Performance limit at take off

[danielwest 1]

Dear Captains, 

 

I encountered a problem that I'd like to discuss with you.

 

I recently am into flying the NGX again and I like to do flights for the airline transavia.com (TRA). Using PFPX I planned a flight from the relatively new but very small airport LTFG (Gazipasa) to EHAM. Since it is summer season I reckon that in real life flights would be fully loaded.

 

My flight was specified as follows:

Equipment: 738

TOW: 72,5k

Fuel: 13,5k

temp: 33 C

wind: 220/04

QNH: 1016

rwy: 26

 

The TOPCAT tool calculated that the requested take off performance was well above the performance limit of the aircraft in these circumstances.

 

I don't know the exact elevation of the field, but it is close to sea so it cannot be that high. The runway length is 6500ft/2000m.

 

I know for sure that in real life TRA (and other airlines) take fully loaded planes from LTFG to EHAM without a tankstop in between. The question is, how do they actually get their flights into the air without running out of runway?

 

Thanks in advance, 

 

Daniel W.

[KriVa 307]

Slow down there, Captain Duracell. Clicking the "submit" button once is more than enough.

[FlyGuy42 4]

It's probably the 404 error. There should probably be a sticky explaining not to hit post again after encountering it, as the thread gets started anyway.

 

Back to Daniel's question, though. Generally I'd imagine they wouldn't fully load the flights due to performance considerations. I learnt this from a Flydubai captain who explained to me that due to the engine's limited performance at hot and high airports such as Kathmandu and Kabul, they can't load the plane too close to it's MTOW. They also tend to use the takeoff thrust bump for the added thrust necessary, plus a pretty high flaps setting, fifteen of higher, if I recall correctly, for lower V-speeds.

 

Regards.

[danielwest 1]

Sorry for the multiple posts :(

 

Anyways, according to pfpx and topcat, I am more than 4 tons overloaded. That would mean a serieus cut in payload. I can't imagine that is right. Secondly, is the maximum flap setting for take off not 15? At least I thought it was.

 

I also know that TRA uses it summerleases from GOL that have a short field package installed. That should help. On the other hand, other airlines don't operate spf's to LTFG.

 

Daniel W.

[FlyGuy42 4]

You may be right about the flaps setting, Daniel. Haven't flown the NGX in a while.  :rolleyes:

 

Try adding the takeoff bump to the thrust setting, that may help with the payload capacity.

 

Regards.

[Fabo 213]

TOPCAT does not support bump calculations.

 

Other than that, well...

A limit is a limit. 2000m is not much for a full 800, not sure even SFP would help.

 

Some points to help a bit:

-Make sure Air Conditioning is set to off - use APU to packs supplementary procedure for departure. That will give you 400kg extra.

-Runway is sloped - take a look at taking off downslope - this gives me something like 70-80kg in case of Gazipasa.

-Take a look at what time of day Transavia flies. Flying in at early morning probably gives them lower temperature.

-Take a look at your fuel planning. Try to push it down. I've been able to get my required fuel under 12 tonnes - look at your alternate, try using Rotterdam or Lelystad. You might get away with lower CONT fuel if you nominate enroute alternates. Use CI of 0 to minimize fuel needed at cost of time...

[danielwest 1]

Thanks, Fabo.

 

I'll try to work with that. Transavia mostly flies out late in the evening, I believe. The runway is indeed sloped but I cannot take that into consideration when doing perf calculations. I'll work with the packs off take off option and a TO bump. Let's see whether that gets me off the ground. Fuel I will have to take a look at. Most of the times I take some contingency fuel with me but already set that to 10 mins. Perhaps I have to go with the bars minimum. Alternate is already set to Rotterdam. I don't believe that Lelystad currently can handle the 737.

 

I welcome any other suggestion.

[KriVa 307]

When you say this:

 

 

I know for sure that in real life TRA (and other airlines) take fully loaded planes from LTFG to EHAM without a tankstop in between.

 

Where do you get that knowledge from?(Not trying to be a smart cookie here, I want to ask this as a serious, valid question.)  Have you looked at actual load sheets used by TRA, or do you "guesstimate" that by having a look at the amount of passengers on board on real life flights?

The first is a good method, the second one really isn't.

[787flyer 633]

Hi Daniel,

 

I think the MTW you are operating at is too high in this particular scenario. Based on the -800 takeoff/runway length charts you'll need around 57t MTW for LFTG assuming std temp (15C) at sea level. When you're operating at higher daytime temps like 33C, you'll need more take runway length due to the less dense air thus your MTW would have to be significantly below 57t in order to use the available runway length at LFTG.

 

Also, 737NG is certified for flaps 25 takeoffs where runway length is limited, so you can try this also by increasing your flaps setting. Not sure if you will accomplish your goal by increasing flaps alone. Combination of the two may be needed.

 

 

Regards,

[scandinavian13 5,192]

 

 

I know for sure that in real life TRA (and other airlines) take fully loaded planes from LTFG to EHAM without a tankstop in between. The question is, how do they actually get their flights into the air without running out of runway?

 

Load limiting.

 

They take less fuel (where possible - or at least take less discretionary fuel), fewer passengers, less cargo, and so on.

 

I highly doubt they're operating a fully loaded 738 out of a field with that length.  Close to fully loaded?  Maybe.  Full?  No.

[danielwest 1]

Unfortunately I don't work for TRA so I don't get to see the loadsheets. What I do know is that deboarding planes on eham from LTFG are pretty full. Anyways. Just did the take off with the weights specifiek above. I used a b738 from GOL with SFP. Flaps set at 15, bumped TO and bleeds off. Temp was 29 degrees and qnh at 1006. Calculated V2 was 149. Parking brakes set, advanced to 40% N1, released brakes and hit TOGA. I got up in the air well before the end of the runway only one odd thing.

 

The calculated stab trim was around 4.15 which I found quite low. On rotation it took me ages to get the 15 deg nose up. Why does the fmc give such a low trim setting?

 

Thanks for all the replies so far.

[KriVa 307]

 

 

Unfortunately I don't work for TRA so I don't get to see the loadsheets. What I do know is that deboarding planes on eham from LTFG are pretty full.

To be honest, that's not really an exact form of measurement. Without proper load sheets, it's pretty impossible to define wether an airplane is "full" or not.

For all we know, they are flying a plane full of passengers, with only 20 bags in the holds.

[danielwest 1]

Unlikely but I agree!

 

Let's just say that they will load their planes up to the highest cost-effective load.

[scandinavian13 5,192]

For what it's worth, we routinely filled an E170 with people and only bulked out the front bin on certain occasions.  Most of the time, we only had a couple bags in the rear bin.  The sim's implementation, TOPCAT and PFPX also assume that the airline is also shipping cargo.  Mainlines often do, but some don't, and it depends on the route.  My bet is that this route receives little to no cargo other than a little bit of COMAT.

[pcubine 143]

Runway is sloped - take a look at taking off downslope - this gives me something like 70-80kg in case of Gazipasa.

It is my understanding that all runways in FSX are level.