Fuel Planning Terminology

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Fuel Planning Terminology

Author	Message
lhe	lhe posted 7/25/2024 12:45:16 PM Post Details Share Post
Group: Forum Members Posts: 154, Visits: 445	+x Tim Dawson - 7/25/2024 9:02:53 AM We're implementing a Final Reserve fuel line in our next version, which I am pretty sure will be specified in minutes. In addition, it will be possible to reduce the existing (and somewhat anachronistic) Holding Time value down to zero. That sounds great! Do note that according to part-NCO, the Final Reserve Fuel should be computed using the holding speed fuel flow. (Except for the unlikely special case where you are taking off and landing at the same airport, having it in sight during the whole flight, in which case you can use 10 minutes of fuel at the maximum continuous power fuel flow.)
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grahamb	grahamb posted 7/25/2024 1:38:33 PM Post Details Share Post
Group: Forum Members Posts: 565, Visits: 27K	+x lhe - 7/25/2024 12:45:16 PM +x Tim Dawson - 7/25/2024 9:02:53 AM We're implementing a Final Reserve fuel line in our next version, which I am pretty sure will be specified in minutes. In addition, it will be possible to reduce the existing (and somewhat anachronistic) Holding Time value down to zero. That sounds great! Do note that according to part-NCO, the Final Reserve Fuel should be computed using the holding speed fuel flow. (Except for the unlikely special case where you are taking off and landing at the same airport, having it in sight during the whole flight, in which case you can use 10 minutes of fuel at the maximum continuous power fuel flow.) Whereas the UK Part NCO regs state that FR fuel should be calculated based on ‘fly for at least 10/30/45 minutes at normal cruising altitude’
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lhe	lhe posted 7/25/2024 1:45:23 PM Post Details Share Post
Group: Forum Members Posts: 154, Visits: 445	+x grahamb - 7/25/2024 1:38:33 PM Whereas the UK Part NCO regs state that FR fuel should be calculated based on ‘fly for at least 10/30/45 minutes at normal cruising altitude’ Do you mean cruising altitude or cruising power? There is no single normal cruising altitude for the kind of aircraft typically used with SD. On the other hand, unless you have a turbine engine, the altitude would have very little (if any) effect on the holding fuel flow.
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grahamb	grahamb posted 7/25/2024 2:50:46 PM Post Details Share Post
Group: Forum Members Posts: 565, Visits: 27K	+x lhe - 7/25/2024 1:45:23 PM +x grahamb - 7/25/2024 1:38:33 PM Whereas the UK Part NCO regs state that FR fuel should be calculated based on ‘fly for at least 10/30/45 minutes at normal cruising altitude’ Do you mean cruising altitude or cruising power? There is no single normal cruising altitude for the kind of aircraft typically used with SD. On the other hand, unless you have a turbine engine, the altitude would have very little (if any) effect on the holding fuel flow. I've quoted the regs exactly as they are. Ask our CAA what they mean! The difficulty with this sort of thing is that there are many scenarios which might drive a pilot to encroach into emergency fuel, so it's best to just use a sensible figure. Arrive back at airport and find runway obstructed temporarily* - fly at a speed for maximum endurance while you orbit overhead. Arrive back at airport to find that a glider has just had a fatal crash on the threshold* - fly at best range speed to an alternate (or a good field if that's your only option). Final Reserve fuel will last longer in the former scenarion that the latter. Tim is taking a good step forward with SD by making this change, and it would be impossibly complex to try and accommodate every subtle nuance, expecially with regulations that diverge. I don't envy his job trying to keep everyone happy (and I don't envy the Regulators trying to come up with something realistic without it being over complex). *BTW, both of these scenarios have happened to me, but I invariably carry significantly more fuel than I need, and certainly more than the regulations require, so encroaching Final Reserve wasn't a consideration on either occasion.
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F70100	F F70100 posted 7/25/2024 4:11:42 PM Post Details Share Post
F Group: Forum Members Posts: 5, Visits: 7	+x grahamb - 7/25/2024 2:50:46 PM +x lhe - 7/25/2024 1:45:23 PM +x grahamb - 7/25/2024 1:38:33 PM Whereas the UK Part NCO regs state that FR fuel should be calculated based on ‘fly for at least 10/30/45 minutes at normal cruising altitude’ Do you mean cruising altitude or cruising power? There is no single normal cruising altitude for the kind of aircraft typically used with SD. On the other hand, unless you have a turbine engine, the altitude would have very little (if any) effect on the holding fuel flow. I've quoted the regs exactly as they are. Ask our CAA what they mean! The difficulty with this sort of thing is that there are many scenarios which might drive a pilot to encroach into emergency fuel, so it's best to just use a sensible figure. Arrive back at airport and find runway obstructed temporarily* - fly at a speed for maximum endurance while you orbit overhead. Arrive back at airport to find that a glider has just had a fatal crash on the threshold* - fly at best range speed to an alternate (or a good field if that's your only option). Final Reserve fuel will last longer in the former scenarion that the latter. Tim is taking a good step forward with SD by making this change, and it would be impossibly complex to try and accommodate every subtle nuance, expecially with regulations that diverge. I don't envy his job trying to keep everyone happy (and I don't envy the Regulators trying to come up with something realistic without it being over complex). *BTW, both of these scenarios have happened to me, but I invariably carry significantly more fuel than I need, and certainly more than the regulations require, so encroaching Final Reserve wasn't a consideration on either occasion. Both those scenarios make the case for separate fuel allocations: Want to wait for a runway which is temporarily obstructed to be cleared? Use Holding Fuel. Find that your planned destination is going to be closed for some time? Use Alternate Fuel. Of course, Non Commercial Ops don't require Holding Fuel or Alternate Fuel but if you want to cover the risk that these scenarios present, fuel for that should be extra to Minimum Fuel Reserves. I fully accept that most of this is semantics. In the NCO world, people rarely operate on minimum fuel. The economies that commercial operators gain by doing so are not really relevant in the NCO world. I'm pleased though that Tim and the team are changing the fuel planning terminology in SkyDemon to reflect what Part 21 requires.
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Tim Dawson	Tim Dawson posted 7/29/2024 9:21:10 AM Post Details Share Post
Group: Forum Members Posts: 8K, Visits: 9K	The way we work out the fuel burn for the "holding time" part of the flight, and the new "final reserve" part is to look through all the power settings for the aircraft and find the one with the lowest fuel burn, and we assume that's the one you'll be using if waiting around. We multiply that by the number of minutes defined.
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lhe	lhe posted 7/30/2024 8:53:24 AM Post Details Share Post
Group: Forum Members Posts: 154, Visits: 445	+x F70100 - 7/25/2024 4:11:42 PM Of course, Non Commercial Ops don't require Holding Fuel or Alternate Fuel but if you want to cover the risk that these scenarios present, fuel for that should be extra to Minimum Fuel Reserves. Actually they do. The relevant parts of NCO.OP.125: The pilot-in-command shall ensure that the quantity of fuel/energy and oil that is carried on board is sufficient, taking into account [...] any delays that are expected in flight [...] And a non-commercial IFR flight generally needs an alternate.
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