Stall Warning/AOA Failure Poll

[201er]

Who has ever experienced an AOA device failure? Stall warnings are the most common type of AOA sensing device. Anyone experience a stall warning or other AOA device give wrong readings? Ice over? Outright fail? How common are these failures and how do they manifest?

Edited September 19, 2016 by 201er

[kpaul]

Your poll requires you to answer both questions, even if the answer to number 1 is never.

[201er]

Just now, kpaul said:

Your poll requires you to answer both questions, even if the answer to number 1 is never.

Thanks, fixed it by adding a never option to the second.

[Vance Harral]

I'm not inclined to vote in the poll because I don't think it's well designed and I suspect you have a preconceived agenda.  But by way of anecdote, I've had the vane-type stall warning sensor fail in our M20F.  Went up to practice stalls and was able to go all the way to the break without the stall warning going off on the first attempt.  It operated normally on subsequent attempts, as well as back on the ground.  Possible failure modes include the vane being stuck and not actuating the switch, or the vane moving but not making good electrical contact.  I suspect it was the latter.

Failure of electrical switch vane sensors is not an uncommon problem, and a shot of contact cleaner sprayed into/around the vane is the typical advice.  We do this as a matter of course at every annual, but I know from experience the device can still fail.  Ideally, a pilot makes use of all available information, including control feel, airspeed indicator, and stall warnings and AOA devices if so equipped.

[201er]

Just now, Vance Harral said:

I'm not inclined to vote in the poll because I don't think it's well designed and I suspect you have a preconceived agenda.

How can I make the poll better. I'm just trying to get a feel for how common AOA device fail and bring up awareness of how to prevent or deal with that.

[takair]

I've had the basic stall warning vane fail in two ways.  First time was an intermittent ground at the vane.  Second went on for a while.  Intermittent failure of the switch in the vane.  I would test it and it would work on the second or third activation.  I would notice that I would never get a chirp of stall warning when landing.  In a perfect world we should check it prior to each flight.  Open the vent window, turn master on, flick the vane, shut power off.  

I have wondered if failed or misadjusted vanes contribute to the classic stall/spin in the pattern.  I know that my buzzer is an attention getter.  Some of the sonalert types are not so attention getting.  The vane should be adjusted to give adequate margin to stall.  On the flip side, too much margin might lead to a false sense of security.  Perhaps the ultimate AOA system would have a head up visual indication as well as a variable tone or voice alert to provide additional clues as to margin.  

Ultimately, the basic aircraft has three things to provide stall margin....airspeed, stall warning system and stall buffet from the stall strips....so as you know, there are backups if we understand the margin provided by each.  I know you were not a big fan of intentional stalls, but I find it to be a good reminder of the margin to stall provided by the various instruments.  Even with an AOA instrument, I would think that you would take it at least to the imminent stall to calibrate it and validate it every so often.  

[kpaul]

Just now, Vance Harral said:

I'm not inclined to vote in the poll because I don't think it's well designed and I suspect you have a preconceived agenda.

Even with an agenda, the poll my reveal interesting data. I have over 5000 hours and have never had a failure.

2 minutes ago, 201er said:

How can I make the poll better. I'm just trying to get a feel for how common AOA device fail and bring up awareness of how to prevent or deal with that

I think the poll is fine for trying to pull out the frequency of failures, however is one only gets into the approach to stall range during the flare they may never know it failed.  CFIs will likely see it more just through exposure.

Your poll does not address your interest in "awareness of how to prevent or deal with that."  But my guess is known pitch and power settings will be the primary way to deal with a failure, just like a failure in ASI.

I have thousands of hours flying behind dual vane AOA connected to shaker/pusher in a plane that will roll on it's back if brought to a full stall power on or power off.  Multiple pages in the EP section on how to handle a failure, but have never had to use them.

In the multiple GA aircraft I have flown, none have had anything other then traditional stall warning, never have had one not indicate approach to stall.

[201er]

Just now, kpaul said:

Even with an agenda, the poll my reveal interesting data. I have over 5000 hours and have never had a failure.

Well yes, I want to get a glimpse at real world failure rate in our group. I have a hypothesis. You can probably guess what it is. How it plays out will hopefully be left to honesty and truth. And then everyone can evaluate and draw their own conclusions or dive into further discussion.

Just now, kpaul said:

Your poll does not address your interest in "awareness of how to prevent or deal with that."

Well that's what the discussion is for. I don't have specific values to poll for that element.

Just now, kpaul said:

I have thousands of hours flying behind dual vane AOA connected to shaker/pusher in a plane that will roll on it's back if brought to a full stall power on or power off.  Multiple pages in the EP section on how to handle a failure, but have never had to use them.

In the multiple GA aircraft I have flown, none have had anything other then traditional stall warning, never have had one not indicate approach to stall.

Ever had issues due to icing?

Edited September 19, 2016 by 201er

[kpaul]

Just now, 201er said:

Ever had issues due to icing?

Tons, just not with AOA, and thank goodness never in my Mooney.

[201er]

5 minutes ago, kpaul said:

Tons, just not with AOA, and thank goodness never in my Mooney.

I mean, ever had an AOA or stall warning freeze over?

[kpaul]

14 minutes ago, 201er said:

I mean, ever had an AOA or stall warning freeze over?

Yeah, I got your meaning, never had AOA/stall warning freeze over.

[takair]

9 minutes ago, 201er said:

I mean, ever had an AOA or stall warning freeze over?

I think that even trace ice will make the basic stall vane inop unless it is heated.  Had it happen a couple of times and had to land that way once.  Carried extra airspeed and things worked out ok.  Not my proudest moment, taxing in covered in ice.  In addition, the buffet to stall may no longer be valid nor is the feel and sight picture.  Even AOA guage would not be valid, as the stall AOA is likely lower.  Airspeed margin is beneficial and perhaps the only protection, assuming pitot heat was on.  I suppose you could fly lower AOA indication if the AOA is heated.

Did some work on corporate AOA systems in a previous job.  The heating system is crucial to maintain accuracy.  Some aircraft automatically increase the shaker and pusher points in ice. 

[Bennett]

Dynon's AOA probes come in heated and non-heated versions.

[Vance Harral]

1 hour ago, 201er said:

How can I make the poll better. I'm just trying to get a feel for how common AOA device fail and bring up awareness of how to prevent or deal with that.

Since you specifically asked...

First, the sample size of contributors on Mooneyspace is almost certainly too small to be meaningful, especially since respondents are self-selecting rather than random.  That's the biggie.  But even if we set that aside, you should be interested in failure rate per hour flown, not per pilot.  In other words, kpaul's "vote" based on 5000 hours should count 5x that of someone with 1000 hours of exposure, and 50x that of someone with 100 hours.  Next, the poll doesn't separate pilot experience from equipment flown.  If your poll shows zero failures for "airfoil shaped probe sensors", that's much more likely to mean none of us have flown with such a device than to mean those devices are ultra-reliable.  On a related note, some of the technologies you mention are so new there's simply no meaningful failure data for them yet, at least not in the GA fleet.  Finally, since your poll doesn't allow one to select multiple options, it can only be meaningful if all the options are mutually exclusive.  You have multiple overlapping choices, and that distorts the data.

I'm sure some people are going to read this as the nit-picking rant of a pedant.  But data gathering and analysis is a pretty sophisticated science, requiring significant effort to get right.  The way you've constructed the poll suggests you don't understand it very well, and I cringe at the idea that you think you're going to get meaningful data from it.  If I come off as a grumpy old man who happens to have taken some graduate-level statistics courses that most people don't care about, well, that's just the risk of posting on the internet.

To the extent people share anecdotes of particular failures like I did, I think that's helpful to everyone.  I don't want to be a jerk about you starting the thread - anyone is free to contribute, of course.  But please don't draw any conclusions about the reliability of various AOA technologies from your poll.  It's not meaningful.

[Yetti]

A search for "vane" turns up lots of threads

[MyNameIsNobody]

Nit-picking rant of a pedant.  Ya I am so using that one.  

 

As opposed to "unsophisticated science"...which is__________(see poll questions)

Funny.  Both Ha Ha and Strange.  Who said engineers aren't funny?  Besides me...

That was a corker.

[Yetti]

12 minutes ago, Vance Harral said:

To the extent people share anecdotes of particular failures like I did, I think that's helpful to everyone.  I don't want to be a jerk about you starting the thread - anyone is free to contribute, of course.  But please don't draw any conclusions about the reliability of various AOA technologies from your poll.  It's not meaningful.

One of three responses

"These are not the droids you are looking for"

Did you hear about the statistician that drowned crossing a stream of an average depth of 3 feet

 

[carusoam]

So I says to the statistics professor... 

 

My stall vane silently left me for an unknown period of time...

I mechanically tested it prior to each flight, but not with the electricity running.

It was a challenge to notice it not sounding.

Now it gets tested with the electricity running.

Best regards,

-a- 

[cnoe]

I once had a stall vane malfunction,

which was traced to an electrical junction.

I'm pleased to report,

after fixing the short,

that I now have stall warning resumption.

Sent from my iPad using Tapatalk

[carusoam]

A road divided in a yellow wood...

being a single traveler, I couldn't take both...

 

Frost wasn't as good or practical as CNOE!

Best regards,

-a-

[JohnB]

I bet the underlying agenda is what is the most reliable type of AOA warning system. Still spending several months replacing and trying to fix my bonky mechanical stall warning switch, where my alpha aoa system works fine, mechanical switches are far less reliable, as coming up in the poll here. Nice one!

[Jerry 5TJ]

On September 19, 2016 at 8:50 PM, Yetti said:

Did you hear about the statistician that drowned crossing a stream of an average depth of 3 feet?

No, but I've heard about the statistician with his feet in an ice bucket and his head in a furnace who remarked that on average the temperature was about right.