DEST ETA/FUEL

[MFarhadi]

Beautiful idea, Simon!
The reason I asked is I used to put 0000.0z T/O TIME in PROG RTA to have the Total Estimated Elapsed Time (Total EET) and Estimated Fuel On Board (EFOB) over the destination, and I couldn't see the benefit of printing the route report. Now that you mentioned you get a copy before pressing TOGA P/B, it actually makes a lot of sense and can be a valuable tool to generate a self-filled OFP with actual T/O time and fuel.

[Hardy Heinlin]

Hi,

Although I am still copying "DEST ETA/FUEL" data into a spreadsheet on every flight, they are not that reliable for the average values that you are looking for: quite often in the climb the destination fuel number changes, but so does the ETA (to a later or to an earlier arrival time). Since a month or so I am now also making notes of the fuel remaining numbers as shown on the "Print" (RTE page 1) and CALC Fuel (PROGRESS page 1).

On a number of these flights, I am seeing Fuel to Climb as:
- 11,7 (print)/10,6 (CALC) - LX-JCV; factor: 1,1
- 8,9 (print)/8,1 (CALC) - LX-UCV; factor: 1,1

In general - at TOC - I am seeing CALC fuel numbers to be between 1,0 and 1,5 tons less than print values. But same tail numbers sometimes show larger differences (up to 2 tons, so that's not very helpful...). 10 % addition here perhaps?

For fuel to descend, I am seeing:
- 0,7 (print)/1,3 (CALC) - LX-UCV - Fuel at TOD: 18,8 and close to the airport 18,1 (print) / 17,1 and 15,8 (CALC)
- 0,6 (print)/1,4 (CALC) - LX-UCV - Fuel at TOD: 16,6 and 16,0 (print) / 12,8 and 11,4 (CALC). *

Descent fuel for the NG FMC models in general is 0,6-0,7 tons more than for the legacy models, irrespective of the model used (GE, RR, PW). Perhaps factor for the descent set at 0,92 - 0,93 of the fuel at TOD? Hence: landing fuel equals 0,925 * (fuel at TOD) 17,1 = 15,8.

Regards,
Simon

* The large difference between CALC and print TOD fuel numbers has evolved during flight and is specific for RB211 models, Cargolux anyways... Some 0,8 tons per hour 

Hi Simon,

thanks for the tips.

Are the predicted T/C at takeoff and the actual T/C overflight in your tests less than, say, 10 nm apart? If the CLB distance increases, the high-FF duration also increases, as we know.


Regards,

|-|ardy

[simonijs]

Moin moin,

I will have to check those files/OFPs, and/or spend a rainy morning doing several tests with different models. Then I'll let you know. Can't recall if TOC is listed on the "Print" version, TOD isn't.

Regards,
Simon

[Hardy Heinlin]

Moin Simon,

never mind. I just modifed something here in my climb fuel prediction algorithm, and the tolerance is now reduced to less than 0.5 tons between predicted RTE DATA at takeoff time and actual RTE DATA at T/C overflight. I could probably fine-tune it further to <0.2, but for now I'll keep this new mod (<0.5) for PSX update 10.163.

I also increased the DES FF for the NG FMC.


Regards,

|-|ardy

[simonijs]

Good to know, and already a big thank you now for 10.163 .

Regards,
S.

[Hardy Heinlin]

CLB and DES fuel prediction modifications are now available in PSX update 10.163:

https://aerowinx.com/board/index.php/topic,4191.0.html


Regards,

|-|ardy

[MFarhadi]

Dear Hardy,

Regarding the 163.05: CLB and DES fuel prediction modifications, It's now working perfectly on CF6 engines. But I'm seeing a fuel rundown on RB211-524G2 during the descent (+NG FMC: SPD | VNAV PTH descent). The estimated EFOB at DEST was 14.7 at T/D (RNAV STAR, No radar vector legs, with DES FORECAST winds inserted the same as corridor descent winds), while it was reduced in 0.1 steps down to 13.5 during the descent.

Is the updated modification applicable to all engine models?

Best,
Reza

[Hardy Heinlin]

Dear Reza,

yes, all models.

Does the difference of 1.2 tons occur on all flights and weather setttings?


Regards,

|-|ardy

[MFarhadi]

Not sure yet
The difference was present during the past two flights; gonna test it out furthermore.

[Hardy Heinlin]

Did you use any TAI and didn't enter a TAI altitude in the FMC?

[MFarhadi]

No. I didn't use any anti-ice nor entered TAI ON ALT values.

[Hardy Heinlin]

Just did a descent from FL390 to sea level over 170 nm in ISA with RB211, and the DEST fuel difference between T/D and touchdown was just 0.5 tons.

[MFarhadi]

Your results are much better than mine!
Was the 0.5 ton difference with NG FMC (Off-idle descent)?

[Hardy Heinlin]

Yes.

[MFarhadi]

Tried an RB211-524G2 today with Legacy FMC and still had 1.1 tons of difference in EFOB at DEST compared between T/D and landing (EFOB at DEST when at T/D was 10.4 and landed with 9.3).
I believe I narrowed it down to the Idle Fuel Flow. It was between 1.0 and 1.1 for each engine at FL430 (descending) in idle power (EPR 0.98). Is it the correct value?

[Hardy Heinlin]

Yes.

[Hardy Heinlin]

DES fuel prediction for RB211 is now further fine-tuned in PSX update 10.164:

https://aerowinx.com/board/index.php/topic,4191.0.html


Regards,

|-|ardy

[simonijs]

Hi, sorry as well, to open this topic again of some time ago.

@ Hardy: At some point in the discussion, you were asking

Are the predicted T/C at takeoff and the actual T/C overflight in your tests less than, say, 10 nm apart? If the CLB distance increases, the high-FF duration also increases, as we know.

And then:

never mind.

which I did.

Some time ago, however, I again started making notes of RB211 times and distances to TOC as compared to what was predicted on PROG page 1/4. It turns out there is quite a difference between predicted and actual data. On a flight ELLX-UAAA (TOW: 343MT) LX-VCV took an additional two minutes and 31 NM to TOC. On another flight ELLX-SBKP (TOW 396MT) LX-VCV needed an additional six minutes and 68 NM to TOC. On this last flight 19 minutes and 110 NM were predicted to climb.

CF6 and PW models reach TOC at predicted times, usually within 10 NM.

Situation files are available.

@ Steve Bell: Tried to reach you by e-mail last year, but that no longer is working on the forum page. With respect to PFPX Data files would you be willing to email me at s.ijspeert@upcmail.nl ?

Kind regards to all
Simon

[simonijs]

https://www.dropbox.com/s/lkybnnktq7b0z2c/--Event%20record%20ELLX-SBKP.situ?dl=0

Here is that situation file...