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  • #61
    Originally posted by Peter Kesternich View Post
    Gabriel - check out the thread on "Reclearance in flight". Most of your questions are covered there, especially the question about the 10%.
    I did and I don't find them covered. MCM says the plane always has enough fuel to reach a "suitable airport" including the 10%.

    As I've said, as far as I know the regulations and the flight plan don't know or care about "suitable airports" other than those intended for landing in the flight plan (the destination and the alternate, and eventually an optional fuel stop and its alternate). I guess that to consider all airports within reach from the route as "suitable" one should check the status of all and every airport, NOTAMs, weather, etc to verify that they are actually "suitable", and define a "suitbale" alternate for each of them (as it's done for the optional fuel stop).

    The regs don't know if you are fileing from Buenos Aires to Awkland with Sydney as alternate (where you don't have any "suitable" airports for most of the route) or London to SFO with San Jose as alternate where you would have potentially "suitable" airports every few NM for the last 1/2 of the trip.

    And as I've said, my questions are not related to the safety due to the plane eventually running oput of fuel, but about how do those flight plans meet the regulations and about the logic behind a flight plan that would PRETTY LIKELY (not just once every 100 flights) end with a fuel stop.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

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    • #62
      G'day Gabriel.

      You have to be careful about what assumptions you make for foreign operators. Regulations around the world vary wildly.

      For example, my airline does not require you to carry 10% of the flight fuel as a variable reserve. Why? Because it would not be practical to do so on a lot of the flights we do. Instead, you must, at all points during the flight, have flight fuel, plus fixed reserve, plus 10% variable reserve to a suitable airport. Yes, that involves checking the notams for certain key airports along the route, and monitoring the weather there... but its easy to see how it only becomes critical towards the end of the flight (as early in the flight you have large amounts of fuel). While we don't carry the full 10%, we do always carry a certain amount to protect us against having large numbers of diversions.

      I do not know Air France's fuel policy... but it is possible, as a longhaul carrier, that they operate under a similar philosophy. The concept of RIF as some apply it effectively achieves the same thing, allowing you to depart with a reduced variable reserve, but realising you may then have to stop for gas.

      You can see here that it is not a safety issue at all, it is purely an economic one for the beancounters.

      Also I wouldn't read too much into the fact that a 'RIF' plan was filed, as opposed to direct. The flight plan is lodged with ATC hours in advance, and sent to all the stations. The fact it is RIF means absolutely nothing to them, and doesn't change how they fly the aircraft. It is entirely possible that it was lodged that way because they thought it was going to be required, then at the last minute when the final loading was lower and it was now possible to go direct, they didn't re-lodge their flight plan... and I can't see any reason why they would, or and requirement for them to do so.

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      • #63
        Originally posted by MCM View Post
        \While we don't carry the full 10%, we do always carry a certain amount to protect us against having large numbers of diversions.

        I do not know Air France's fuel policy... but it is possible, as a longhaul carrier, that they operate under a similar philosophy.
        When you say that your airline allows you to go with less than 10% variable reserve, do you mean 2.5% instead, or 0.7% with the RIF plan? That apparently is Air France policy.

        Originally posted by MCM
        The concept of RIF as some apply it effectively achieves the same thing, allowing you to depart with a reduced variable reserve, but realising you may then have to stop for gas.
        The key difference is economics, specifically the cost of fuel reserves when you have to use them. If they are loaded on the aircraft in adequate quantity, then they cost the airline exactly the price of jet fuel that day, plus the cost of lost payload revenue. When the RIF is used, the cost also includes the cost of landing, servicing the aircraft, climbing back out and probably compensating the passengers. I'd like to see a chart comparing the cost differential there.

        Obviously, the added cost of RIF fuel is offset by the low frequency of fuel stopovers vs. the cost to carry larger reserves, otherwise they wouldn't do this. To make this work, the frequency of fuel stopovers must be kept to a bare minimum. What I want to know is how do they keep that frequency so low even with such spare reserves, and if there is a threat to safety hidden therein.

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        • #64
          When you say that your airline allows you to go with less than 10% variable reserve, do you mean 2.5% instead, or 0.7% with the RIF plan? That apparently is Air France policy.
          For us it is a fixed amount, not a percentage. It is there to ensure some level of commercial assurity (as the safety aspect has already been accounted for).

          Sometimes, however, I have departed being 95% sure we would be doing a technical stop unless something changed at destination. Its part of flying longhaul aeroplanes. I can understand why the concept is foreign to someone used to domestic ops... but the costs associated with carrying unnecessary fuel are extreme long haul, and so the odd diversion is really not expensive in the big scheme of things.

          I'm also not prepared to accept something thats been published for one flight that wasn't even flown as an indication of the Air France fuel/commercial policy. Remember, it WASN'T flown. Maybe thats because when they ran the plan, it didn't give enough commercial assurity and was rejected.

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          • #65
            Originally posted by MCM View Post
            For us it is a fixed amount, not a percentage. It is there to ensure some level of commercial assurity (as the safety aspect has already been accounted for).

            Sometimes, however, I have departed being 95% sure we would be doing a technical stop unless something changed at destination. Its part of flying longhaul aeroplanes. I can understand why the concept is foreign to someone used to domestic ops... but the costs associated with carrying unnecessary fuel are extreme long haul, and so the odd diversion is really not expensive in the big scheme of things.

            I'm also not prepared to accept something thats been published for one flight that wasn't even flown as an indication of the Air France fuel/commercial policy. Remember, it WASN'T flown. Maybe thats because when they ran the plan, it didn't give enough commercial assurity and was rejected.
            Ok, as flown the reserve was less than 4%, which is a far cry from 10%. Is this in range with what you are loading?

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            • #66
              BTW - What exactly do you mean by 'commercial assurity'?

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              • #67
                I'm still not convinced: AF 447 looked willing to depart in a 9 hours flight across the Atlantic Ocean and across some serious weather with 10 minutes of route reserve if the expected payload had shown. The chances to need the fuel stop to prevent landing at CDG wiht less than the alternate plus 30 minutes fuel (or to go for CDG and land with less than that) would have looked pretty real. Out of 100, how many 9 hours flight across known serius weather land 10 minutes or more past the ETA estimated at take-off? Lacking data, let me gues it at about 50%.

                I aknowledge that:
                - They always had enough fuel to reach a suitable airport (inlcuding the 10%).
                - That was not how the flight was finally flown like. Some payload didn't show, they used the now available useful load for fuel, and they had 20 minutes of route reserve. It is possible (but for some irrational reason I doubt it) that had the expected payload shown the PIC would have said "Sorry, no. Ground some boxes and put more fuel".
                - There is absolutelly no evidence that I know off that AF put the pilots under any mission oriented pressure that would bias a decision towards acomplishing the mision at the cost of safety. And rationally I very much that a company like Air France would have anything but a world class safety culture. But, while I try not to, irrationally I can't help but have some doubts. Questions like "why didn't the pilots go-arround at the Canada landing accident" or "why it looks like they were willing to depart with only 10 minutes of route reserve, or maybe even as low as 3 minutes" flash in my head.

                However, since there is absolutelly no evidence that this accident had anything to do with all this, and evidence or not I think it didn't, I will stop here, at least by now.

                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                --- Defend what you say with arguments, not by imposing your credentials ---

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                • #68
                  Ok, as flown the reserve was less than 4%, which is a far cry from 10%. Is this in range with what you are loading?
                  It depends on the day, the flight, and the aircraft type, but 2.5% is closer to the mark. Its enough, because its a lot of fuel. We're not talking 2.5% of 30t, we're talking 2.5% of 150+ t. If we were departing with 80t, then we'd have the same amount of fuel, so probably then closer to 5% and so on.

                  Commercial assurity is probably a bad effort at trying to explain what I mean. Basically I'm talking about a commercial approach at making destination. For example, commercially, it is probably important you don't divert one in every X number of flights... which is not related to safety, if you get my drift. Destination integrity might be a better way of putting it.

                  Out of 100, how many 9 hours flight across known serius weather land 10 minutes or more past the ETA estimated at take-off? Lacking data, let me gues it at about 50%.
                  Don't forget, Gabriel, that by arriving 10 minues late they might actually be landing with MORE fuel. It is a common technique available to crew to save some fuel at the expense of schedule.

                  Just because you land later doesn't for a minute mean that you're using more fuel.

                  I also am very hesitant to say WHAT they were willing to depart with. Just because some planner produced a plan with minimum legal fuel doesn't mean the crew would ever accept it... and you don't know the conversations that were going on in the dispatch room as to how to launch the flight.

                  There are massive assumptions being made on far insufficient information.

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                  • #69
                    Originally posted by MCM View Post
                    Don't forget, Gabriel, that by arriving 10 minues late they might actually be landing with MORE fuel. It is a common technique available to crew to save some fuel at the expense of schedule.
                    That's true and I hadn't think of this.

                    In fact, the third flight plan presented by the dispatcher (which was then "trashed") to the crew was one where thy would be flying M.01 slower (from M.82 to M.81) and that was enough to make it a non-stop flight (no RIF), take all the expected payload, and the TOW was still below the MTOW (what means that there was still "room" to add even more fuel).

                    I also am very hesitant to say WHAT they were willing to depart with. Just because some planner produced a plan with minimum legal fuel doesn't mean the crew would ever accept it... and you don't know the conversations that were going on in the dispatch room as to how to launch the flight.

                    There are massive assumptions being made on far insufficient information.
                    I agree and that's why I've aknowledged that those "feelings" I have are not rational, and why I've said what I've said in the last line of my post (and now I have just violated it )

                    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                    --- Defend what you say with arguments, not by imposing your credentials ---

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                    • #70
                      Originally posted by MCM View Post
                      Don't forget, Gabriel, that by arriving 10 minues late they might actually be landing with MORE fuel. It is a common technique available to crew to save some fuel at the expense of schedule.
                      That, in turn should depend on why you are arriving late... if it is due to going a longer way, or because of flying more slowly.

                      May I repeat my question on weather radars (even if weather might be a secondary factor only, if any - but certainly the fuel issue could be a factor only if weather was one, too): Are there any known limitations to these systems? Does the effective range vary when crossing an area of actual precipitation? How "thick" must a red area be, before the radar cannot look through anymore? Are there actual calculations from the satellite maps as to what the on-board radar might actually have shown? Say, before entering the minor storm system over SALPU?

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                      • #71
                        Originally posted by mfeldt View Post
                        That, in turn should depend on why you are arriving late... if it is due to going a longer way, or because of flying more slowly.
                        Originally posted by Gabriel View Post
                        Out of 100, how many 9 hours flight across known serius weather land 10 minutes or more past the ETA estimated at take-off? Lacking data, let me gues it at about 50%.
                        And don't forget: the most common reason for a flight being late ist still congestion at the departure airport and having to wait in line before you can take off.
                        Last edited by Peter Kesternich; 2010-03-15, 14:42.

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                        • #72
                          Originally posted by Peter Kesternich View Post
                          And don't forget: the most common reason for a flight being late ist still congestion at the departure airport and having to wait in line before you can take off.
                          Which still consumes fuel (maybe more than the last segments of cruise flight when the FL is high and the wight is low). And if that waiting was more than planned, that additional fuel must come from the fuel that was planed as route reserve.

                          But I've said "10 minutes or more past the ETA estimated at take-off".

                          Recently in a flight from Munich to Atlanta, shortly after take off (when the seat belt signs were turned off) the captain went PA and said "we estimate that will be arriving some 20 minutes earlier than schdulled". We ended up arriving 20 minutes late. This is the type of "error" that I said 10 minutes or more (to either side) seems to happen more often than not.

                          --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                          --- Defend what you say with arguments, not by imposing your credentials ---

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                          • #73
                            Originally posted by Gabriel View Post
                            Which still consumes fuel (maybe more than the last segments of cruise flight when the FL is high and the wight is low). And if that waiting was more than planned, that additional fuel must come from the fuel that was planed as route reserve.
                            Nah - fuel use on the ground is small compared to what is used in flight on a longhaul trip. During prolonged taxi half the engines can be cut off to save fuel as well so that the taxi fuel wouldn't eat into the trip fuel that much.

                            Originally posted by Gabriel View Post
                            But I've said "10 minutes or more past the ETA estimated at take-off".

                            Recently in a flight from Munich to Atlanta, shortly after take off (when the seat belt signs were turned off) the captain went PA and said "we estimate that will be arriving some 20 minutes earlier than schdulled". We ended up arriving 20 minutes late. This is the type of "error" that I said 10 minutes or more (to either side) seems to happen more often than not.
                            Bear in mind, Gabriel, that pilots use the time from takeoff to landing when they talk about flight time, whereas the flight times published in airline schedules are from "chocks away" to "chocks under".

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                            • #74
                              I am really confused!
                              I do work for a domestic US airline, and it should be noted that I do not represent such airline, or any airline. My opinions are mine alone, and aren't reflective of anything but my own knowledge, or what I am trying to learn. At no time will I discuss my specific airline, internal policies, or any such info.

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                              • #75
                                Originally posted by Myndee View Post
                                I am really confused!
                                Why is that?

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