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Old 1st Jun 2006, 09:47   #1 (permalink)
 
Join Date: May 2006
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Contingency fuel...

When using the Jeppesen flt planning system to calculate max payload, fuel required for given payload etc. Why does the system assume that the 5% contingency fuel is burnt by the time you arrive. The fact is that this fuel is a buffer of extra fuel in case the situation arises where you might need it, but if this situation doesnt arise, then you arrive at your destination with it still in the tanks. If you are arriving at max landing weight, the reality is that you are arriving at your max landiing weight, plus the weight of the contingency fuel. In other words an overweight landing, which could be several tons over your max ldg wt. This is concurred when the loadmaster completes his loadsheet, where the maths don't lie. His loadsheet in this case will show an overweight landing...
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Old 1st Jun 2006, 13:11   #2 (permalink)
 
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Not sure if all flight planning systems do the same...ours isn't Jepp but it also assumes you will have burnt CONT fuel by the end of the trip.

Doing lots of short sectors we often come up against this problem but its easily solved at flight planning stage by working forward...

Simply add TRIP fuel figure to MLW and bingo you have a figure for MTOW. If you burn your CONT fuel then all is well. If you make fuel on the trip then you have to consider options for burning off fuel prior to landing but thats life.
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Old 1st Jun 2006, 15:11   #3 (permalink)
 
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Contingency fuel

I take your point, but you shouldn't have to look for ways to increase your fuel burn in order for the a/c to land within limits. In a lot of situations it is not practical to do, and it certainly is not professional from an aviation point of view. Also, in this situation, as the loadsheet speaks the truth, the Capt wont sign it as it shows an overweight landing. So the loadmaster then has to falsely increase the fuel burn in order to reduce the landing weight, to give the appearance on paper that the a/c is arriving within limits, but in reality it is still landing at the MLW plus the weight of the contingency fuel. Three things have happened here: 1. The a/c has been operated illegally, 2. The loadmaster has falsified an official aviation document. 3. The Capt has signed a falsified document.
If there was an accident and these issues came to light, where would the company stand from an insurance point of view ?
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Old 1st Jun 2006, 15:41   #4 (permalink)
 
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I might be missing something here, but wouldn't you just add the the contingency fuel to your max landing weight figure ( or any other method that suits ) and load fuel accordingly ? I appreciate that on any given day the loadsheet and the reality may well differ to some degree as it concerns the actual fuel burn. The former is obviously based on the planned situation. Clearly if the situation results in a fuel saving such that the max landing weight would be exceeded then that needs to be addressed to rectify the situation en-route.

1.The aircraft hasn't been operated illegally since the initial consideration would be the max take off weight. The fuel burn en-route can only be an estimate and can be modified as necessary to ensure the max landing weight is not exceeded when that landing actually takes place.

2.The loadmaster has falsified an official aviation document how ? The captain is responsible for signing the document and liasing with the dispatcher. If he decides it is acceptable to up the burn and likewise ensures the MLW will not be exceeded what is the problem ?

3. A bit of a nonstarter since the Captain is agreeing to an increased fuel burn the document is not "falsified". So unless this theoretical accident was as a result of actually landing overweight it would hardly seem relevant.

The main reasons for landing at MLW are because the sector length is relatively short or because of a desirabilty to tanker fuel. In the latter case there is little point in tankering to the limit if there is a reasonable chance of then having to burn off any fuel saved. A reduction to the tankered fuel would be sensible and justified in these circumstances. In the case of a MLW restriction that limits payload then that would only be an issue at the planning stage, since arriving with too much fuel would become apparant during the flight and the relevant action taken during the latter part of the cruise or descent.
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Old 1st Jun 2006, 17:22   #5 (permalink)
 
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Contingency fuel

Ok Bealzebub, here's the deal. I run a plan for say a 6 hour sector, requesting max payload to land at MLW. The system gives me my payload, say 70,000 kgs, and tells me my trip fuel, something like 62,000 kgs, of which contains the expendibles, i.e burn fuel and taxi fuel. What is left in the tanks after landing is the alternate fuel + 30 min hold fuel at alt , also the 5% contingency fuel, which typically would be around 2,500 - 3,500 kgs. The Jepp system calculates that this conting fuel is burnt, but as stated earlier it is not burnt. So we will land 3,000 kgs overweight. Even though the burn fuel is approximate, by increasing the burn on paper by 3,000 kgs is a falsification of a document, and is morally devious which ever way you look at it. If it wasnt an issue, why wont the Capt sign the loadsheet when it shows the a/c to be landing 3,000 kgs over the MLW? And, by the way we are still at the planning stage here, so this is avoidable if we offload frt to equal the weight of the conting fuel. Finally, having dicussed this with many Capt's, I can assure you that it is often almost impossible to burn off the extra fuel en route, also very impracticable. Are you going to request a lower fl to burn more fuel ? are you going to put your gear down with 100 miles to run ?, I dont think so. I know for a fact that there have been many, many overweight landings because of these circumstances..................
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Old 1st Jun 2006, 19:11   #6 (permalink)
 
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Ok so if I understand you correctly you are planning to land with minimum fuel ( diversion plus 5 % + 30 minutes holding ), however by not consuming the trip fuel 5% contingency element you will hopefully have an additional 2500-3000kg at the time of landing ? I am not familiar with the aircraft type or operation, but am guessing it is a large widebody airliner and possibly a cargo freight operation. From what you say it also would seem that the Max zero fuel weight is fairly close to the maximum landing weight ? This is on the assumption that a reasonably close diversion plus the holding and say 3000kg of excess arrival fuel moves you significantly from one limit to the other ? that does seem a little odd ? On the 757 the difference is 6500kg and on the 767 it is around 11,300kg and both of these are obviously smaller aircraft than your example. In these two examples the aircraft could arrive at a typical European destination with standard reserves plus 3000kg (757) and 7000kg (767-300) before the max landing weight was superceded by the max zero fuel weight limitation.

If indeed this is the case then it would seem there are a number of choices. Obviously you need to carry sufficient fuel to satisfy the planning requirement. This may be subject to adjustment to allow for actual weights and expected winds etc. Additionally it may transpire that the alternate airport on the plan can be substituted with a closer one. You could consider using an en-route alternate procedure which would reduce the fuel contingency fuel to 5% of the onward trip fuel from over or abeam the en-route alternate to the destination.

If (as you suggest) experience is proving that on certain trips the contingency fuel is not being used, then simple common sense would suggest reducing the payload to compensate for the fact. If this is commercially frowned upon then you are left with the choice of either seeking a flight level that is worse than optimum, increasing drag in the descent ( spoilers ), or holding at the destination until the maximum landing weight is achieved. Given that you may indeed need to use any of these methods it is quite appropriate and indeed necessary to include the additional fuel used in the trip fuel box of the loadsheet. Why this would be commercially beneficial I do not know, but it might be.

Contigency fuel is carried to allow for deviations from standard fuel consumption data for an individual aircraft, deviations for forecast met' conditions, and deviations from planned routings or cruising levels etc. This since not all the factors which might have an influence on the trip fuel consumed to the destination can be foreseen.

Again increasing the fuel burn on the paperwork is not a falsification of the paperwork since clearly you intend to do that and consequently need to do so to get down to your max landing weight. Neither can I see why it is morally devious ? I still maintain that the sensible thing is to reduce the payload and I am sure many airports would be less than impressed if you flight plan to have take up a hold to burn off excess fuel, however if that is the only option you feel is open to you then that is what you would have to do.

You say that there have been many overweight landings because Captains have found it impractical to increase the burn to arrive at the maximum landing weight. Then that presumably is their choice. There are circumstances when it may be unavoidable to make overweight landings and that would no doubt be reported as appropriate, however the responsibility for the safety of the flight lies with the crew and ultimately with the captain, and it is they who should consider all the known and likely factors when deciding on the fuel requirement. It is also incumbant upon them to take a course of action that in the ordinary course of events does not result in any of the weight limitations being exceeded. Any overweight landing requires engineering checks and in all likelyhood an air safety report, so I am a bit surprised that you suggest you and your Captains are routinely accepting such occurences ?

Finally a Captain cannot sign a loadsheet that shows the aircraft landing 3000kg overweight since he would be declaring an intention to do so at the planning stage. That is why we have had the discussion on increasing the trip fuel figure. He can land at any weight he likes provided the limiting weights and speeds are not exceeded and the runway length permits the performance figures used.

You seem to be suggesting that because the trip fuel does not in some cases consume the contingency (and contingency by definition is hopefully not consumed unless such contingencies actually arise) that the aircraft must be landed overweight ? This is simply not the case. You also ask "are you going to ask for a lower level to increase the burn off". My answer would be in the latter stages of the flight if this scenario is looking very likely then yes why not ? Are you going put the gear down with 100 miles to run ? My preference would be to increase the drag with spoilers, but if the gear usage is within limitations and practical, then again yes why not ? As long as the methodology satisfies the requirement to be down to your landing weight and your required fuel reserves are intact there are many choices open to you.
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Old 1st Jun 2006, 19:34   #7 (permalink)
 
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Maybe I've missed something in the above but, as contingency fuel is 5% of the trip fuel, after the trip fuel has been used (ie. the end of the trip) there's no need for it to be there so, in computer flight planning terms.....it isn't!

At the end of the trip other reserves come into play and contingency fuel is history.

In reality if you are planning to land at/near max landing weight, you need to bear in mind that your contingency fuel probably will/might still be in the tanks.
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Old 1st Jun 2006, 19:43   #8 (permalink)
 
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Our computer generated flight plan show the 5% contingency fuel on arrival. I have always worked on the policy that this fuel is a buffer should you need it. Why not get Jeppesen to amend your programme to show the 5% contingency on arrival, which is normally the case. I have no idea what type of aircraft you are flying, as a matter of interest how is your landing speeds calculated ?
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Old 1st Jun 2006, 20:16   #9 (permalink)
 
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Congintency fuel (ok, a glass or red going down nicley...)

Thanks for replies guys. I don't think i'm making my point as clear as I should be. Will come back at a later stage, please watch this space.

Regards.....
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Old 2nd Jun 2006, 08:07   #10 (permalink)
 
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Contingency fuel.........

The fuel burn is estimated by the Jepp calculation with the given A/C limitations, met conditions, sector time/distance, alternate info, and payload requirements. When the Capt instructs the LM to increase the burn by the weight of the conting fuel, he is only doing it so he doesnt have to sign a loadsheet which shows an overweight landing. I take your point about ways of actually physically increasing the burn en route to bring the A/C to within limits for landing, but I can assure you that this never happens and there are no intentions to do so. So the A/C lands overweight at destination. This always happens when we request max payload to arrive at MLW. Also, you have touched on re clear planning, again that option in this situation is never considered. The only time a re clear is considered is when we try to run a payload request on the Jepp system and it wont allow the requested payload because of sector length. Frt is never offloaded as long as the Jepp plan shows the A/C operting within limits, but of course this comes back to my original argument that the Jepp system assumes that we burn the conting fuel when we actually dont. Finally, reports are never ever submitted concerning an overweight landing.
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Old 2nd Jun 2006, 17:19   #11 (permalink)
 
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Apoligies if the following is incorrect, still a bit drowzy (as I was yesterday when I initially replied) from a stinkin cold but just realised that I missed one thing out from my original answer.
The Navlog systems I have used have always assumed CONT fuel is gone at arrival at destination (ie. on arrival at destination it assumes minimum fuel that being FINAL RESERVE + ALTERNATE). The main reason I can see for this is it makes the en-route fuel monitoring simple. At or abeam a waypoint you check fuel. If the fuel onboard is greater than on the Navlog you are up on your fuel plan, if its less then you are down. Idiot proof which with my limited capacity suits me.
As a result (and as Bealzebub and Flaps hinted at) on short trips with max payload you may have a reduced MTOW as we are landing weight limited. We therefore have to ensure that, if we do actually take off at this revised MTOW we actually burn the planned TRIP fuel (by which I mean only trip fuel (ie planned BURN)and not CONT fuel or any other additional fuel onboard) to be sure of meeting the MLW limitation.
It is that simple.
To take it one step further, MLW+PLANNED BURN- ZFW (or MZFW if planning Max payload) gives you MAX FUEL at Take Off without reducing payload). If this is LESS than the fuel figure provided by your planning system then either replan or reduce payload.
Now if your Captains aren't willing to simply modify the actual fuel loaded, burn off more en-route or stand up and get payload reduced in order to meet their legal obligations I think you have a serious Company culture problem that needs to be addressed. However its not the fault of the flight planning software... .
Having said that, as said earlier get it modified to assume CONT fuel isn't burnt and perhaps 'management' won't notice
What type do you operate? It seems stange to me that you can fly 6hrs with a full payload and still hit your landing weight limit unless you are tankering a huge amout of fuel or burn very little en-route. But then long haul for me is a 3 hour trip so what do I know....
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Old 3rd Jun 2006, 01:04   #12 (permalink)
 
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I still don't fully understand the nature of the problem here.

The flight planning paperwork (plog) should show how the fuel requirement is calculated. For simplicity and without going into the constituent sub requirements of each section, this should be :

A) Taxi fuel.
B) Trip fuel.
C) Contingency (5% of Trip fuel).
D) Alternate fuel.
E) Final reserve fuel ( 30 minutes holding fuel ).

In a situation ( as you describe) where you are limited by max landing weight, the maximum take off weight is ordinarily the MLW + (B)
The maximum ramp weight is MLW + (A+B).
Having arrived at this figure (x) you then deduct the aircrafts dry operating weight (DOW) plus the minimum fuel required (items A-E) giving you a wet operating weight, from the figure (x). This is your maximum payload.

The plog may well calculate for each leg a proportion of the contigency fuel used throughout the trip to show a fuel figure on arrival that would amount to items (D + E) in other words the normal minimum fuel required at destination. These plog waypoint figures are provided to show the how the fuel remaining at any given waypoint should be in order to arrive at destination with minimum diversion fuel ( D+E) onboard. The planning system that I am familiar with does not include the 5% contingency figure, but possibly yours does ? However in any event the planning fuel and payload derived would be unaffected. This waypoint figure simply provides a reference number for your actual fuel onboard computation at any given time , in order to establish a trend. Again I would make the point that by using the calculations from the fuel block (as described above) even if the contingency fuel was unused during the flight you should not ordinarily arrive in excess of your MLW.

If you are saying that your planning system ( for some reason ) incorporates items (B+C) into one trip fuel figure, then that contingency element needs to be seperated prior to calculating the payload allowable figure. If you are saying this is not being done, then your company is seemingly applying an erroneous method of flight planning and not using the documentation properly. However I would again make the point that the trip fuel can be increased to whatever you require so long as it is sufficient for the planned flight and the minimum required fuel is onboard at destination. That does not mean that is then OK to land overweight, it means that if the actual trip burn is not achieved such that an overweight landing would otherwise appear likely then the burn should be adjusted by whatever method is appropriate (holding ?) to land at the MLW or less.

From what you say, it appears that you are substituting items (B+C) for item (B) only in your loadsheet preparation ? If so this is not correct. I can see how increasing the trip fuel on a MLW restricted plan would allow for an increased payload, and provided the fuel is actually used ( by whatever method) there is no problem with that in theory, however landing overweight is not a naturally allowable consequence of such a practice and I am surprised this is being done regularly and not being detected by reference to the tech log fuel arrival figures etc ? If this is the case then the problem lies more in the violations that are happening when you exceed the actual certified landing weight rather than what was shown on the loadsheet as trip fuel.
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Old 3rd Jun 2006, 07:44   #13 (permalink)
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As bealzebub and Schmoogle said, the MTOM calculation SHOULD take that all into account on the loadsheet, so if your 'loadmaster' is not doing that he/she will trip up in any case at the loadsheet stage - and should be shot or hung by the neck. In my experience most trip plans assume cont to have been burnt at touchdown.

In any case most wise pilots always reduce trip fuel by x% for MLW calculations anyway in case the route is shortened or winds/levels are BETTER than planned so as not to arrive 'overmass' as I believe I have to call it now
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Old 4th Jun 2006, 22:21   #14 (permalink)
 
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Schmoogle

u as the pilot give the LM the loadsheet info. so it is up to u as the pilot to provide them with the correct trip fuel figure so that exceeding MLW will not be a problem. ie if 5% is included into the trip fuel calculated by ur program then minus 5% from the trip fuel figure that u give to the LM.

So that if u dont burn it u will land at MLW and if u do burn it u will have more of a margin over it. Ie plan on the safe side.
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Old 5th Jun 2006, 04:13   #15 (permalink)
 
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Quote:
Originally Posted by Schmoogle
When using the Jeppesen flt planning system to calculate max payload, fuel required for given payload etc. Why does the system assume that the 5% contingency fuel is burnt by the time you arrive. The fact is that this fuel is a buffer of extra fuel in case the situation arises where you might need it, but if this situation doesnt arise, then you arrive at your destination with it still in the tanks. If you are arriving at max landing weight, the reality is that you are arriving at your max landiing weight, plus the weight of the contingency fuel. In other words an overweight landing, which could be several tons over your max ldg wt. This is concurred when the loadmaster completes his loadsheet, where the maths don't lie. His loadsheet in this case will show an overweight landing...

We use the Jeppesen Flight Planning system at my airline. I've read through most of this thread, and have to apologize if I offer some redundant information, as I got a little lost in all the postings.


The Maximum Landing weight calculated in the Jep System is the Take-off weight, minus the "Trip Fuel" and "Taxi Fuel". The "Route Reserve" (Contingency) is included, along with the Alternate and final reserve fuel in the landing weight computation, and is assumed to NOT be burned during flight.


In the Airbus there is a simple test to prove this. In the FMS (MCDU) INT-B page, set all the fuel parameters as indicated on the Jep Flt plan (Trip fuel and alternate are computed, but normally the same as the Jep System), and the others can be manually entered.


Then, read the landing weight with a 5% route reserve. Now, set the route reserve to 0% and read the landing weight. It will indicate No change to the original weight, but the "Extra Fuel" available will show an increase.


This was confirmed when I asked a dispatcher to run two flight plans for the same route, but with different Route Reserve (contingency) settings. 5% and 0%.


Not sure why you have different numbers on your load sheets though. Possibly your Jep Sys, and Load Planning System are not configured in a compatable manner.


Hope this simplifies the answer for you.

Cheers
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Old 21st Jun 2006, 11:59   #16 (permalink)

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Our Jepp planning show landing fuel as final reserve + alternate + full contingency. Whether it had been modified to do so, I do not know. But that is the way it works.

What strikes me is the large amount you describe. If you are a JAR-OPS operator, I believe you can at least halve the figure by using either "en-route alternate" or "pre-determined decision point" scenarios. I believe other OPS regulations have similar provisions. If this is wise, I would rather not comment neither am I a commander to do so.

FD.
(the un-real)
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Old 21st Jun 2006, 12:03   #17 (permalink)
 
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Quote:
Originally Posted by FlightDetent
Our Jepp planning show landing fuel as final reserve + alternate + full contingency. Whether it had been modified to do so, I do not know. But that is the way it works.
What strikes me is the large amount you describe. If you are a JAR-OPS operator, I believe you can at least halve the figure by using either "en-route alternate" or "pre-determined decision point" scenarios. I believe other OPS regulations have similar provisions. If this is wise, I would rather not comment neither am I a commander to do so.
FD.
(the un-real)
I guess I missed that point in my previous post. Yes, ours does the same thing.
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