POS REPORT logic

[Will]

Please help me understand some of the POS REPORT logic.

When you pass a waypoint, certain parameters are sent to the POS REPORT page, including:

LAST waypoint
ALT at the last waypoint
NEXT waypoint
ATA at the last waypoint

These are fixed.

The POS REPORT also includes:

TEMP
WIND
SPD
ETA
DEST ETA
FUEL

These are not fixed; they continue to update in real time.

To me this seems a little difficult. If you want to send a position report that includes your fuel AT THE LAST WAYPOINT, then you need to hit "SEND" immediately upon passing the waypoint. But this can be a bit awkward, as passing a waypoint might be a high-workload time. You might be recording your fuel remaining on your flight log, you might be looking at your ANP, you might be calculating your difference between expected time and actual time, expected fuel and actual fuel, etc.

It might be easier if all the data on the POS REPORT were fixed, as if all the data on the page were a snapshot in time. So for example, 5 minutes after you passed the waypoint, you could look at POS REPORT and see what your fuel on board, winds, etc. were, when you crossed the waypoint. If this were the case, then you could also refer to POS REPORT if you were a little bit late in observing the actual time you crossed the waypoint -- the crossing info would be stored for you. And you could hit "SEND" later, and your company could see if your fuel burn was on target.

As it is now, you (or your company) could figure out your fuel on board when you crossed the waypoint, but you'd have to get there by back-calculating, based on the rate of fuel burn and the difference between the time you hit "SEND" and the time you crossed the waypoint.

It seems Boeing missed an opportunity to save a few steps. Unless, of course, I'm missing something, which it all too often the case.

Thoughts?

[Hardy Heinlin]

As far as I understand this feature, the position report is a report that can be requested at any point along your route, not just exactly at the waypoint sequencing point. The LAST and NEXT waypoint name is just a way to indicate your current leg, I think. And the current fuel is just that: The current fuel, regardless of the last waypoint. The weather data is also the current one and not the one at the last waypoint.

[Mariano]

On all 767 FMC versions, the POS FUEL is static and reflects the fuel onboard at the last (fix) position, which is very useful when recording fuel scores in the OFP after everything else is done, and for Dispatch to keep track of fuel burn trends (and for all interested parties to be able to calculate endurance should search and rescue operations be needed).

I did notice a while back that in PSX the position fuel keeps changing as fuel is burned, although I assumed that this was a 767-to-747 difference, albeit a bit cumbersome.

Best regards,

Mariano

[Hardy Heinlin]

Interesting. It's probably the same on the 744 then. Is the weather data also static?

Maybe it was different on the legacy FMC where the last fuel was stored on the PROGRESS 1 page in line 1. That line 1 was removed in the NG FMC as it's now implemented on the POS REPORT page anyway. So it makes sense to make the fuel static indeed.


Edit: Is the SPD data in 2R static as well?

[Will]

Trying to think like a Boeing engineer, a flight crew member, and a dispatcher/ops guy all at the same time...

If all the data are static, then you have a snapshot of a moment in place and time. You can use that snapshot to see if the fuel burn is progressing as predicted, to see if the weather has been a factor, etc., and to comply with ATC position reporting requirements where they want the last waypoint, the next waypoint, etc.

If half the data are dynamic, then in order to get that performance functionality described above, you'd need to send the actual current position information as well. You'd also send the lat/long of the aircraft at the moment you pressed "SEND." Then you could back-calculate the fuel at the last waypoint, assuming you also sent or recorded the fuel burn. But this seems needlessly complicated.

(Or, as another option, you could only hit "SEND" within an arbitrarily short time after passing the waypoint, except that for the reasons I gave above, this may not be practical.)

It's much more straightforward to simply hold the performance and environmental data as static on the POS REPORT page, as Mariano says was the case with "fuel" in the 767. If I were designing the POS REPORT page, I'd probably have all the data recorded as static data for the purpose of routine position reports.

But what if you wanted to send a position report between waypoints? For that case (still thinking as a Boeing engineer, a flight crew member, and a dispatcher/ops guy all at the same time here), I'd have a new action, not called POS REPORT (because a "position report" is an ATC thing), but called "SEND PRESENT POSITION" that would send a snapshot of the current lat/long, current fuel on board, current winds, and whatnot. This would give the crew two options: (1) the POS REPORT page with static data, for the purpose of ATC reporting requirements and routine performance checks, with (2) a new "SEND PRESENT POSITION" functionality that you might use to let someone know where you were in an unusual situation, kind of like downloading an "Event Record" to the company.

But that's just thinking out loud, pure fantasy.

Back to reality: it would make sense to me that all the data on POS REPORT are static, a snapshot of what was going on when the aircraft passed over the most recent FMC waypoint.

[Britjet]

It's all in the FCOM, of course.
My understanding is..
Last waypoint, ATA, FOB and altitude are hard-coded. All the rest are current data, so if you wanted to also pass wind and temp at that point you would have to have recorded it some other way. Fortunately any datalink will have done that for you..

Peter.

[Mariano]

As stated above, atmospheric data is dynamic. Speed is also dynamic (target, no actual, of course) - (767).

Best regards,

Mariano

[DougSnow]

For us at work, our aircraft also send a report every 30 minutes in addition to the report at the fix, like NIPPI along R220. While the flight monitor in our flight planning system will use the fuel over NIPPI in the fuel score, the every 30 minutes report is just the FMCs way of saying "we're still here".  I can use all the fuel scores and and attempt to determine how my fuel trend is going - am I ahead on gas or behind on gas...

The position report downlinks automatically once the Fix has been overflown. Crews can also manually downlink a report at any point, I'll see the manually downlinked report, but its hard to correlate those manual reports, or the 30-minute AUTOPOS reports to a fix on the OFP, so our system doesn't try to. I can still use the AUTOPOS reports and attempt to eyeball the fuel trend, but I prefer to base my fuel score on the flight plan fix locations.

If a crew takes a direct, as long as they build the direct with Abeam Waypoints (which is the FOM-required procedure), our flight monitor works as advertised. if they don't, I lose all those position reports (and the ability to compare the fuel), and truly monitor the progress of the flight.

[Hardy Heinlin]

The fuel display is now last waypoint fuel -- in PSX 10.150: https://aerowinx.com/board/index.php?topic=4191.0


|-|ardy