Calculation of TOC and TOD

SimBrief Dispatch
1

Hi everyone

I have a query about how Dispatch calculates TOCs and TODs. I have created a very simple flight from LGIK to LGPL, which is just 67NM. The only thing that I have specified is that I will be flying a Beechcraft Baron B58, which when selected in Dispatch auto-populates the associated climb profile and descent profile, shown as follows:

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I also take care to not set any altitudes, leaving this as ‘AUTO’. Dispatch then identifies the route as being direct to AKINA waypoint, and then from there direct to LGPL. I then save the flight plan and ask Dispatch to generate the flight, which it duly does. However, when I look in the flight log, I see the following:

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Initially it looks good that for this short journey Dispatch has identified a cruise altitude of 3500ft. However, where I am puzzled is where Dispatch is defining the TOC and TOD as follows, at least by my reading of the flight log, which I am assuming and hoping I have got right:

  • TOC is listed as 23NM after the departure airport LGIK. This seems rather far based even on the Dispatch climb profile for this aircraft of 139KTS, with the climb of little over 3000ft surely not requiring 23NM to perform.

  • TOD is listed as around 48NM before the arrival airport of LGPL (based on total distance between TOD, AKINA and LGPL), despite Dispatch having identified the descent profile for this aircraft as being 500FPM.

Furthermore, referring to the route map that Dispatch then produces as follows:

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  • The TOD is shown (highlighted in green) as accordant with the flight log (i. e. 1NM before AKINA).

  • The TOC is shown (highlighted in pink) as not being accordant with the flight log, which lists the TOC as being 23NM after the departure airport of LGIK, but yet on the map it is barely a few miles after that.

I have consulted the Dispatch help guide on how to read the flight log, and to my knowledge I am reading it correctly. If I am reading it correctly, would anybody have any ideas as to why the TOC and TOD calculations appear to not make sense, but also in the case of the TOC, not match with what is shown on the map. I had thought that perhaps winds may also influence this, and accordingly I provide as follows the wind information provided:

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Thanks for your help.

Regards

Jason

2

Hi Jason,

The discrepancy between the TOC on the map versus in the flight log is due to departure maneuvering. Basically, because you’re departing runway 33 (opposite your direction of flight), the system considers the distance required to depart opposite your route and then make a U-turn back towards the first waypoint. This is why it says it takes 23nm to reach the TOC, yet the TOC is only 2 nm from the airport (the maps don’t show the maneuvering segment).

The inflated TOC/TOD distances and times are a side-effect of SimBrief being tuned to airliners. Basically, it’s considering that it takes up to 10 nm to make a U-turn after takeoff. Likewise, it plans a 10 nm final at destination. For GA aircraft this is obviously too much.

In any case, I’ve improved the maneuvering additives for GA aircraft now. I think it should be a bit better in the future.

Best regards,

3

Thanks for looking into this issue, it’s much appreciated. What you have indicated makes sense and explains why I was struggling to understand this. Referring again to the map, indeed I can see what you mean by it not taking into the account the initial climb from runway 33 and then the U-turn back. As I recall when I flew this route as I passed back over the airport I had already climbed significantly, which in practice would accord with the TOC shown on the map. As an aside, I’m also relieved that I had read the flight log incorrectly and that my question was ultimately a valid one, and not symptomatic of a lack of understanding on my part. Thanks also for improving the additives for GA aircraft.

Regards

Jason