Flex/Derate take-off
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Well there are lots of variations on this.
On the e-jets we have ATTCS, TO1 TO2 and sometimes TO3 depending on the engine.
The ATTCS system will in the event of an engine failure automatically cancel the flex and boost thrust to reserve for the rating selected.
VMC are based on TOx-RSV
Advancing the Thrust levers to MAX will never give more than TOx-RSV when you are engine out. But when both engines are running If you have chosen TO-3 the ATTCS will give you TO3-rsv if you have windshear warning but the pilot can push to max and get the equivalent of TO1-rsv.
It's all getting a bit out of hand don't you think?
On the e-jets we have ATTCS, TO1 TO2 and sometimes TO3 depending on the engine.
The ATTCS system will in the event of an engine failure automatically cancel the flex and boost thrust to reserve for the rating selected.
VMC are based on TOx-RSV
Advancing the Thrust levers to MAX will never give more than TOx-RSV when you are engine out. But when both engines are running If you have chosen TO-3 the ATTCS will give you TO3-rsv if you have windshear warning but the pilot can push to max and get the equivalent of TO1-rsv.
It's all getting a bit out of hand don't you think?
Join Date: Jul 2005
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Assumed thrust method: ATM IS NOT considered a limitation.
Derate IS considered a limitation.
Derate IS considered a limitation.
In the case of de-rate. Let's say Full rated thrust (TO) of the engine is 50,000 lb and de-rated thrust (TO-1) is 45,000 lb. The Vmcg for using TO-1 is derived using 45,000 lb thrust. Now if you have a take-off situation where V1 = Vmcg using TO-1, and for some reason you decided to firewall the engines at V1 and happen to lose an engine, directional control will not be assured with full rudder. This is because Vmcg for TO is higher than Vmcg for TO-1.
So this brings me to another question. If you take off using TO-1, and you encountered "Windshear! Windshear!" at V1. What will you do? I was thinking that on contaminated runways or other situations when V1 was reduced, the V1/Vr spread is larger and the exposure to this scenario can be significant. Are my worries without a cause?
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I believe this has to do with Vmcg
FE Hoppy, we chose to operate with only TO-1, do you know of many operators that are using all 3 ratings?
Mutt
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So this brings me to another question. If you take off using TO-1, and you encountered "Windshear! Windshear!" at V1. What will you do? I was thinking that on contaminated runways or other situations when V1 was reduced, the V1/Vr spread is larger and the exposure to this scenario can be significant. Are my worries without a cause?
Simple solution .. if you continue, you consider/do firewall(ing) the levers ...
(a) the risk of dying due serious windshear is real and staring you in the face
(b) the risk of then having an engine failure and departing .. is far smaller
(c) if you've already had the failure and then get the windshear ... it just wasn't your sort of day and you are probably best positioned to take your chances in the overrun.
... first, attend to the thing which is going to kill you first ... noting that, if it succeeds, then the next threat doesn't even get the chance to try ...
Simple solution .. if you continue, you consider/do firewall(ing) the levers ...
(a) the risk of dying due serious windshear is real and staring you in the face
(b) the risk of then having an engine failure and departing .. is far smaller
(c) if you've already had the failure and then get the windshear ... it just wasn't your sort of day and you are probably best positioned to take your chances in the overrun.
... first, attend to the thing which is going to kill you first ... noting that, if it succeeds, then the next threat doesn't even get the chance to try ...
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Just for clarification:
most engines(i know anyway) are flat rated.
A flat rate is quite simply a way of protecting the engine from surpassing it's limits when temperatures drop.
f.e.
when we do power setting calculations we refer to a form of maximum thrust, call f.e. N1ref
engine flat rated at 23°C will produce it's maximum thrust at it's maximum RPM(say N1ref=95%N1) at 23°C.
Going into a lower temperature, say 20°C, you enter the purely structural/thrust-limited section and you would see the resulting required RPM is lower, say N1ref=92%N1.
If you go into a higher temperature, say 30°C you enter the engine's temperature limited zone. this is where you meet your EGT/TGT/ITT whatever you call it - limits. again, result is a lower N1ref=92%
Flexing is making the engine believe it's hotter outside than it actually is.
Depending on you runway and conditions you can calculate a maximum ambient temperature for which running your engines at N1ref would give you still sufficient margin on your takeoff/climb performance required. (This is usually done by the company's engineering dept and presented to you in a performance chart specific for 'a runway/intersection/flap setting/runway condition' and contains values to correct for anti icing, bleed selections and wind.
So if it were really 'that' flex temperature outside, we'd be very sweatty and selecting our max thrust N1ref, would be able to takeoff from that runway.
So now we do this with a temperature which is actually lower than that flex temperature, giving us an additional margin on performance. And most importantly, we will have a lower N1ref setting sparing our engine and increasing its life thus reducing company costs.
It's important to know aswell that when your flex temp for a given rwy/condition/flapsetting is lower than the flat rate of your engine, you should not perform flex takeoff.
most engines(i know anyway) are flat rated.
A flat rate is quite simply a way of protecting the engine from surpassing it's limits when temperatures drop.
f.e.
when we do power setting calculations we refer to a form of maximum thrust, call f.e. N1ref
engine flat rated at 23°C will produce it's maximum thrust at it's maximum RPM(say N1ref=95%N1) at 23°C.
Going into a lower temperature, say 20°C, you enter the purely structural/thrust-limited section and you would see the resulting required RPM is lower, say N1ref=92%N1.
If you go into a higher temperature, say 30°C you enter the engine's temperature limited zone. this is where you meet your EGT/TGT/ITT whatever you call it - limits. again, result is a lower N1ref=92%
Flexing is making the engine believe it's hotter outside than it actually is.
Depending on you runway and conditions you can calculate a maximum ambient temperature for which running your engines at N1ref would give you still sufficient margin on your takeoff/climb performance required. (This is usually done by the company's engineering dept and presented to you in a performance chart specific for 'a runway/intersection/flap setting/runway condition' and contains values to correct for anti icing, bleed selections and wind.
So if it were really 'that' flex temperature outside, we'd be very sweatty and selecting our max thrust N1ref, would be able to takeoff from that runway.
So now we do this with a temperature which is actually lower than that flex temperature, giving us an additional margin on performance. And most importantly, we will have a lower N1ref setting sparing our engine and increasing its life thus reducing company costs.
It's important to know aswell that when your flex temp for a given rwy/condition/flapsetting is lower than the flat rate of your engine, you should not perform flex takeoff.
