View Full Version : TOGA Time Limit

Port Strobe
15th Mar 2009, 20:07
Quick question re toga time limits that a search hasn't yet answered;

Where could I find a defined time interval to respect between applications of toga thrust? Full beans is acceptable for take off and for go around, but how long should one operate at mct or less before applying toga thrust again?


15th Mar 2009, 20:17
Is there such a limitation?
Boeing (737) nor Airbus (320) talk of this in their pilot lecture.
Is there a specific scenario you are thinking of?

15th Mar 2009, 20:17
Doh :ugh: must read the question first.

Don't think a limit exists, but oil temp must be above a set value for t/o power at departure.

15th Mar 2009, 20:46
for takeoff power the limit is 5 minutes. for max continous thrust there is no limit hence max continious. remeber the power goes from takeoff thrust to climb when the flaps are up. you can always select mct in the fmc.

15th Mar 2009, 21:03
TOGA is generally a 5 minutes limitation.
If you are not taking off or going around, max power is "MCT" max continuous.
MCT - as long as you want...
One limitation I once came accross to, is "ACCELERATION" - 2 minutes limit.
Read your manuals, if nothing specified, I would say the above applies.
So technically, TOGA could not be used in cruise.
Except maybe in emergency - i.e. stall recovery.
Happy contrails

Spooky 2
15th Mar 2009, 22:24
On the B777, 767, 757 and probably the 737 and 747, TOGA give what ever power necessary to climb at approximately 2,000' fpm. This power setting is dynamic and is way below MCT or T.O. power. So to answer your question, there is no published TOGA power limit. Not usre how you would get TOGA power in cruise as the TOGA function is not armed with the flaps up. Simply stated there is no TOGA limit per se, just the required power to achieve the "go around thrust", which is a function of your gross weight and ambient conditions.

16th Mar 2009, 01:01
The takeoff limit for the B744 manual I have states the takeoff limits are available for 5 minutes with all engines operating or "10 minutes with a loss of thrust on 1 engine during takeoff" for the CF6 or "10 minutes provided its use is limited to situations where an engine failure occurs" for RB211.

CON limit is exactly that - continuous.

There may be some confusion with the question - as the TOGA refers to the AFDS system which in turn will control the TMC and associated thrust setting. Obviously - TOGA mode and associated thrust settings are used for takeoff and go-around.

My manuals have no specifics regarding a go-around limit with either the 2000 fpm first click of TOGA or the full Toga go-around (second click). The manual simply states that the above mentioned limits are for the "Takeoff condition". Further research reveals that at SL ISA the Full rating takeoff thrust is 108.4%N1 for the CF6 and the go-around thrust limit is 103.8%. In addition the RR211 shows around 1.71 EPR takeoff limit and around 1.69 EPR limit for go-around from the manual.

In a practical sense - even if you apply a 5 minute all engine operating takeoff limit to the go-around thrust setting - that is a climb of around 10,000' with the first TOGA switch depress (most likely much less than full go-around thrust at landing weight in any case). Any missed approaches need a 10,000' climb?

With regards to part of the question - Full beans is acceptable for take off and for go around, but how long should one operate at mct or less before applying toga thrust again? - I can find no reference in the manuals for any EGT cooling period or any other restriction - on that one I have no idea..... all I can say in practical experience that it would most probably be an emergency condition that would warrant such action as a GPWS pull up or windshear recovery maneuver - in which case all bets are off. Otherwise normal operations would most probably not see a need to return to takeoff or go-around thrust having completed the takeoff or go-around maneuver.

Hope it helps to answer your question.

16th Mar 2009, 01:31
In the big Boeings I have flown, B747-400 and the B767, both with RB211s and GE CF6s installed, take off thrust EGT very rarely gets even close to the MCT limit because of de-rating.

Does that then mean I could operate at that thrust level contuously as long as the CON EGT is not exceeded? I don't, but could I?


16th Mar 2009, 02:43
1. TOGA time limits: engines do not immmediately go BOOM if you would not heed the TOGA time limit. How would an engine know whether to blow after 5 minutes or 10 minutes (the applicable time limit depending on having an engine failure or not).
Thrust higher than Max Continous is time limited because of engine long term life considerations.
MCT is not time limited (what's in a name), but it's use may be restricted by other considerations.
Even lower limits may be set in place for other phases of flight (CLB for climbs, CRZ for use in cruise).

2. TOGA thrust can be obtained at any time by pushing the thrust levers all the way forward to the stop. The little lines along the EPR or N1 gauges that indicate lower limits like CRZ, CLB or MCT are not physical limits for thrust generation, only the orange tic marks are.
The "lower than TOGA limits" are limits to the auto thrust system, ignoring those limits can only be done by physically pushing the thrust levers farther forward.

3. On take-off, heeding the time limit means, selecting another thrust limit (CLB) before the time limit has expired. Formally speaking, it doesn't matter whether actual take-off thrust is only as high as the climb thrust number (as can easily be the case with high assumed temperatures).I
f T/O thrust would be 1.42 EPR and CLB thrust, after selecting it would als be 1.42, still it would constitute a bust of limits to leave thrust in T/O mode for 15 minutes.

Above points only to explain the technicalities. In practice of course, always respect limits as given in FCOM and OPS manuals.

Time limits "in between" applications, well, how do you envision that? A take-off is made once in a flight, how do you want to repeat a T/O a very short time after the first one? The closest approximation would be a flight of circuit training, where the limit mode would almost constantly be GA, do to flaps being extended all the way around the pattern, but surely actual thrust would be very far below the limit most of the time.
And in case you want to practice stalls, sure you would use full thrust for the recovery, but even heavy civil airliners don't need 10 minutes to accelerate out of a stall back to normal flying speeds.

Spooky 2
16th Mar 2009, 13:48
Simply amazing on all the opinons offered here. Somebody needs to go back a look at their FCOMS. :}

16th Mar 2009, 14:02
In the big Boeings I have flown, B747-400 and the B767, both with RB211s and GE CF6s installed, take off thrust EGT very rarely gets even close to the MCT limit because of de-rating.

Does that then mean I could operate at that thrust level contuously as long as the CON EGT is not exceeded? I don't, but could I?
No. The CON limit is a thrust limit as well as an EGT limit.

Port Strobe
16th Mar 2009, 15:07
In hindsight perhaps it's not a very practical question then, perhaps I should try to explain. Circuit training was the closest scenario I could think of which might have to adhere to this limitation, if indeed there is one. What sparked the question was a discussion a while ago with someone who swore they'd adhere to the toga (as in take off or go around thrust, not afds mode) time limit blindly whereas I said I'd be more inclined to use six minutes or whatever on a five minute engine if need be until cleaned up because ten minutes is merely a matter of coughing up more money without any change to the engine itself. Coupled with the fact assumed temperature take offs frequently yield N1 values less than MCT, so unless you advanced the thrust lever(s) on the operative engine(s) to full take off thrust immediately after the failure, then chances are you won't be overcooking the engine neither. I thought if I knew of a minimum time spent at MCT between applications of toga thrust in the manufacturer's model then this might give a better idea quite how important it may be to observe the limit?

17th Mar 2009, 01:57
Let me give a bit of my experience in ground (bench) test of big fans:

We ran a performance test schedule as follows - 5 min. MCT for warm up - 5 min. at highest TO rating - then 5 min. each at a series of lesser TO ratings, then a few points 5 min. each at lower settings. All this without any cooldown settings. It was not unusual to accumulate 30 min. above MCT with no interruption. It short, we completely ignored FAA/JAR time limits.

There was never any question of mechanical problems, although we could measure some creep of EGT/TIT and fuel flow deterioration. This would be expensive for an operator, but NOT hazardous.

Not a legal answer, to be sure, but it should put to rest any fear of exceeding a time limit. :ok: