6 ms·

Here's the directive: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/448c46c035e93a6e862583e0007291d8/$FILE/2019-08-51_Emergency.pdf http://rgl.f

Here's the directive: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/448c46c035e93a6e862583e0007291d8/$FILE/2019-08-51_Emergency.pdf http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/... This isn't really a grounding, at least not the way the 737 MAX is grounded. Cirrus jets can't be flown until the AD is complied with, but complying with the AD is a (relatively) simple matter of replacing the angle of attack sensors. Once that's done, the aircraft is airworthy again. The issue is a "quality escape," i.e. the existing sensors weren't built to spec. There are two screws that attach the vane to the potentiometer; the factory didn't torque the screws properly and didn't apply thread locker to them. So this is a manufacturing error, not a fundamental problem with the design. I say that just to provide contrast with the MAX issues since the problems are superficially similar, but quite different once you get into the details.

pdx_flyer 8y ago
Exactly. The AD says that the plane can be flown once the part is replaced.
AceyMan 8y ago
Another data point to remind everyone how AoA is one of the most important metrics wrt flying an airplane (airspeed is right up there, too). Obligatory citation; imho, one of the webs's great resources— https://www.av8n.com/how/htm/aoa.html#sec-aoa-intro https://www.av8n.com/how/htm/aoa.html#sec-aoa-intro
- mikeash 8y ago
  Airspeed is mostly, although not entirely, important as a proxy for angle of attack.
- dsfyu404ed 8y ago
  But you don't need a dedicated sensor for it. The artificial horizon does that job too. Edit: To be more clear, the artificial horizon combined with other sources of information available to the pilot (airspeed, stall indicator) provide the pilot with the same level of situational awareness as knowing his/her AOA outright from a dedicated sensor.
  - danaliv 8y ago
    The artificial horizon doesn't indicate angle of attack. Please see this comment: https://news.ycombinator.com/item?id=19638250 https://news.ycombinator.com/item?id=19638250 Or consider an aerobatic airplane at the first vertical point in a loop. The airplane's pitch is 90° but the angle of attack is less than 10°.
    - dsfyu404ed 8y ago
      You're right but the vast majority of the time the difference between the AI and the AOA is close to zero (plus whatever the angle of the wing is relative to the fuselage which is fixed and should be pretty small anyway). The times when the difference between the AOA and the AI is very different than zero in a bad way the little stall switch on the wing and some sort of chime/buzzer will be more than happy to let the pilot know. My point is that the AI combined with the little stall switch on the wing seem to be good enough for the overwhelming majority of cases. Add in airspeed and you're more than covered. We keep trying to add systems to cover whatever remaining edge cases we find but those systems have failure modes too so we take three steps forward and two steps back. These systems pick up the slack when the pilot might be inattentive but the increased complexity and cognitive load poses other risks.
      - lutorm 8y ago
        Loss of control during approach and landing because of poor airspeed control kills pilots every year. It's important enough that the EAA has a dedicated "loss of control initiative" to try to figure out what to do. See for example https://www.eaa.org/eaa/news-and-publications/eaa-news-and-aviation-news/news/01-17-2019-Loss-of-Control-in-Homebuilts-Program-Video https://www.eaa.org/eaa/news-and-publications/eaa-news-and-a...
      - mikeash 8y ago
        Climbs after takeoff are a situation where they will significantly differ, and also one of the times when this information is more important. Attitude indicator? Look out the window! Stall horn? Just feel the pre-stall rumbling through the controls. You can fly a plane with no instruments. None of them are strictly necessary, but it’s a good idea to have them.
- cjbprime 8y ago
  > everyone how AoA is one of the most important metrics wrt flying an airplane Pretty difficult argument to make when most planes do not have AoA sensors!
  - astrodust 8y ago
    The "sensor" is often the pilot.
  - DamnYuppie 8y ago
    I believe he means jets, which I believe all of them do.
    - AdrianB1 8y ago
      He does not. Let's read as it is written.
  - briandear 8y ago
    Almost all new airplanes have them. The Skyhawk got one as standard equipment in 2016. Here’s a thesis on the topic: https://kb.osu.edu/bitstream/handle/1811/68634/1/AbramsHonorsThesis.pdf https://kb.osu.edu/bitstream/handle/1811/68634/1/AbramsHonor...
    - cjbprime 8y ago
      Sure, but almost no-one flies brand new airplanes. What percentage of GA flights do you guess contain an AoA display? And the argument's supposed to be that they're a most important indicator for airplanes?
  - mikeash 8y ago
    And yet it’s absolutely true. Note that many light aircraft have stall warning horns, which are just AoA sensors that only detect when the AoA exceeds a certain amount. In many other planes, you can detect excessive AoA by sound or feel.
- AdrianB1 8y ago
  I am qualified to fly several types of small planes, none has an AoA. I was able to fly with a faulty Pitot reading (airspeed), but I would not do it often; I had never felt the need for an AoA sensor, not even when I was flying in "unusual attitudes" (intentionally).
  - 0xfaded 8y ago
    My second ever solo my airspeed indicator froze :)
dsfyu404ed 8y ago
I used to work as an apprentice for a GA mechanic (never pursued it, went to college instead). Disassembling something, inspecting it then performing reassembly and properly torquing the screws with locktite per some published procedure is one of those things aircraft mechanics do all day. Unless the design of the sensor would make it inaccurate after being reassembled (I'm skeptical of this, it wouldn't make sense for a few reasons) this is kind of a dick move to the aircraft owners that they're probably doing in the name of "look how careful we're being" Any certified mechanic anywhere can do the former with no lead time and if it turns out the threads are close to stripped out from a loose sensor banging around on there then replace the sensor. It doesn't make sense to replace the sensor off the bat unless you just want to be seen "doing something".
- toomuchtodo 8y ago
  It’s probably the right call from an optics perspective so soon after the 737 MAX fiasco. It’s more expensive than a workbench fix, but cheaper than bad publicity and a loss of faith in FAA governance. It’s a shame the cost is being foisted on GA owners though, owning a private plane is expensive enough already.
  - dsfyu404ed 8y ago
    I'm not going to shed any tears over CEOs that suddenly have to get first class flights but being thrown under the bus so that someone else can optimize their political situation does not feel good no matter how minor the slight is in the grand scheme of things.
    - briandear 8y ago
      CEOs aren’t flying Vision jets. The ridiculous attitude that general aviation is somehow a class issue is getting old. Cessna Mustangs and other similar types are used frequently for air ambulance operations as well as plenty of non-CEO uses. General Aviation is a lot more than Sergei flying in his Gulfstream. Look at the 1989 earthquake for example and how GA was a huge part of delivering relief supplies to Watsonville. Look at Angel flights and the value that brings to people. GA is also essential to organ delivery.
peteradio 8y ago
Is this the same manufacturer as the sensors on the MAX?
- danaliv 8y ago
  Good question. I don't think so but I can't tell for sure. They make pitot-static probes for Boeing and Airbus jets but I don't know if their AoA sensors are used in commercial aircraft.
duxup 8y ago
It's really amazing how AA and airspeed are so... difficult for pilots to perceive that they're totally reliant on the sensors to tell them. Speed I guess makes sense, just amazing how a pilot so easily can slow a plane too much, change the angle too much and have no idea what is up.
- bwilliams18 8y ago
  Angle of Attack doesn't refer to the angle of the plane relative to the horizon but the angle of the plane relative to airflow.
  - nosianu 8y ago
    To illustrate further using the most extreme example I can think of - flying a loop: The angle of attack will remain in its usual very narrow range at any point when you fly a loop. The critical or stalling angle of attack is typically around 15° - 20° for many airfoils (so your AoA should be less than that). Note that if you fly upside down (negative-G capable aerobatics airplane) you will still have a positive AoA, just on the other side of the wing. > If the airplane you’re flying is equipped with an angle-of-attack indicator, it will illustrate an abstract concept that pilots learn to recite during ground school but rarely fully comprehend—which is that an airplane can stall in “any attitude” and at “any airspeed.” For me, it took stalling on the back side of a loop (while pointed straight down at a high power setting) for that idea to sink in. https://www.aopa.org/news-and-media/all-news/2013/may/pilot/technique-learning-to-loop https://www.aopa.org/news-and-media/all-news/2013/may/pilot/...
    - ummonk 8y ago
      Eh, that would generally be considered a negative angle of attack, since we arbitrarily label one side of the wing as positive direction.
      - nosianu 8y ago
        As a private pilot who has done a bit of aerobatics, I disagree. It still is a positive AoA. Using a negative would be in conflict with what you would mean when you mean.. well, a negative AoA, for example when people ask questions such as this one: https://aviation.stackexchange.com/questions/51477/do-negative-angles-of-attack-create-lift https://aviation.stackexchange.com/questions/51477/do-negati... I would use AoA in relation to the direction of flight, not the up or down orientation of the airplane. Even upside down I still fly quite normally (in straight & level upside-down flight), and the lift created is positive: Up/down in relation to the earth don't change, so the direction of lift does not change. In this context it would be a bit confusing to use negative numbers as you suggest, IMO. However, since you can set your relative coordinate system and context however you like this is a topic we could discuss this ad infinitum without convincing one another if we insist on our respective PoVs. When faced with the linked question you would have some more explaining to do though, because there are negative AoA and no upside-down flight (now imagine adding that to the question to make it even more confusing...) :)

pdx_flyer 8y ago

Exactly. The AD says that the plane can be flown once the part is replaced.

AceyMan 8y ago

Another data point to remind everyone how AoA is one of the most important metrics wrt flying an airplane (airspeed is right up there, too). Obligatory citation; imho, one of the webs's great resources— https://www.av8n.com/how/htm/aoa.html#sec-aoa-intro https://www.av8n.com/how/htm/aoa.html#sec-aoa-intro

mikeash 8y ago
Airspeed is mostly, although not entirely, important as a proxy for angle of attack.
dsfyu404ed 8y ago
But you don't need a dedicated sensor for it. The artificial horizon does that job too. Edit: To be more clear, the artificial horizon combined with other sources of information available to the pilot (airspeed, stall indicator) provide the pilot with the same level of situational awareness as knowing his/her AOA outright from a dedicated sensor.
- danaliv 8y ago
  The artificial horizon doesn't indicate angle of attack. Please see this comment: https://news.ycombinator.com/item?id=19638250 https://news.ycombinator.com/item?id=19638250 Or consider an aerobatic airplane at the first vertical point in a loop. The airplane's pitch is 90° but the angle of attack is less than 10°.
  - dsfyu404ed 8y ago
    You're right but the vast majority of the time the difference between the AI and the AOA is close to zero (plus whatever the angle of the wing is relative to the fuselage which is fixed and should be pretty small anyway). The times when the difference between the AOA and the AI is very different than zero in a bad way the little stall switch on the wing and some sort of chime/buzzer will be more than happy to let the pilot know. My point is that the AI combined with the little stall switch on the wing seem to be good enough for the overwhelming majority of cases. Add in airspeed and you're more than covered. We keep trying to add systems to cover whatever remaining edge cases we find but those systems have failure modes too so we take three steps forward and two steps back. These systems pick up the slack when the pilot might be inattentive but the increased complexity and cognitive load poses other risks.
    - lutorm 8y ago
      Loss of control during approach and landing because of poor airspeed control kills pilots every year. It's important enough that the EAA has a dedicated "loss of control initiative" to try to figure out what to do. See for example https://www.eaa.org/eaa/news-and-publications/eaa-news-and-aviation-news/news/01-17-2019-Loss-of-Control-in-Homebuilts-Program-Video https://www.eaa.org/eaa/news-and-publications/eaa-news-and-a...
    - mikeash 8y ago
      Climbs after takeoff are a situation where they will significantly differ, and also one of the times when this information is more important. Attitude indicator? Look out the window! Stall horn? Just feel the pre-stall rumbling through the controls. You can fly a plane with no instruments. None of them are strictly necessary, but it’s a good idea to have them.
cjbprime 8y ago
> everyone how AoA is one of the most important metrics wrt flying an airplane Pretty difficult argument to make when most planes do not have AoA sensors!
- astrodust 8y ago
  The "sensor" is often the pilot.
- DamnYuppie 8y ago
  I believe he means jets, which I believe all of them do.
  - AdrianB1 8y ago
    He does not. Let's read as it is written.
- briandear 8y ago
  Almost all new airplanes have them. The Skyhawk got one as standard equipment in 2016. Here’s a thesis on the topic: https://kb.osu.edu/bitstream/handle/1811/68634/1/AbramsHonorsThesis.pdf https://kb.osu.edu/bitstream/handle/1811/68634/1/AbramsHonor...
  - cjbprime 8y ago
    Sure, but almost no-one flies brand new airplanes. What percentage of GA flights do you guess contain an AoA display? And the argument's supposed to be that they're a most important indicator for airplanes?
- mikeash 8y ago
  And yet it’s absolutely true. Note that many light aircraft have stall warning horns, which are just AoA sensors that only detect when the AoA exceeds a certain amount. In many other planes, you can detect excessive AoA by sound or feel.
AdrianB1 8y ago
I am qualified to fly several types of small planes, none has an AoA. I was able to fly with a faulty Pitot reading (airspeed), but I would not do it often; I had never felt the need for an AoA sensor, not even when I was flying in "unusual attitudes" (intentionally).
- 0xfaded 8y ago
  My second ever solo my airspeed indicator froze :)

dsfyu404ed 8y ago

I used to work as an apprentice for a GA mechanic (never pursued it, went to college instead). Disassembling something, inspecting it then performing reassembly and properly torquing the screws with locktite per some published procedure is one of those things aircraft mechanics do all day. Unless the design of the sensor would make it inaccurate after being reassembled (I'm skeptical of this, it wouldn't make sense for a few reasons) this is kind of a dick move to the aircraft owners that they're probably doing in the name of "look how careful we're being" Any certified mechanic anywhere can do the former with no lead time and if it turns out the threads are close to stripped out from a loose sensor banging around on there then replace the sensor. It doesn't make sense to replace the sensor off the bat unless you just want to be seen "doing something".

toomuchtodo 8y ago
It’s probably the right call from an optics perspective so soon after the 737 MAX fiasco. It’s more expensive than a workbench fix, but cheaper than bad publicity and a loss of faith in FAA governance. It’s a shame the cost is being foisted on GA owners though, owning a private plane is expensive enough already.
- dsfyu404ed 8y ago
  I'm not going to shed any tears over CEOs that suddenly have to get first class flights but being thrown under the bus so that someone else can optimize their political situation does not feel good no matter how minor the slight is in the grand scheme of things.
  - briandear 8y ago
    CEOs aren’t flying Vision jets. The ridiculous attitude that general aviation is somehow a class issue is getting old. Cessna Mustangs and other similar types are used frequently for air ambulance operations as well as plenty of non-CEO uses. General Aviation is a lot more than Sergei flying in his Gulfstream. Look at the 1989 earthquake for example and how GA was a huge part of delivering relief supplies to Watsonville. Look at Angel flights and the value that brings to people. GA is also essential to organ delivery.

peteradio 8y ago

Is this the same manufacturer as the sensors on the MAX?

danaliv 8y ago
Good question. I don't think so but I can't tell for sure. They make pitot-static probes for Boeing and Airbus jets but I don't know if their AoA sensors are used in commercial aircraft.

duxup 8y ago

It's really amazing how AA and airspeed are so... difficult for pilots to perceive that they're totally reliant on the sensors to tell them. Speed I guess makes sense, just amazing how a pilot so easily can slow a plane too much, change the angle too much and have no idea what is up.

bwilliams18 8y ago
Angle of Attack doesn't refer to the angle of the plane relative to the horizon but the angle of the plane relative to airflow.
- nosianu 8y ago
  To illustrate further using the most extreme example I can think of - flying a loop: The angle of attack will remain in its usual very narrow range at any point when you fly a loop. The critical or stalling angle of attack is typically around 15° - 20° for many airfoils (so your AoA should be less than that). Note that if you fly upside down (negative-G capable aerobatics airplane) you will still have a positive AoA, just on the other side of the wing. > If the airplane you’re flying is equipped with an angle-of-attack indicator, it will illustrate an abstract concept that pilots learn to recite during ground school but rarely fully comprehend—which is that an airplane can stall in “any attitude” and at “any airspeed.” For me, it took stalling on the back side of a loop (while pointed straight down at a high power setting) for that idea to sink in. https://www.aopa.org/news-and-media/all-news/2013/may/pilot/technique-learning-to-loop https://www.aopa.org/news-and-media/all-news/2013/may/pilot/...
  - ummonk 8y ago
    Eh, that would generally be considered a negative angle of attack, since we arbitrarily label one side of the wing as positive direction.
    - nosianu 8y ago
      As a private pilot who has done a bit of aerobatics, I disagree. It still is a positive AoA. Using a negative would be in conflict with what you would mean when you mean.. well, a negative AoA, for example when people ask questions such as this one: https://aviation.stackexchange.com/questions/51477/do-negative-angles-of-attack-create-lift https://aviation.stackexchange.com/questions/51477/do-negati... I would use AoA in relation to the direction of flight, not the up or down orientation of the airplane. Even upside down I still fly quite normally (in straight & level upside-down flight), and the lift created is positive: Up/down in relation to the earth don't change, so the direction of lift does not change. In this context it would be a bit confusing to use negative numbers as you suggest, IMO. However, since you can set your relative coordinate system and context however you like this is a topic we could discuss this ad infinitum without convincing one another if we insist on our respective PoVs. When faced with the linked question you would have some more explaining to do though, because there are negative AoA and no upside-down flight (now imagine adding that to the question to make it even more confusing...) :)