Fly-By-Wire
$ begingroup$ The uncontrolled flight was likely a spiral dive due to loss of instrument reference in IMC - that's the main danger with a total power loss. Also, the DC-9 family uses servo tab primary controls (the rudder and elevator have hydraulic boost, but it isn't needed all that much), and Boeings from the 707 through the 737 have manual reversion in at least pitch and roll. Now I receive the folder name MINWINPC and inside it there are one backup folder with date and size is about 20GB. When I went inside it there are two files named Backup.1.exe (size 2440KB) and Backup.2.fbw (size 20263431 KB), I tried to open Backup.1.exe and couldn't open anything and for FBW.
From SKYbrary Wiki
Article Information | ||
---|---|---|
Category: | Flight Technical | |
Content source: | SKYbrary | |
Content control: | SKYbrary |
Description
Fly-by-Wire (FBW) is the generally accepted term for those flight control systems which use computers to process the flight control inputs made by the pilot or autopilot, and send corresponding electrical signals to the flight control surface actuators. This arrangement replaces mechanical linkage and means that the pilot inputs do not directly move the control surfaces. Instead, inputs are read by a computer that in turn determines how to move the control surfaces to best achieve what the pilot wants in accordance with which of the available Flight Control Laws is active.
Why it is useful
The advantages of reduced weight, improved reliability, damage tolerance, and more effective control of a necessarily highly manoeuverable aircraft, were first recognised in military aircraft design. The first aircraft to have FBW for all its flight controls in place of direct mechanical or hydraulically-assisted operation, was the F-16 in 1973. In the context of military fast jet need for agility, and therefore relatively more unstable aircraft, FBW provides the ability to ensure that unintended increases in angle of attack or sideslip are detected and rapidly, and automatically, resolved by marginally deflecting the control surfaces in the opposite way while the problem is still small. FBW also enables highly reliable flight envelope protection systems which, provided the FBW system functions at its normal level, significantly enhances safety.
How it Works
The principle used is that of error control in which the position of a control surface (the output signal) is continually sensed and ‘fed back’ to its flight control computer (FCC). When a command input (the input signal) is made by the pilot or autopilot, the difference between the current control surface position and the apparently desired control surface position indicated by the command is analysed by the computer and an appropriate corrective signal is sent electrically to the control surface. Feedback compensation functions as error control and the FCC regulates the system by comparing output signals to input signals. Any error between the two becomes a command to the flight control surface until output equals input.
In an FBW system the signal route from FCC to control surface is called the forward path while the signal route from the control surface to the FCC is called the feedback loop or path. Gain is the amplification or attenuation which is applied to the forward signal to achieve the desired aircraft response. A filter may be used to block feedback of signals or motion which occur at an undesirably frequent interval.
An advantage of a feedback system such as this is that the flight control system (FCS) can be used to reduce sensitivity to changes in basic aircraft stability characteristics or external disturbances. The autopilot, a stability augmentation system (SAS), and a control augmentation system (CAS), are all feedback control systems.
In a SAS, a damper function is formed in the feedback loop and usually has low gain, or authority, over a control surface. A CAS is implemented in the forward path and represents high-authority 'power steering,' providing consistent response over widely varying flight conditions. The CAS and SAS principles were used independently in military aircraft prior to fly-by-wire, integrated into an FCS, they can operate with more precision and much greater flexibility. Consistent aircraft response is achieved over a broad flight envelope through CAS gains that are programmed as functions of airspeed, mach, center-of-gravity position, and configuration.
Control Laws
The FCCs at the centre of an FCS are programmed with control laws that govern the feedback control system. Control laws are commonly named after the primary feedback parameter as ‘xxx feedback’ or ‘xxx command’. Typical feedbacks are:
- Pitch Channel: vertical load factor ‘g’, pitch rate ‘q’, pitch angle ‘θ’, angle of attack ‘α’.
- Roll Channel: bank angle ‘f’, roll rate ‘p’.
- Yaw Channel: yaw rate ‘r’, sideslip angle ‘b’, rate of change of sideslip angle ‘b with a dot over it’ verbalised as ‘beta dot’).
‘G command’ which is a desirable capability at high speeds, means that for a particular amount of control column force, you get (available energy permitting) the same ‘g’ regardless of prevailing airspeed. Similarly, in a pitch-rate command system, you get the same amount of pitch rate for a given control column force regardless of prevailing airspeed.
To balance the need to communicate pilot commands rapidly whilst at the same time maintaining a context for them as a basis for precision over time, the FCC provides a direct path to the elevator via the ‘proportional line’ or ‘feed forward gain’ but also routes the same command through a parallel circuit ‘integrator’ which produces a control surface command until the feedback signal is equal to the pilot's original command signal. Engineers must ‘tune’ the integrator gain setting so as to prevent excessive lag.
Pure integrator control, or too much integrator gain ‘K’ would cause excessive lag in aircraft response which is why the proportional line is used as well. This arrangement, called 'proportional plus integral' control, is found in most fly-by-wire designs, including those of both Boeing and Airbus.
If undue lag exists in an FCS, causing delay in changing direction from, say, nose-up to nose-down, the effect would be analogous to the human performance lag well known as pilot-induced oscillation or PIO.
An aircraft controlled in pitch by pitch-rate command or g command gives you attitude hold with controls free, similar to the control wheel steering (CWS) feature of an Autopilot. If you change pitch attitude and release control pressure at the desired attitude, the system holds that new attitude because the FCS reacts to bring pitch rate to zero. The aircraft should fly easily with only moderate control forces required and precise attitude control. A consequential benefit of either pitch-rate or g feedback is auto trim in that you can change speed without needing to re-trim for level flight. The same applies to thrust or configuration changes. Auto trim provides apparent neutral-speed stability. Even though positive speed stability was a generally accepted design requirement for conventionally controlled aircraft, the lack of it seems to be acceptable to those flying FBW aircraft with this effect un-moderated. Some FBW types, though, do retain conventional trim 'feel'.
A common control law which blends g and pitch-rate feedback is called C* (verbalised as C star) At low speed in a C* airplane, pitch rate applies whereas at higher speeds, g applies. The changeover is transparent and occurs, for example, at about 210 kts388.92 km/h
107.94 m/s
in Airbus A320 series aircraft. Boeing have made use of a modified C* control law called C*U where U’ represents aircraft forward speed and which provides apparent speed stability. This works by having the trim switches set a reference speed that is summed with the actual speed in the FCC feedback loop in such a way that the pilot feels conventional control force cues as speed changes. You 'trim a speed,' not the pitch control surface. Because the maximum trim reference speed is 330 kts611.16 km/h
169.62 m/s
, a pilot would have to push on the control wheel to further increase speed toward Vmo which conveniently provides a tactile high-speed cue.
107.94 m/s
in Airbus A320 series aircraft. Boeing have made use of a modified C* control law called C*U where U’ represents aircraft forward speed and which provides apparent speed stability. This works by having the trim switches set a reference speed that is summed with the actual speed in the FCC feedback loop in such a way that the pilot feels conventional control force cues as speed changes. You 'trim a speed,' not the pitch control surface. Because the maximum trim reference speed is 330 kts611.16 km/h
169.62 m/s
, a pilot would have to push on the control wheel to further increase speed toward Vmo which conveniently provides a tactile high-speed cue.
Backup 2 Fbw Custom
Looking in more detail at specific phases of flight, FBW allows designers to optimise the effective dynamics for different flight phases by introducing, for example, an approach mode or a flare mode and creating a multi-mode FCS.
In both the Airbus A320 series and the Boeing 777, the control laws are not fully active until after the aircraft gets airborne because the sensors used for feedback would sense a lot of vibration and ‘noise’ during the take off roll. Landing requires other transitions. Because taking ground effect into account is a ‘one off’ factor in executing a successful landing, the ruling control law may need ‘flare compensation’ to ensure that the usual rearward control column movement is required to flare. In the case of the C* control law in the Boeing 777, an artificial nose-down pitch command is input at 30 feet radio for this purpose. Boeing 777 control laws have also been used to improve the de-rotation characteristics compared to those of the Boeing 757 and 767 by fine-tuning the C*U integrator gain during flight tests. See also the separate article Flight Control Laws, which has more detail on Airbus and Boeing control laws.
System Redundancy?
Rather than providing a conventional FCS for backup, the approach with commercial aircraft normally controlled wholly by FBW is to provide redundancy for the FCCs and sensors by installing more of them. Civil airliner FBW design has generally employed triplex FCSs as is the case with the such as the Boeing 777 and Airbus A340 which both also have limited mechanical backup to allow a period of ‘survivability’ at cruise to sort out any electrical problems. Any duplex FBW systems should be expected to have a full mechanical backup.
When all components are operative, an FCS is commonly said to be operating in normal law. Limited failures usually cause auto reversion to some degraded, but still computed, FCS mode. The lowest level of FBW backup mode normally features analog electronic signals that bypass the FCCs and go directly to the flight control actuators - Direct Law. Under Direct Law, there is no feedback control and there may be fixed gains aimed at providing acceptable control forces proportional to control surface deflection. The gain selected may optimise control forces for the landing configuration, or might provide different gains for cruise and landing, switched, for example, through the flap selector.
Flight Envelope Protection
Feedback control of airspeed, Mach Number, attitude, and angle of attack can be used to ensure that the FBW aircraft stays within its certificated flight envelope. Two strategies have been used to achieve this: the Airbus strategy of` ‘hard limits’ in which the control laws have absolute authority control unless the pilot selects Direct Law; or the Boeing strategy of ‘soft limits’ in which the pilot can override Flight Envelope Protection and so retains ultimate control over the operation of the aircraft.
Accidents and Incidents
The following events included flight envelope protection as a factor:
- A319, vicinity Tunis Tunisia, 2012 (On 24 March 2012, an Air France Airbus A319 Captain continued descent towards destination Tunis at high speed with the landing runway in sight well beyond the point where a stabilised approach was possible. With 5nm to go, airspeed was over 100 KIAS above the applicable VApp and the aircraft was descending at over 4000fpm with flaps zero. EGPWS activations for Sink Rate, PULL UP and Too Low Terrain apparently went unnoticed but at 400 feet agl, ATC granted a crew request for a 360° turn. The subsequent approach/landing was without further event. Investigation attributed the event to “sloppy CRM”.)
- A320, vicinity Tel Aviv Israel, 2012 (On 3 April 2012, the crew of an Air France Airbus A320 came close to loosing control of their aircraft after accepting, inadequately preparing for and comprehensively mismanaging it during an RNAV VISUAL approach at Tel Aviv and during the subsequent attempt at a missed approach. The Investigation identified significant issues with crew understanding of automation - especially in respect of both the use of FMS modes and operations with the AP off but the A/T on - and highlighted the inadequate provision by the aircraft operator of both procedures and pilot training for this type of approach.)
- A321, en-route, near Pamplona Spain, 2014 (On 5 November 2014, the crew of an Airbus A321 temporarily lost control of their aircraft in the cruise and were unable to regain it until 4000 feet of altitude had been lost. An investigation into the causes is continuing but it is already known that blockage of more than one AOA probe resulted in unwanted activation of high AOA protection which could not be stopped by normal sidestick inputs until two of the three ADRs had been intentionally deactivated in order to put the flight control system into Alternate Law.)
- A332 MRTT, en-route, south eastern Black Sea, 2014 (On 9 February 2014, the Captain of a military variant of the Airbus A330 suddenly lost control during the cruise on a passenger flight. A violent, initially negative 'g', pitch down occurred which reached 15800 fpm as the speed rose to Mach 0.9. In the absence of any effective crew intervention, recovery was achieved entirely by the aircraft Flight Envelope Protection System. The Investigation found that the upset had occurred when the Captain moved his seat forward causing its left arm rest to contact the personal camera he had placed behind the sidestick, forcing the latter fully forward.)
- A332, en-route, near Dar es Salaam Tanzania, 2012 (On 27 February 2012, the crew of an Airbus A330 en route at night and crossing the East African coast at FL360 encountered sudden violent turbulence as they flew into a convective cell not seen on their weather radar and briefly lost control as their aircraft climbed 2000 feet with resultant minor injuries to two occupants. The Investigation concluded that the isolated and rapidly developing cell had not been detected because of crew failure to make proper use of their weather radar, but noted that activation of flight envelope protection and subsequent crew action to recover control had been appropriate.)
- A343, Bogotá Colombia, 2017 (2) (On 19 August 2017, an Airbus A340-300 encountered significant unforecast windshear on rotation for a maximum weight rated-thrust night takeoff from Bogotá and was unable to begin its climb for a further 800 metres during which angle of attack flight envelope protection was briefly activated. The Investigation noted the absence of a windshear detection system and any data on the prevalence of windshear at the airport as well as the failure of ATC to relay in English reports of conditions from departing aircraft received in Spanish. The aircraft operator subsequently elected to restrict maximum permitted takeoff weights from the airport.)
![Backup Backup](/uploads/1/1/0/4/110407335/917110556.png)
Related Articles
Further Reading
- A Simple Summary of the FBW Systems installed on an Airbus A330 is found in: ATSB Aviation Occurrence Investigation AO-2008-070 Final Report, Section 1.6.3 Electrical flight control system (EFCS)
- Airbus fly-by-wire: a process toward total dependability by Taverse, Lacaze and Souyris - Paper presented to ICAS in 2006
- Aviation Safety and Pilot Control: Understanding and Preventing Unfavorable Pilot-Vehicle Interactions, by the US National Academy of Sciences, 1997
Retrieved from 'https://www.skybrary.aero/index.php?title=Fly-By-Wire&oldid=129292'
To see the 'bottom line' solution, scroll to the bottom of this post.)A friend of mine had a major computer meltdown a month or so ago. She, like many other people, had not made 'system restore' disks when she first bought her HP laptop (HP being too cheap to include them with the system). With multiple Blue Screen of Death (BSOD) issues..
..we decided that the best thing for her to do would be to restore the system back to factory condition. There WAS a 'recovery' partition on the hard drive, so we figured we could get it back to 'good as new' using that. But first, she ran a backup (using HP's supplied Backup and Recovery Tool) onto an external hard disk. That backup ran all night..and still seemed to stop in the middle..but it was all she had, at that point..she couldn't access her files anyway given that she couldn't get into Windows Vista.
So she ran the System Restore from the Recovery partition, and..more BSOD issues. (Now, we couldn't really understand why that would happen..wouldn't the Recovery partition contain a WORKING copy of Vista?!?!) Well, in any case, we finally decided the Vista install was toast, and that she should upgrade to Windows 7, which made sense for a whole lot of reasons. (For one thing, Windows 7 is, according to most commentators, vastly superior to--and faster than--Vista. For another..she'd have her CDs if she bought an upgrade.)
So, she upgraded to Win7, successfully..and has been running it, happily, since.
Of course, after she got her laptop working again, she was eager to get her files from the backup. There were two files in the backup (as I mentioned, I don't think it ever finished doing it's thing)..about 8 gigs of stuff (we're sure she had much more than that on her laptops 200 GB hard drive..but that's all she got). The files were backup.1.exe and backup.2.fbw. According to all the instructions we had read and could find, to restore the files, all you needed to do was..run backup.1.exe.
Well, no. Running the file caused C++ run-time errors.
Despite looking around the 'net for workarounds (and learning ALL about how to make sure to delete the 'System Recovery Files' folder before trying to run the damn thing AGAIN).. being tempted to follow instructions to copy these files onto CD or DVD (um..not possible..too big) and even transferring the files to my Windows XP machine to see if we could run it there (nope..more run-time errors)..she pretty much gave up.
Well, as those who know me know..I..don't..give up. (A friend of mine calls me the 'bulldozer' or, variously, the 'snow plow' for this aspect of my personality.)
So last night I spent a few hours poking around trying to find another solution. I searched for 'hp backup repair' and 'hp backup *.fbw' and 'Softthinks backup tool.' I followed each of these trails for a while.
You can see my persistence, in a way, in the list of sites I visited looking for a solution (from my Firefox 'history'):
Backup 2 Fbw Torrent
(Fortunately, I had a glass of wine to keep me company.) However, most of the things I tried were dead ends. (It's amazing to me how many 'fix-it' sites will show up in a search for something like 'backup repair'..when all they're really hawking is some kind of all-in-one registry repair tool..based on the probably erroneous assumption that the problem with the backup restore process is something in the registry. Um..not in this case.)(It's also pretty interesting how much anger and vituperation there is towards HP about this issue..you'd think they would want to put an easy solution to the problem on their web site..but such a thing I could not find.)
One of the things I tried, based on a whim, was to download from HP the entire 231 MB HP Backup and Recovery software..but after a nearly one hour download, the damn software wouldn't recognize the backup files..it was looking for a completely different file extension (not *.fbw)..clearly a different version of the software from what had been on my friend's machine (although from the same French company, Softthinks).
The search in Google for 'hp backup .fbw' proved to be most useful. Appearing at the top of the search was a VERY long thread on an IT discussion forum, Toward the bottom of the thread, I found some links to some recovery tools.
First, I tried something called the 'HP Backup and Recovery Fixer,' but it couldn't find the 'catalog' of the backup (which is stored in the last backup file, it turns out..and since this backup didn't finish..there was no catalog, I guess). Strike one.
But, I was in luck! (I thought): in a FAQ associated with the Fixer, it says:
(Q) HPBackupFixer says it cannot find the catalog or the catalog is corrupt. What does this mean?
A) If the catalog cannot be found, it is very difficult to extract the files from the archive. Try using the Emergency Recovery Tools.
I followed that link, which went directly to a download, ertools.zip. Unfortunately, when I extracted the file for XP, and ran it, I got
(If you can't read that, it says 'The file could not be patched. It could be because it's on a read only disc [nope], already patched [nope?] or because the searched sequence couldn't be found.' VERY helpful!! :-)) 'Searched sequence'? I have no idea what that was (although, thinking about it now, it must have been the 'header' to the 'index' in the backup files..something different from the 'catalog,' I believe. In any case: strike two.
Back to the IT forum page. http://forums13.itrc.hp.com/service/forums/questionanswer.do?admit=109447627+1285079352875+28353475&threadId=1116746. After scanning through it some more, I found a post from one Jose F. Ugarte, who wrote, in part,
'Guys, believe it or not, i got feedback from Softthinks!!!
Find below the instructions. (from a Softthinks web page)
First option didnt work for me, but the second actually did!
I have my personal files back!!!
Hope this helps you too!'
I had seen this post before (search the forum page for 'Aug 29, 2008 14:47:35 GMT' to find it), but didn't see a link to the tool, and, when I went to the Softthinks page that he quotes (which I found by following a link on their 'Support' page which reads ' For Customers who experience troubles with HP Configurations.' (!), there was no link there as well, so I'd given up on that.
But now, looking at Jose's post more closely, I saw a little paper clip icon in the upper right of the post:
Now, when I clicked on that link, I got a 'download' dialog:
..which I dutifully downloaded and opened into Winzip:
.and extracted, then ran (saying 'run' in response to the warning that the publisher could not be verified), 'load'ed the backup.1.exe file, and got
:
(By the way, the instructions for this ARE at the Softthinks site (and in Jose's post on the forum)
..then I clicked 'analyze,' and (after clicking 'OK' to warning that this might take several hours), about 20 minutes later, got
(have no idea what happened to those 30000+ files that 'could not be found')..and after clicking 'ok' got:
..and clicked 'Emergency Extract,' which I ran overnight, resulting in
including over 4000 files without any 'type' or extension and the folders you see with plenty more files named 'ExtractedFile-20-09-2010..' with extensions like .doc and .mp3 and .jpg, altogether about 12 gigs of stuff. Again, MUCH less than what we hoped for..but it's something.
Now, my friend gets to go through these files-without-real-filenames and figure out what is what. Lucky her!!!
Bottom line: if you have an HP backup set that you can't recover because you are missing the final backup file (or another reason..not sure what will work beyond that), with backup.1.exe and one or more backup.n.fbw, use this Emergency Recovery Tool. (I've put it on my web site so you can download directly rather than going through the forum.)
Enjoy!