AF 447 Search to resume

[Machinbird]

PJ2
Thanks for helping
. I've been using the same Airbus derived reference. I see that my recollection was wrong about Load factor protection in Direct Law. (It is lost).
I haven't re-located my reference regarding the airspeed as the source for alpha protection in Alternate law-but look at this footnote in your diagram!

(1) Protection is totally lost, in case of VS1g computation failure (loss of weight, or slat/flap position).

If you had actual angle of attack sensor derived protection in Alternate Law (1) or (2)-Why would you lose it with loss of the VS1g computation?
I guess I'm on the hook to come up with the reference.
Machinbird

[mm43]

PJ2 et al,

Reading a schematic of the Flight/Protection Laws on its own can be a little confusing - or that's my feeling. For that reason, I have conferred with Andy Tracy regarding his well presented description followed by a table showing the protections, which is at:- http://www.andytracy.net/files/27FLTCTL.doc

The same document has been produced in HTML form, and Andy has said that he is happy for anyone to make use of it if it helps them in understanding the complexities of Airbus flight control.

Andy Tracy ...
That particular document was written as I did my original Airbus course and
variously amended over the years. Not much has changed recently so the file
is not much changed.

From my perspective, other than a global discussion on what optimal
fly-by-wire protections might be, the only open questions with the Airbus
system is a clearer understanding of ALTN law. Reading into Emerg Procs
appears to show that ALTN Law is actually a variety of things, not the simple
305kt or 330kt and few still grasp the implications of feedback gains being
set to the VMO/MMO point of any flap setting.

So, the document of reference that Andy Tracy produced has been converted into HTML and presented in an easily readable format, and can be found at:-

A340 - A330 Control: Flight & Laws

Hopefully the description and the tabulated list of protections may help with this discussion. It is acknowledged that it is not the document recognised by the regulatory authorities, but it attempts to make sense of something that even confuses those who fly the aircraft.

mm43

[PJ2]

mm43;

Thank you for providing the document and thank you to Andy Tracy for providing his kind permission. I think there is great value in posting such a comprehensive, well-written paper on important aspects and understandings of the A330/A340 flight control system. The target audience for the document is clearly A330/A340 pilots but a bit of reading, thought and patient enquiry will assist understanding of the abbreviations, relationships and reasons why, etc.

machinbird;

If you had actual angle of attack sensor derived protection in Alternate Law (1) or (2)-Why would you lose it with loss of the VS1g computation?

I believe the usefulness of Andy Tracy's paper may already be apparent. From the paper:

Pitch air mode is a load factor demand law with auto-trim and full flight envelope protection.

Not sure I can help but I'll try.

First, in the same way that the sidestick does not control the ailerons and instead requests roll-rate as previously described, the sidestick does not directly move the elevators in Normal Law. The pitch request of the sidestick is a 'g' request moderated through the PRIMs/SECs as available in Normal Law and normal law alpha protections.

As per a previous post on VLS, the references (essentially) are to VS1g in Normal Law.* Since pitch is referenced to 'g' and since the FMGECs (Flight Management, Guidance and Envelope Computers) require both 'g' and aircraft weight/CG inputs for VS1g computation (as well as Slat/Flap position as VLS computation changes with such extensions), when such data is lost, reversion is to speed reference.

Obviously with loss of inputs the FMGECs must have "some place to go". The default reference is airspeed even though AoA itself may be available; In direct answer to your question machinbird, I am unsure how, if at all, any use or blend of AoA from one or all of the three sensors, is done - it may be, I don't know.

One outcome of loss of alpha protections in any reversion to Alternate 1/2 Laws (as described in the Tracy paper) which is immediately visible to the pilots is the change in the speed scale, (schematic posted in the earlier thread on AF447) which no longer displays the alpha speeds but reverts to displaying a red-and-black strip the top of which is VSW**.

*My thanks to HazelNuts39 for an extensive and informative discussion which helped me greatly in understanding this certification issue. Perhaps he may be coaxed into posting a suitable, brief discussion on VS1g and VLS certification (which is slightly different than VS certification)? I think it is germane.

From an A330 FCOM:
**Vα MAX : Maximum angle of attack speed.
Corresponds to the maximum angle of attack that may be reached in pitch normal law.

Represented by the top of a red strip along the PFD speed scale, in normal law.

VSW : Stall warning speed.

Represented by a red and black strip along the speed scale when the flight control normal law is inoperative.

[im1234]

Reuters coverage of the Recife press conference
Air France black box search on again | Video | Reuters.com

[torquemada60]

flight path

I found this link Trajectoires du vol AF447 et des autres vols ayant parcouru la zone dans la même période de temps
Which shows the flight path of 6 airlines during the same period of time. Notice how most of them deviate from the storm. Interesting

[jcjeant]

Hi,

Those animated flight paths were already posted here:

http://www.pprune.org/rumours-news/3...ml#post5518718

@ChristiaanJ

I've searched the BEA site and can't find anything new on AF447. I did find an interesting animation showing the flight paths of AF447 and other aircraft that crossed the ITCZ around the same time. I don't recall seeing it in any of the other AF447 threads.

And this was also followed by some poster claiming the list of planes in the vicinity was incomplete on this animation .. and it's appear that some other aircrafts take the same path or like of the AF447 (If I remember well .. those involved can correct me)

[lomapaseo]

Which shows the flight path of 6 airlines during the same period of time. Notice how most of them deviate from the storm. Interesting

Be careful of interpreting the catch all phrase "during the same period of time"

The weather is constantly changing and only your own radar knows what is ahead. Backing out exact time and route of a given flighti vs other radar images in timing may be a more reliable means of judging

[mm43]

Lomapaseo's comment says it all.

The images in the animation are integrated from satellite images taken every 15 minutes. The animation period is 2.5 minutes, and the integration is done by merging shot #1 with shot #2 etc.. to give the possible changes for 5 periods between observed images using Scalable Vector Graphics.

But that's not the point that Lomapaseo was making. Your own radar has a different aspect of view - horizontal with +/- tilt. What it sees and the depth of penetration are very variable factors, and the picture painted (in plan view) will bear no resemblance to that observed by the satellite, which is taking infra red images of what is on top, and has no way of determining what is below.

mm43

[PJ2]

Originally Posted by lomapaseo

Be careful of interpreting the catch all phrase "during the same period of time"

Absolutely agree. There is no rule for the timing of diversions; only the radar signal, as it is interpreted by the PF, is available unless the moon is out and one is clear of cloud to pick one's way through the towers.

Originally Posted by mm43

Your own radar has a different aspect of view - horizontal with +/- tilt. What it sees and the depth of penetration are very variable factors, and the picture painted (in plan view) will bear no resemblance to that observed by the satellite, which is taking infra red images of what is on top, and has no way of determining what is below.

Again, absolutely agree.

The other side of mm43's first point is, not everyone can interpret the radar's signal with equal depth of knowledge and, with understanding of what is being presented in a two-dimensional digital image essentially only of moisture returns, pick the best diversion. Experience helps a great deal but cells change very rapidly and what first appeared to be the best path through can close or can reveal another cell hidden by the first.

[HazelNuts39]

More on VS1g, VLS and AoA

Originally posted by PJ2 #604 (26th March):
*My thanks to HazelNuts39 for an extensive and informative discussion which helped me greatly in understanding this certification issue. Perhaps he may be coaxed into posting a suitable, brief discussion on VS1g and VLS certification (which is slightly different than VS certification)? I think it is germane.

I’m not entirely sure what PJ2 has in mind but, for whom it may interest, here are some further thoughts on what we’ve been discussing. I PM’d PJ2 because I doubted the speeds from the CBT in PJ2’s post #502: VLS=214kt and ValphaMax=196kt; i.e. VLS = 1.09 ValphaMax. On the other hand, PJ2 finds it difficult to believe that the airplane stalls at an angle as low as 6.5 degrees at FL 350, and I tend to agree with him on that. (Edit: The question that PJ2 and I still have is - what is the stall AoA in cruise?)
If we assume that the CBT’s VLS is defined by the stall, but alphaProt and alphaMax are somehow ‘adjusted’ for buffet boundary, we could estimate alphaMax(stall) as either:
VLS/1.18 = 181kt; alpha = 7.7 degrees, or –
VLS/1.23 = 174kt; alpha = 8.5 degrees.

For reference purposes, some elements that contributed to our discussion are repeated below:

Originally posted by PJ2 in #518 quoting from the FCOM:
V2=1.2 * 0.94 VS1g = 1.13 VS1g
VREF=1.3 * 0.94 VS1g = 1.23 VS1g
(...)
The AOM uses VS for VS1g.

PJ2 quoting from FCOM in his PM of 17th march
(HN39: only relevant part copied here):

VLS : Lowest Selectable speed.
Represented by the top of an amber strip along the airspeed scale on the PFD. It is equal to:
- 1.13 VS at take-off
- 1.18 VS when the flaps are retracted.
- 1.23 VS when in clean configuration. (It remains at this value until landing).

VLS is corrected for Mach effect to maintain a 0.3g buffet margin.

(note by HN39: 0.3 g buffet margin means that VLS >= 1.14 Vbuffetonset)

Regulatory minimum speeds for performance calculation:
In the takeoff configuration: V2 >= 1.13 VS1g
In the enroute configuration (clean) VFTO >= 1.18 VS1g
In the landing configuration VREF >= 1.23 VS1g

Discussion:
‘VS’ in the FCOM is VS1g in regulatory terms, and is also known as ValphaMax. Thus the FCOM's definition of VLS is conform the regulatory minima for takeoff and landing, but differs for the clean configuration. This does not mean there is a conflict, 1.23 is a larger margin than the minimum required for enroute. VLS = 1.09 ValphaMax is not conform the FCOM nor the regulation. As suggested by CONF iture in #514, the CBT software may be inaccurate. Another possibility is that these speeds are governed by buffet margin rather than stall:

CONF iture #582 quoting from FCOM 3: The aircraft can also enter alpha protection at a high level where it protects the aircraft from the buffet boundary. (...) This value of alpha is not however the same as the values used at low speed (sic): alpha for alpha protection is reduced as a function of Mach so that a typical cruise value is in the order of 5°.

[Mud Skipper]

Does any one have an idea of which type of radar was fitted on this specific aircraft.

Was it the newer Multi Scan type or the older radar.

[DJ77]

Mud Skipper, this subject came up in the older AF447 thread. As I remember, the radar was not a MultiScan. If you need more info, you could make a search on the old thread.
cheer.

[PJ2]

HazelNuts39;

Thanks for taking the time to post in some detail parts of our discussion on VS, VLS and AoA. I think this kind of discussion is valuable. As airline pilots we are never taught or even pointed towards certification information. I think some understanding of the more important certification standards of one's aircraft is part of professional work. To this end, there was some discussion by safetypee on take-off distances and RTO certification of various failures and changes in the "Kiwi B777 burst 12 tyres in aborted takeoff at NRT" thread .

Though the diagrams do not say, (probably because they are representative and necessarily not aircraft-specific), HN39 posited that the graphs in Davies (kindly posted by machinbird) were perhaps representing a wing with extended high-lift devices raising the stall AoA into the 15 to 20deg range which may account for the impression that stall AoA's were that high. Yes, you're correct in stating that I still find it difficult to believe that a clean wing (of the type under discussion -transport category, swept, super-critical airfoil) would stall as early as 6.5deg but as is also stated we don't yet have information on high-altitude stall AoAs. I look forward to continuing this.

The ACARS can provide the information (and a huge amount of other flight data) and it is easily accessible in-flight; I recall typical AoAs were 2.3deg approx. in cruise.

PJ2

[Finn47]

The Wall Street Journal says EU regulators want to examine using satellites to send real time flight data, in the way which has been suggested here:

EU Makes Push for Real-Time Flight Data - WSJ.com

The matter is on the agenda of the ICAO High-level Safety Conference which starts today in Montreal and lasts for four days, however looking at their work program, they are only going to devote a maximum of 1 hour and 15 minutes to this subject, it´s under "safety initiatives arising from recent accidents" on Wednesday

http://www2.icao.int/en/HLSC/Work%20...%20HLSC.en.pdf

[mm43]

Update: "Anne Candies" & "Seabed Worker"

The Sunday departure from Recife has come and gone and both vessels were still berthed there at 0300m Monday.

Well, today is another day, and possibly one day less budget-wise for the search.

------------------
Finn47

I expect the ICAO Safety Committee will just rubber-stamp the BEA Flight Data Recovery Working Group Report as an interim measure. Wouldn't expect speed of light progress there!

mm43

[PJ2]

mm43;

Is the weather in the search area suitable? Perhaps a day will be attached to the end of the schedule. PJ

[broadreach]

Our AIS showed Seabed Worker distancing Recife at 09:36z today on a course 298.5.

[CONF iture]

Originally Posted by PJ2

Yes, you're correct in stating that I still find it difficult to believe that a clean wing (of the type under discussion -transport category, swept, super-critical airfoil) would stall as early as 6.5deg but as is also stated we don't yet have information on high-altitude stall AoAs. I look forward to continuing this.

The ACARS can provide the information (and a huge amount of other flight data) and it is easily accessible in-flight; I recall typical AoAs were 2.3deg approx. in cruise.

I don’t think either that such a wing would stall at 6.5 degrees of AoA, but I would rather think that a level flight at such AoA/attitude is unsustainable due to the lack of available thrust versus the tremendous increase in drag in a low air density environment.

During a Airshow, any airliner can demonstrate its capability to maintain a high AoA at low level thanks to its engines. The same demonstration at high level would be impossible. Just not enough thrust to maintain level flight above 5 degrees of attitude. Soon the altitude cannot be maintained, the attitude would be still anywhere between 5 and 7 degrees but as the aircraft is descending, the AoA could increase to the usual 15 to 20 degrees where stall usually happens … Just a thought.

[Idle Thrust]

Thread creep is often frowned upon but I must say that the discussion here about AOA had been fascinating. Some great contributions.

Regarding the use of AOA indicators by the military (at least by the fast jets, especially in the navy) and its rejection by civil transports I'll add this:

When I left the navy for airline flying I was not surprised to see a little instrument on the early model DC-8 captain's glareshield since it was identical to one fitted in the Grumman S2F Tracker. We called it an SFI because it was manufactured by a company called Safe Flight Instruments. While it was not calibrated in units (just fast,OK & slow) I believe that it was an AOA indicator and we used it for carrier approaches. I was surprised to find that the airline told us to ignore it, did not maintain it, and eventually they were removed. Check the next post for a link to a related page.


Then came the DC-9 with its Collins FD-109 flight director and the Fast/Slow indicator on the right side of the attitude indicator. I know that this was not driven by the pitot-static system but got its input from the vanes mounted on the fuselage. Once again we were told to ignore the information provided and fly airspeed on approach. I think that one reason might have been because you were "on speed" when the airspeed was at Vref and of course we always carried additives - 5 knots minimum with wind added to that. Not sure how the thing was calibrated but it was a nice visible backup to the ASI even though we were not supposed to use it.

My mob was strictly an airspeed bunch.

Edited to remove faulty link. Thanks Machaca, I'm not too adept with some of this stuff!

[Machaca]

Corrected link:

speed control | safe flight | flight instrument | 1958 | 0666 | Flight Archive