Originally Posted by Gabriel
I will present this "exhibit" that I prepared with no other comment by now but that something looks odd.
(Sorry for the crappy quality. I prepared a pdf that barely weights 1/5 of this jpg and has much better quality, but the forum would only accept 19 KB of pdf while several MB of jpg. If someone wants the pdf please PM your e-mail)
I'll come back to this now. There are a lot of things that I don't understand or that I am not sure about, so please help me with this. If there is a flight dispatcher, his/her input would be very much appreciated. Pro pilot too, please.
1- To begin with, and as I've said before, as far as I know the regulations regarding fuel requirements don't know or care about whether there are other suitable airports along the route. They just mention the destination and the alternate. That's at least for non-stop (not RIF) flights.
2- This flight from Rio to Paris was how much, 9 hours? So 10% of that would be 0.9 hours, or 54 minutes. 10% of the trip fuel is what the FARs require for route reserves. I know that this plane was not flying under the FAR, but I'd expect other regulations to be similar.
3- The FAR requires fuel for the trip (taking into account the weather forecast along the route) plus a 10% (route reserves), plus enough fuel to miss the approach at the destination and fly to the alternate, plus 30 min at holding speed at 1500ft.
4- In general (that is, when an alternate is required), you are supposed to land at your destination still with the fuel to fly to the alternate plus the 30 minutes, so if you have to go around at the last minute you still have enough juice to fly to the alternate and land there with the 30 min reserve.
5- In this way, the fuel you have when you start the take-off minus the fuel the you plan for the trip minus the fuel to fly to the alternate minus the 30 min reserve that you shouldn't use except in an emergency is the fuel you plan as available for "normal" contingencies along the flight, such as headwinds that are stronger than forecast (or tailwind that are lighter), additional flying around weather, increased fuel consumption due to ATC not clearing you as high as filed, etc... This amount of fuel should be at least the required route reserve (10% of the trip fuel), but the plane can also have "extra fuel" in excess of that.
6- In a RIF (re-clearance in flight) flight plan, you take-off with all the trip fuel, the fuel to the alternate, and the 30 minutes that's required, but less than the required route reserves. However, you file an optional fuel stop at an alternative destination (together with its own alternate airport) where you have all the required fuel, including all the required route reserves. At some point during the flight, if you have not used the route reserves you can legally decide to skip the optional fuel stop and go for the intended destination, because the untouched route reserves that were then not enough for the direct flight are enough now that the remaining flight is much shorter (are, say, 10% what remains of the flight).
Now let's move to the jpg:
For this flight, the dispatcher expected a given payload that didn't leave enough "room" (i.e. useful load) for enough fuel for a non-stop flight plan to Paris.
They presented to the pilots two options (there was a third one but not shown here): They either take less payload than the expected one (leaving off the plane passengers or luggage or cargo if necessary) and added just enough fuel or they used a RIF flight plan with an optional (and hopefully avoidable) fuel stop at Bordeaux.
The RIF plan had fuel reduced enough that it allowed a payload of even more than what they expected for this flight.
Finally the RIF plan was filed, but for some reason the plane took even less payload than what would have been required to enable the non-stop flight, and then the useful load was maxed adding as much fuel as would fit. This means that the flight, while flying under a RIF flight plan, depart with more fuel than required for a non-stop flight where the optional fuel stop would not be considered.
The charts have 4 columns.
The first column, Plan 1 (RIF) is the "second option" mentioned above, and is the plan that was finally filed.
The second column, "Expected", show the conditions (especially the amount of fuel) had the payload been the expected one.
The third column, Plan 2 (DTC), is the other option presented by the dispatcher (and then discarded) and corresponds to the max payload and min fuel that would make it legal to file a non-stop flight.
And the fourth column shows the actual condition of the flight, with a payload that is even less than expected and a fuel that is even more that required of the non-stop flight plan (but remember, they still filed the RIF plan).
Now let's focus on the bottom-right chart, that shows the amount of fuel in excess of what was required that the plane would have had when landing at CDG had it used exactly the trip fuel as planned. That fuel is the reserve that was available for, as said, stronger headwinds, weather detours, etc. that might make the actual fuel used for the trip greater than the planned trip fuel. This fuel includes the required route reserve and any extra fuel that the plane might be taking beyond what's required.
The plane had 20 minutes of fuel. That is that the flight, at the same fuel burn, could have lasted 20 minutes more than planned and still made it to CDG with the required fuel in the tanks when landing there.
20 minutes is under no way 10% of the trip, but I'm Ok with that in the sense that, after all, they were in a RIF flight with an optional stopover in Bordeaux which is about 30 minutes short of Paris, so they had some 50 minutes of fuel over what was required to fly from Rio to Bordeaux, and that's probably about 10%.
HOWEVER: (and now the odd part starts)
Since the plane had essentially the same take-off weight than the Plan 2 (DTC), but less payload and more fuel, that 20 minutes reserve would have been good to go even in non-stop (not RIF) flight plan. Now 20 minutes is NOT EVEN ONE HALF of 10%.
Not only that, but the proposed non-stop flight (Plan 2) was legal to go non-stop with ONLY 12 MINUTES OF ROUTE RESERVE FUEL.
And not only that, but had they have the expected payload, they would have had just 10 minutes of route reserves over Paris, and the RIF plan (Plan 1) still was good to go with only 3 minutes of reserve over CGD.
Now, I'm not judging the safety aspect of this given that they had suitable places to land short of Paris, (basically anywhere from Casablanca to Bordeaux and then some).
But what I don't understand is:
- How this DTC flight plan matched the fuel regulations.
- The "economical soundness" of choosing a strategy that would leave only 10 minutes of reserve. I don't know what's the distribution of actual fuel vs planned, but based in my limited passenger experience I'd say that a 9 hours flight arriving at its destination 10 minutes or more sooner or later than expected at take-off happens more often than not, so they were seriously risking an expensive fuel stop, probably much more expensive than leaving a couple of tons of payload off the plane. (or, they were willing to land at CDG with less than the required alternate plus 30 minutes fuel and not tell anyone? Now that WOULD be a very serious safety breech). I'm not insinuating that that was the case, and I wouldn't expect that from Air France.
But as said, things looks odd at least. And probably that' because there's something flawed in my logic or my understanding, in which case help is very much appreciated.