This isn't good...

[Robert3512 21]

I was climbing out from SFO and had failures turned on. Just wondering: is there a sort of cascading failure mode? Or did I do something horribly wrong? Because the image below is pretty scary:

https://imgur.com/a/je7XB

If you can't see the image, what my EICAS is displaying is:

>AUTOPILOT
>GPS RIGHT
>NO AUTOLAND
>SNGL SOURCE ILS
>IRS CENTRE

[Captain Kevin 586]

Did you....go through the QRH and see what all those messages are trying to tell you? Do keep in mind that some of these things get triggered as a result of other things. In this case, you have an issue with the center IRS, so with any one IRS out, you won't be able to do an autoland, which is why that one popped up.

I just had a quick look, and out of the five messages, only one of them has steps to troubleshoot it. The other four appear to just be advisory. You'll have to look at the QRH to see which is which.

[Robert3512 21]

Yes, that's the problem. I'm wondering if there is a procedure for the other messages. As I understand it the ILS and GPS shouldn't fail just because the centre IRS did. 

[VHOJT 172]

That looks very similar to an error I got when I accidentally turned off the ground power without connecting the APU first, causing a bunch of things to power down.

[berts 97]

2 hours ago, Robert3512 said:

I was climbing out from SFO and had failures turned on. Just wondering: is there a sort of cascading failure mode? Or did I do something horribly wrong? Because the image below is pretty scary:

https://imgur.com/a/je7XB

If you can't see the image, what my EICAS is displaying is:

>AUTOPILOT
>GPS RIGHT
>NO AUTOLAND
>SNGL SOURCE ILS
>IRS CENTRE

>AUTOPILOT = The selected autopilot is operating in a degraded mode because the engaged pitch and/or roll modes may have failed.
>GPS RIGHT  = Right GPS failure
>NO AUTOLAND = Autoland is not available
>SNGL SOURCE ILS = Both pilots displays are referenced to the same ILS Localizer or Glideslope receiver

>IRS CENTRE = The Centre IRS has failed.  Without knowing exactly how you had the aircraft configured when these messages first appeared I suspect this one is the main cause of your problem and it has probably resulted in all the other Careted Messages appearing.

The QRH procedure for any IRS failure is to initially select an operable IRS using the IRS Source Selectors, then position the FMC Master Switch to the most accurate IRS and turn the affected IRS Mode selector to ATT.  You should follow the QRH carefully and observe what happens to these messages.  Some of them will normally clear, but if there are any remaining then you will need to determine what you may have lost and plan your approach and landing accordingly. For example, with a LEFT IRS failure you will not have any Body Gear steering.

Bertie Goddard 

[downscc 1,327]

4 hours ago, VHOJT said:

That looks very similar to an error I got when I accidentally turned off the ground power without connecting the APU first, causing a bunch of things to power down.

This

[Robert3512 21]

Thanks for all your replies, also I think the 747 has 3 ILS receivers, so for SNGL SOURCE ILS to happen 2 must be down, right?

Also,  "with a LEFT IRS failure you will not have any Body Gear steering", why would the left IRS affect body gear steering? 

[Qavion2 39]

8 hours ago, Robert3512 said:

SNGL SOURCE ILS to happen 2 must be down, right?

Or your instrument source select switches are both in the same position.

 

8 hours ago, Robert3512 said:

Also,  "with a LEFT IRS failure you will not have any Body Gear steering", why would the left IRS affect body gear steering? 

Although the IRUs send groundspeed data to the body gear steering system, I'm not sure if it would generate a body gear steering message. I used to sit in the cockpit during towing operations with the IRUs off, but the body gear steering still operated. The techincal gurus at Boeing told me that if the IRUs are off, the body gear steering system ignores groundspeed.

[Robert3512 21]

I see, 

4 hours ago, Qavion2 said:

Or your instrument source select switches are both in the same position.

 

Although the IRUs send groundspeed data to the body gear steering system, I'm not sure if it would generate a body gear steering message. I used to sit in the cockpit during towing operations with the IRUs off, but the body gear steering still operated. The techincal gurus at Boeing told me that if the IRUs are off, the body gear steering system ignores groundspeed.

My ILS switches are both in the corresponding position (L for captain, R for F/O). 

[Qavion2 39]

On 08/02/2018 at 0:07 AM, berts said:

For example, with a LEFT IRS failure you will not have any Body Gear steering.

Interesting. Apart from the comment in my previous message, my training notes say that IRU signals come from both the Left and Right IRUs:

One of the requirements for operation is:

"The left or right IRU ground speed signal indicates less than 40
knots."

 

[berts 97]

16 hours ago, Qavion2 said:

Although the IRUs send groundspeed data to the body gear steering system, I'm not sure if it would generate a body gear steering message. I used to sit in the cockpit during towing operations with the IRUs off, but the body gear steering still operated. The techincal gurus at Boeing told me that if the IRUs are off, the body gear steering system ignores groundspeed.

John, when you say "my training notes say that IRU signals come from both the Left and Right IRUs"  Don't you mean the Left and Right FMC's?

It is always difficult commenting on a technical issue, because no B744 is exactly the same.  In the case of the RR engined B744, when an IRS fault is detected in flight then automatic selection of an operable IRS should occur for display purposes. However, if the ND or PFD display is unreliable or incorrect then the QRH directs the crew to select an operable IRS using their IRS Source Selector.  Their next action is to select the FMC which is giving the most accurate FMC position, so that the best source is used for LNAV purposes when radio updating is not available.  The third action is to select ATT on the affected IRS Mode Selector and - provided ATT mode is available - the crew should see IRS ALIGN MODE and SET IRS HEADING displayed as EICAS Memo messages for approximately 30 secs in straight and level flight or until the alignment is complete.

If whilst actioning the QRH the IRS LEFT message is still displayed at this point then the Body Gear Steering will definitely not be available.  Incidentally, CAT3B autolands are also not available with any single IRS failure, whereas 2 IRU's have to be in NAV mode for CAT2 and CAT3A autolands.

Although there are subsequent actions to follow in the QRH procedure they are not relevant to this discussion.  However, I couldn't find any reference to the 40kts groundspeed you mention,  Body Gear Steering normally activates when the nosewheel steering angle exceeds 20 degs with the ground speed reducing below 15kts and is deactivated as the speed increases above 20kts  Fortunately, the lack of Body Gear Steering will only affect the flight crew during low speed ground operations when sharp turns should be avoided.  Incidentally, I presume you didn't get a body gear steering message because the IRS's were switched off and therefore their normal system/detection logic wouldn't be working?

Bertie

[Robert3512 21]

It's pretty peculiar that a (mostly) mechanical system (the body gear steering) would be affected by the IRS, isn't it? Logically it shouldn't be, right? NWS isn't affected by the IRS, so why is body gear steering affected?  

[rcoultas 21]

1 hour ago, Robert3512 said:

It's pretty peculiar that a (mostly) mechanical system (the body gear steering) would be affected by the IRS, isn't it? Logically it shouldn't be, right? NWS isn't affected by the IRS, so why is body gear steering affected?  

I would believe because the body gear steering system is dependent on the nosewheel steering angle and groundspeed as indicated in the FCOM as stated by @berts?

 

1 hour ago, berts said:

Body Gear Steering normally activates when the nosewheel steering angle exceeds 20 degs with the ground speed reducing below 15kts and is deactivated as the speed increases above 20kts  Fortunately, the lack of Body Gear Steering will only affect the flight crew during low speed ground operations when sharp turns should be avoided.  Incidentally, I presume you didn't get a body gear steering message because the IRS's were switched off and therefore their normal system/detection logic wouldn't be working?

Bertie

 

[skelsey 765]

1 hour ago, Robert3512 said:

It's pretty peculiar that a (mostly) mechanical system (the body gear steering) would be affected by the IRS, isn't it? Logically it shouldn't be, right? NWS isn't affected by the IRS, so why is body gear steering affected?  

As mentioned above, the the body gear steering system relies on knowing the aircraft's ground speed in order to know when to activate/deactivate. 

What system provides ground speed information? ;)

[berts 97]

19 hours ago, skelsey said:

What system provides ground speed information? ;)

I believe the inertial navigation units (IRU's) calculate the actual ground speed - as if by magic to most pilots and navigators!   However, on the B744 the source of the ground speed displayed on the PFD and ND will depend on the status of the FMC's, the IRU's and the position of the IRS and Navigation source selectors.  These items will also affect the source for heading, track angle, drift angle, slip/skid, and wind direction and speed displayed on each pilot's PFD and ND units.  

Well, you did ask, Simon! :-)