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AS332L2 Ditching off Shetland: 23rd August 2013

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AS332L2 Ditching off Shetland: 23rd August 2013

Old 5th Sep 2013, 16:50
  #1221 (permalink)  
 
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Originally Posted by HeliComparator View Post
Jwscud, out of interest do some modern fixed wing have flight envelope protection whereby autothrottle is automatically engaged if airspeed is reducing too much, for example due to too high a pitch attitude or vertical speed demand for the power set?
Depending on various modes and settings, a Boeing auto thrust system is included in the flight envelope protection, but there are various modes in which this is inhibited. See http://www.pprune.org/tech-log/51864...rust-hold.html

I believe the Airbus system is more simple, with the envelope protection system on roll / yaw / pitch only (and it has quite a different auto-thrust philosophy).
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Old 5th Sep 2013, 16:53
  #1222 (permalink)  
 
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I would be curious to know if there are any 225 back to L2 issues.

225 back to 332L1 is pretty easy - It all goes manual. But L2 is a bit of hybrid, 'similar but different' scenario.

I remember converting onto the 225 and being shown how it will fly a coupled approach, even having lost almost everything. Very impressive, but my gut reaction was that I just wanted to take out the automatics and fly manually. At least that way, I knew who was controlling what, not that I have airspeed on the collective, the AP has Glideslope on the cyclic etc etc. Unless you're a TRE and forever in the Sim, I think you are liable to cock it up.
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Old 5th Sep 2013, 16:59
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TS, yes, and the BHL Nigeria 332L, the Bond 225, the KLM S76B, the BHL Australia 330J, G-TIGH 332L and the BIH S76A in the Fulmar field. Different means of getting to the same basic predicament - low power plus low airspeed equals high rate of descent!
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Old 5th Sep 2013, 16:59
  #1224 (permalink)  
 
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Kaky C - I think one problem is that when the L2 was introduced (1992) all this talk of automation, automation dependancy etc etc hadn't been invented even by FW. Once you start down a bad path its harder to put it right. I recall doing an OPC in an L2, during the autorotation excercise I engaged IAS mode at 80 kts (Vy). The Training Captain / examiner took exception to this and said "you can't do that" but couldn't explain why not. Of course with IAS engaged, the whole excercise becomes much easier and you are guaranteed to maintain Vy until the flare, something which rarely seems to happen when people are flying it manually!

We were still banned from using the (admitedly limited) automation of the 332L during checks, being forced to fly the otherwise fully serviceable autopilot but without using the upper modes. Crazy! For the L2 I tried to introduce some use of automation during checks, but met a lot of resistance! So it was regarded as an extra set of sissy buttons that real men wouldn't use, and therefore the training given in its use was minimal, SOPs for its use didn't exist.

When we introduced the 225 (2005) we did try to look across at FW and hopefully took on board some of the lessons. For example, our SOPs require extensive calls and monitoring for use of the automation. One pilot calls presetting a parameter (eg ALT.A), the other pilot calls that he has crosschecked the setting. One pilot calls engaging a mode, the other calls what he now sees on the AFCS status display (ie what mode has actually been engaged). When there is an automatic transition between modes, eg an ILS localiser going from Armed to Engaged, that is called too.

We also show a video on automation dependancy - ie sometimes its best to drop down a level of automation. eg from coupled to ANAV on an overlay approach, drop down to HDG mode, or even drop down to manual flying (gasp!).

So I believe and hope that many of the bases are covered on the later fleets, its the earlier fleets that perhaps lag behind - although I have no idea what CHC's SOPs for automation use on the L2 are.
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Old 5th Sep 2013, 17:01
  #1225 (permalink)  
 
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Which takes us back to the subject of automation confusion which seems to be becoming a major issue nowadays in many different guises.

When the unexpected happens you dont always have time to figure out what it is doing, especially when low and slow.
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Old 5th Sep 2013, 17:09
  #1226 (permalink)  

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Just read the latest AAIB report (link emailed to me).

My eyes were also drawn straight to the paragraph about the autopilot modes in use at the time.

As a "3 axis only" rotary autopilot user, (not Puma) I'd be most interested to know what the company SOP is, regarding which AP modes should normally be engaged during an ILS approach.

"VS" mode isn't one I would choose to use at that stage of flight, although I do often use it for the initial descent, or for a non-precision approach.
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Old 5th Sep 2013, 17:15
  #1227 (permalink)  
 
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ST, it was an NPA - localiser/dme
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Old 5th Sep 2013, 17:43
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TAG yes I think there is some truth in that, but surely the answer is to improve training rather than to get rid of the automation?

Training is a limited resource in practice. Why is it that we spend hours doing single engine stuff when (turbine) engines never seem to fail in reality, and much less time (and its not mandatory) dealing with the likes of partial automation? When you look at the causes of accidents, it seems to me that we don't really train to address them, we spend hours training in accordance with the legal requirements, on stuff that is never ever put into practice and never causes accidents. Something wrong there, too many legislators living in the past of unreliable piston engines, single pilot mandraulic ops etc!

Last edited by HeliComparator; 5th Sep 2013 at 17:44.
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Old 5th Sep 2013, 18:07
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HC, we're gonna make you an honorary Canadian!
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Old 5th Sep 2013, 18:33
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Ob Fwit ...
First off, deeply grateful for your explaining to me some of the nuances of the auto systems.
It seems, from the report, that the crew had not "selected" an airspeed, and were operating with just VS and Localiser coupled. In this instance the vertical mode is being controlled by cyclic, snd airspeed is being controlled manually by collective.
You will I hope forgive me for offering the opinion that this is counterintuitive to helicopter flying. Maybe it is due to me having flown and instructed in both fixed and rotary wing, but I have found that it is best to pick an airspeed as an approach speed, and adjust rate of descent with power (and then of course modest counter corrections with stick/cyclic) when trying to stay on a glide path. I do realize that once one has the landing spot in sight, the transition through translational lift and to touchdown requires adjustments.

I got into a discussion on the Asiana thread about pitch and power equalling performance over at R & N -- I had airline pilots inform me that they were pointing their noses and relying on power via automation to get their airspeed right. That is counterintuitive to how the coupling between pitch and power gats you performance, in a general sense. It took a while for me to understand that they were discussing flying in a mixed mode of hand and auto. While I think I better understand the issue now, I do not find the practice to make sense ... and the Asiana crash is a data point firmly in my favor.

Having taught a bit of instrument flying in rotary wing, a while back, I hold that the same basics apply to flying a helicopter on instruments in actual IFR as they do in fixed wing. Power in this case is collective, as you note.

I do understand the logic behind choosing a RoD in an effort to get a nice constant descent angle. Not a bad thing by itself. Your explanation of the mixed mode traps is an eye opener for me.
If the collective is set too low, ie not producing enough 'power', then the aircraft will reduce airspeed to try and maintain the desired VS.
That's all well and good until one gets below max conserve airspeed, and/or into translation lift since one will begin feel the effects of being on the wrong side of the power curve.

While the details of "the power curve" are not identical between fixed wing and rotary wing, the result of "the bottom drops out from under you" is very similar. I've experienced it in both kinds, without bending metal, and feel comfortable making such comparisons from experience.
However, once the speed passes Vy (which is usually around 68/70kts) the rate of speed drop can be very quick, until at an airspeed none of us can remember the autopilot gives up the ghost and the upper modes drop out.
"You've got it, I'm outta here" says HAL, eh?
In a 225, there are protections built in such that, should for some reason you elect to fly it 3-axis, at 60(?) kts the IAS upper mode automatically kicks in and the ac becomes 4 axis coupled.
It appears to me that maybe those "protections" are overrated.

To sum up:

Please don't beat me up too much for being a dinosaur. I am a bit disturbed with the traps that mixed modes provide when combined with a likely demand from management to use the auto features to the greatest extent possible. No doubt each company will have differences in SOP.

I guess even helicopter pilots must now ask themselves more frequently:

Are you flying the aircraft, or is the aircraft flying you?

Awaiting the more detailed findings with great interest.
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Old 5th Sep 2013, 18:44
  #1231 (permalink)  

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212, thanks. My first look at this and I promise to try to keep up in future.....
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Old 5th Sep 2013, 19:07
  #1232 (permalink)  
 
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Lonewolf, you're right it is counterintuitive, it is however the way the L2 is set up. First upper mode selected goes on the cyclic, whether Alt or IAS. If the other one is selected, making it 4-axis, then Alt is on collective and IAS is on cyclic.
225 simplifies it, Alt is always collective, IAS is always cyclic

That's all well and good until one gets below max conserve airspeed, and/or into translation lift since one will begin feel the effects of being on the wrong side of the power curve.
Exactly!!
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Old 5th Sep 2013, 19:07
  #1233 (permalink)  
 
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Originally Posted by malabo View Post


HC, we're gonna make you an honorary Canadian!
Malabo, I don't really understand why, but honoured anyway!
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Old 5th Sep 2013, 19:07
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Pitts
the industry has the system it deserves.
The industry has the system forced upon it by the same people who conduct witch-hunts based on scant evidence, chase scapegoats as early in the process as possible, and then sue if a mistake is made. Add in the fact that aviation has a much higher profile than, for instance, road accidents or boats.

HC
They have said what happened in detail, but it takes time to work out why (since at first glance I suspect it defies logic).
italics added

Defies logic? I doubt it. But finding the root cause, separating the wheat from the chaff, will take more time than just stating the facts.

I can think of several very plausible and different sequences of events that may or may not have led to this result. Most are AP related but not all. We recently had an intermittent 26VAC bus Inverter issue on a 76C+. The result was seemingly random decoupling of the upper modes with minimal indication to the crew.

FFF
My posting a couple of pages back got trampled in a handbagging incident between Pitts and HC (Ladies, please!). Any thought on this as a theory?
http://flightsafety.org/hs/hs_may_june97.pdf
It certainly sounds like a good place to start.

These are the things the AAIB must now determine. They have a significant amount of data to sift through, including the CVR, to determine what the crew intended, what really happened, and how the difference between the 2 came about.

SAS
I shall take a bit of a Contrarian view on this Special AAIB Report.

My view is this report should not have been released.

The AAIB should have waited until they had digested the CVR data and decided what it meant....then released a Special Report that would go much further in describing the sequence of events and the time line of the CVR.

The Report as it reads now...tells very little and only generates more conjecture than it would otherwise had they waited to put out the CVR information.

Far too little information to justify a Report at this time.
Sorry SAS, I have to disagree here too. Given the anti-Super Puma/225 witch-hunt that was going on, it was inevitable and, SADLY, necessary to tell the world that there was not an obvious design issue.

HC
Because the L2 doesn't have the same power limiting functionality, its not normal to fly the L2 in 4-axis in the cruise or climb, but no reason not to for an approach. However much of the time the L2 will be being flown in 3 axis and perhaps that makes the fleet culture a bit different.

We are presuming of course that the collective axis was functional at the time, but that the crew chose not to use it.

As I mentioned earlier, I suspect that after this, there will be a tightening up of SOPs for use of automation, something which has mostly been at pilot's discretion up to now.
Finally, something to discuss. OUR 76C+ also lacks some of the power limiting functionality I hear about in the 225. As result, in the highly compressed sim sessions we are now being given (bean counters pay attention with shame!) one can expect nearly every approach to end OEI. The standard I have seen is a consequent discouragement to use 4-axis to prevent troubles related to power limiting. We tend to fight the way we train, which is to then avoid 4-axis.

I personally dislike rigid automation SOP's. I prefer to 'mix it up' from flight to flight in order to explore the capabilities and limitations of both the system, and my knowledge of it. I therefore am comfortable choosing the modes that will best help me when things get busy or difficult, but not surprised when the system is degraded.

HC
there should be an aural warning anytime autopilot functionality was lost to the point the pilot had to take manual control, but so far that hasn't been implemented.
As mentioned above a couple times, easy to miss on many types.

I won't quote you again, HC, on automation philosophy and how it has changed. As I have changed employers, continents, types, and years have passed I agree things changed from all hand flown rides, to all coupled, to something else. Inevitably there is an incident that highlights another chink in the armour and the world rushes to fix it. All this to say you are correct as to the progression.

-----------------
Again, my own personal defense is to, when allowed within the SOP's, use the various modes, in different combinations, and see how it reacts. This way I avoid, as much as possible, having to ask on a dark and stormy night: "what is it doing now?"
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Old 5th Sep 2013, 19:43
  #1235 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post

(ref the 225)

It appears to me that maybe those "protections" are overrated.
LW in general I agree with a good bit of your post, however I don't think you have quite grasped that this accident happened to and L2, not a 225. On the latter, the protections are not overrated (the former has none). To decry them is to deny the benefits of technological progress.

For example (on the 225), if you engage VS alone but have too little collective, the airspeed reduces until about 65 kts, then IAS automatically engages and stabilizes the speed at 65 kts (actual speed varies slightly according to dv/dt). That's fairly easy, but what if the collective channel is not working for some reason? ( its an MEL allowable defect, although I've never known it to be inop). Well then you have VS engaged on the cyclic with insufficient power to meet the needs. This time the IAS cannot engage automatically because the collective channel is inop. So what happens?

Well, what would you want to happen? You wouldn't want the IAS to go much below Vy, and that's exactly what happens. The VS mode starts to soft-limit the IAS to around 65 kts. So even though VS is still engaged according to the AFCS status zone, nothing engaged on the (inoperative) collective, the protections prevent the IAS getting too low.

So if, after that brief explanation of some of the protections, you still think they are over-rated, then perhaps you would tell us what sort of protections you think should be incorporated?

Last edited by HeliComparator; 5th Sep 2013 at 19:43.
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Old 5th Sep 2013, 19:51
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Originally Posted by obnoxio f*ckwit View Post
Lonewolf, you're right it is counterintuitive, it is however the way the L2 is set up. First upper mode selected goes on the cyclic, whether Alt or IAS. If the other one is selected, making it 4-axis, then Alt is on collective and IAS is on cyclic.
The reason for the L2 autopilot 'leading with the cyclic/attitude' was explained to me because it isn't a true 4-axis autopilot (although it is sold as such). It is in effect a '3 plus one' autopilot, ie a 3-axis autopilot with the 4th axis tagged on. This is why the L2 will always use attitude first to control or achieve speed or height, followed by power. (eg when the GA button is used ).

Added to the analogue nature of the inputs and/or outputs (TBH, I can't remember which it is) and you have an autopilot that is less than ideal for some of the tasks that it is used for.
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Old 5th Sep 2013, 19:56
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Prioritize airspeed

The many crashes I see in the 76 sim are nearly always preceded by a loss of airspeed, whether or not an autopilot is used or installed. Certainly in the 76 if you look after the airspeed everything else will follow. If you don't look after the airspeed everything will fall apart. This applies in manual flight or in autoflight. Hence, if you are climbing, descending or on approach I firmly believe that you should have the autopilot look after airspeed first. Full coupling on approach is better, but if you can only engage one vertical mode, make it airspeed.
I can produce a crash 100% of the time in the sim when 2 cue by having the students set the power too low in a climb with VS engaged, or too low when approaching an ALTPRE level off.
I wonder whether autopilots tend to reduce our attentiveness and monitoring of flight instruments.
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Old 5th Sep 2013, 20:04
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Originally Posted by Bravo73 View Post
The reason for the L2 autopilot 'leading with the cyclic/attitude' was explained to me because it isn't a true 4-axis autopilot (although it is sold as such). It is in effect a '3 plus one' autopilot, ie a 3-axis autopilot with the 4th axis tagged on. This is why the L2 will always use attitude first to control or achieve speed or height, followed by power. (eg when the GA button is used ).

Added to the analogue nature of the inputs and/or outputs (TBH, I can't remember which it is) and you have an autopilot that is less than ideal for some of the tasks that it is used for.
However, in the case of this accident, the autopilot would have been better coupled in 4 axis and in that mode, its quite capable of flying a safe NPA.
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Old 5th Sep 2013, 20:05
  #1239 (permalink)  
 
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PA,

I would have liked for the AAIB to include the CVR data....a couple more days would not make a difference one way or the other as to the future of the SP on the North Sea. It would have made a huge difference in the ability of the Operators and others to provide a better explanation of what happened and why. It could still be well short of a full report but the inclusion of the CVR data would remove a lot of speculation yet to come.

One thing I noticed in the Sim was when things started going wrong....one of the first reactions of a lot of Pilots was to de-select the Autopilot and revert to hand flying.

Part of that stemmed from the newness of both Sim Training and Autopilots. I would think as Automation and one's experience/familiarity with modern Autopilots this tendency would decrease.

The single most glaring mistake I saw was the failure to increase power upon executing a Missed Approach.....and when that happened....we saw a slow motion crash. The Crew would decide to go Missed....hit the G/A button....make their Radio Call....start looking for charts, maps, changing radio frequencies or whatever.....and the Autopilot would do its best to comply but at some point the climb rate could not be produced by the decrease in Airspeed and then the loss of control happened.

Generally, Unusual Attitude Recovery training is done with lots of airspeed and at higher altitudes. Low Airspeed events close to the ground are where helicopters are the most at risk.

What is the system in the UK for such training and testing on Base Checks?

Do you practice low or zero airspeed upsets?

Last edited by SASless; 5th Sep 2013 at 20:12.
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Old 5th Sep 2013, 20:08
  #1240 (permalink)  
 
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Originally Posted by GS1140 View Post
I wonder whether autopilots tend to reduce our attentiveness and monitoring of flight instruments.
Yes unfortunately I think this is a worry. The better the autopilot, the more tempting it is to stop monitoring. But what is the answer? Get rid of autopilots and make all flying manual? (back to the 1970s) or have a bit of a new paradigm in training where there is much more attention placed on monitoring skills? I'm not sure I have ever received any training in monitoring (or, to be honest, given it) but I have certainly "given feedback" when monitoring has been found to be lacking, a relatively common occurrence. Its a skill that we expect everyone to have innately, but maybe that is expecting too much?
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