Cirrus Vision Jet Grounded for AOA Malfunctions

[Dusty Rider]

Seems the B737 MAX isn't the only airplane afflicted by problems with stall prevention systems.

"While the airplane was under manual pilot control, the airplane activated several downward pitch commands coincident with stall warning, stick shaker, and several associated alerts. The pilot reported “AOA FAIL” and “STICK PUSHER FAIL CAS” messages preceding the pitch command. The pilot was able to stop the automatic pitch commands by pressing and holding the autopilot disconnect button in accordance with the emergency procedure in the airplane flight manual and safely landed at his destination."

A little further in the report:

"Cirrus and Aerosonic (manufacturer of the technical standard order AOA sensor) have identified the probable root cause as an AOA sensor malfunction due to a quality escape in the assembly of the AOA sensor at Aerosonic."

Here's the link to the AD: https://tinyurl.com/yxadc8gm (rgl.faa.gov)

Has there been a sudden increase in the number of unrecoverable stalls happening in airplanes thereby creating a demand for these stall prevention systems? Or have these systems existed in airplanes longer than I'm thinking (more than the past ten years, for example)?

[Larry sreyoB]

Of course the MCAS system in the 737 MAX aircraft, despite numerous reports to the contrary, is not a stall prevention system.

[Reams Goodloe]

Larry -

If a system that is designed to prevent adverse nose up pitching moment isn't a stall prevention system, just exactly what is it?????

https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610/

Reams

[Larry sreyoB]

Larry -

If a system that is designed to prevent adverse nose up pitching moment isn't a stall prevention system, just exactly what is it?????

It is exactly what its name says; a Maneuvering Characteristics Augmentation System. It provides a nose-down bias, through the introduction of stabilizer trim, in unusually high AoA situations so as to produce a similar pitch "feel" to that of the older generations of 737s.

A stall prevention system, aka a stick pusher, is installed on other airplanes which have less than favorable stall characteristics. No such system exists on any of the 737 models.

[Reams Goodloe]

Larry -

As far as I can tell, this is the old hardware v software argument. On system uses software, one system uses hardware. Same result.

Reams

[Larry sreyoB]

They're both hardware. One aggressively pushes the control column nose-down so hard that it literally rips the yoke out of the pilot's hands. The other adds incremental burst of nose-down stabilizer trim (soon to be a single application). The purpose of each is entirely different.

One is required to meet the stall recovery certification requirements due to otherwise unfavorable stall characteristics. The other is to increase the control pressure at excessively high AoA to better match the pitch feel to that of earlier 737 models.

[Ray Tackett]

It is exactly what its name says; a Maneuvering Characteristics Augmentation System. It provides a nose-down bias, through the introduction of stabilizer trim, in unusually high AoA situations so as to produce a similar pitch "feel" to that of the older generations of 737s.

A stall prevention system, aka a stick pusher, is installed on other airplanes which have less than favorable stall characteristics. No such system exists on any of the 737 models.

Thanks again, Larry, for your patient, clear discussions with us non-airline pilots.. It's a great way to reach a segment of the passenger public which can understand and simplify for non-pilot folks.

[Russell Holton]

Thanks again, Larry, for your patient, clear discussions with us non-airline pilots.. It's a great way to reach a segment of the passenger public which can understand and simplify for non-pilot folks.

Ditto! Thanks Larry.

[Dusty Rider]

Yes, thank you for explaining, Larry. As I understand it, then, these systems are in place because these aircraft are really difficult to recover if they actually make it to a full stall? Everything I've flown has had pretty straightforward stall characteristics, so the concept of stall prevention, or MCAS systems is pretty foreign to me.

[Larry sreyoB]

Yes, thank you for explaining, Larry. As I understand it, then, these systems are in place because these aircraft are really difficult to recover if they actually make it to a full stall? Everything I've flown has had pretty straightforward stall characteristics, so the concept of stall prevention, or MCAS systems is pretty foreign to me.

MCAS has nothing at all to do with stalls or stall recovery.

An airplane that has undesirable stall characteristics, that would otherwise not meet certification requirements, would have a stick-pusher system. None of the 737 models, or any of Boeing's jet airliners that I know of, have a stick-pusher system.

[Terry Carraway]

Yes, thank you for explaining, Larry. As I understand it, then, these systems are in place because these aircraft are really difficult to recover if they actually make it to a full stall? Everything I've flown has had pretty straightforward stall characteristics, so the concept of stall prevention, or MCAS systems is pretty foreign to me.

MCAS increases stick forces, so that the pilot does not over pitch the aircraft.

[Larry sreyoB]

Here's an article that corrects many of the inaccuracies from the IEEE article.

https://abnormaldistribution.org/index.php/2019/04/30/ieee-spectrum-on-possible-software-involvement-in-two-recent-airliner-crashes/

[Ralph Jones]

[QUOTE=Larry sreyoB;n11108]Here's an article that corrects many of the inaccuracies from the IEEE article.

Abnormaldistribution.org...how deliciously Gaussian <g>. And I haven't seen mutatis mutandis or ceteris paribus in eons...Seriously, a great analysis. Everybody listen up.

[John O'Shaughnessy [FCM]]

I love this comment:

"One last comment, on a small aircraft this time. Travis suggests that “the Lycoming O-360 engine in my Cessna has pistons the size of dinner plates“. The cylinder bore for 0-360 engines (I flew one for 12 years) is 13cm (see the Wikipedia article). My dinner plates, small as they are, have a diameter of 21cm. My espresso saucers are 12.5 cm. I commend Travis’s nourishment discipline, but suggest it does not easily generalise."