FMC offset route

[emerydc8]

Wow, that was fast. Thanks, Hardy! I'll still see what I can find in the United 767 sim next week. I have to make a stop at our HQ for about four hours next Monday and we have the 744 sims and FTD there. Maybe I can get one of the brain surgeons to check it.

[Markus Vitzethum]

Hi Hardy,

> Why should the FMC pull it from the nav database if the pilot refers to an existing route fix?

you're right ... this make no sense.

Besides, it does not make any difference anyway because the FMC works internally such that any given fix is only stored once in the database and any procedure or airway making use of it uses just a pointer to the waypoint, navaid, airport or runway database. (Just like any proper database would do. It's more efficient, too)

Markus

[Hardy Heinlin]

SID/STAR offset features are now implemented in PSX 10.39:

http://aerowinx.com/board/index.php?topic=4191.0


Regards,

|-|ardy

[emerydc8]

Just a follow-up on this, Hardy. I just tried the offset trick in the United 767 sim between KSFO and KLAX on the WESLA 3 Departure EBAYE transition to AVE, FIM and the SADDE 8 Arrival to LAX. I was able to get the offset to show at 6R in the RTE page by first going direct to PORTE on the SID. After that, going to the PLN page, as you can see in the picture below, it offset the SID and entire route but it stops abeam the first fix on the STAR into LAX (in this case FIM). Keep in mind that the picture below is the PLN page so you are looking at a north-oriented ND even though we were going south.

Also, out of curiosity, on climbing out on the SID, I put in /9000B at SUSEY and ran the MCP up to 10,000. The aircraft leveled off to obey the 9000' altitude restriction even though it was offset.

Also, the T/C doughnut appeared on the offset route, just as the T/D appeared on the offset T/D route on my previous video.
Jon

[Hardy Heinlin]

Thanks! So all is correctly modified in the latest PSX updates.


Cheers,

|-|ardy

[emerydc8]

Thank you!

[Hardy Heinlin]

I'll have to modify the descent path prediction calculation for offset routes. It currently uses the DTG to the true active waypoint as shown on the ND's upper right corner, and this DTG will never reach zero when flying an offset route. When passing the active waypoint on a 2 nm offset at the correct altitude constraint, the FMC thinks the DTG is 2 nm, concluding the aircraft is below the path (too early to hit the constraint). So the DTG should refer to the abeam point of the true active waypoint (while the ND indicates the DTG to the true active waypoint).

Does anybody know whether the DTG on the LEGS page for the active waypoint indicates zero when passing the active waypoint on an offset route? E.g. when the offset is 2 nm and the active waypoint will be sequenced in a second, will the first LEGS page line indicate 0 nm or 2 nm? The ND will indicate 2 nm.


|-|ardy

[emerydc8]

Hi Hardy,
I think the LEGs page is displaying the distance to the offset waypoint so it should say 0 (or very close to it) when it crosses over and switches to the next waypoint, just like the ABEAM PTS feature displays when you are perpendicular to the waypoint; otherwise, on a routine crossing, all the ETAs on the LEGs and PROG pages would be slightly off if you offset right by say 2 miles. I can check it out in the airplane, but unfortunately it will be a few weeks (still recovering from Continuing Qualification). I'd bet Peter knows the answer to this one.

Jon

[emerydc8]

Just a follow-up on this from the real plane. On a trip I just did from KATL to KCVG, we were on the PADGT2 Departure SMTTH transition, direct DOLLI then the JAKIE4 Arrival to CVG. DOLLI is the first fix on the JAKIE4 to CVG. While on the SID, heading to SMTTH the offset was not available on the RTE page until I down-selected SMTTH and installed it in 1L. This allowed the offset to appear on the RTE page (see pic). I offset 15 miles right of course to see where the offset stopped. As I expected, it stopped at the first fix on the arrival (DOLLI). So, the "trick" previously discussed to get an offset on the SID will offset the current SID and enroute portion (the leg from SMTTH to DOLLI, connecting the SID to the STAR), but it will not offset the STAR.

[Hardy Heinlin]

Very nice. Thank you for the confirmation.


|-|ardy


P.S.: Another question here: http://aerowinx.com/board/index.php?topic=4847.msg51694#msg51694

[emerydc8]

I just talked to a friend of mine in HKG who flies the G650. We talked about the Chinese ATC apparent obsession with offsetting on SIDs and STARs. He did some digging and found out the reason -- They are using ancient radar screens and if the flights are close enough together they can't see the identifier strip info for each flight. I would have never thought that. He's going to see if the offset feature discussed above will work on his modern FMS since it's also a Honeywell. We'll see.

[Jeroen Hoppenbrouwers]

Oof... not being able to move the data block around is a major pain. I've been playing ATC games for 30 years now and without that feature, you are indeed lost very quickly.

Kudos to Chinese ATC for putting up.


/-/

[JohnH]

I was doing a flight today from EGLL to CYYZ. I created the flight plan using Simbrief, all seemed to go well however on the departure I went to use RTE offset but 6R did not say 'offset' it was just blank. I read in a previous post from Hardy that offset was enabled in sid/stars. Am I doing something wrong, I am using 10.68.

Thanks John

[Hardy Heinlin]

The offset is only available when no conditional waypoints are included in your SID.

Conditional waypoints are waypoints whose location may drift depending on current aircraft position, altitude, performance, wind etc. -- When the active waypoint is a conditional waypoint, the top right corner of the ND will display dashes "-----" instead of a waypoint identifier.


|-|ardy

[emerydc8]

I haven't tried the conditional waypoint on a SID so I can't confirm this in the real plane; But another thing I noticed this morning coming into SFO is that if you are not on a STAR yet, but you are given direct to the first waypoint on a STAR, you still can't offset the course until one of the waypoints on the STAR has cycled through.

In other words, on the DYAMD 5 Arrival we were cleared direct to INYOE and I tried to offset, but the option wasn't available on the RTE page. Once INYOE sequenced through (we passed over it), and DYAMD was the TO waypoint, I was able to get the offset feature if I brought DYAMD down to the scratchpad and brought it up to 1L and executed.

[emerydc8]

The offset is only available when no conditional waypoints are included in your SID.

Just checked this a few hours ago out of SFO RW01R on the SSTIK 4 Departure. There is a conditional waypoint at 520A right off the end of the runway. That is the first waypoint in 1L. There is no way to downselect it, so no way to get the RTE OFFSET to appear. I suspect that once passing the conditional waypoint you could get it to offset, but I didn't have time to try it.
Jon

[turbodiddley]

I have flown out of CGO three times this week, and all times asked to offset while on the SID.

Proceeding direct to the active waypoint (Legs page, LSK1L, LSK1L, EXEC) did not give an offset cue on the Route page.

Only by line selecting all remaining points on the SID (there were three remaining) were we able to see an offset cue.

We did this by:  (Legs Page, LSK1L, LSK1L, LSK2L, LSK2L, LSK3L, LSK3L, EXEC).
At this point, the SID did not appear an the left side of the Route page at all. Only Direct for all remaining points.

Eventually we did this prior to departure, to avoid having to fiddle with it while airborne.

Funny, the aircraft behind us told Zhengzhou Departure they "Could not offset departure route due to aircraft limitations." To which, the controller replied, "Then offset the course manually." 

[Hardy Heinlin]

Replacing a VIA identifier (airway, procedure etc.) with a DIRECT on the RTE page by pushing the related left LSK on the LEGS page twice, -- is this a general feature in all FMC versions? (I mean the other LSKs beyond #1.)

Re offset on SID: I think this is FMC version specific; older versions probably deny it for all procedure legs (be it a conditional waypoint or not), and newer ones may only deny it for conditional waypoints.

[turbodiddley]

Hardy,

I had not known of the ability to modify the Via column of the Route page through manipulation of the Legs page, except for the top (Active) waypoint, until this week. You know, proceed direct to a waypoint by dropping it on top of LSK1L, then execute, and the Via on the Route page becomes Direct. In the plane, this works for all subsequent waypoints on the legs page. When the waypoints are selected into the SP and dropped back on themselves, the associated Via on the route page is replaced by a Direct. It is as if you manually loaded the waypoints by sequentially loading them on the Route page, but with the advantage of retaining the speeds and altitudes associated with points from the SID.

I have not read of this technique in the system manual or Honeywell manual.

Thus, with no associated SID routing in the via column associated with the points, the box allows a route offset. Pretty slick!

[Hardy Heinlin]

Thank you. I will implement this effect in the next update PSX 10.80.


|-|ardy