B737 IRS Switches

[Sean]

This is a pic of the Ryanair cockpit companion. Also mentions pulling out the knob to get to OFF.

[archen]

Oh god, a third version??? Looks like I have to go with the most common option. I'll post back tomorrow when I got the report from my pilot friend.

Boeing NG documents doesn't tell anything about a detent between ALIGN and OFF, only NAV. RYR option maybe? Wrong in FCOM? Can it really be so many different versions of a switch?

Anders


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[Sean]

I couldn't see any video links in your post, but I found a one on YouTube which looks like the classic version, and this one on aviafilms...

http://www.aviafilms.com/boeing-737.php

Scroll to 4th video

[archen]

I was referring to my video (works like the 300's.

I just checked my FCOM from TUIFly 2010. That does only have an detented NAV.






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[fsaviator]

Bill Bulfer's 737NG Cockpit Companion says OFF-knob must be pulled out which decreases risk of accidental selection and NAV is detented.

ATT has a two second delay to prevent accidental selection

[archen]

Ok thanks. Looks like there are some versions out there. I don't really see the usage of a detented off position. In flight it's important not to get out of NAV, not important you don't go to off.

This just got even more interesting I hope get a report from my friend tomorrow. He is flying yr 201* NGs. He's report will weight heavy in my decision.




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[archen]

Got this video from Phil. From an NG.

http://youtu.be/AM1qtXa0bYw

Big thanks to Phil for this video!


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[archen]

The more I read about them the more convinced I get that they work like Phil's NG switch. Almost every documentation I've found tells NAV is detented, nothing more.

Have anyone seen the other switch documented in RYR FCOM and Bill buffler? Video or real life, please share all your experience from the real switches.

No report from my friend yet.


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[andthiel]

Bill Bulfer's 737NG Cockpit Companion says OFF-knob must be pulled out which decreases risk of accidental selection and NAV is detented.

ATT has a two second delay to prevent accidental selection

Warren, this is exactly what can be seen in the Ryanair FCOM photo.

And this makes absolutely sense. When switching from ALIGN to OFF accidentially you will loose aligning immediately.

Best,

Andreas

[archen]

Can you see any date of published on the FCOM or Bill bufflers? Trying to sort out when this could have been changed or if this is an option available which RYR have. TUIFly don't have this feature in 2010's FCOM.

Mickc: thanks for your input! Based on real world experience or documentation?


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[mickc]

Just to throw more confusion into the mix  :

Here is the extract from the 738-800/900 Maintenance Manual:

The mode selectors have a feature to decrease the risk that the
flight crew will accidentally put the ADIRU in a mode that will
disable its operation. When the selector is in the NAV position,
the operator must pull the knob to put it in the ATT mode. When
the selector is in the ALIGN position, the operator must pull the
knob to put the selector in the OFF position. All other position
changes do not require the operator to pull the knob.

And similar in the 737-300/400/500 Version:

Each mode select switch has detented positions. The detented positions prevent accidental
movement of the switch. In a detented position, the switch must first be pulled out of the detent before
selecting another position to prevent damage to the switch. In the NAV position, the switch must first
be pulled out of detent before selecting the ATT position. In the ATT position, the switch must first be
pulled out of detent before selecting the NAV position. In the ALIGN position, the switch must first be
pulled out of detent before selecting the OFF position.

[archen]

I'll disregard the information about 300/400/500 as this is not what I'm trying to simulate but according to the information given in the NG manual it appears to work like my switch does today. Have I understood it correctly?


If we try to learn more from what happens with the different modes maybe we can figure out how it should be.

What happens if the pilot in-flight turn the knob from NAV to ALIGN and then back to NAV? Will they lose reference? I know that they will lose reference if turned to ATT for more than 2 seconds (therefor the detent)

But if there is no harm in moving the switch to ALIGN in-flight the detent should maybe be to OFF?



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[mickc]

Looks like it!

[archen]

Mickc, updated my post. Any thoughts?


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Edit: Found this: http://www.37000feet.com/report/794992/B737-700-captain-selected-both-IRS-switches-to-align-in-flight-believing

Looks like moving the switch from NAV -> ALIGN causes IRS to lose reference. In that case, guarded NAV, like in Phil's video feel like the best solution. The detent to OFF does not help much if you lose everything by moving it to ALIGN if there is no detent between NAV-> ALIGN.

[mickc]

I agree, that sound like the best option. 

Ill dig out my other docs and see if theres any more info.

[archen]

I did Sean. Interesting video! But I could only see the switch operated from OFF to NAV. All versions works the same that way.

What's I'm looking for is how the switch operates when moving from NAV to ALIGN and ATT. Also from ALIGN to OFF where RYR (Unknown year) FCOM actually tells you to lift the knob to go to OFF. I haven't seen that anywhere else except RYR manual and bill buffler. Bill buffler is dated 1998 so that can be outdated.

I Asked a friend who knows a guy flying for RYR to check this in their fleet next time.




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[mickc]

If we try to learn more from what happens with the different modes maybe we can figure out how it should be.

What happens if the pilot in-flight turn the knob from NAV to ALIGN and then back to NAV? Will they lose reference? I know that they will lose reference if turned to ATT for more than 2 seconds (therefor the detent)

But if there is no harm in moving the switch to ALIGN in-flight the detent should maybe be to OFF?

This is the only other reference in the AFMM about what happens when changing modes:




Although the NAV to ALIGN is listed, it states "Aircraft not moving"

[archen]

Thanks! I guess they did not list NAV-> ALIGN in-flight because that is not normal operation.


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[fsaviator]

OK,

I've attached the pertinent page from Boeing's FCOM (Not Airline Specific) on the 737-800 for the IRS.  It only mentions detent on NAV.

[archen]

Thanks warren. Looks like my FCOM from 2010 (tuifly branded).

Looks like that is the most common. Still, would be interesting to know why they differ to others. Options or revisions?




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[archen]

Just did the other mechanism.. To compare.


http://youtu.be/LPc_h31PKr4


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[fsaviator]

I like them!  Have you decided on a price range?

[archen]

Thanks, just tested the switch in prosim and it worked perfect. I like this one more when NAV is guarded. I'll probably offer both versions though. In prosim you are able to regain the IRSes when turning them to ALIGN. Don't know if that's correct or not but it would definitely explain why some airplanes have the other version I did with detents between ALIGN -> OFF. If ALIGN don't hurt you midair in NG, I guess that detent does more sense to protect the pilot from turning it to OFF rather than ALIGN.


Haven't decided if I should price them as a pair or single. Pair?

The switch has the same costs and manufacturing time (CNC machining, assembly) so they will be priced like the autobrake switch is per each.


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[archen]

So I just got one of two reports from real world pilots. Looks like there are quite many different IRS switches out there.

This one is a Norweigian 738.

http://youtube.com/watch?v=UPwVBzfomIc


http://youtu.be/dqYsv3prqqo


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[fsaviator]

Outstanding!  I like that one.