PPRuNe Forums

Go Back   PPRuNe Forums > Flight Deck Forums > Tech Log
Forgotten your Username/Password?

Tech Log The very best in practical technical discussion on the web


Reply
 
Thread Tools
Old 7th Dec 2012, 17:32   #21 (permalink)
 
Join Date: Jul 2009
Location: Not far from a Great Lake
Age: 72
Posts: 1,066
Quote:
Originally Posted by Microburst2002
Roll direct is hardly a dangerous thing. Pitch alternate is Ok, no danger at all.
True if you make minimal & smooth control inputs and your scan is working.

Not so true if you are ham handed, surprised, tired, and bumping along at night in the weather (particularly if you fly for a certain French airline it seems.)
Machinbird is online now   Reply
Old 7th Dec 2012, 19:46   #22 (permalink)
 
Join Date: Aug 2009
Location: Texas
Age: 55
Posts: 2,968
beardy, it would seem to me that during type rating training, you'd learn the terms and ask questions about what some of them mean, espectially if you were converting from another airframe.

I'll even bet that such discussion goes into training.
Lonewolf_50 is offline   Reply
Old 7th Dec 2012, 21:55   #23 (permalink)
 
Join Date: Nov 2000
Location: UK
Age: 59
Posts: 505
Lone wolf, I do believe that you are correct. Some who contribute here, so freely, are so involved in training and are so far away from operations that they seem to have lost sight of reality.

Last edited by beardy; 7th Dec 2012 at 21:55.
beardy is offline   Reply
Old 7th Dec 2012, 22:15   #24 (permalink)
 
Join Date: Oct 2007
Location: UK
Posts: 142
Quote:
RISK OF UNDUE STALL WARNING is prompted by the ECAM in several malfunctions

The new bulletin tells us to switch off two ADRs to get in Alternate Law.

We don't want Direct law, direct law is dangerous
So your comment implies flying an aircraft that needs to be trimmed and with manual thrust is dangerous. Quick - Ground all Boeings!!
Right Engine is offline   Reply
Old 8th Dec 2012, 13:53   #25 (permalink)
 
Join Date: Nov 2000
Location: UK
Age: 59
Posts: 505
Quote:
So your comment implies flying an aircraft that needs to be trimmed and with manual thrust is dangerous.
No it doesn't, now stop being silly.
beardy is offline   Reply
Old 8th Dec 2012, 15:42   #26 (permalink)
 
Join Date: Jan 2005
Location: W of 30W
Posts: 1,758
Why silly ... ?
You should maybe question the initial comment first :
Quote:
Originally Posted by M2002
We don't want Direct law, direct law is dangerous
CONF iture is offline   Reply
Old 8th Dec 2012, 17:38   #27 (permalink)
 
Join Date: Nov 2000
Location: UK
Age: 59
Posts: 505
Silly because you confused Direct Law with Boeing; there is no relevance. If you believe there is then you do not know what direct law entails, which, from your rather glib definition, I don't believe you do: you seem to (deliberately) misunderstand and in proposing the grounding of all Boeings you are being rather silly and possibly trying to be provocative. (Did I misunderstand your exclamation mark for an emoticon?)

I don't really have much to add to the technical discussion here since the contributors seems to be people who are unfamiliar with and are antagonistic to the aircraft. However, I don't think that Direct Law is dangerous, just different.

Last edited by beardy; 8th Dec 2012 at 18:24.
beardy is offline   Reply
Old 9th Dec 2012, 01:20   #28 (permalink)
 
Join Date: Jun 2009
Location: Australia
Posts: 61
Quote:
So your comment implies flying an aircraft that needs to be trimmed and with manual thrust is dangerous. Quick - Ground all Boeings!!
The issue people are trying to get at is that when you drop you're already in a higher than normal pressure situation and now flying a new beast. It can not be helpful considering all the details changes one must now deal with cognitively as opposed to autonomously. Take for example someone who ended up constantly pulling back on a stick which would have different results in each mode.

Last edited by Phalanger; 9th Dec 2012 at 01:22.
Phalanger is offline   Reply
Old 9th Dec 2012, 01:23   #29 (permalink)
 
Join Date: Aug 2000
Location: the Alamo battleground
Posts: 853
Warning! Thread Drift!!

Quote:
pilots should never need to do such a thing in response to QRH directions - which must be clear and unambiguous.
BEagle,

if the QRH directions must be clear and unambiguous then there's not really a need for pilots to sit in the cockpit. They can be replaced by software, AI, Otto Pilot etc.

Having said that, I have been involved in incidents where thinking (shock, horror!) and system knowledge were required. Not all incidents and problems can be foreseen by design engineers. Decision making and interpretation are two of many factors that justify humans sitting and piloting airplanes (or aeroplanes if you wish ).
Squawk7777 is offline   Reply
Old 9th Dec 2012, 06:38   #30 (permalink)
 
Join Date: Mar 2010
Location: South Korea
Age: 53
Posts: 94
I think what BEagle was referring to when he said

“pilots should never need to do such a thing in response to QRH directions - which must be clear and unambiguous.”

is documentation should be clear and unambiguous as much as possible, sure it is impossible to get things perfectbut a pilot has enough to learn and figure out without making things more difficult than necessary by providing loose documentation. Technical writers really have a big responsibility and they should have a good understanding of the words and be able to convey concepts clearly and unambiguously.
Cool Guys is offline   Reply
Old 9th Dec 2012, 07:33   #31 (permalink)
 
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,197
Quote:
Quote:
Originally Posted by M2002
We don't want Direct law, direct law is dangerous
Imagine O'Leary told airbus to make a cheap airbus 320 version, without normal or alternate law. So they would be much much cheaper.

Well, he would be dissapointed. They cannot certify such aeronautical aberration.

The Airbus in direct law is much different than a 777 in direct law. It doesn't even have a proper pitch trim. We have a THS wheel, but we have no stick forces that we can trim.

In direct law you can fatally and brutally overstress the airframe with inputs that would not seem dangerous in normal or alternate law. In a 777 I believe you would still need to exert very high forces on the yoke to do that, in direc law.

Airbus Direct law is highly undesirable... Because it is dangerous. In the simulator, after a go around with a dual hidraulic... How does it feel? Conventional? No way! Normal and alternate feel conventional. Direct is more like a 767 with the yoke artificial feeling inop. MANOEUVER WITH CARE is not a silly ECAM line. You better manoeuver it with care!

With the trim wheel you don't trim forces, but you have to ease back the sidestick to neutral as you move the wheel, resembling the action of trimming. It is just like the microsoft FS with a joystick? That is NOT conventional. It doesn't feel right for a pilot instinct.
Microburst2002 is offline   Reply
Old 9th Dec 2012, 08:26   #32 (permalink)
 
Join Date: May 1999
Location: Quite near 'An aerodrome somewhere in England'
Posts: 21,589
Cool Guys - precisely!

As for calls to provide an Immediate Direct Law option, that would be extremely undesirable for many flight phases as the sidestick lacks conventional force / displacement artificial feel simulation. However, an Immediate Alternate Law option would perhaps not be unreasonable, rather than a workaround involving the deliberate deselection of air data reference units.
BEagle is offline   Reply
Old 9th Dec 2012, 08:43   #33 (permalink)
 
Join Date: Nov 2000
Location: UK
Age: 59
Posts: 505
Under what circumstances do you think you would wish to select Alternate Law and which flavour of Alternate Law do you think you would like?
Bearing in mind, of course, all those circumstances when the aircraft will give you Alternate Law automatically.
beardy is offline   Reply
Old 9th Dec 2012, 09:39   #34 (permalink)
 
Join Date: May 1999
Location: Quite near 'An aerodrome somewhere in England'
Posts: 21,589
Quote:
Under what circumstances do you think you would wish to select Alternate Law and which flavour of Alternate Law do you think you would like?
Since most of the uncommanded A320/330/340 flight path excursions which have been reported seem to have involved incorrect sensor information being faithfully acted upon by Normal Law protection features, the minimum necessary action to countermand such spurious events before an extreme event is reached would perhaps be appropriate - so probably Immediate Alternate 1 ?

Far better though to eliminate any source of sensor failure in the first place.
BEagle is offline   Reply
Old 9th Dec 2012, 11:53   #35 (permalink)
 
Join Date: Nov 2000
Location: UK
Age: 59
Posts: 505
So this is what you would like to happen:

Quote:
Low speed stability
At low speed, a nose down demand is introduced in reference to IAS, instead of angle of attack, and alternate law changes to direct law.
It is available, whatever the slats/flaps configuration, and it is active from about 5 kt up to about 10 kt above the stall warning speed, depending on the aircraft's weight and slats/flaps configuration.
A gentle progressive nose down signal is introduced, which tends to keep the speed from falling below these values. The pilot can override this demand.
Bank angle compensation is provided.
In addition, aural stall alert (“STALL, STALL” synthetic voice then cricket) is triggered at an appropriate margin from the stall condition.
The PFD speed scale is modified to show a black/red barber pole below the stall warning.
Vα prot and Vα max are replaced by Vsw (stall warning speed).
The α floor protection is inoperative.
High speed stability
Above VMO/MMO, a nose up demand is introduced to avoid an excessive increase in speed.
The pilot can override this demand.
The high speed protection symbol (VMO + 4) disappears.
In addition, the overspeed warning (VMO + 4 or MMO + 0.006) remains available.
Pitch attitude protection
Lost.
If I read you correctly you are advocating that with a faulty sensor input leading to the aircraft believing it is going too slowly, you would like it to revert to Direct Law. IMHO that is a not a very good idea. Far better to have angle of attack protections in Normal Law.
Perhaps you have tried your theories out in the sim?
beardy is offline   Reply
Old 9th Dec 2012, 12:45   #36 (permalink)
 
Join Date: May 1999
Location: Quite near 'An aerodrome somewhere in England'
Posts: 21,589
Quote:
...a faulty sensor input leading to the aircraft believing it is going too slowly...
Such an event would surely require the 'Unreliable Air Speed' procedure, rather than a deliberate selection of Alt Law.

The situation which raises greater concern is faulty AoA signalling, resulting in spurious pitch excursions. Under such circumstances it might be better to inhibit AoA protection by deliberate crew action, before the aircraft reaches an extreme attitude.
BEagle is offline   Reply
Old 9th Dec 2012, 14:38   #37 (permalink)
 
Join Date: Jan 2005
Location: W of 30W
Posts: 1,758
Quote:
Originally Posted by M2002
Airbus Direct law is highly undesirable... Because it is dangerous.
  • In direct law, the pilot uses the THS conventionally to fly in trim.
  • Use small control inputs at high speed, since in direct law the controls are powerful.
  • MANEUVER WITH CARE
  • The sidestick is directly coupled to the controls via the computers, but without any of the stabilization feedbacks. In effect, this law turns the aircraft into a conventional aircraft
  • The flight crew must fly the aircraft carefully at all times. Control is precise, but there are no protections.
Those are comments from the FCOM, hardly synonyms of 'DANGER', but applicable to any aircraft.

When is the last time you flew direct law, in the sim at least ?
CONF iture is offline   Reply
Old 10th Dec 2012, 05:45   #38 (permalink)
 
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,197
I know what the FCOM says, but the airplane in direct law is NOT turned into a conventional airplane. Because conventional airplanes must have stick forces that provide pilots with aerodynamic feedback. Without that, you are in the MIrcrosoft FS, which is not conventional at all.

Nearly every sim I fly direct law, for a while. The difficulty and danger of Direct Law is more apparent in the GO AROUND. Typically we find it in final approach, after L/G DOWN. The airplane is almost in trim and it takes only minor inputs and trim settings to have the job done. However, all that changes in case of go around. Then, it is difficult to switch my mind to direct law, so I find myself releasing the sidestick (springloaded to neutral) after inputs, which equates to make brisk inputs back and forth, like jerks. If more angle the input had, the worse. Imagine a conventional 767 where there is no feedback from the yoke, but it will return to neutral if you release it.

With practice you can fly direct law quite decently, but you have to actively think so that your instinct and habit doesn't put the airplane at risk. And, as I say, you could not certify an airplane with a direct law system without artificial feeling in the stick.

That FCOM reference repeats a lot that you fly with care, that you are not protected, that controls are powerful, that you use small inputs... That sounds like "hey be careful" to me, and therefore there is danger.

Dangerous means that you can get in trouble easily and you have to be careful to stay out of trouble. It doesn't mean you have to panic and pray. I will never revert to direct law on purpose as a reversion to conventional, because it is not a reversion to conventional, in the first place. Normal law is much more conventional than direct law, in my opinion.

The bulletin procedure is just what the situation needs. You get rid of the rogue sensor inputs and keep flying almost normally (alternate law is very much like normal law, except for some protections).
Microburst2002 is offline   Reply
Old 10th Dec 2012, 08:12   #39 (permalink)
 
Join Date: Nov 2000
Location: UK
Age: 59
Posts: 505
Quote:
Since most of the uncommanded A320/330/340 flight path excursions which have been reported seem to have involved incorrect sensor information being faithfully acted upon by Normal Law protection features, the minimum necessary action to countermand such spurious events before an extreme event is reached would perhaps be appropriate - so probably Immediate Alternate 1 ?]
Quote:
The situation which raises greater concern is faulty AoA signalling, resulting in spurious pitch excursions. Under such circumstances it might be better to inhibit AoA protection by deliberate crew action, before the aircraft reaches an extreme attitude.
This represents a welcome change of tone from your mocking first post. However, it seems that you think that Airbus have not considered, risk assessed nor trialled what you propose. I do not know if they have or not, but I do know that their resources and knowledge and greater than mine or yours and that their investment, both in cash and reputation, is much more than yours or mine. Since I operate the aircraft, I have to trust them and their judgement. This does not stop me questioning, but each time I have questioned Airbus there has been a satisfactory response. If your are an operator or client they are quite willing to help, perhaps that would be a more suitable channel for your scepticism and offers of suggestions.

Last edited by beardy; 10th Dec 2012 at 08:12.
beardy is offline   Reply
Old 10th Dec 2012, 09:49   #40 (permalink)
 
Join Date: May 1999
Location: Quite near 'An aerodrome somewhere in England'
Posts: 21,589
Quote:
I know what the FCOM says, but the airplane in direct law is NOT turned into a conventional airplane.
The significant change is from manoeuvre demand to attitude demand. However, the control system doesn't provide any stick force per G gradient, neither does it provide any Q-dependent feel. So perhaps not all that conventional?

beardy, I note your post. However, I remain somewhat exasperated by the....let's call it 'unusual' English used by Airbus in many of their publications.

Last edited by BEagle; 10th Dec 2012 at 09:50.
BEagle is offline   Reply
Reply
 
 
 


Thread Tools


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT. The time now is 03:06.


vBulletin® v3.8.7, Copyright ©2000-2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
© 1996-2012 The Professional Pilots Rumour Network