737 NG Derate / Assumed temp benefits
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737 NG Derate / Assumed temp benefits
My company prefers us to use a combination of Derate and assumed temp to take off with the minimum N1 (EGT).
I understand the long term fuel reduction benefits of this and the extended engine life /reduced maintenance costs but is there any evidence that lower take off power reduces EFATOs.
The reason I ask is that (even on a dry runway with no crosswind) many of the guys refuse to assume after a derate (the feeling seems to be that you are taking an uneccessary risk by keeping the aircraft on the concrete longer than normal).
Thanks in advance
I understand the long term fuel reduction benefits of this and the extended engine life /reduced maintenance costs but is there any evidence that lower take off power reduces EFATOs.
The reason I ask is that (even on a dry runway with no crosswind) many of the guys refuse to assume after a derate (the feeling seems to be that you are taking an uneccessary risk by keeping the aircraft on the concrete longer than normal).
Thanks in advance
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I saw some documentation from GE that showed clearly the reduction in Engine failure rates gained from fully reducing TO thrust. I don't have a copy but I bet google does.
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I think this has came up before, but I've had exactly the same reluctance from some people to do it. Yes, it uses more runway, but your V1 will still give you enough distance to stop, albeit further down. The other downside is that it can increase the risk of tailstrike in crosswind or gusty conditions and as such my operator doesn't use is when x-wind in excess of 10 knots.
However when properly understood (which personally I dont think it is) ATRT in the Boeing, Flex in the airbus (which is different to de-rate in both aircraft!) is actually quite safe. It lowers the Vmca and personally if I lost an engine on a wet runway at V1, I would appreciate having less thrust initially while trying to control the yaw. And obviously there is the serious reduced wear on the engine, less noise, less change of failure etc. If you feel you dont have enough thrust at any point, its just a matter of pressing TOGA again to get full N1. Like many things in this job, it requires airmanship to decide what is the most prudent course of action taking into account all the factors.
I would imagine there are quite a few posts on this scattered across pprune.
However when properly understood (which personally I dont think it is) ATRT in the Boeing, Flex in the airbus (which is different to de-rate in both aircraft!) is actually quite safe. It lowers the Vmca and personally if I lost an engine on a wet runway at V1, I would appreciate having less thrust initially while trying to control the yaw. And obviously there is the serious reduced wear on the engine, less noise, less change of failure etc. If you feel you dont have enough thrust at any point, its just a matter of pressing TOGA again to get full N1. Like many things in this job, it requires airmanship to decide what is the most prudent course of action taking into account all the factors.
I would imagine there are quite a few posts on this scattered across pprune.
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I think what your bringing up is...'is it really safer being 3000 ft farther down the runway, waiting for VR, then if I had just done a max thrust take off' ..the answer is obviously not....
Or...'is it safer to barely get over those obstacles doing a reduced thrust departure, vs get over them faster, higher?'
the answer is obviously not...
Reduced thrust is all about one thing = Stretching out the engine overhauls as far at the mechanic with a boroscope will allow it, and still sleep at night..
And what do the mechanics look at....the blades basically...and reduced thrust departures, will be easier on blades, less sufidation, less pitting.....
but they can't look at bearings...and having had a bearing failure....
Now while others in here are probably tired of me ranting against reduced thrust departures, technically I am not against them...long runways, no obsticles...no problem.......you just have certain airlines that stuff the right seat with 200 hour pay to fly marsh mellows, then plan the accel/stop numbers into the grass, flying overweight, with blind mechanics behind the boroscopes....
Or...'is it safer to barely get over those obstacles doing a reduced thrust departure, vs get over them faster, higher?'
the answer is obviously not...
Reduced thrust is all about one thing = Stretching out the engine overhauls as far at the mechanic with a boroscope will allow it, and still sleep at night..
And what do the mechanics look at....the blades basically...and reduced thrust departures, will be easier on blades, less sufidation, less pitting.....
but they can't look at bearings...and having had a bearing failure....
Now while others in here are probably tired of me ranting against reduced thrust departures, technically I am not against them...long runways, no obsticles...no problem.......you just have certain airlines that stuff the right seat with 200 hour pay to fly marsh mellows, then plan the accel/stop numbers into the grass, flying overweight, with blind mechanics behind the boroscopes....
