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Aquadalte: "If this aircraft was equipped with ISIS, it was surely also equipped with Back-Up Speed Scale and Back-Up Altitude, that displays on PFD's and gets information from AoA probes and GPS, respectively.
This is very important, once Back-Up Speed Scale and Altitude are only displayed when ALL ADIRU's are switched OFF. The old procedure (for the stand-by horizon equipped aircraft), would call for the trouble-shooting of the IR fault, and in case of all confirmed to be faulted, one would be advised to switch off those connected to Captn PFD and FO PFD, i.e., IR1 and 2. This would allow the aircraft to revert to Alternate Law. This system (although brilliantly designed) seams to work fine in rather smooth air and on flight simulators, but I find it very difficult to see it properly working in a heavy turbulent environment, as seemed to be the case of AF447." Believe that the Back-Up Speed option was available in 07, the ISIS does indicate Speed/Altitude and Attitude...the instument is only about 1.5" square. |
I have a very simple question and I've reviewed virtually all of the posts in both threads and not found an answer.
Of the pilots' flight instrument displays, what do they lose if all 3 pitot sources fail? Do they lose everything including bank, turn and vertical airspeed or do they just lose the airspeed display? |
I'd like to direct a comment toward the VS/Rudder separation. From AA587, we know the failure was complete, and purportedly caused by pilot input beyond structural limit. Here, we know the failure was complete, though the cause and sequence is unknown.
A short aside re: MD11 gear. In Narita, one noticed how astonishingly robust the NG and one of the MG were, the nose gear remaining attached even after that last horrific nose plant, the Main pushing up and through the main spar of the wing. BA038 lost the gear and saved the hull. Here's the thing. The composite VS is exceedingly strong, as well as relatively light, and demonstrably resistant to failure except at the root, where it attaches to the fuselage. It remains pristine, not a crack in its skin. Its failure at the root is obviously related (Lateral failure, if such was the case, as I believe) to its leverage on the root, a tall structure that is acting through its moment arm on a robust attachment. I am pointing out that its only failure was complete; it resisted until the total failure was unavoidable. If however the structure was designed to have top down sequential failure, a component at a time, each loss of surface area would reduce its advantage on the root, allowing for the remainder of the fin to operate in reduced effectiveness, but allowing for directional stability. Something as simple as two or three parallel seams such that the first piece to depart might be the topmost one meter, the next failure point halfway, until the moment arm was short enough that the fuselage attachment would be virtually failure proof, though providing very limited D/S. I can't take my eyes off that nearly perfect fin. One can envision 587 retaining some fin if not rudder. Rudder is a trimming device, without it things are difficult, lose the VS and you lose the a/c. WF |
A very interesting suggestion, allowing for partial disintegration of the VS. I suppose it goes against the design philosophy that the main flight surfaces were meant not to fail, not as a whole nor in part, at all. That might need to be reconsidered.
I wonder however whether removal of the VS as we see it in the AF case would not rupture the hydraulic lines. B, G and Y HYD systems are all operating the rudder surface in the A332. If the entire VS was ripped off, I'd imagine that would depressurize B, G and Y hydraulics, and that in itself should be triggering a whole host of ACARS warnings back to base? Also, the rudder travel limiter remembers the last limit in the case of a double SEC failure, and won't reset and allow full travel until the slats are extended. Based on that rational, I think we are looking at the VS separation being an effect of the sequence of events after departure from controlled flight rather than a cause. Cheers Doc |
Just to follow on with ZeeDoktor...
If the VS failed early on would the A/C have remained stable enough to transmit the ACARS msgs? Also from the pics of the VS the rudder is damaged at the lower rear edge which could mean the VS failed first at the leading edge and rolled back over the tailcone as opposed to AA587 where the rudder is gone completely and the VS was apparently broken of from side pressures. |
On the 330/340 try putting ''aoa'' into the ACMS on MCDU 3. This gives a readout of current angle of attack which at 350-370/.81 usually reads 2.2 to 2.3 degrees. Could help with loss of all speed/mach and/or PFDs. Obviously only good for benign conditions and you would have to do it in advance as you cannot do it in the middle of the emergency. But don't think it would've helped in Af's extreme condns....
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> If the VS failed early on would the A/C have remained stable enough to transmit the ACARS msgs?
This could be reworded as "is relatively stable flight possible without a rudder and VS?" A B52 managed it once, but I suspect in general it would be a neat trick, especially in the middle of a storm at night. That said, if the plane was stable enough to send messages and the VS decided to leave suddenly, I'd guess that it might remain stable enough to send messages for another few seconds, maybe longer. So if the VS had been the first thing to go, there is a reasonable chance that we would have seen a message about it. Instead we have a cabin descent speed warning. Note that when the VS left it ripped up the back of the plane. The forward bolt support structure is very near the aft pressure bulkhead. So it might have peeled open the aft bulkhead. That could relate to the early reports that the bodies being found were from the back of the plane. Its possible the hole might not have been all that big, so it might have required some seconds to depressurize the plane. |
ISIS
The ISIS, if operational and not in need of reset, can on its own determine all the correct indications to display on its face (pix by A33Zab at post 1940), except that the indication of IAS and FL depend on the probe PITOT3 and the probes STATIC3 (same ref post 1935). [If these probes are giving erroneous readings, there is in theory some ability to detect gross divergence from speed made good and true altitude-- I cannot say if this is implemented in some way, or if this display can show that.] I do not know the effect of the loss of bus power; is there an internal floating battery or capacitor source, and of what duration?
It is reasonably clear that the inputs from ADIRU-1 and -3 are used to initialize ("reset" button) the ISIS before each flight (to the heading, pitch, roll, and altitude of the standing A/C), and that if these inputs are lost, an ISIS FAIL message to ACARS may be generated for maint, if for no other reason than possible loss of ability to make this AF SOP required reset at the next terminal. Obviously, in an emergency, a reset in flight into an erroneous input from either ADIRU needs to be avoided, and in general should be unnecessary. So the questions are: 1. Is an inflight erroneous reset blocked by disagreement of ADIRUs 1 and 3? Or otherwise? 2. Does crew training include instruction on how, when, and when not to make inflight reset? 3. Does crew training include how and when to bring the ISIS up for flying, if needed? 3a. Or how, when, and why it becomes the instrument for flying, if automatic? 4. Does crew training include mention that all the ISIS displays are normally accurate (IMO), except that IAS and FL may err due to probe icing? 5. Is there any SIM training with ISIS as the only flight instrument? with its ILS feature? 6. [I omit mentioning again all the proper flying procedures covered by others.] 7. Does the QRH cover all this? Can or should it be memory trained? 8. Are electric power issues covered? LCD screen readable with flashlight if necessary (that external 5vac)? And a final question: 9. If an ISIS FAIL message is generated for ACARS due ADIRU input fail (see above), does it blandly repeat on the PFDs in just those words? Can we tell from the ACARS? (I know... not easily.) [I recall a respected pilot here saying we should have a TV record of just what appears on the PFDs. The point is, is there an ISIS FAIL on the PDFs, when in fact the ISIS is functional? And does the SIM replicate the A/C in this detail?] BTW, the 3 gyros are not one operational gyro and 2 backups-- all 3 are operational with specific functions. That makes it self-sufficient as to A/C attitude. It isn't actually necessary to know more than this to know that it doesn't need the ADIRU inputs to generate its display. Hope this helps. OE |
SO, back to ISIS and Ranamin's and my question. A33Zab appears to show that aguadalte's posts are incorrect, and that ISIS does have its own IRS system and should be capable of providing basic attitude info in the event of failure (or isolation) of all 3 ADIRUs. The $10,000 question, of course, is what 'interference' does the aircraft 'management' software place in the way of ISIS ACHIEVING this aim? 'icarusone' and AZ tell us that it is possible that the Hot battery bus supply could have been 'interrupted' due to the air/ground switching (was 'ESS' unaffected?), and of course there would appear to be no heading info with loss of the 2 ADIRUs, so back to the standby compass:eek:.
No, this does not 'solve' the accident by any means, but if the ISIS was somehow 'prevented' from providing this basic information it makes an accident far more understandable given the other system failures they appear to have suffered in those weather conditions. The whole software side is indisbutably very clever, but IF it has been coded on the basis that there are so many redundancies and backups that 'nothing can go wrong', is it time for a big red switch which says 'take ALL the computers out of this and give us Basic information so we can try to fly it'? NB That is for ALL modern aircraft of whatever type/manufacture. Lots of fingers crossed for the search. A different question for those familiar with that route. From what I can make out in terms of where this might have occurred in the actual area of CB activity, carrying on on track after 'recovery' from whatever happened would appear to be a better weather solution than turning back to the mainland. How would this fit with a possible 'worse case' ETOPS fuel scenario ie low level 2 engines vis a vis ETPs and excess fuel, and where would ETP 1 be likely to be in relation to TASIL? |
Old Engineer:
Thank you for your post !! I think we've all made it CLEAR to non airbus / non ISIS familiar colleagues (BOAC and others..) that the ISIS is a STBY / back up instrument independant from ADIRUs as a SOURCE of displayed flying DATA. 1. Is an inflight erroneous reset blocked by disagreement of ADIRUs 1 and 3? Or otherwise? From FCOM: ATT flag (red) on ISIS appears when attitude data is lost, the red ATT flag appears. ATT RST The attitude indication can be reset by pressing this pushbutton for at least 2 seconds. The aircraft must be level during this procedure. During the reset time (approximately 10 seconds), the "ATT 10s" message is displayed on the screen. This pushbutton is also used to realign the system, if excessive aircraft movement is detected during the alignment phase. 2. Does crew training include instruction on how, when, and when not to make inflight reset? 3. Does crew training include how and when to bring the ISIS up for flying, if needed? 3a. Or how, when, and why it becomes the instrument for flying, if automatic? 4. Does crew training include mention that all the ISIS displays are normally accurate (IMO), except that IAS and FL may err due to probe icing? 5. Is there any SIM training with ISIS as the only flight instrument? with its ILS feature? 6. [I omit mentioning again all the proper flying procedures covered by others.] 7. Does the QRH cover all this? Can or should it be memory trained? 8. Are electric power issues covered? LCD screen readable with flashlight if necessary (that external 5vac)? Yes you could read the LCD with the flash light. And a final question: 9. If an ISIS FAIL message is generated for ACARS due ADIRU input fail (see above), does it blandly repeat on the PFDs in just those words? Can we tell from the ACARS? (I know... not easily.) ACARS message re:ISIS, we need a decode. Could be the Airspeed flag if STBY pitot has a problem, as simple as that. By the way, NAV ADR DISAGREE can come up with 2 erroneous AOA data as well (ADRs). OK. My opinion is that is all else fails, the ISIS is available to maintain at least the attitude of the A/C. I think we can leave the ISIS to rest now ! no ?:rolleyes: |
ISIS
Gents just to shed some light:
Post#1910 The problem, as said earlier, is that ISIS containts are classified. I know it sounds weird but again, no one opens up this box !! While it is true that it gets inputs from ADIRU 1 and 3, it is also true that it contains gyros !! Inertial Measurement Unit (IMU). It contains three single-axis rate sensors and their temperature structure. This assembly is connected to the Programmed Motherboard "probes, two acceleration sensors and their temperature probes, one IMU board and one mechanical It is not an IRU (Inertial Reference Unit) it ONLY detect it's position in space, not movement in it. And in regards to ADIRU inputs. ADIRU (IR1 or IR3) Two ARINC 429 high-speed buses provide the ISIS indicator with the ADIRU ground speed information. This information is used as a backup source for the ISIS ground/flight condition. In normal configuration, the parameters used by ISIS indicator come from the ADIRU 1. When a failure is detected, switching to the ADIRU 3 must be done manually through the ATT/HDG selector switch on the SWITCHING panel. But U can ask me every time :ok: |
Originally Posted by captainflame
I think we've all made it CLEAR to non airbus / non ISIS familiar colleagues (BOAC and others..)
I think we can leave the ISIS to rest now ! no ? |
H3dxb:
Brilliant ! finally I find out what's inthere ! Yes it's not on IRU. But it provides "gyroscopic attitude information" right ? Thanks for the post !:ok: |
cf - you must have missed #1934? A superb description of the system.
It would seem that once alignment is complete (and presumably kept updated by the IRUs, the Quartz Rate Sensors (modern equivalent of laser ring) will in fact provide attitude information as would an IRU. The Q is what happens if/when the IRU input is blocked or fails. EDIT: Just seen your post - it does NOT contain any 'gyros'. Read h3's post again? |
BOAC:
Sorry to say but if you can't make up your opinion on how it works and answer most of your questions on ISIS, then I am at loss to help out. Following the latest ISIS post by h3dxb (#1951), and taking into account other well informed posts (even excluding mine if you wish), you can have a pretty good idea on how the ISIS functions by now. Key fact is it contains a gyro, indicating attitude. I never said it's an inertial plateform !! Aguadalte implied it got its attitude info from ADIRUs, and that's plainly false. He standed corrected earlier. No problem. Fact is, tech info on ISIS is not disseminated as profusionnally as one would wish. Personnally, I learned more now on ISIS than on any other ground course I followed recurrent or not ! |
I think we are talking about the same thing. Confusion with terms perhaps ?
For me a gyro, whether spining, laser or quartz, provides attitude info. the Quartz Rate Sensors (modern equivalent of l@ser ring) will in fact provide attitude information as would an IRU As to the Q question: i don't have an answer. |
Gents
Fully access to Manufacture documents . It looks like the IMU is equipped with single axis Sensors working as Gyrometers. An IRU detects it's position in space and movement through it, an attitude indicator only it's position. Standby horizon function The ISIS indicator can operate from -180 to +180 deg. in pitch and roll without deterioration. - gyrometers (3): a monitoring is triggered when the angular speed in x, y or z axis becomes greater than 95 deg./s. ISIS can follow a 10,000 deg./square second angular acceleration. - accelerometers (2): the associated monitoring is released when the constant acceleration in x and/or y axis becomes greater than 3.25 g. If this monitoring is triggered, the "WAIT ATT" message is displayed. If the conditions become normal again and if the attitude performance remains adequate for 10 seconds , the "WAIT ATT" message disappears and is replaced by the horizon display. Otherwise, after 10 seconds or if the attitude performance is affected, the attitude function is considered as failed and the "ATT:RST" message is displayed in place of the "WAIT ATT" message Pressing the RST pushbutton switch more than 2 seconds in steady flight quickly resets the attitude information. Anyhow, it is an seperate standby unit, even when connected to several computers, it acts alone and gets it's physical infos from it's on sources. BOAC , I hope this Info about the quick reset possible in flight answers yr question. I think steady flight means in this philosophie less than 3.25 g. kind regards |
I remember an article from Aviation International News from a number of years ago regarding the use of accelerometers in standby instrument systems.The article went on to state that the accelerometers were identical to those used in car airbag systems and that they isis could run off a watch battery for 24 hours. Unfortunately I have been unable to find the article
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ISIS
Quote:
While it is true that it gets inputs from ADIRU 1 and 3, it is also true that it contains gyros !! Not so true. It does not contain gyros. It's containing a IMU (Inertial Measurement Unit) described as " Inertial Measurement Unit (IMU). It contains three single-axis rate sensors and their temperature structure. This assembly is connected to the Programmed Motherboard "probes, two acceleration sensors and their temperature probes, one IMU board and one mechanical It is not an IRU (Inertial Reference Unit) it ONLY detect it's position in space, not movement in it. And in regards to ADIRU inputs. ADIRU (IR1 or IR3) Two ARINC 429 high-speed buses provide the ISIS indicator with the ADIRU ground speed information. This information is used as a backup source for the ISIS ground/flight condition. In normal configuration, the parameters used by ISIS indicator come from the ADIRU 1. When a failure is detected, switching to the ADIRU 3 must be done manually through the ATT/HDG selector switch on the SWITCHING panel. Captainflame: As written (by me among others) in previous posts, the ISIS is a self contained instrument providing Airspeed from stby pitot, attitude from internal gyros, Altitude from STBY static ports, and slip/skid info from accelerometers, Captainflame: What happens when ALL ADIRUS fail? |
h3dxb
But U can ask me every time I'm not necessarily referenced by "U", but anyhow: In an earlier post you stated that the SATCOM phased array antenna needs inertial reference to control it's beam steering. http://www.pprune.org/rumours-news/3...ml#post4997265 How then could it have been able to transmit ACARS messages stating that no inertial reference is available? Or am I missing something? |
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