MD-11 Fuel Calculation

M

Mario Hirschmugl

Users Local time
Today 12:39 AM
Hi,

I've noticed that the fuel calculation for the MD-11 is quite inaccurate, especially for the cargo version and in general on long haul routes. I've experienced problems with very low fuel quantity on final several times now. I have then recalculated the values based on empirical values. As I do not know, which algorithms you use for calculating the amount of fuel, I would like to give you a comparison (without critic, just tips for improvement :) )

Air Child Fuel Planner: (As i was able to gather the info from the dispatch sheet)
Cruise Fuel: 6-7 tons on average
Contingency Fuel: 5%
Final Reserve: 4tons
Taxi: 1ton
Alternate: dependend on weight and distance

My empirical values:
Cruise Fuel: 10tons/hour => why?
If you look at the MD's Fuel flow you will notice that on departure and inital climbout the Fuelflow is about 4.2-4.7tons per engine depending on the weight and the. Makes up 12-13tons per hour.
As soon as established in cruise flight the fuel flow noticeably reduces to 2.7-3.2 (common value for stiff breezes head on) tons per engine making up a total of 8-9.4 tons/hour. During descend little fuel flow is obvious. Therefore 10tons/hour on average will be a good estimate. For Example: 7hours of flight > 70tons trip fuel.

Contingency Fuel: 5%
This is a realistic value, as the cont.fuel for the 767 for example is 3%. I also use 5% for my calculations, giving a reseve of 30-40 Minutes depending on the weight. No changes for me :rofl:

Taxi fuel: 1 to 1.5 tons
This is a value that can't be taken into account by the dispatch programm at high accuracy. Sometimes the taxi-time and the size of the airport is vast (Barajas, ...) sometimes not. 1ton is a good value - in case the pilot is expecting a long taxi than he/she is asked to board some more fuel on their own ;)

Holding Fuel: 3-4tons
Again depending on the weight of the aircraft and the pilots descicions.
4tons will give you 30 mins of holding time if you are heavily loaded. 3tons are ok for a std. or passenger flight. The value of Air-childs dispatch is fine.

FInal Reserve: 3-4tons
4 tons is recommended for long haul and heavily loaded aircraft.
3 tons is ok for short-to mid-haul flights and pax-Flights.
This value has to be taken into account by the PIC as this is a ICAO std. 30mins are mandatory.
Again this is a task of the pilot flying not the dispatch programm.

---------------------------------

It would be kind, if some other pilots could verify or correct these values.
Hopefully this helps to improve the fuel calc for the MD-11 :rofl:
Maybe it's possible to take some of the aspects into account within the dispatch script.
 
Hello Mario,
Mario Hirschmugl said:
(without critic, just tips for improvement :) )
Click to expand...

Oh, we are lucky about every critic that will bring Air-Child one step further :yes:
Because I`m a little bit less of time today, I will have a look to the fuel data of the MD11 tommorow.
 
Hi Norbert,

I think we have to disregard the post about the fuel calculation I wrote :)

Assuming that AirChild's dispatch script uses great circle distances for fuel and distance calculation (same as TOPCAT for example), than it does not make sense to change the current fuel figures.

The reason is the mistake in acquiring the distance.
My current leg (TNCC-EHAM) for example is considered with a flight duration of 10 hours using the VAs dispatch - pretty much the same as TOPCAT's output. This is the great circle distance.
My routing may be a bit shorter or longer - depending on enroute-weather, winds, ...
(Things that are nearly impossible to take care of for every individual flight)

I'm always checking my routings at simroutes.com/generate routes. There I have entered the exact route, chosen MD-11 for the airplane and entered 460kts for the estimated TAS - giving me 8:30h flight duration. This number is very accurate as it uses AIRAC-cycles for the waypoint data and the estimated enroute time. Furthermore it uses actual NATs ...
Based on this information the fuel calculation I've done in the above post makes sense.
I've noticed that this is the major reason for the (sometimes excessive) deviation in the amount of fuel our dispatch script puts out.

I think it would be best to leave the values as they are right now.
For short to mid-haul the numbers are perfectly fine. For long-range flights the fuel calc should be done based on information regarding the exact routing (vroute, simroutes ...) by the pilots.
If you are using my estimates with the great circle distance you will end up with 22tons of fuel at the destination, which is no good for the company and you will be fired one day :D
 
Mario, yes you are right. For sheduled flights we are using the actual route distance. For Charter Flights we are using the great circle distance. If you put in a route for a charter flight, it has (at the moment) no effect to the fuel planning. It is only for information if you are fliying online for example, and you have to send your flightplan before starting the flight.
But we are just working on a new and very detailed flight briefing, with actual wind, actual NAT Tracks and so on. This will also working for charter flights then.

But I have had a look into many MD11 flight reports the last two days. And I have seen a little mistake in the script. So your post was very helpfull.

Best regards
Norbert
 
i found i get a really close fuel calculation wit 8 to 8.5 ton per hour and i added 1-2 ton if i fly on a event
and at the end of the flight should still have and 45min to about 1 hour of fuel
note my calculation dont include weather
 
Thanks for the info, Jerry. The optimized fuel calculation (with weather / aloft winds) is still work in progress but it will come this year. Maybe we also have to adjust the general MD-11 parameters a little.

ps: your signature is a tad big, isn't it? ;) hint: better use the
 
@ Jerry:

I can confirm your values:
I have gathered the fuel data of 20 short haul flights, which gives me
taxi-fuel 1100kg and trip-fuel 7900kg per 3 engines/h on average

For 20 long haul flights (more than 5h)
taxi-fuel of 1200kg and trip fuel of 7400 kg per 3 engines/h

These values are taken from all kind of flights (high payload, low payload, any kind of range, whatever cruise-level ...)
Of course this is unrealistic, as you would have to distinguish between payloads, cruising level, crossing the pond E-W or W-E (winds ...) ... I just tried to get numbers that are as independent as possible.

In my opinion, your values are a very good estimate for the planning tool ! :)
 
You must log in or register to reply here.
Back
Top Bottom