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Martinlest
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Joined: Sun Nov 06, 2016 9:54 pm

Question re. B737 & TOGA

Sun Mar 14, 2021 1:41 pm

Just wanted to ask (particularly of any real-world pilots who may read this), in the B737 (-700/800/900-NG) how standard a procedure is it to engage TOGA during the takeoff roll? Do many airlines/pilots set N1 with the throttles - i.e. 40% to stable, then c.90%) or is TOGA now the pretty much usual procedure with most airlines? (Is the choice to use TOGA left to the pilots, in fact, or is it more dictated by the airline?)

Also, at what stage is VNAV set in this a/c type? Before T/O even?

Many thanks
 
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Starlionblue
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Re: Question re. B737 & TOGA

Sun Mar 14, 2021 2:45 pm

The vast majority of takeoffs are at reduced thrust. FLEX/Assumed Temp or Fixed Derate. TOGA is used when that much thrust is needed.

TOGA saves a bit of fuel, but the extra wear costs more than the saved fuel.

If the conditions suggest TOGA is advisable, e.g. windshear reports, TOGA may be set or briefed as an option. This is a pilot decision at most airlines.

Stabilising at a lower thrust setting is standard. Going immediately from idle to takeoff thrust is not done because if the engines accelerate with a significant difference, this can lead to asymmetrical thrust severe enough to overcome directional authority, meaning you'll go off the side.

In the civilian world, they're thrust levers, not throttles. ;)

Typically, NAV (VNAV) on Airbus is armed before takeoff and activates once out of RWY mode just after liftoff. I don't know for Boeing but I imagine a similar logic is followed.
 
Avgeek21
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Re: Question re. B737 & TOGA

Sun Mar 14, 2021 3:18 pm

On the 737NG I fly t's 100% always TOGA. Unless in the sim and they want to teach/train. Boeing procedure is to set 40% N1 and then press TOGA switch. FMA's on PFD will say N1 - TOGA.
For VNAV it depends on the FMC version your airline has and the SOP it uses. But a long time ago it was changed to be armed prior to pushback together with Autothrottle and LNAV. (standard Boeing 737 SOP)
 
DualQual
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Re: Question re. B737 & TOGA

Sun Mar 14, 2021 3:32 pm

Pressing the TOGA button on the 737 thrust levers will do a few things. It affects the thrust levers if the autothrottles are engaged and it also drives flight director settings if the FDs are selected.

Normal ops on takeoff would be to spool the engines up to 40% N1 or so to compensate for different spool times on different engines. This allows the engines to stabilize at a lower thrust setting and avoid asymmetrical engine output at higher thrust (mo’ thrust mo’ control problems). Then stand them up to about 70% or so, let them stabilize again and then press the TOGA button. This will engage the auto throttle system and drive the engines to the selected takeoff thrust setting (either full thrust if selected in the FMC or reduced thrust if a temperature is entered. There’s also fixed de-rate which my shop doesn’t use. We just use assumed temperature method). It also sets the pitch and roll modes to TOGA. If the authothrottles are MEL’d you have to set the thrust levers manually to the desired takeoff N1 setting but you’d still hit the TOGA switch to engage the flight directors into the correct mode. If LNAV and/or VNAV are armed prior to takeoff they will engage automatically after liftoff at their respective engagement altitudes and become the active roll and pitch modes for the flight directors.

Similar for a go around you again hit the TOGA switch which will put the FDs into the go around mode. If the airplane is updated with TOGA to LNAV then LNAV will automatically engage above 400 feet if not you’d have to select it manually to fly a published missed (assuming you have the approach loaded into the FMC) or select HDG SEL for vectors as applicable. At acceleration altitude you have to select the pitch mode (my shop uses LVL CHG) and speed in the MCP. What and where the thrust levers go depends on if the autothrottles were engaged at go around or disengaged. If the autothrottles were engaged at the go around then one push of the TOGA switch will provide thrust for a 1-2000 FPM climb, a second push will give you full go around thrust. If they were not engaged at the go around, the 737 cannot re-engage them because the switch on the mode panel releases to the off position when you click the autothrottle off switch on the thrust levers. So you have to manually push the thrust levers up and in this case you push them all the way to “the carat” which means full go around thrust. During acceleration and cleanup you re-engage the auto throttle switch to have auto throttles active again.
 
Martinlest
Topic Author
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Re: Question re. B737 & TOGA

Sun Mar 14, 2021 5:16 pm

Starlionblue - thanks, but you are talking about an Airbus of course: I was really asking about Boeings (no FLEX option there!).

I think I was aware of the various options, but wondered if using TOGA had become pretty much standard. I note that "On the 737NG I fly it's 100% always TOGA", even though "TOGA saves a bit of fuel, but the extra wear costs more than the saved fuel".

Thanks for the information guys.
 
thepinkmachine
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Re: Question re. B737 & TOGA

Sun Mar 14, 2021 9:43 pm

Pushing TOGA on takeoff is not the same as TOGA takeoff...

Boeing airplanes also use reduced thrust for takeoff - they just call it ATM instead of FLEX, but the basic principle is the same.

Pushing TOGA button before takeoff make the thrust levers advance to the previously programmed thrust setting.

If you want TOGA (ie. full rated) thrust, you need to either set it up in the FMS, or advance the thrust levers manually...

Full takeoff thrust, however, is used as rarely as possible, due to reasons stated by Starlion before...
 
CanukinUSA
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Re: Question re. B737 & TOGA

Sun Mar 14, 2021 11:41 pm

All current Boeing Aircraft have been approved to reduce the take-off thrust used by 2 methods. These methods can be used individually or both may be used at the same time if weather, runway and obstacle conditions permit. The aircraft must still be able to perform safely and legally to takeoff and climb allowing for regulations, weather, runway, obstacles, etc.. It is in the airline customers interest to use the minimum allowable thrust for longer engine life. Typically the most critical part of the engine is the High Pressure Turbine blades which are subject to creep at higher temperatures and RPMs. The takeoff thrust and performance calculations may be be done by the Aircraft Performance Engineers for a large airline or it may be done by the Flight Crews at some airlines if the airline and regulator permits it by using Aircraft Performance Software. Boeing has software called Onboard Performance Tool (OPT) that may be purchased by customers that will do these calculations. There are additionally more powerful software programs available from Boeing that may be used to optimize aircraft performance more by Aircraft Performance Engineers.
1) There may be available takeoff thrust derate ratings which typically are a reduction of 5, 10, 20, 30 or 40% of available engine thrust. The exact derate settings available are a customer option so the customer decides with Boeing and the engine manufacturer which of the available derate % options they will have installed on their aircraft. If installed the customer can select the derate they want to use on the Thrust page on the Flight Management Computer (FMC) or by another selection method.
2) The other method is the Assumed Temperature Method (ATM) which involves assuming a higher temperature then is present to use less thrust when extra runway length and/or obstacle clearance is available. The temperature may be selected on the Thrust page on the FMC or may be selected in some aircraft using another selection method.
As mentioned the TOGA button push will drive the Engine thrust to the selected setting by the flight crew.
 
GalaxyFlyer
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Re: Question re. B737 & TOGA

Mon Mar 15, 2021 12:39 am

There’s a big difference between a “derate” and “reduced thrust”. One changes the thrust rating, the other doesn’t.
 
CanukinUSA
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Re: Question re. B737 & TOGA

Mon Mar 15, 2021 1:06 am

That's correct!
 
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Starlionblue
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Re: Question re. B737 & TOGA

Mon Mar 15, 2021 1:51 am

Martinlest wrote:
Starlionblue - thanks, but you are talking about an Airbus of course: I was really asking about Boeings (no FLEX option there!).

I think I was aware of the various options, but wondered if using TOGA had become pretty much standard. I note that "On the 737NG I fly it's 100% always TOGA", even though "TOGA saves a bit of fuel, but the extra wear costs more than the saved fuel".

Thanks for the information guys.


Boeing does have FLEX. It's just called ATM* instead of FLEX. ;) Both work on assumed temperature.

My statement about fuel vs wear was a generalisation of course. But it does hold true that using more thrust and thus climbing faster saves fuel in total, even though you're using more fuel during the actual takeoff.

* Assumed temperature

GalaxyFlyer wrote:
There’s a big difference between a “derate” and “reduced thrust”. One changes the thrust rating, the other doesn’t.


Indeed.

In general:
- Reduced thrust (variously called FLEX, ATM, etc...) uses an assumed temperature. TOGA thrust is always available, so you can go to TOGA at any time as needed (e.g. windshear, engine failure).
- Derated thrust (AKA fixed derate) uses a percentage reduction. TOGA thrust may not be used due to VMC limitations (except for windshear events). Derated thrust is typically used on contaminated runways, in which case derated thrust often gives higher possible takeoff weight.

In both cases, performance on one engine is sufficient for runway length and obstacle clearance.
 
CanukinUSA
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Re: Question re. B737 & TOGA

Mon Mar 15, 2021 2:23 am

Both methods are ways of obtaining Reduced Thrust. They obviously have different limitations on when and how they may be used. They are there to reduce engine wear to provide longer life, ensure reserve engine thrust availability in the event of some emergencies and better economics.
For details see FAA Advisory Circular 25-13 "Reduced and Derated Thrust (Power) Procedures" at
https://www.faa.gov/regulations_policie ... ntID/22468
 
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Starlionblue
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Re: Question re. B737 & TOGA

Mon Mar 15, 2021 2:44 am

CanukinUSA wrote:
Both methods are ways of obtaining Reduced Thrust. They obviously have different limitations on when and how they may be used. They are there to reduce engine wear to provide longer life, ensure reserve engine thrust availability in the event of some emergencies and better economics.
For details see FAA Advisory Circular 25-13 "Reduced and Derated Thrust (Power) Procedures" at
https://www.faa.gov/regulations_policie ... ntID/22468


Adding to the reasons, a fixed derate is typically used to increase acceptable TOW whilst maintaining controllability in case of an engine out.

I'm not sure that reserve engine thrust availability is a reason for reduced thrust. If you need that extra thrust, you'd use it from the start.
 
CanukinUSA
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Re: Question re. B737 & TOGA

Mon Mar 15, 2021 3:01 am

What I was thinking of is the reduced wear and tear on the engine would make it have better reliability in obtaining full thrust if it is required in an emergency event. Obviously one cannot use full thrust if a derated takeoff was planned for a number of reasons mainly aircraft control. Wording was not that good.
 
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Starlionblue
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Re: Question re. B737 & TOGA

Mon Mar 15, 2021 6:57 am

CanukinUSA wrote:
What I was thinking of is the reduced wear and tear on the engine would make it have better reliability in obtaining full thrust if it is required in an emergency event. Obviously one cannot use full thrust if a derated takeoff was planned for a number of reasons mainly aircraft control. Wording was not that good.


Ah. I see what you mean. :)

Yeah, that makes sense I suppose. Reduced thrust saves the core from being heated to the max every single time, so less risk of damage.

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