One IRS To Command FMC For Input To AutoFlight

[Buzz313th 0]

So I had an IRS fail. I went through the procedures and I understand the redundancy on the 73 with two IRS and two FMC's. For the life of me I am unable to to get one IRS to command one FMC to Allow Auto Flight reingagement.Someone correct me if I am wrong, but shouldn't one functioning and aligned IRS be able to satisfy the FMC to allow the 73 ng to operate on limited autoflight?So at cruise, I lost the left IRS. At that moment I lost the left PFD and ND. This should happen, since the captains side is being fed by the left FMC, which is also being given data from the left IRS. Then I switched the IRS source switch to, "Both on right", which should send all the FMC's data from the functional right IRS. This worked and I got my captain side PFD and ND back. Now here is the problem. As soon as I switched I was unable to get my FD's back. I recycled the Flight Director switches, but was unable to get the FD on either the capt or FO side. Unfortunately, without the Flight Director being active, I was unable to couple the Autoflight system, which meant I had to continue the flight flying manually for the next 2 hours, which was ok, but without another crewmember, executing flows and just changing frequencies was a bear and almost alway resulted in a slight climb or descent when I got back to flying the plane. Anyways...Shouldn't one functional IRS be enough to still allow for Flight directors and also autoflight?JB

[voske 34]

According to the QRH (11.8-11.12), the autopilots either shouldn't be engaged or can't be engaged.

[Buzz313th 0]

As per the FCOM2 one functioning ground alligned IRS with the other IRS in ATT mode and flight alligned should allow AF engagement. But the QRF does not recomend flying the plane on Autopilot unless both IRS are in NAV mode and aligned. It doesn't say that the autopilot won't work. It does however say that if one IRS is in Nav mode and the other cannot be flight alligned and in att mode then the AP will not work.So when I was doing my flight I had the left IRS fail completely. It would not align in ATT mode and the fault light stayed on, thus a complete IRS failure. This would not allow any AP engagement. But, I just did a test where I took off with both IRS in nav mode and ground alligned and once at alt, I switched off the right IRS. I then lost AP. The procedure in the QRF says, to switch the failed IRS to ATT mode and fly level for 30 seconds at which point the IRS will flight allign, you should get back the corresponding instruments and then you should be able to enter a magnetic heading for that IRS in the POS Ref page on the CDU, or the IRS display while in HDG/STS mode. Once that is done, you should have a complete flight allignment and the FMC's should be fully functional with the slight limitation that you will need to keep entering mag heading on the ATT IRS to maintain correct flight allignment.So I turned off the right IRS and waited for the allign light to extenguish and then set it to ATT. I flew straight and level for 30 seconds and got back the FO's PFD and ND, but I was unable to enter the Mag Heading into the IRS display and or the POS ref page to complete an ATT IRS Align.PMDG, mind me asking if the IRS/FMC system is fully modeled to accomidate for the procedures in the QRF regarding an IRS fault?JB

[davierosoft 13]

There is something wrong with ATT function, it gives heading and cannot modify it...It must be reviewed...I tried it, putting from off to ATT or from nav to ATT will result in a immediate show of all attitude and heading data. SET HDG appears in POS INIT page, but all entry will be disregarded, also if data is putted through ISDU panel.

[Buzz313th 0]

Ok, just finished two more tests.. And yes the IRS system is modeled correctly as per the FCOM in flight ATT alignment. Also, once flight aligned, you will get the AP back. Durring alignment, you must really hold a stead course and altitude for the complete alignment to succeed.1. normal flight both IRS fully ground aligned.2. Climb to a cruise alt with ap coupled.3. Turn off right IRS. (This is to simulate a loss of alignment. If you fail the IRS with the failure menu, then you will have a complete IRS failure with flight alignment not possible)4. Once Align light is extinguished, then move selector over to ATT.5. You should get your displays back and the IRS ALIGN light will still be lit.6. Open the CDU to POS REF Page.7. Fly as straight and level as you can. after roughly 30 seconds your IRS align light will extinguish and on your CDU POS REF page at Line select 5 you will see a place for heading entry. Input magnetic heading and excecute. You will now be fully flight aligned on that IRS and you will have full AP capabilities back.Note... You have the option to enter heading in either the CDU or the IRS display. To enter the heading in the IRS display.... After the ALIGN light is out, switch IRS to selector to the unit in alignment and also HDG/STS mode. Press the "H" key on the IRS keypad then your heading and then enter. Check CDU for reference. JB

[davierosoft 13]

I tried on ground and it did not work as is supposed to do in real life.I will try inflight, but there is something wrong on ground.As I put from OFF to ATT on ground I can immediately see the sky/ground raster and the heading on pfd/nd and stby, this without entering the value.If you follow the checklist, without seeing what you are doing, at the end of checklist all works, as it is working already when ATT is selected.ATT works either on ground or inflight (leveled) in the real life. IT is used sometimes to test systems that needs attitude information.Attitude information cannot be given in just a millisecond after selecting ATT from OFF, and gyros are unable alone to detect current heading. So, How it can give me heading information without entering it?Also, if you put an incorrect heading it must accept and turn the ND heading to the new heading (left irs moves also the stby heading on the digital standby instrument), so, in my case I was having already 125° of heading after ATT selection from OFF, then tried to put 200 in POS INIT page or on the ISDU HDG/STS page, it accept it, but still reading 125°System not working here.

[fjsharry 0]

Ok, just finished two more tests.. And yes the IRS system is modeled correctly as per the FCOM in flight ATT alignment. Also, once flight aligned, you will get the AP back. Durring alignment, you must really hold a stead course and altitude for the complete alignment to succeed.1. normal flight both IRS fully ground aligned.2. Climb to a cruise alt with ap coupled.3. Turn off right IRS. (This is to simulate a loss of alignment. If you fail the IRS with the failure menu, then you will have a complete IRS failure with flight alignment not possible)4. Once Align light is extinguished, then move selector over to ATT.5. You should get your displays back and the IRS ALIGN light will still be lit.6. Open the CDU to POS REF Page.7. Fly as straight and level as you can. after roughly 30 seconds your IRS align light will extinguish and on your CDU POS REF page at Line select 5 you will see a place for heading entry. Input magnetic heading and excecute. You will now be fully flight aligned on that IRS and you will have full AP capabilities back.Note... You have the option to enter heading in either the CDU or the IRS display. To enter the heading in the IRS display.... After the ALIGN light is out, switch IRS to selector to the unit in alignment and also HDG/STS mode. Press the "H" key on the IRS keypad then your heading and then enter. Check CDU for reference.JB

I try this procedure in flight,not work for me...always ALIGN light illuminated.Not thing happen.

[RYR738 9]

Very interesting thread !!I will test this tomorrow. Fred.

[davierosoft 13]

Just start with the right things:Error code 9 is shown on ISDU untill heading is entered.Now, wrong things:Just one inflight test, so, try yourself:From Off to NAV and then rapidly to ATT, when in ATT displays came back in just a second (real one begins ATT alignment after 2 seconds from selecting ATT) , with full data on them also if the light "ALIGN" was still on, Attitude was exact for the plane at the moment, same for heading. I tried leveled, but as soon as I see te raster I tried to move the plane during alignment and the sky ground was following me.Also heading was here, exactly as it must be for a full alignment, Set IRS heading is fictional as I cannot set any heading, setting will not affect heading. Code 9 disappears, so it virtually accepts the setting.It seems that this part of simulation, as for speed brakes autorestow, responds as expected only if used by checklist without needing to see what really the switch does.

[fjsharry 0]

In my situation is has 03 number(or empty) in right window with ATT mode,and try to enter heading number on fmc or overhead keyboard but can not type anything..But when after manual landing,i saw has "SET IRS HDG" in fmc corner...well i was landed....

[davierosoft 13]

What about the PFD and ND attitude and heading information in ATT? Are you seeing them?

[fjsharry 0]

I only sawing PFD and ND from un-alignment become normal condition,and ALIGN light still illuminated even SET IRS HDG not appear on fmc overhead pand.And other question,if just during flight turn NAV to ALIGN,then SET IRS POS on fmc,this situation can return to IRS? I not saw this in manual.

[davierosoft 13]

NAV alignment is only avaiable on ground, as it align the accelerometers. If you turn to ATT (in real life to prevent it there is a notch, you must pull and turn) you have 2 seconds to move back to NAV, if you fail you will lose your NAV for the rest of the flight.After 2 seconds you will have that ATT mode starts alignment, this means that there are other 30 seconds to align the sky ground symbol, and 30 seconds before having Set irs HDG on the bottom right of the POS INIT page of the FMC.On the IRS panel (ISDU) there will be no messages (except for code 9 in HDG/STS knob position), you need to push ten Key 5 (H) and put heading, then ENT that will be lit.

[davierosoft 13]

You can see that putting on ATT with ll the attitude we want, will result in a full attitude data, if compared with FO they are the same.If ATT is not aligned with te correct attitude, it will not extinguish the ALIGN light and SET IRS HDG will not appears, so your problem is that you don't wait the 30 seconds (or whatever is set on pmdg) with aircraft leveled.However is still useless to wait as all works as soon ATT is selected. The FCOM ATT aligning procedure is completely useless on pmdg at the moment.These last screens are on ground.

[fjsharry 0]

It's a bug? Whatever i try many time still can't get anything.