How to select correct T/O mode.

[ols500 43]

Hi,

How do I know what takeoff mode I should use?

Is it in a simbreif flight sim, like if I should use CLB-1 or CLB-2?

Or is it something I can calculate.

 

Thanks, Ollie.

[Nick Dobda 24]

Short answer you need a program that will calculate it for you, such as TOPCAT (about $20). I think it suggests that in the tutorials. The program will do the calcs and tell you which take off modes are acceptable to use. Before I splurged the $20 to get TOPCAT I used a free spreadsheet I scrounged up that made an estimate for me. 

I'm sure there's a way to manually calculate which modes are acceptable. You could probably find the resources (graphs, charts I'm guessing) on the internet to do the calculations if  you wanted. Personally that was more in depth then I wanted to get, I just learned the concept the takeoff mode (what are takeoff modes, why are there different takeoff modes, and when would you use one takeoff mode over another) and that there are some calculations that need to be done based on various factors to arrive at whichever mode options are available. Theres also a thing called de-rating that is another interesting concept to learn about.

Someone can correct me if I'm wrong, but I was also under the impression the takeoff mode (and derate) was handed to the pilot on a dispatch sheet prior to takeoff. For this reason I figured it wasn't cheating if I just typed in the info to TOPCAT and it spit out results. 

[ols500 43]

Thanks I'll look into this TOPCAT tool 🙂

[MarkJHarris 128]

In real life, the dispatcher will give you either a loadsheet or a load form if your company is using a self generated one. Ours is self generated, on our iPad. Companies like RYR used manual loadsheets for years.

 

What they give you is a Zero Fuel mass and trim %MAC figure.

Your fuel load determines actual Trim %MAC and gross weight.

You need the gross to determine how you will accelerate and to what speed. Some programmes use increased speeds to give better climb gradients for further out obstacle clearance or simple payload capability.

 

We use DS. Enter gross take off weight (less taxi fuel), airfield, runway with intersection, wind, temperature, WING and/or ENGINE ANTI ICE, wet, dry or contaminated, etc. and pressure.  We get an Acceleration alt, OEI emergency turn procedure, Fixed De-rate, assumed temp,  flap setting, and V speeds.

 

We then go to the PERF page, enter ZFW into the FMC, check the Gross (NEVER enter the gross directly)... The CRUISE % MAC is entered  here also.

Next go to the NI LIMIT page, enter Fixed derate, and assumed temp/actual temp. Then to TAKE OFF page, now enter flap, % MAC (you can double click it in PDMG as it knows, and V Speeds.

As to CLB-1 CLB-2, it should automatically schedule this to avoid a power increase at N1 setting. You can override, my old company used full climb as a default, you only softened this on a lightweight flight with lower climb altitude. A -700 with 50 pax on full climb is hilarious when it kicks in, especially if you've launched with 18K 60 degrees setting....

 

Some aircraft you can enter data on page 2 of TAKE OFF page. Winds, slope wet or dry, and also acceleration height (above aerodrome), and on some climb height. If you have this option and enter a climb altitude, it will auto select N1 at that altitude.  (Remember, if you take off from a 300ft high runway and enter 1,500 in the climb box, it will change over at 1,800ft.

 

If you've entered wind, runway state and slope, the FMC may offer you QRH speeds. You can double click on these if they are the same as your calculated ones. In my last company we used these speeds. In my current one we don't.

 

Hope the detail helps.

 

As to what to do in the SIM without a helping hand,

 

1. Double click both ZFW and Take off %MAC lines to get the actual mass and trim of the model as loaded. Cope this to the cruise trim on the other page.

 

As to what de-rate. Experiment! for a 3,000m runway, 10,000ft, you'd probably use 22k and 50 degrees for an -800. On a 1,800m runway, still air you'd go full 26k no temp. Play with the settings and look at the N1 offered on the FMC as a target. you'll see you can easily get a lower N1 with 24K and some temp than 22K full. 

Remember if you lose an engine, the other can go to the full de-rated thrust. So a 22k 30' takeoff with V1 cut will be safe if you put the other to a full 22k thrust.

some folks will change it to 24K with more temp rather than the higher assumed 22K. This will give more thrust in the event of needing it.

The advantage of the sim is you can play with it and try a few changes.

 

In the real world, we max de-rate and use improved climb speeds. Take off is quite a long winded affair even on 3,000m runways and we get disturbingly close to the other end before lift off!

 

Enjoy.

 

 

[ols500 43]

Wow,

That explanation was very thorough and VERY useful. 🙂 😃

Thanks, Ollie.

 

[Ray Proudfoot 8,924]

Late to the party but I’ve been using PFPX together with TOPCAT for years. It’s especially useful together as the weights are automatically fed into TOPCAT by PFPX. My takeoffs are usually TO1 5 flaps with full CLB.

Both available here. http://www.flightsimsoft.com/pfpx/

[MarkJHarris 128]

Different programmes produce different settings. 

Try this for simplicity.

75,000kg. 2000m runway. You'd use full thrust. 

75,000kg. 3000m runway. you'd use 22k 50' assumed.

That 2000m runway at 65 tonnes you'd use 22k and about 40' assumed. 

Rough guides. in reality it depends on a lot more, such as climb gradients required for surrounding terrain. 

 

[MDFlier 2,031]

I've been using the Onboard Performance Tool in the EFB, and it seems to be working pretty well. I am not a RL 737 pilot so I have no way to know if it is really working right.

The only "issue" that I have is that there always seems to be a .8 to 1% difference between the %N1 value the OPT provides, and the %N1 shown in the CDU after I set the temp and derate values according to the OPT.

The instructions for the OPT are in PMDG_EFB_Manual.pdf which can be found in the .\Prepar3D v4\PMDG\EFB\EFB Documents Library\ folder.

 

[el_kab0ng 29]

You might take a look at QSimPlanner (freeware) which does a good job giving you derates and flex temps for the 737/747/777. Cheaper than topcat and does pretty much the same thing.

[MarkJHarris 128]

Up to 1% is acceptable in the real world. Don’t worry about it. 

[MDFlier 2,031]

On 12/5/2019 at 10:02 AM, MarkJHarris said:

Up to 1% is acceptable in the real world. Don’t worry about it. 

Thank you, Mark! That eases my mind.

On 5/18/2019 at 1:28 PM, MarkJHarris said:

As to what to do in the SIM without a helping hand,

1. Double click both ZFW and Take off %MAC lines to get the actual mass and trim of the model as loaded. Cope this to the cruise trim on the other page

I've never done this step before. Good info. What would be the ramifications of lust leaving it blank or default in real life? Could it cause a dangerous condition in any particular phase of the flight? 

[MarkJHarris 128]

If both were blank you wouldn't get any take off speeds up onto the display.

As to mistakes, putting the ZFW into the take off line is a known gotcha on type. There are several videos about of 737s rotating far too early and not getting airborne till the end of the runway. This is the reason.