Sign in to follow this  
BeechPapa

777 FMC/ND limitations

Recommended Posts

Considering the fact that the 777 has been certified for ETOPS 330 (which PFPX gives a max range of 1652nm for) I am surprised that the ND's max range is 640nm in both MAP and PLN modes. On certain journeys there is simply no way to zoom out far enough to get a sense of perspective for the ETOPS range rings and the CRPs. It's also a bit frustrating to only have 4 fix pages available. If there are 3 ETOPS alternates with 2 CRPs you have to juggle which fixes get priority on what segment of the flight. Throw in your final destination alternate and possible approach fixes and that's even more juggling of fixes. It surprises me that an airplane specifically designed for long range flight, touted for its modern avionics and huge amounts of processing power would have such basic limitations. Do these limitations annoy real 777 crews?

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Considering the fact that the 777 has been certified for ETOPS 330 (which PFPX gives a max range of 1652nm for) I am surprised that the ND's max range is 640nm in both MAP and PLN modes. On certain journeys there is simply no way to zoom out far enough to get a sense of perspective for the ETOPS range rings and the CRPs. It's also a bit frustrating to only have 4 fix pages available. If there are 3 ETOPS alternates with 2 CRPs you have to juggle which fixes get priority on what segment of the flight. Throw in your final destination alternate and possible approach fixes and that's even more juggling of fixes. It surprises me that an airplane specifically designed for long range flight, touted for its modern avionics and huge amounts of processing power would have such basic limitations. Do these limitations annoy real 777 crews?

 

The newer AIMS 2 equipped B777s (All -200LR/F-300ER) only have 12 MB of FMC navigation database storage capacity. Yes, you read that correctly, 12MB! The older AIMS 1 equipped B777s only had 2MB. Pretty much every FMC with the exception being those on the A380/B787/A350 is very low on memory and slow in processing power.

 

Boeing offers two customer options regarding FIX pages: 

2 FIX pages or 4 FIX pages.

 

With 2 pages the maximum fix range is 511nm. With the 4 page option it is 9999nm I believe. BA for example purchased 2 on their -200ER/-300ERs. Cathay and most other -200LR/-300ER operators chose 4. Simply depends on what they need and thus justify the extra cost when picking the countless customer options.

 

On the older AIMS 1 equipped -200/200ER/-300 aircraft, the 511nm limitation was hardware/software based.

 

As a very experienced SQ B777 TRE explains in more detail:

 

I certainly agree that one must juggle FIX pages, especially on the ULR's with multiple CTP/ETP's. However this is part of the action and helps with situation awareness on the loooong flights.

 

In any case there is no need to enter your destination alternate until you are approaching T/D and conduction you approach briefing. 

 

Personally I typically set the following on my FIX pages.

 

Departure: Departure ICAO/25nm (good for MSA situational awareness and SOP/encouraged at many operators), the engine out procedure (can also use RTE2 for this). Clear at 10,000 or above.

 

Cruise: FIX 1/4: ETOPS alternate 1 ICAO and associated range ring. FIX 2/4: ETOPS entry point, cleared for other use after passing overhead. FIX 3/4: (ETP1 scenario requiring the most fuel, 1EO and depress). clear when overhead. FIX 4/4: ETOPS alternate 2 ICAO and associated range ring.

 

In summary, for cruise: FIX 1/4 and 4/4 are the associated ETOPS alternates and their range rings, while FIX 2/3 and 3/4 are populated by ETOPS entry/exit points and ETP/CTP's. 

 

Before T/D during the descent planning, I typically set arrival airport ICAO and /10nm and or 25nm for situation awareness. 

 

Quick answer, the FMC programme is written in Octal 3 digit code (Incredible to believe that it's not Hexidecimal).

 

511 is 8 raised to the power of 3 minus 1, i.e. 8X8X8 = 512 - 1 = 511!

 

Now, if they'd only used the first three 'digits' of the four available in Hexidecimal, that would allow FFF, of which &H(FFF) = 4096 - 1 = 4095, a much better distances for fixes!thumbs.gif

 

The minus 1, of course, is because all counting begins at zero, not 1.

 

There's all sorts of number bases available, Octal, Decimal, Hexidecimal etc. In the FMC/LNAV programmes that I write, I use a base of 215, which allows for extremely large numbers to be "crunched" into a few digits of computer codethumbs.gif

 

Regards,

 

Old Smokey

 

Regarding the ETOPS 330 at ANZ. The distance for that time is significantly greater than 1652NM. Cathay plan 1506nm for ETOPS 207. 

 

I believe it is somewhere in the region of ~2400nm. Impressive.

 

 

 

 

 

 

  • Upvote 1

Share this post


Link to post
Share on other sites

The newer AIMS 2 equipped B777s (All -200LR/F-300ER) only have 12 MB of FMC navigation database storage capacity. Yes, you read that correctly, 12MB! The older AIMS 1 equipped B777s only had 2MB. Pretty much every FMC with the exception being those on the A380/B787/A350 is very low on memory and slow in processing power.

 

Boeing offers two customer options regarding FIX pages: 

2 FIX pages or 4 FIX pages.

 

With 2 pages the maximum fix range is 511nm. With the 4 page option it is 9999nm I believe. BA for example purchased 2 on their -200ER/-300ERs. Cathay and most other -200LR/-300ER operators chose 4. Simply depends on what they need and thus justify the extra cost when picking the countless customer options.

 

On the older AIMS 1 equipped -200/200ER/-300 aircraft, the 511nm limitation was hardware/software based.

 

As a very experienced SQ B777 TRE explains in more detail:

 

I certainly agree that one must juggle FIX pages, especially on the ULR's with multiple CTP/ETP's. However this is part of the action and helps with situation awareness on the loooong flights.

 

In any case there is no need to enter your destination alternate until you are approaching T/D and conduction you approach briefing. 

 

Personally I typically set the following on my FIX pages.

 

Departure: Departure ICAO/25nm (good for MSA situational awareness and SOP/encouraged at many operators), the engine out procedure (can also use RTE2 for this). Clear at 10,000 or above.

 

Cruise: FIX 1/4: ETOPS alternate 1 ICAO and associated range ring. FIX 2/4: ETOPS entry point, cleared for other use after passing overhead. FIX 3/4: (ETP1 scenario requiring the most fuel, 1EO and depress). clear when overhead. FIX 4/4: ETOPS alternate 2 ICAO and associated range ring.

 

In summary, for cruise: FIX 1/4 and 4/4 are the associated ETOPS alternates and their range rings, while FIX 2/3 and 3/4 are populated by ETOPS entry/exit points and ETP/CTP's. 

 

Before T/D during the descent planning, I typically set arrival airport ICAO and /10nm and or 25nm for situation awareness. 

 

Very interesting information. Hard to believe the 777 only has 12mb of memory and that the computers we all use are exponentially more powerful than the FMCs used to shuttle millions of people around the world. I suppose each is engineered to different failure standards, but 12mb does seem quite low. 

 

I'll try out your method of using the FIX page. I like the logic you use of assigning 1/4 to ICAOs and 2/3 to entry/exit/CRPs. I agree that actively swapping fixes over the length of a flight can help situation awareness. It does tend to make me pay more attention during the flight, and what segment I am on. 4 fixes in conjunction with RTE2 can do the job fine, but it would still be nice to see all the ETOPS data simultaneously on the map. And a larger zoom range to give more context to it.

 

 

Regarding the ETOPS 330 at ANZ. The distance for that time is significantly greater than 1652NM. Cathay plan 1506nm for ETOPS 207. 

I believe it is somewhere in the region of ~2400nm. Impressive.

 

I got my numbers switched around a little. PFPX actually has 1652nm as the range for ETOPS 240 and ETOPS 330 range in PFPX is 2328nm. Sorry for the mix up. I recently flew ANZ3 KLAX-NZAA and tried to squeak by with ETOPS 240 instead of 330, and had the numbers backwards in my head still. Anyway, that is truly impressive. One of the few planes that exist that can fly from anywhere in the world to anywhere else in the world.   

Share this post


Link to post
Share on other sites

Very interesting information. Hard to believe the 777 only has 12mb of memory and that the computers we all use are exponentially more powerful than the FMCs used to shuttle millions of people around the world. I suppose each is engineered to different failure standards, but 12mb does seem quite low. 

 

I'll try out your method of using the FIX page. I like the logic you use of assigning 1/4 to ICAOs and 2/3 to entry/exit/CRPs. I agree that actively swapping fixes over the length of a flight can help situation awareness. It does tend to make me pay more attention during the flight, and what segment I am on. 4 fixes in conjunction with RTE2 can do the job fine, but it would still be nice to see all the ETOPS data simultaneously on the map. And a larger zoom range to give more context to it.

 

 

 

I got my numbers switched around a little. PFPX actually has 1652nm as the range for ETOPS 240 and ETOPS 330 range in PFPX is 2328nm. Sorry for the mix up. I recently flew ANZ3 KLAX-NZAA and tried to squeak by with ETOPS 240 instead of 330, and had the numbers backwards in my head still. Anyway, that is truly impressive. One of the few planes that exist that can fly from anywhere in the world to anywhere else in the world.   

Truly impressive. ANZ's numbers for 240 and 330 are probably even slightly greater! 

 

Here is the max diversion time and distance table for the -300ER. As you can see, the lighter the aircraft becomes, the greater the maximum diversion distance becomes for a given time.

 

 

WEIGHT TIME(min)

(kg)       |   60   75   90 120   138    180   207   240  270   300   330

----------------------------------------------------------

360000 | 425 529 632 839   963  1252 1438 1665 1872 2079 2285

320000 | 439 545 652 865   993  1291 1483 1718 1931 2144 2357

280000 | 450 559 668 885 1016 1321 1517 1757 1974 2192 2410

240000 | 462 574 686 910 1044 1358 1559 1806 2030 2254 2478

200000 | 472 587 702 933 1071 1393 1600 1853 2083 2313 2543

160000 | 477 595 712 946 1086 1414 1625 1883 2117 2351 2585

 

 

Share this post


Link to post
Share on other sites

I like to put the ETPs and Entry/Exit points in the LEGS sequence, made easy by PFPX format report such points. For example ETP1 at 240 nm before ABCDE, simple create an along path point at ABCDE/-240.

 

I reserve two FIXES for the ETOPS diversions, updating as I move along. That gives me one to play with such as for example a preferred verses planned diversion point and still leaves one for "I need right now" use.

Share this post


Link to post
Share on other sites

Hi Dan,

 

I like to put the ETPs and Entry/Exit points in the LEGS sequence, made easy by PFPX format report such points. For example ETP1 at 240 nm before ABCDE, simple create an along path point at ABCDE/-240.

 

I'm lead to believe this practice (entering ETPs on the active route) is discouraged as it screws up the ADS-C position reporting (technically you're flying to a point which isn't on your cleared route and ATC get upset).

 

Fine to do it on RTE2 (and have that displayed behind), just not on the active.

 

Happy to be corrected by one of our real-world pilots though!

Share this post


Link to post
Share on other sites

I'm lead to believe this practice (entering ETPs on the active route) is discouraged as it screws up the ADS-C position reporting (technically you're flying to a point which isn't on your cleared route and ATC get upset).

 

Fine to do it on RTE2 (and have that displayed behind), just not on the active.

 

Happy to be corrected by one of our real-world pilots though!

 

Not a real world pilot who flies the NATs, but one of my tasks at the day job is to manage a database of issues across the NATs (and any other Oceanic area, honestly, but primarily the NATs) when people screw up.

 

Entering something in the LEGS page will cause issues on an ADS-C aircraft, as ADS-C will fire off a position report with the fake fix in there, which will throw all kinds of flags on the controller and CMA (central monitoring agency) side. This will also cause issues with me, as I will then be firing off an email to your company asking you to tell your pilots to knock it off  :P

 

Basically, the system is set up to monitor route compliance by looking at the position reports. Note that oceanic reporting is FIX, NEXT FIX, NEXT +1. This is compared to your cleared route (not simply filed - you'd be surprised at how many pilots screw that up and not update the filed to cleared when approaching the NATs), and if it doesn't match, the controller must query the pilot and check why things are out of sorts. Since being off route can mean potential conflict with another track (or the same track, depending), it's a very serious issue.

Share this post


Link to post
Share on other sites

Ah ah, well that is why I visit the forum. Learn something every day. To be fair, ADS-C is not simulated to much depth and I would not be aware of this until this post. Well, back to using FIXES then.

Share this post


Link to post
Share on other sites

Ah ah, well that is why I visit the forum. Learn something every day. To be fair, ADS-C is not simulated to much depth and I would not be aware of this until this post. Well, back to using FIXES then.

 

For what it's worth, I got lazy in the NGX in the Cross the Ditch event a few weeks ago and did exactly what you'd referenced earlier. Like you said, ADS-C isn't simulated, so it isn't a huge deal.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this