MD11 - Couple of logic bugs

[marcom 139]

Hi folks,a couple of observations:1) If at the beginning of the IRS alignment process some of its conditions are not met when you move the switch to NAV (for example lack of elec power) it seems the IRS will never truly enter the alignment process. The MCDU will display INITIALIZE IRS but the LAT/LON fields will be empty and if I try to enter something manually it reports "NOT ALLOWED". Also, after 10 minutes, nothing happens. The only solution I found so far was to reload the aircraft (!!) Powering down everything and restarting didn't help.2) Once IRS alignment has started, and you don't enter position data, the IRS will "loose" its alignment after 10 minutes. This is how it works on the real aircraft (I tried it :( ):The IRS will remain in alignment mode and wait for a position input. Once the user enters the data, the units jump directly into NAV mode. This is a trick you can use to force the IRU's to remain in alignment a little while longer.3) I'm missing the ATT mode - if I power down the IRU in flight and reset it to NAV, nothing will happen. On the real aircraft, it takes around 30 seconds in level, unaccelerated flight to display the attitude data.4) Sometimes my APU just won't start correctly. N1 spools up to about 4%, EGT up to 111

[Check_Airman 3]

1 & 2- This is my understanding of how the system should behave. Is there something wrong?3- I know the Airbus quick align method is to momentarily turn the selector to off. Haven't tried it in the MD. I'll have a go and report later.4- I haven't seen this. Are you running FS9 or FSX?5- Does it eventually reduce power?

[marcom 139]

1 & 2- This is my understanding of how the system should behave. Is there something wrong?3- I know the Airbus quick align method is to momentarily turn the selector to off. Haven't tried it in the MD. I'll have a go and report later.4- I haven't seen this. Are you running FS9 or FSX?5- Does it eventually reduce power?

Hi,well, if you're gonna try #3 I suggest you try 1 & 2 as well.3 is not about quick aligning the IRU's - its about the ATT mode where alignment is lost during flight.4) FS95) Yupp, but you loose a couple of track miles in terms of deceleration.

[Check_Airman 3]

I haven't gotten around to it yet (om my list of things to do this evening), but 1 & 2 are fine. That's how it's supposed to be. If all conditions are not met, the IRUs simply will not align. You must enter a valid position for alignment to take place.

[marcom 139]

That's not what I was referring to.1) If at the beginning of the alignment a condition is not met, the IRS will of course not align. BUT as soon as the condition is met, the IRS will immediately begin its alignment process (you don't have to turn it off and then back on). Naturally, you can't enter a position as loon as it has not entered the alignment process.2) Again, I think my post was pretty clear. You only need to enter the position data to make sure the IRU can enter NAV mode after the 10 minute alignment process. If you don't enter the data, the IRU will wait for it (no time limit here) and as soon as you input the data, the IRU will ump into NAV mode (provided over 10 minutes have elapsed).I don't know if its my English that is not up to par or if I have difficulty describing my observations but I have the feeling too many people don't read my notes carefully enough and jump to the conclusion that I must be doing something wrong :(Please, give me the benefit of the doubt, if there is any :( RegardsMark

[Guest krullenbol]

2) Just checked it but I don't see a problem here. If you wait 10 minutes after selecting the IRS's to NAV, the NAV OFF lights will start flashing. When you enter a position in the MCDU, the alignment process is complete and all lights will extinguish.3) Resetting of IRU's in flight isn't a normal procedure. If a IRU fails in flight, you just simply turn it off by checklist. During an IRU failure, the Attitude mode will continue to work.

[marcom 139]

2) Just checked it but I don't see a problem here. Except for the level 1 alerts -IRS x NO ALIGN - do not appear in real life. If you wait 10 minutes after selecting the IRS's to NAV, the NAV OFF lights will start flashing. When you enter a position in the MCDU, the alignment process is complete and all lights will extinguish.3) Resetting of IRU's in flight isn't a normal procedure. If a IRU fails in flight, you just simply turn it off by checklist. During an IRU failure, the Attitude mode will continue to work.

2) Did you try it? Ie. not entering present position, waiting 10 minutes and then pressing the INITIALIZE IRS prompt? I did and in my case the IRU's did not switch into NAV mode. I had to restart the alignment process. (Present Pos was accurate!)3) Did you try it? I turned the switches to OFF (all three of them), waited a bit and then reset them to NAV. At no time did I regain the PFD (not even partially). (I waited around 2 minutes in level, unaccelerated flight)CheersMark

[NathanX 2]

2) I just tried it and confirmed the irs flashing after 10 minutes. Upon pressing the INITIALIZE IRS the IRS switched into NAV mode with no problems.3) Systems manual inst 10.7 - 10.8 "In-flight realignment of the IRS is not possible." a. Fcom A.10.36 "Attitude data remains usable"Nathan

[Guest krullenbol]

2) Yes I did, I waited 10 minutes, lights were flashing, pressed the IRS Align button on the CDU and all the IRU's were aligned.3) No. I don't know how the real aircraft handles that. The only thing I know is that you don't cycle IRU's in flight. If one fails, you just turn it off. The IRU's know if ATT or position data are invalid. If ATT data is invalid, you will get a LEVEL 2 IRU FAIL. The procedure tells you to switch the IRU to OFF. If the navigation part fails, you will get a level 1 alert IRU NAV FAIL. You will leave the IRU in the nav position, but select IRS AUX on the SISP.Floris

[marcom 139]

Ok I'm gonna try #2 later on, I want to find out what went wrong yesterday (where it didn't switch into NAV mode)#3 yeah, IRU's can't be aligned when the platform is moving (ie the aircraft) (well except for hightech biz jets) but you should have basic accelerometer data (ie attitude) - you don't need a specific reference for it.