Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor.

Looks like you copied that from Wiki. Did you notice this at the top of the page?

This article is about autorotation of rotary wing aircraft. For autorotation of fixed-wing aircraft, see Autorotation (fixed-wing aircraft).

Aaah; you mean incipient spin. In other words, when close to the stall, it's best not to introduce a boot-full of rudder. Used to be called "airmanship"

I'd describe that as "handling" rather than "airmanship" but whatever, it's easy to take such a view if you have been trained in spinning. Not so easy if you haven't. And yaw can be introduced by asymmetric thrust without any need for an unwise application of rudder. So, add "don't stall in an asymmetric thrust condition" to your airmanship list. Everything would be fine if people would just stop screwing up.

Easy Street. Agree with you there, but rather than training in spinning, it's better (and safer) to train to recognise the incipient spin. or better still, the incipient stall.

ManaAdaSystem

Thanks - with over 11,000 rotary hours I have some familiarity with the term as it applies to helicopters.

Like I said - “B over A and all that” but I guess that got missed. I know easy street will get it.....

212; You made me spill my coffee.... thanks.

Manadasys... 212, herod and co are quite correct. The inertial and aerodynamic forces that act on an aircraft result in "autorotation" the difference in incipient to developed spin is essentially the axis direction of flight, (and that can be argued) both can be stable or oscillatory (er, incipient is generally not a stable case over any time frame),. The B/A ratio is an expression of the inertial moments on the longitudinal and lateral axis, which affects how cross-coupling will develop in passing. B/A is suggestive of the ease of entry or exit of a spin, and of the impact of a control input to the spin. Supposedly. Weird stuff can happen anyway. In a spin, there are continuous changes in accelerations on all axis, and as the apple dropping showed, that has to take forces to change, those forces come from the autorotative moments of inertia and from drag and lift variations that will either be pro rotation or anti-rotation. Break one of the axis moments will change the spin mode and establish into a recovery. (well, kind of...)

For the B737, that was a new "improved" function for that sim, it was eye-watering to see. the takeaway was that an off-axis entry into a microburst is exciting, it adds to the common or garden initial pitch up, (speed/aoa stability) the yaw component, and that is a blast. None of these are a deal-breaker by themselves, but being ham-fisted, pulling through to stall gives a memorably wild ride, yelps and a face plant (sim freeze after the 1st one) DL did Dallas, and that data shows an off-axis entry, the guys had a lot going on. A probability of entry angle relative to the core will show that the least likely entry is the one we practiced previously, which gives a pitch effect mainly. It is easier to simulate, but it doesn't reinforce the point that if y'all iz wobbling in yaw, respecting the aerodynamic stall is of more than passing interest.

Observed roll rates in excess of control authority suggest its time to lower AOA.... so when the accident data shows 180 deg/sec roll rates (not an uncommon rate in the recovered data) , with up-elevator, it's a given as to what is occurring. your ailerons will give a certain rate, and rudder another, both are non linear functions, rudder effectiveness increases at higher AOA, and lower speeds if a limiter is involved, up to the tail falling off.... ailerons increase in effectiveness as AOA reduces and as speed increases. But at any time, there is a limit to what they can give, and above that, you are having a wild ride from autorotation. [fixed wing thingys]

When that crew came back from coffee, the techs and I showed them the QTG overlay and what we had looked at and recorded in the coffee break. they redid the same entries with a bit more care on pitch control and had a pleasant ride out the other side. The downside was, the IPs got around to avoiding the simulation of off-axis entry, which seemed to be a missed opportunity to get a learning point across. The set up for the IP had a set of entry geometries that seemed to be a good idea.

For helos, autorotation merely indicates that there is a derived torque to the rotor to drive the system. As the books show that is achieved through the magic of relative airflow inflow angles to the blade and happens to give a drive force in the mid-span of the rotor blade, to offset the drag force at the tip and at the root section of the blade. That brings up some wacky twist oddities that are interesting to read about, martin Hollman had a nice graph on that I seem to recall.

I have done this exercise in the sim and never came close to a “ face plant “
Pulling through to a stall?
3.5 to 4 Gs?
That's what the pitch limit bars are for.
180 deg/sec roll rate ?
WTF?
You have got to try really hard to screw up this badly in a B737.
It wont be the aircraft.

Does your sim model give an off-axis entry into the microburst model? Fujita's model had been in use for over 20 years when I saw this in a sim, and it was in only one of the sims following an upgrade of the aeromodel.

a microburst is not a circular column of descending air that gets to ground level and then.... does.... a splat like an egg. It may have nearly vertical flow neatly for some point up fairly high, but then it will have a stagnation point in the center of the surface, and a roughly toroidal donut shape from the flow around the stagnations point, and above the donut, you will get an inverted trumpet form of the flow field, you can probably neglect the Coriolis induced axial rotation of the flow field, but that will be there as well in the real world. So. if yon sim sluf is aligned with the center axis, then you get a pitch up due to the flow direction to the aircraft. your stab is trimmed to maintain an AOA on the wing, and that results in a pitch up. m'kay?
Now, look at a planform flight path past yon pesky roundy planform downwash, and that is aligned with the centerline of the aircraft only when your pointy bits are pointing at its center. Every other path will result in yaw towards the core in the entry into the core. Get a bunch of bananas, tape them up by one end with the curvy (Queenslander workshop inspired) bend going outbound, and put the taped ends at the top. pass your wine glass past the bananas, and you will see that the vector is not aligned with the direction of your red wine. That's the yaw bit. If you happen to stall with a yaw rage, fun stuff happens.

FYI, when this was seen in the sluf sim, it was not on the B777 B747 744, A330 MD11 B767 or B757 sim models, they didn't introduce yaw at that time, or if they did, it was not observable in the QTG. Only one of our 3 737 sims had this software at that time, the others didn't behave like this... Progress,

?
A comment was made about the SJ182 plane spinning by another poster. I suspect it is improbable. The stall speed for the B737-500 clean is around 120KCAS roughly. I have the actual data, but that is for 51T and 38T at FL170 for forward and aft limit CG, so I am guessing, in the absence of the AFM which has the SL VS for various configs as well as it does have the buffet boundary for high and low-speed buffet. For a stall speed about 120, a CAS of double that would give a 4g pull to buffet,

Indeed.
The PLI is a thing of beauty. they also are dynamic and as you race up to them. they will be racing down to meet your pitch up input, the pilot response, and the aircrafts alpha stable pitch response, just add a bit of G, a bit of turbulence, and a new model that gives not just pitch, but pitch, yaw, and roll as well.

Yup, thats what the PLIs are there for.

The roll rate on UAL585 and USAir 427 exceeded 180/s, for starters.

Really roughly,....

A 2 aileron Pitts S1 got about 150/s, 4 ailerons about 230/s on a good day An A-4, 720/s, helmet knockin'. Rudder on a B737 gives about 25/s secondary roll, aileron gives about 45/sec. very roughly... A T-38/F-5 has 2 rates, the wild rate or the insane rate. P51 around 100/s these are rough rates, WW2 figher roll rates were as good as they could get, but they are anaemic, give beautiful graceful aeros though, and a big difference if going with or against the prop. The F-4 had fair rates, even better if you put in aileron at alpha over 12.... :) Transport aircraft have relatively low rates as that is what is needed. tactical aircraft have greater rates, exact figures will depend on what the book said, and what the control input is. Oddly, a number of transport aircraft have a real problem getting full deflection on the ailerons anyway, as the control yoke gearing to the deflection needs hands to be swapped to get the rotation angle on. That came up in one report a long time back. ( I think that was actually the B734 of USAir IIRC...) On other planes, the addition of a hard rudder is an issue, unless you have a parachute, The A300 was the poster child for that, and the same structure more or less went on to the 310, 320, 330 340.. at least. alternating torsion-bending suuuuuucks with harmonic yaw rates. AA587.

Well may you say WTF, as nothing will save the Governor Gen'l....


And yet collectively, we do so. If at first...

Airplanes are humble tools. They are the result of our design, so it's always us...

Fun fact, as far as sims go, they can be great to questionable. One sim you could take to an aerodynamic break, and the plane would climb at 6000FPM below that speed. I want that on my own jets. It was also nearly impossible to envoke a wing drop, but the flight testing had great movies of the belly uppermost in a stall. Outside of 1.3Vs and MMO, a lot of what you see is questionable. Even the departure stuff was an issue. At one conference on sims, the point was made that the airlines were routinely training in a sim that the model had not qualified data for. The OEMs in the part 125 testing obtained data that was not needed beyond (trying to recall.... ) 8 Seconds? from meeting the min speed condition. I suggested that there was a bucket of data in accident archives that provided all of the info that was needed, and got a lot of frozen stares in response. 2 major OEMs were bemoaning the data desert, and also stared blankly when I suggested using accident data.

I have been around for while and have done the rudder hard-over on the -400 in the sim.
Scary , no question.
But why speculate on yaw being added ?
Never seen anywhere close to 180 deg/sec roll in any wind shear sim. training.
And my company has the latest and the best sims.
For what its worth , I suspect somebody disconnected the autothrottle and mishandled a level-of in severe turbulence.
It can go pear-shaped from there easily and is a much simpler explanation.

Flaps,

There is almost no chance this aircraft spun. I didn't say it did, I was referring to another post that had suggested the term, and I was indicating that it was unlikely. Go back, and read what was written. On wind shear, I did not say the sim got 180/s, it did not, it did go nose flat 2 times in a row while whizzin' about. Got to thank the guys for repeatability.

The DFDR will tell the story, the guys will already know in this case what happened, they may not know why. It seems to still fit around a clutch pack issue that left a thrust lever at a climb thurst level and brought only one back to maintain speed, which then went pear-shaped. The weather adds distractions and complicates both the detection and the recovery. In this sort of bingle, it's going to be a spiral dive, not a spin, at least to start with. Without being stalled, KCAS is going to wind up quickly, making a stall less likely along with recovery.


https://cimg1.ibsrv.net/gimg/pprune....95f823b6f0.png

As you are from south of the border, it's probable that the sim you refer to is one of the two that I evaluated at the end of 1994 for fidelity in respect to control loss. Hope they were improved in between. using the available data at that time, neither the 300 nor the 400 sim did a great job of the control authority that existsed, and they didn't match the rates that were achieved in 427. Also did run-throughs of the 585 event and it was also not very close to the event data which was pretty sketchy anyway. The classic was different to the 200 but not that much. The 585 event I had queries about that being an off-axis gust front vortex and the maths had suggested that the roll, pitch and yaw needed to plonk in 9.x seconds (its a while ago...) were achievable from the vortex alone. There were contemporaneous reports of severe gust activity across the area of the flight path, The CVR was harrowing. Yes, the 427 rudder was consistent with a rudder reversal and got to take my hat off to George S for holding out for the tests to be done until failure was finally detected by P-H. the SE event, also consistent with the rudder. 585 didn't need the rudder reversal, and it also did not match the flight conditions that were needed to trigger the problem with the single spool double acting servo. 585, like CAL006 didn't stall, nor has the SJ182 likely to have stalled.

OK
Maybe we are close to agreement.
Guarding the throttles during level of , top of climb , approach etc. is a pretty simple risk mitigator don’t you think ?
Cant believe that anybody can be that unaware of thrust lever position.
It was always lesson 101 on the B737

We should know more soon enough, the 30 day deadline for the initial report is upon us.
However, from the snippets of information already in the public domain, I suspect that the recovery of the CVR will prove to be the key, and that we will not learn too much in the way of new information when the initial report is published.

Teddy Robinson

"However, from the snippets of information already in the public domain, I suspect that the recovery of the CVR will prove to be the key, and that we will not learn too much in the way of new information when the initial report is published."

You might be right. But given the amount and variety of speculation, not least in these columns, the FDR traces (which will presumably be in the initial report) will at least narrow down the range of likely scenarios.

but based on what I read above among all the traces it seems like the FDR has already been wrung out leaving us with theory on top of theory

14:00 WIB = 02:00 EST

lomapaseo

I don't know what "wrung out" means in the context of the FDR.

AFAIK, nobody outside the investigation yet knows what's on it.

alf5071h

I would consider a possible icing issue, stab gimbal failure, rear pressure bulkhead rupture or rudder reversion.

Flaps1Pls

Our environment is stochastic, with a bucket of inputs and factors that impact every moment of our interface with the job at hand. from noise of heavy rain impact, accelerations at the seat from turbulence, ATC interactions, cockpit coordination, cabin needs, flight path management and systems. In this case, yon driver is levelling off at the same time as assessing weather on the radar and manoeuvering. Assuming the APLT is engaged at first, then if the LH driver is handling, when he decides to turn the plane to avoid weather, he needs 3 hands. His left hand is on the wrong side of the tracks; his right hand is on the throttles guarding them because that's a thing we are all going to do... and his 3rd hand is selection the heading bug on the MCP, while he looks at the heading relative to his EHSI radar overlay. Having 3 hands, he is now going to identify the APLT mode has gone from speed or VS or VNAV to ALT, and the ATO has changed from THR to SPD. And nothing goes wrong, the clutch dropping a TL (if that has happened) gets to be detected immediately, as the pilot is as sharp as everyone else that ponders their eventual fate.

Almost all adverse outcomes, from our aircraft accidents to Chernobyl, TMI, Apollo 13, even arguably Challenger, and even Columbia, Nimitz fire, ANZ901, AA905, EA401, KE801, the Bali B737 submarine, the Chuuk B737 submarine, AS214 at SFO, AFR 447, AIRBUS A330-300, Bombardier test accident, Gulfstreams test accident, CAL006, SIA006, etc etc etc, all have their roots in a loss of SA, either someone somewhere sometime didn't recognize an unexpected difference between expectations, and reality or didn't comprehend the significance of that having recognized it, or were unable to project the consequences that issue would result in later.

ASSumptions

Computers and automation bring improvements in some matters of reliability of outcome but make the SA issue harder for the operator. AA905 insert a DCT Rozo, "R" and assume the algorithm is going to give the closest WPT, and by a quirk of the NDB, questionably non-compliant with the standard, the WPT that is the top of the pile just ain't so... and the plane does an unexpected left turn... thereafter the crew busy in their activities are surprised to see the plane turning away from where they expect it fo go, and recover, in a way that reduces their time to recognize and recover the SA loss they have identified. and bonk into the top of a hill. The hill has been there for a few hundred million years So, as 905 taught, automation expectation can snowball quickly, and recovery from that can be hard. With 3 hands, 2 heads, per person, then things may be better. In the absence of those enhancements, mnemonics like OODA are a good way of remembering, like Caesar that thou are mortal. Shakespeare would have had some pithy line for that for sure, Mel Brooks will do though.

I would contend that few pilots will pick up a fault and respond correctly every time, in fact, I would go further, I'm not sure I have ever seen a pilot in a critical event respond exactly per the checklist or the training. That includes my direct observation, auditing, safety reviews, accident investigations.... pretty much the whole bunch. Maybe, It just doesn't come to mind. We can do something for 10 years in the sim exactly as written, and won't do it on the plane...

OTOH, have seen some innovative solutions to stuff like takeoff warnings, USA's etc, that are at least entertaining if there is no blood spilt.

ISA+18C... 11,000' 250CAS ~..... Thats a normal day in JKT, which gives a FZL around... ~FL170... The OAT at 11K is around +11C, and the 250kts adds around 18C ruffly. The swept wing of the 737 doesn't pick up much at all in almost all cases other than SCLD. Trying to get it to ice up takes effort. With convective weather, entry increases temp.

That will surprise the boys... and everyone else. it wouldn't give a turn, or the recorded ADSB data. if the tail fethers separated in flight, they would be found early on floating in almost all cases, and would have low levels of damage relative to the catastrophic fragmentation of a high speed impact. If bits separated in flight they should be already in plain sight.

dP is not large at 11,000', and so a collapse would give... floor collapse? Post THY the floor venting got better, to stop the collapse of floors in decomp, and the control cables were separated. Have to open up an IPC or AMM Ch 27 to work out where they do go on the B737, but elevator cables are duplexed. The rudder is single control run. Aileron runs go to the PCU's which are in the gear wells.

[img]https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1760x1148/screen_shot_2021_02_10_at_10_44_28_am_31ebf9def28778ee21401e 04e2a90385828ff059.png







https://cimg1.ibsrv.net/gimg/pprune....dddbe005c4.png



reversal? unlikely for the conditions needed to give the historical freeze of the inner sleeve of the valve.

fdr

interesting

“Our environment is stochastic, with a bucket of inputs and factors that impact every moment of our interface with the job at hand. from noise of heavy rain impact, accelerations at the seat from turbulence, ATC interactions, cockpit coordination, cabin needs, flight path management and systems.”

Quite true. But I always thought that that was the job.

I have 20,000 hours flying Boeing aircraft with most being routine interspersed with moments , uuhm , not routine.
In the not routine moments my crew has responded as trained. Professionally and effectively.
Maybe I have just been lucky.
I have also operated in Indonesia.

It wont be the aircraft.

Educated guess - the speculation of a thrust lever clutch failure will be correct. One engine throttle failed to move in response to the autothrottle command at level off (bad clutch, or high downstream forces due to a seized pulley or kinked push-pull cable). Crew was rusty, possible distracted by something else, and failed to notice the throttle split. Aircraft rolled due to the thrust asymmetry, crew caught off-guard by sudden AP disconnect, lost SA, and did all the wrong things. Specifics of why the crew failed to react appropriately to a relatively benign failure will remain a mystery unless the CVR memory module is located.
Critics and lawyers will try to blame Boeing (deep pockets - unlike the operator), ignoring that the autothrottle defect had existed and gone uncorrected for some time, and SOP for the pilots is to monitor T/L position and engine parameters.

Preliminary KNKT Accident Report is published: http://knkt.dephub.go.id/knkt/ntsc_a...y%20Report.pdf

"The thrust lever position of the left engine continued decreasing while the right engine thrust lever remained."

Aircraft rolled to the left...

Left engine thrust lever and corresponding left engine N1 decreasing. Pilots preocupied with ATC communication and bad weather, requesting heading change due to weather and then ATC ordering leveling off at 11.000 feet due to traffic. Further reduction in left engine thrust. AP disconnection followed by rapid left roll past 45 degrees. End of recording only 20 sec later.

No FDR readout provided in the report. Problems with the AT in the days before the accident.

The virtual absence of FDR data, apart from a handful of snapshots, is unusual compared to recent KNKT preliminary reports.

There is no indication of how, during the last 20 seconds of flight, the aircraft progressed from an "over 45°" left bank (QRH criterion for an upset condition) to a RH spiral descent.

I suspect, David, it is called "Passing through the inverted"? Done any aerobatics?

Maybe. Maybe not.

It just seems rather strange to describe a 180° roll (if indeed that's what occurred) simply as "over 45°". There are no references to "inverted" anywhere in the preliminary report, which would seem a curious omission if the case.

And the problems were "fixed" by cleaning the contacts. This is reminiscent of the "fixes" done to the Inertial Reference Systems before the AdamAir accident in 2007. From the Final Report (ASN link):

Didn't work then, and probably didn't work now.

If this is what happened then sadly it would have all been displayed in front of them - a big thrust lever and N1 split with one thrust lever stuck at climb thrust while the other reduced to a low setting for levelling off. No autopilot control of the rudder on B737 to compensate for a large engine thrust difference, so the ailerons would have been hard over - again plain for the pilots to see on the yokes.

(When I flew B737, we were told to have hand on thrust levers whenever they were expected to move, e.g. levelling off from a climb.)

The autopilot suddenly dropping out would have been the final straw - the ailerons were being held hard over, but once the autopilot dropped out they would have returned to neutral, and unless correct manual action was taken quickly, the pilots would have been hard pushed to retain control.

Perhaps there should be some sort of alarm that the autopilot is approaching its drop-out point, so crews would know before it actually happens?

So, given what's not in the report ... how would upset recovery with split thrust set look like?

(Pax) Sorry to butt in but can someone explain to me what ' off axis entry into a microburst' means pls as I can't follow the discussion. Does it just mean asymmetric wrt the centreline of the aircraft? Thanks.

And the BITE result - obvious after the first repair attempt - wasn't a good indication if the repair was effective. Nevertheless it was sufficient for sign off after the third try.
How are these situations supposed to be handled by maintenance?

Uplinker, Different causes, I know, but the result not unlike this one:- https://en.wikipedia.org/wiki/China_Airlines_Flight_006

It sounds like an asymmetric situation was badly mishandled. More thrust on one side than the other, anyone with a multi engine rating knows what happens next. The cause could just as easily have been a real engine failure, the result was the same.

Six years ago TransAsia flight 235, an ATR72 crashed in Taiwan after the crew proved unable to control a twin on one engine. The regulator required all the operators pilots to undertake a test in the simulator in handling an engine failure, not all passed.

Why would the thrust lever of the left engine reduce?
 

The preliminary report says that the "thrust lever of the left engine started reducing, while the thrust lever position of the right engine remained." Assuming the RH remained at a high power setting, I cannot see whey the LH thrust lever would start coming back.

The A/T drives both levers together, if one jams, the other lever still moves. If the motor fails, the levers will stay in the last position. Both levers run off the same air data source so one would not be commanded to drive back.

I can see no reason why the A/T would drive one lever back, or if the clutch slips the lever would fall back itself.

With nose low:
1. BOTH thrust levers to idle.
2. Unload the wings (ie push to less than 1g).
3. Roll wings level (nearest horizon).
4. Pull nose up towards horizon.
5. Set an appropriate attitude and smoothly increase thrust (5 degrees & climb thrust are good ballpark settings).
6. Take a few slow deep breathes.

Note: If at recovery step 5 and you still have asymmetric thrust, increasing thrust will need to be combined with coordinated rudder to prevent yaw.

@FiveGirlKit:
The auto-thrust computer will change from commanding climb thrust to looking at IAS when levelling off from a climb. The IAS will increase, so auto-thrust starts pulling the levers back. It does this via motors* which engage to the levers via clutches which are designed to slip above a certain torque.

One thrust lever jams with its engine at climb thrust but the auto-thrust does not know this, it only knows the IAS is still increasing, so it keeps driving the motors to pull both levers back. One lever is still stuck on climb thrust, so the auto-thrust keeps driving the motors to pull both levers back - but only one lever moves; the other lever is jammed and its clutch slips.

In this way you could end up with one engine at, say, 87% N1 and the other at say 35% N1 - a big split.

*Edit: Sorry, I originally claimed one motor for both levers, which is not the case. My bad.
.

knkt.go.id/public/files/uploads/posts/posts/postbody/ip.201-1-13-knkt-2021.pdf

Preliminary report of Sriwijaya Air crash.. (sorry in Indonesian languange. Use google translate copy paste to translate).

From Report..
1. Auto Throttle broken. Repaired twice.
2. During take off AT pulls back left engine. AP engaged around 2000 feet.
3. At around 8000 feet, AT again pulls left engine down. Right Engine stays. Continue climb.
4. At 10600 feet, AT again pulls left engine. Right engine stays.
5. Altitude drop. Pitch nose up. Roll started (to left). Then AP disengage. Then nose pitch down.
6. FDR stops recording after 20 seconds. No detail data released.

What can cause AT to pulls 1 engine? Too much engine's vibrations? Faulty sensor data, computer error? Or, (God forbids) thrust reverser deployed during flights?

The preliminary report doesn't explain what pilot do next after 3rd AT pulls down left engine. But i find it hard to believe, even for (i apologize to use the word) un-intelligence pilot NOT to noticed that 1 of the engine start pulling down power, and creates rolls. OR am i wrong? I'm not pilot btw. I just curious (my background is electronics).

That's the latest news from Sriwijaya accident report (preliminary)..

Uplinker

That's not true. 737 A/T has two servomechanisms, one per each lever. Have a look at , particularly around 0:45, where you will see that A/T can move each thrust lever separately.

This functionality is required to synchronize the engine RPM, as the same thrust lever angle might not result in exactly the same N1, depending on many factors, particularly with these hydromechanically-controlled engines.