744 IRS Question

[Guest alexhn]

just a quick question concerning IRS in the 744... Anyone with knowledge in this area please reply :) In the 744 AOM, it states the procedure for an IRS full alignment to be to place the IRS mode selectors in OFF then into NAV... -Is the ALIGN (on the IRS mode selector switch) function used at all in full alignment, or is it only used in Fast Alignment? -It says the IRS will be ready when all systems enter navigation mode.. How does one tell when the IRS systems are in navigation mode.. (As the select switches are already in NAV for Full alignment, so i probably wouldn't tell if IRS was in navigation mode from the switches, would i? Is there an EICAS message or something displayed on the POS page of the FMC?)also, does attitude alignment have to be taken care of before IRS navigation alignment is taken care ofthanks in advance for the help

[744pilot 0]

HiIt's very easy actualy.You just place the switches to NAV, enter the coordinates in the POS INIT page of the FMC then you see on the ND (upper left corner):IRS L: +7IRS C: +7IRS R: +7This is the minutes still to go before the full alignment is complete.Also on the EICAS y'll see IRS L,C,R Align mode.Once the Alignment is complete all these message disappear and the attitude on the PFD will pop up.The align mode is mostly used for a quick re-alignment but can also be used for full alignmnet.

[Guest alexhn]

could you or someone else post the full procedures for full alignment, attitude alignment, and fast alignment... or at least explain what to do and what i should see?

[Guest Babubhai]

Wait for the PMDG 744 operations manual to release :)

[Guest Flightfreak]

Ok let me get this straight.....You're first step is to make the AC ready to fly, you power up the AC, you turn on your hydaulic and fuel pumps, and so on. You guys know what I'm talking about.Then you put the IRS Selector Switches in NAV Mode, you enter your current position (using SHIFT+Z in FS you can check you're current POS). Then you line up you're IRS's, and then you can continue with your FMC Initialization.If I think about this, this is the only thing that's coming across my mind..........THIS PLANE WILL ROCK!!!!!! :D :D :D

[CF104 0]

>could you or someone else post the full procedures for full>alignment, attitude alignment, and fast alignment... or at>least explain what to do and what i should see?Hi Alex,Here is the complete procedure from the real 744 AOM.------------------------------------------------------IRS AlignmentFull AlignmentRotating the IRS mode selector from OFF to NAV begins IRS alignment.Alignment requires approximately ten minutes. Present position (latitude andlongitude) must be entered on the CDU position initialization page to completealignment. Alignment can be accomplished only when the airplane is parked.Alignment stops if an IRU detects motion during alignment. Alignment continuesand completes in approximately ten minutes after motion stops. The IRS is alignedwhen all IRUs enter the navigation mode. Latitude and longitude entries thenblank on the SET IRS POS line on the CDU position initialization page.Alignment is lost if the selector is moved out of the NAV position.A full alignment, accomplished by rotating the IRS mode selector to OFF andback to NAV, must be accomplished when the time from the last full alignment tothe next expected arrival time exceeds 18 hours.Fast AlignmentFollowing operation in the navigation mode and with the airplane parked,performing a fast alignment removes accumulated track, ground speed, andattitude errors, relevels the system, and updates present position. This isaccomplished by positioning selectors to ALIGN, entering present position, andrepositioning selectors to NAV. Fast alignment completes in approximately 30seconds.Fast alignment can be accomplished without entering present position. However,greater navigational accuracy is attained by entering present position.IRS AttitudeIf alignment is lost in flight, the navigation mode is inoperative for the remainderof the flight. Attitude information can be obtained by moving the selector to ATT.The IRU enters align mode for 30 seconds. This relevels the system and providesattitude displays on the PFD. For best accuracy, the airplane must be in straightand level flight. Some attitude errors may occur during acceleration. Afteracceleration, errors are slowly removed.The attitude mode can also provide heading information. A magnetic headinginput is required to initialize the IRU while in attitude mode. This heading isavailable for backup if all three IRUs fail. Heading information displayed on thePFD and ND is from an IRU operating in the navigation mode. This informationis independent of the IRS source selector position if an operating FMC is selectedby the navigation source selector.IRS PowerThe IRS can operate on AC or DC power. The center IRU operates on DC powerfor five minutes, then shuts down. If an IRU loses both AC and DC power,alignment is lost.--------------------------------------------------Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[Guest alexhn]

thanks! now i understand! the ALIGN switch position is momentarily selected when doing a full alignment because you must cycle past this to get to nav. but first, i must select ATT, enter the current heading, then start a full alignment...? or will doing a full alignment automatically adjust my attitude?

[CF104 0]

>thanks! now i understand! the ALIGN switch position is>momentarily selected when doing a full alignment because you>must cycle past this to get to nav. >Well, sort of but align has nothing to do with a full align. ALIGN is know as a fast align and is only used after a full align as per the previous info I posted to remove accumulated track, ground speed, and attitude errors, and relevels the system, and updates present position.>but first, i must select ATT, enter the current heading, then>start a full alignment...? or will doing a full alignment>automatically adjust my attitude?No. ATT mode can only be entered after a full align and is purely a non-standard mode. A full align carries out the ATT adjustment before flight. Here's a quote from the 744 QRH;-----------------------------------------------------------Condition: IRU fault detected.IRS source selectors (Operable IRU) . . . . . . . . . . . L, C, OR RIRS mode selector (Affected IRU) . . . . . . . . . . . . . . . . . . . . ATTMaintain straight and level, constant airspeed flight untilattitude displays recover (approximately 30 seconds).If IRS message no longer displayed.IRS heading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ENTEREnter heading on the SET IRS HEADING line of theCDU position initialization page. Maintain straight andlevel flight while entering the heading.IRS heading may have to be updated periodically.If IRS message remains displayed:IRS mode selector (Affected IRU) . . . . . . . . . . . . . . . . .OFF-----------------------------------------------------------Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[Guest glenlee]

Hi, I've never used one of these type IRS systems but I have used another Inertial Nav type setup on a real aircraft and that needed to be aligned in 'Align' and then when the counters had gone down (from around about 7 to zero) you had to put the switches into 'Nav' in order to use the nav data.It's probably one of those 'specific to type' wording issues but surely this way makes more sense? You align in 'Align' and Navigate in 'Nav'.Just my input, I'm not correcting anyone.Glen.

[CF104 0]

>Hi, I've never used one of these type IRS systems but I have>used another Inertial Nav type setup on a real aircraft and>that needed to be aligned in 'Align' and then when the>counters had gone down (from around about 7 to zero) you had>to put the switches into 'Nav' in order to use the nav data.>>It's probably one of those 'specific to type' wording issues>but surely this way makes more sense? You align in 'Align' and>Navigate in 'Nav'.>>Just my input, I'm not correcting anyone.>Glen.Hi Glen,That is common with INS systems but with the 744 IRS and most others, you go directly from OFF to NAV for the full allignment and enter your POS into the FMC/CDU. This starts the full allignment process. Align, as I stated aerlier, is only used after a full allign to erradicate accumulated errors and can only be used when the aircraft is stopped.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[michal 44]

I visualize ALIGN as used when you say arrived at your destination and want to update your position before your return leg. APU is running, IRS is powered so there is no need for complete full allignment. The new crew moves in and just goes through ALIGN.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[CF104 0]

Hi Michael,Yes, that would be the primary use for ALIGN.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[Guest glenlee]

OK, that makes more sense.Cheers.G

[Guest yawdamper]

I guess that's a company thing then.We do quick aligns when we have residual groundspeed or a noticeable psotion shift. But then again we only have 2 IRU's.Whenever there is a crew change we turn the IRU's completely off. I wouldn't feel too comfortable flying with a "used" alignment.Luckily we still have more than 10 minutes at the gate during turnarounds ;-)Adrian