your GPS GS. Has it changed by the same amount? If yes, you're actually slowing. I have a picture of the Aztec's panel with ASI at 0, 8500 MSL, 155 kts GS on GPS.

When a vacuum failure occurs, usually you'll notice your AI/DG (assuming both vacuum) start showing a turn/climb/descent when you aren't. The AI can be a dangerous one to go bad from vacuum. It is extremely disorienting when it happens, and many carry instrument covers to just cover it up if it happens for real. Imagine your AI saying you're in a climbing 90 degree bank right turn, when you're straight and level.

When an electric HSI fails, it either just starts spinning (if it's slaved and that quits) or it stops moving at all (if the motor quits). If your AP is attached to it like a Century III, your AP will not behave well if it's on, so turn it off.

 

[Clark1961]

When an electric HSI fails, it either just starts spinning (if it's slaved and that quits) or it stops moving at all (if the motor quits). If your AP is attached to it like a Century III, your AP will not behave well if it's on, so turn it off.

Which gets us to autopilot failure modes which can be "interesting" to say the least. The 'kota used to make random right turns...it took a trip to Tulsa to fix it.

 

[FORANE]

I need a better way to visualize what happens to instrumentation when failures occur, for my learning purposes.

For example: what conditions pitot-static instruments will show when iced over in flight (comes to mind). I don't quite get that particular failure mode of using them as baro indicators considering that I have only experienced an Attitude Indicator failure, which I picked up in a new to me airplane.

Although I know this is tested during the Instrument written, is this also typically part of the Instrument Interpretation portion of a CFII curriculum and best covered and drilled there?

What can I do to resolve this deficiency and also to drill on other instrument interpretation skills?

You ask and you receive:
http://www.luizmonteiro.com/learning_pitot_sim.aspx

Once you have seen it it is easier to recognize the second go around.

 

[Ted]

Which gets us to autopilot failure modes which can be "interesting" to say the least. The 'kota used to make random right turns...it took a trip to Tulsa to fix it.

Yeah, the Century IIIC has a lot of issues with trim runaway in my experience. Haven't had any issues with random turns if I was using it right, though.

Then there's the old forgetting to turn it off and "Hey, why are my ailerons frozen?" I've found it's easier to do that on the C-III series because it doesn't have some annunciator lights.

 

[poadeleted20]

Understand the vacuum and pitot-static systems. Understand the systems, you will understand the failures.

Amen. Once you know how each instrument works, and how the pitot and static systems work, the rest is a matter of deduction.

 

[Clark1961]

Yeah, the Century IIIC has a lot of issues with trim runaway in my experience. Haven't had any issues with random turns if I was using it right, though.

Then there's the old forgetting to turn it off and "Hey, why are my ailerons frozen?" I've found it's easier to do that on the C-III series because it doesn't have some annunciator lights.

The 'kota had an analogue-to-digital (or vice-versa) converter mis-match with the Aspen which caused a problem. The Century in the 'kota is fairly resistant to pitch trim problems since it works with pitch servo motor load rather than control cable tension.

 

[azure]

Well, I've actually had a lot of these things happen.

Whenever a pitot tube has iced over in my experience, airspeed starts to decay and eventually hits 0. I've never seen it act as an altimeter and hold pressure the way the book says.

Since the "drain hole" has to freeze over too for that to happen, it's probably a fairly uncommon failure mode.

But even to have the airspeed seem to decay would be a pretty scary event until you figure out what's going on. Pitot heat on before entering clouds near or below 0C!

 

[denverpilot]

Jesse and I were doing 40 knots sitting on the ground with a groundspeed of zero one frozen night in Nebraska.

Here was the cool part... It was going up.

 

[redtail]

Well, I've actually had a lot of these things happen.

Whenever a pitot tube has iced over in my experience, airspeed starts to decay and eventually hits 0. I've never seen it act as an altimeter and hold pressure the way the book says. You notice your airspeed is slowing vs. what it should be. The cross check is your GPS GS. Has it changed by the same amount? If yes, you're actually slowing. I have a picture of the Aztec's panel with ASI at 0, 8500 MSL, 155 kts GS on GPS.

When a vacuum failure occurs, usually you'll notice your AI/DG (assuming both vacuum) start showing a turn/climb/descent when you aren't. The AI can be a dangerous one to go bad from vacuum. It is extremely disorienting when it happens, and many carry instrument covers to just cover it up if it happens for real. Imagine your AI saying you're in a climbing 90 degree bank right turn, when you're straight and level.

When an electric HSI fails, it either just starts spinning (if it's slaved and that quits) or it stops moving at all (if the motor quits). If your AP is attached to it like a Century III, your AP will not behave well if it's on, so turn it off.

Reminds me of the Itzhak Jacoby crash in 1999 (3 miles from where I lived at the time), one month after I got my PPL!

I heard about it on the radio and drove to the crash site. Seeing some of the wreckage kind of freaked me out as a newly minted pilot

http://articles.philly.com/1999-11-28/news/25493526_1_david-muzio-plane-pilot

"Jacoby had reported a problem with the gyros within 90 seconds after his 10:49 a.m. takeoff at Linden Airport, about 10 miles from the site of the crash."

http://www.ntsb.gov/aviationquery/brief2.aspx?ev_id=20001212X20151&ntsbno=NYC00FA039&akey=1

 

[Ted]

The 'kota had an analogue-to-digital (or vice-versa) converter mis-match with the Aspen which caused a problem. The Century in the 'kota is fairly resistant to pitch trim problems since it works with pitch servo motor load rather than control cable tension.

Unless you've got a runaway trim event. That was a daily event on the Navajo.

Since the "drain hole" has to freeze over too for that to happen, it's probably a fairly uncommon failure mode.

But even to have the airspeed seem to decay would be a pretty scary event until you figure out what's going on. Pitot heat on before entering clouds near or below 0C!

Yep. And when the pitot heat breaks, then you've got to figure out what's going on. I had one picture of the pitot tube with a giant ball of ice on the front of it after landing.

 

[Jaybird180]

You ask and you receive:
http://www.luizmonteiro.com/learning_pitot_sim.aspx

Once you have seen it it is easier to recognize the second go around.

Bleh....doesn't work on my iPad

I will try on the PC. Thank you.

 

[Jaybird180]

Amen. Once you know how each instrument works, and how the pitot and static systems work, the rest is a matter of deduction.

Thought I did. I'm more of a take it apart to understand how it works kinda guy, but little chance there. I have resources that I haven't used yet.

Thanks for the description of what a PIC student needs to have down pat you wrote in another thread. Helpful stuff, which is why I'm plugging the holes in my understanding and trying to find the earliest moments of misunderstoods in my aviation education then working forward. The fun stuff is fun, but it doesn't mean much if the rudiments are sketchy.

 

[dmspilot]

For example: what conditions pitot-static instruments will show when iced over in flight (comes to mind). I don't quite get that particular failure mode of using them as baro indicators considering that I have only experienced an Attitude Indicator failure, which I picked up in a new to me airplane.

Just think about it logically. What happens if both the front opening and the drain hole of the pitot tube becomes clogged, and the static port remains clear? You will have a fixed amount of trapped air in the pitot side, with a varying amount of static pressure. As you climb, the trapped air in the pitot side remains at the same pressure, while the static pressure decreases. So as you climb, the ratio of pitot to static pressure increases, causing an increasing airspeed indication.

 

[Jaybird180]

Just think about it logically. What happens if both the front opening and the drain hole of the pitot tube becomes clogged, and the static port remains clear? You will have a fixed amount of trapped air in the pitot side, with a varying amount of static pressure. As you climb, the trapped air in the pitot side remains at the same pressure, while the static pressure decreases. So as you climb, the ratio of pitot to static pressure increases, causing an increasing airspeed indication.

Where's the emoticon of the slapping my forehead and saying "Doh!"?

But there's gotta be something else...can't be that simple

 

[Clark1961]

Unless you've got a runaway trim event. That was a daily event on the Navajo.

Like I said, pitch trim problems in the 'kota are unlikely. Century used a couple different systems for pitch trim and the cable tension sensing system is problematic. The pitch servo motor load sensing system is more reliable and fairly easy to repair since it is just an analogue computer.

 

[Ted]

Where's the emoticon of the slapping my forehead and saying "Doh!"?

But there's gotta be something else...can't be that simple

There are a few things.

1) That assumes that the clogging happens instantaneously
2) That also assumes a leak-free system

What has happened in my experience with pitot tubes icing up (it's happened more than once for me) is that the ice builds on the pitot tube slowly, hence the gradual decrease in IAS to 0.

 

[Jaybird180]

There are a few things.

1) That assumes that the clogging happens instantaneously
2) That also assumes a leak-free system

What has happened in my experience with pitot tubes icing up (it's happened more than once for me) is that the ice builds on the pitot tube slowly, hence the gradual decrease in IAS to 0.

The difference between theory and practice. I have to get through theory 1st.

I have no doubt I can pass the FAA written, however I do not yet have certainty that I meet my own standards for completion of knowledge and understanding. I don't like the feeling I get when I get a passing score yet knew I should do better.

 

[azure]

The difference between theory and practice. I have to get through theory 1st.

I have no doubt I can pass the FAA written, however I do not yet have certainty that I meet my own standards for completion of knowledge and understanding. I don't like the feeling I get when I get a passing score yet knew I should do better.

As a PPL candidate, that kind of thinking kept me flying on instructor signoffs until I had accumulated nearly 250 hours. IOW, if your standards are high, if you apply it to the checkride it's a recipe for becoming a perpetual student.

Maybe not quite so much for the instrument, since there's no solo signoff for IFR. But still, there is something to be said for trusting your CFI(I) and just gittin' 'er done.

 

[Jaybird180]

As a PPL candidate, that kind of thinking kept me flying on instructor signoffs until I had accumulated nearly 250 hours. IOW, if your standards are high, if you apply it to the checkride it's a recipe for becoming a perpetual student.

Maybe not quite so much for the instrument, since there's no solo signoff for IFR. But still, there is something to be said for trusting your CFI(I) and just gittin' 'er done.

Understood, however I got an 87 on my PPL written, and that won't cut it for my IR. I have no interest in prolonging training as I haven't started yet, but I want to have good command over the written material; no intellectual laziness.

 

[gismo]

Yeah, the Century IIIC has a lot of issues with trim runaway in my experience. Haven't had any issues with random turns if I was using it right, though.

Then there's the old forgetting to turn it off and "Hey, why are my ailerons frozen?" I've found it's easier to do that on the C-III series because it doesn't have some annunciator lights.

I put some bright orange tape on the top of the C-III rocker switches to make their position more obvious. When the rocker is on the tape "disappears" into the control head.

 

[Ted]

I put some bright orange tape on the top of the C-III rocker switches to make their position more obvious. When the rocker is on the tape "disappears" into the control head.

Good idea. Although as I recall your C-III control head is located on the panel (lower left corner?). On the 310 it's located below the throttle quadrant.