Questions from a sim pilot about real-world use of TO/GA
 

Can any kind expert please tell me:

1. When, in general, is TO/GA used, e.g. is it normal to use it if it is available, or is it used only in special circumstances?

2. I understand that before engaging TO/GA on takeoff, you run the engines up manually to some point, e.g. 40% N1. What is the reason for this?

If it's hard to answer these for aircraft in general, then I'd be interested in hearing the story for (say) the 737-400, or any other specific aircraft.

MTIA...

--
Brian Tooby
TCA Pilot #2658

Pilot's Assistant Home Page:
http://www.tooby.demon.co.uk/P_Assist_Home.html

Engines are manually run up before TO because fan engines have variable response to throttle movement. If you just engaged TOGA with the engines at idle, you are likely to end up with full power on one and the other still running up. You select a low-mid power to get the engines stabilised, and when TOGA comes in you get reliable response from there. Can't fully remember the 737-400 figure, but the 747-400 RB211 power setting is about 1 1/2" forward giving about 1.20 EPR (Engine Pressure Ratio- just a power number, nothing more precise) which I think it was for the 737.

TOGA is always used unless autothrottle is U/S. It gives reliable power settings without overboosting. I think it ends with the first thrust reduction after takeoff and becomes re-armed in the approach when the flaps move away from up or something like glideslope arm until touchdown or thereabouts.

If you're into simming, have you tried IL2? Been having the most amazing time Stuka bombing. What a sim. I find FS2002 typically MS clunky and disappointing.

Some (not all) Boeing aircraft will, by the use of TOGA, automatically set the calculated EPR from the FMC for take-off.

This saves the PNF manually setting it himself. All he has to do then is visually check that the power has been set on the engine parameter display.

If I remember you can engage the autothrottle on flight sim, hit the TOGA switch and the engines will spool up to TOGA power without overstressing the engines......try it.

The only other time you'd use the switch would be in a go-around situation, where you'd require max power instantly, leaving you to concentrate on flying the aircraft without worrying (initially) about power settings.

Hope this helps

The TO/GA buttons on some aircraft actually have more functions that that. The 747-400 buttons act as a thrust limit selector as well, much as the thrust button does on the main control panel.

Pressing the TO/GAs once (if auto throttles are armed) on take off will select the pre set take off thrust - as selected in the pre-flight actions on the Flight Management Computer Control and Display Units. Pressing them a second time will give you Go Around power should you decide you need it.

On an approach, pressing them once will initiate a go around by giving you Flight Director commands and the power required for a climb rate of 2000' per minute. Pressing them a second time will give you full go around pitch up and power.

The Flight Director modes are automaticly swithched to TO/GA on pressing the buttons (having been automaticly armed on the approach), so they will maintain runway heading and the relevant pitch mode until others are selected - usually VNAV and LNAV if the procedure has been pre-programmed.

If an auto approach is flown, the auto pilot modes are switchcd to TO/GA by pressing the buttons, so the Go Around will be automatic.

The TO/GA buttons will only advance thrust by resheduling the Thrust Management System. To reduce thrust, you have to use the thrust switch on the Main Control Panel.

One other point omitted is that most Inertial Reference Systems are reconfigured by pressing the TOGA switch on take-off.

5150 Could you explain what you mean by reconfigured please.

Reconfigured meaning; updating it's position.

Aircraft's lat/long is entered into FMC prior to taxi; TOGA then updates it's position on the presumption that the button is pressed with the aircraft at the end of the runway, lined up for T/O.

Hi Dan,

Just a small point, but on approach, the FD pitch function is the same regardless of number of pushes, but assuming that this pitch attitude is flown, the first push gives power for about 2000fpm, the second, full go-around thrust.

I agree that 'reconfiguring' is not the term for the IRS update. In practice, not all databases have all stand positions for all airports, so the FMC position is often initialised for the aerodrome reference point (usually the centre of the longest runway). This is 'close enough for jazz'. A more precise position is required for flight, so the FMC is given departure runway, and 'knows' the Lat and Long of the threshold. If departing from an intersection, the distance from the threshold may (should) be input. Then, on TO/GA, the FMC position updates to that geographical point. This is checked by the NHP. Once airborne, the FMC position depends upon VOR, DME, and these days, mostly, multiple GPS, positions.

Is that quite clear now?Exam in the morning!

Many thanks to everyone for their helpful replies. Much appreciated.

On a Bus, TOGA is used if the runway is contaminated (wet/icy), if you are going around or if performance (high/hot/short runway) dictates it is required. Otherwise T/O Flex is used.

T/O flex provides less power, less risk of a failure during climb out coz the engines aren't screaming and wears the engines less resulting in cheaper costs in the long run; without compromising safety.

Setting the engines to Flex or TOGA provides the appropriate Flight Director commands, updates the FMS etc. When the thrust is moved back from Flex or TOGA the Autothrust then engages.

Ghost;)

Ghostflyer,

You're not necessarily right about not compromising safety. Efectively, by using max flex, you put almost all V1 values near to the limit, in terms of EDA remaining. Then, airlines get all uppity and start blaming pilots left, right, and centre, for being incompetent, on the odd occasions when pilots reject and go off the end.

Put another way, if you KNEW you were going to have to reject at V1 on a particular take-off, would you be flexing?

Rumbo,

Yep you are right to a degree but its all a giant stats game as you well know. The engine running at higher thrust is more likely to fail than one flexing.

Therefore, you reduce the chances of losing an engine by flexing but have less runway to stop in should that occur. On most occasions getting airborne close to V1 with a failure, on modern jets with decent FBW systems, beats the high speed abort and associated problems on the ground any day.

Having said that if performance is such a big issue why do some pilots jump at the chance of intersection take-offs, even with big jets, when it allows them to take off just a full 2 minutes earlier with 500m less runway? Perhaps all intersection take-offs should be banned!

Normally when the jet goes off the end it isn't a straight performance problem, there are other factors involved that the crew haven't considered, just ask those Warrens from Qantas. By the way going off the end is allowed by the regs thats why we have stopways and clearways.

I am not saying that I am right or that it is right but I do know that safety is always a compromise. Otherwise aircraft would be attached to the ground at all times and called trains, oops they crash too. And, we would have matresses strapped to our arses.

Ghost:)

Some of the above comments may lead some to believe that only the Bus flexes and Boeing bang around on full power all the time. It is only a simple operation to tell the FMS that the ambient temperature is a high figure (according to runway length etc) and a lower power is demanded. On go-arounds, pressing TOGA gives a reduced go-around thrust.

NotSoFantastic,

You would be right if you mentioned that pressing TO/GA ONCE gives reduced thrust. Pressing twice gives you full 'chat'.

Ghostflyer,

Don't forget that a lot of aircraft these days have engines capable of much more than 'maximum' power anyway. Eg B737, engines rated at 27K, operating so that 'full power' is 20K or 22K. I submit that the likelihood of flexing reducing the failure rate when the engine is already producing so much less than design thrust is very slim.

Extention of engine life will be provided by the use of the highest
flexible temperature . However a reduction of a few degrees from a high flexible temperature does not cause significant penalty to engines . There is no need to push to the limits .