Full Length v Intersection Departures

[Al Bundy]

In the 10 short years i have been flying a CFM-powered A320 (as well as the 10 prior years in turboprops), climb thrust has always been less than takeoff thrust. Even in flex.

That's why it's called "Thrust REDUCTION / acceleration altitude"...

I too belive that engines are more likely to fail at initial power up. I just doubt that evidence supports an increased rate of occurrence with flex vs TOGA. Just a guess on my part. I wouldn't know where to look.

First off- it doesn't take a power increase to tank the engine. This is a common misconception. Most engine failures occur during a "power change". That can be an increase or decrease. We typically see the failures during the second segment of the climb. Reason being is if the engine is wounded, it's probably going to be even more injured during the temperature change from being hot on the previous flight, cold during the turn of offloading pax, then getting hot again during the takeoff.

As for if the second segment is a power increase or decrease, depends on your operator/performance engineer guy/how the airline wants to run their engines. Having flown both the comfy Airbus and the noise machine 737...
Fly a CFM56 on a 737NG with CLB 1 default after the TO power setting (Flexed aka "SEL TEMP" on Boeing) you'll get a noticeable increase in power setting, especially when your SEL vs OAT is a large split. Part of the logic in this is the NADP is complied with best by getting the aircraft as high as it can get as quickly as possible, in an effort to reduce the noise over the ground. Add in what some refer to as a "Close-in" and you get even better results.

Other things to consider is that an engineer may feel that the efficiency of the aircraft comes by getting it as quickly as it can get into the upper altitudes and cruise in an effort to save fuel.

Interestingly enough, if you dig deep into the perf engineers graphs, there is a power reduction that happens fairly early in the climb. Simply put, this is due to the loss of thrust an engine produces as it gets higher in altitude.

Next time you fly the A320 note the % when you click back to the CLB detent. Then look at them again later in the climb. You'll see they steadily increase. This is in compensation for the loss of thrust in the thinner air.

Engines fail when they are going to fail. However, TOGA puts a lot more stress/temperature change on an engine than reduced does. TOGA also gives more chance for a "burp" in the engine than a reduced power setting gives. I like reduced. Cringe when I get a "TOGA TAKEOFF REQUESTED" message from mx control.

 

[JustinS]

In our nimble CRJ, sometimes climb thrust after takeoff is a power increase or sometimes a decrease. It depends on whether we did a flex takeoff or not for the most part. Sometimes we're required to do normal takeoff thrust due to high density altitude situations, operational requirements, or wing/cowl anti-ice usage. We had a guy from GE come to our airline and do a seminar talking about the CF34. It was very fascinating, but one of the biggest things that stuck out to me was how drastic engine life can be altered by an operator's amount of reduced thrust takeoffs or lack there of. He said a particular foreign carrier did nothing but normal takeoff power every time, and as a result the engines had to be replaced within a year. Whereas he mentioned US 737 operator which does primarily reduced thrust takeoffs has some engines that he knows of that have been on wing for 10+ years! Along with normal inspection intervals and maintenance, engine life is solely determined by its ability to generate full takeoff thrust without exceeding ITT limitations. Once it can no longer produce takeoff thrust without exceeding ITT the engine has to be taken off the wing (or fuselage...). He also discussed engine failures. What you guys are saying is pretty true. As far as initial thrust application for takeoff that is most likely where a failure is going to happen. Once the thrust is stabilized on takeoff the likliehood of canning an engine (due to internal MX issues) goes down significantly. Of course there are birds and weather conditions which could cause potential for flameouts or compressor stalls.

 

[ctab5060X]

Engines fail when they are going to fail. However, TOGA puts a lot more stress/temperature change on an engine than reduced does. TOGA also gives more chance for a "burp" in the engine than a reduced power setting gives. I like reduced. Cringe when I get a "TOGA TAKEOFF REQUESTED" message from mx control.

I hate seeing "ANTI-ICE ON" and the associated "MAX WT" numbers that come with it where there is no reason to use the anti-ice system for takeoff. I'll bug dispatch to give me Anti-Ice Off numbers so I can reduce as much as possible on the engine power. Even though we can use a derated T/O-2 with no flex when we use "ANTI-ICE ON" numbers, but I much prefer to derate the derate whenever conditions permit

 

[z987k]

I usually don't even go full power on takeoff in my little airplane if there's 2000ft of runway or more. Also helps keep the noise down with the prop slower. In a 185 with the seaplane prop, you go full bore, but as soon as I'm off, pull the prop back. At like 10 ft. Because it's obnoxious.

 

[thevideographer]

I usually don't even go full power on takeoff in my little airplane if there's 2000ft of runway or more. Also helps keep the noise down with the prop slower. In a 185 with the seaplane prop, you go full bore, but as soon as I'm off, pull the prop back. At like 10 ft. Because it's obnoxious.

That's... not really a good idea.

 

[z987k]

That's... not really a good idea.

Please explain.

 

[pljenkins]

That's... not really a good idea.

I think what he's getting at is its generally a bad idea to mess with prop/power setting during takeoff until you are at an altitude that at least gives you a fighting chance of surviving a failure.

I believe any configuration change other then retracting the gear during phase 1 climb would generate raised eyebrows from safety inspectors.

 

[Toobdrvr]

Wow, leave it to pilots to make things more complicated than necessary!

First off- it doesn't take a power increase to tank the engine. This is a common misconception. Most engine failures occur during a "power change". That can be an increase or decrease. We typically see the failures during the second segment of the climb. Reason being is if the engine is wounded, it's probably going to be even more injured during the temperature change from being hot on the previous flight, cold during the turn of offloading pax, then getting hot again during the takeoff.

As for if the second segment is a power increase or decrease, depends on your operator/performance engineer guy/how the airline wants to run their engines. Having flown both the comfy Airbus and the noise machine 737...
Fly a CFM56 on a 737NG with CLB 1 default after the TO power setting (Flexed aka "SEL TEMP" on Boeing) you'll get a noticeable increase in power setting, especially when your SEL vs OAT is a large split. Part of the logic in this is the NADP is complied with best by getting the aircraft as high as it can get as quickly as possible, in an effort to reduce the noise over the ground. Add in what some refer to as a "Close-in" and you get even better results.

Other things to consider is that an engineer may feel that the efficiency of the aircraft comes by getting it as quickly as it can get into the upper altitudes and cruise in an effort to save fuel.

Interestingly enough, if you dig deep into the perf engineers graphs, there is a power reduction that happens fairly early in the climb. Simply put, this is due to the loss of thrust an engine produces as it gets higher in altitude.

Next time you fly the A320 note the % when you click back to the CLB detent. Then look at them again later in the climb. You'll see they steadily increase. This is in compensation for the loss of thrust in the thinner air.

These are all excellent points! However, they have very little to do with what I was trying to say...

Someone was trying to say that they believe that choosing a full length vs. intersection departure would reduce the likelihood of experiencing an engine failure for that takeoff (due to reduced thrust setting). I am simply saying I don't believe that and I will be surprised if actual data supports that. I'm still digging.

So far the study I'm reading, which appears to be a leading study of powerplant faiures conducted by representatives from GE, Pratt, Boeing, Airbus, Embraer, FAA, NTSB, and NASA shows that between 1992-2000, there were a total of 6 failures of High-Bypass turbofan engines worldwide. 4 of which happened during the takeoff and initial climb. I'm still looking for the discussion concerning what thrust setting was selected for each (I'm on the road). However, with that data alone, it appears that the chances of losing a well-designed, well-maintained, and properly operated modern high-bypass turbofan engine in ANY PHASE is soo infinitesimal (yes, I had to look it up), basing a career-long decision to operate a certain way seems (to me) a little silly...

I get the logic. More power = more stress. I've been told this many times as well from reliable sources. I'm just suggesting that actual data (reality) might not support this sufficiently to be considered conclusive...

Either way, enjoying the discussion. I've even (gasp!) learned a few things!

 

[jtrain609]

Wow, leave it to pilots to make things more complicated than necessary!



These are all excellent points! However, they have very little to do with what I was trying to say...

Someone was trying to say that they believe that choosing a full length vs. intersection departure would reduce the likelihood of experiencing an engine failure for that takeoff (due to reduced thrust setting). I am simply saying I don't believe that and I will be surprised if actual data supports that. I'm still digging.

So far the study I'm reading, which appears to be a leading study of powerplant faiures conducted by representatives from GE, Pratt, Boeing, Airbus, Embraer, FAA, NTSB, and NASA shows that between 1992-2000, there were a total of 6 failures of High-Bypass turbofan engines worldwide. 4 of which happened during the takeoff and initial climb. I'm still looking for the discussion concerning what thrust setting was selected for each (I'm on the road). However, with that data alone, it appears that the chances of losing a well-designed, well-maintained, and properly operated modern high-bypass turbofan engine in ANY PHASE is soo infinitesimal (yes, I had to look it up), basing a career-long decision to operate a certain way seems (to me) a little silly...

I get the logic. More power = more stress. I've been told this many times as well from reliable sources. I'm just suggesting that actual data (reality) might not support this sufficiently to be considered conclusive...

Either way, enjoying the discussion. I've even (gasp!) learned a few things!

6 engine failures over an 8 year period worldwide?

My last airline had more than that fail on a yearly basis.

 

[Autothrust Blue]

Please explain.

Power enrichment.

Anything less than full throttle (for small-bore normally-aspirated Lycomings or Continentals) or rated takeoff manifold pressure and fuel flow (for the non normally aspirated kinds of those engines) dramatically increases cylinder head temperatures and the risk of detonation.

(recips are not jets, do not conflate the two)

 

[Toobdrvr]

6 engine failures over an 8 year period worldwide?

My last airline had more than that fail on a yearly basis.

Standby. I'm digging....

Also sitting on a plane...

 

[Toobdrvr]

Oops. My bad. That's just uncontained disk failures (yikes). Lemme see if I can find total failures..

Still won't be that many.

 

[derg]

6 engine failures over an 8 year period worldwide?

My last airline had more than that fail on a yearly basis.

When did you go to Allegiant?

(Too soon?)

 

[JustinS]

6 engine failures over an 8 year period worldwide?

My last airline had more than that fail on a yearly basis.

Keyword in his post being high bypass turbo fans. Not sure where you fly, but I'm going to make a WAG and guess where ever you work only operates low or medium bypass turbofans.

 

[Kingairer]

6 engine failures over an 8 year period worldwide?

My last airline had more than that fail on a yearly basis.

That's was last Tuesday, afternoon, numbers from allegiant.

 

[thevideographer]

Power enrichment.

Anything less than full throttle (for small-bore normally-aspirated Lycomings or Continentals) or rated takeoff manifold pressure and fuel flow (for the non normally aspirated kinds of those engines) dramatically increases cylinder head temperatures and the risk of detonation.

(recips are not jets, do not conflate the two)

Debatable.

By debatable, I mean you're wrong I know which John Deakin article that came from and there is simply zero evidence to support it, and my own experimentation showed the opposite.

But you should still leave the throttle in for takeoff and initial climb.

 

[Autothrust Blue]

Debatable.

By debatable, I mean you're wrong I know which John Deakin article that came from and there is simply zero evidence to support it, and my own experimentation showed the opposite.

But you should still leave the throttle in for takeoff and initial climb.

"Okay"

(educate me.)

@trafficinsight too, plz

 

[thevideographer]

"Okay"

(educate me.)

@trafficinsight too, plz

Well this is 2 parts.

1) Myth that reducing throttle will cause a dramatic increase in CHTs. Not true for all aircraft. The idea is that the last 1/2" of throttle is actually just increasing the mixture, and that when you reduce throttle all you're doing is prematurely leaning the mixture and causing CHTs to rise. I could find no evidence of this including asking Lycoming and Continental (they deflected the question). Testing it in a single engine aircraft has a ton of variables to control - if you try one takeoff at WOT then another takeoff at reduced throttle, your engine is going to be warmer to begin with, OAT may have changed, aircraft weight will have changed, etc etc. I tested it in a twin by reducing one engine after takeoff and found that the engine at lower throttle was dramatically cooler (like 100º cooler) than the one at full power.

2) "Detonation zone". Simply not going to happen on a modern engine running 100LL. The temperature and pressure required to detonate 100LL is so high that there is just no way for the operator to do it accidentally. Nor can any engine pass certification without proving that it can run through its entire operating range at max temperature without detonating.

As for reducing power on takeoff in a single engine, I would say leave it at full power until at least 500' or a safe altitude then reduce. A piston plane doesn't have the power of an airliner, pistons aren't nearly as reliable and you've only got one of them. #1 priority should be getting to a safe altitude as quickly as possible to minimize time low to the ground. Who cares about obnoxious noise on takeoff? Once you're above 500' or so you can pull back the power some and it's not going to hurt the engine or cause detonation.

 

[Autothrust Blue]

That's was last Tuesday, afternoon, numbers from allegiant.

Doesn't ALGT not operate on either Tuesday or Thursday, or something like that?

Well this is 2 parts.

1) Myth that reducing throttle will cause a dramatic increase in CHTs. Not true for all aircraft. The idea is that the last 1/2" of throttle is actually just increasing the mixture, and that when you reduce throttle all you're doing is prematurely leaning the mixture and causing CHTs to rise. I could find no evidence of this including asking Lycoming and Continental (they deflected the question). Testing it in a single engine aircraft has a ton of variables to control - if you try one takeoff at WOT then another takeoff at reduced throttle, your engine is going to be warmer to begin with, OAT may have changed, aircraft weight will have changed, etc etc. I tested it in a twin by reducing one engine after takeoff and found that the engine at lower throttle was dramatically cooler (like 100º cooler) than the one at full power.

How much of a power reduction are we talking, here?

(I'm still not brave enough to try it myself)

2) "Detonation zone". Simply not going to happen on a modern engine running 100LL. The temperature and pressure required to detonate 100LL is so high that there is just no way for the operator to do it accidentally. Nor can any engine pass certification without proving that it can run through its entire operating range at max temperature without detonating.

As for reducing power on takeoff in a single engine, I would say leave it at full power until at least 500' or a safe altitude then reduce. A piston plane doesn't have the power of an airliner, pistons aren't nearly as reliable and you've only got one of them. #1 priority should be getting to a safe altitude as quickly as possible to minimize time low to the ground. Who cares about obnoxious noise on takeoff? Once you're above 500' or so you can pull back the power some and it's not going to hurt the engine or cause detonation.

That much we can agree on. Single or multi, use rated takeoff power until you don't need to use it (in accordance with limitations etc).

 

[Toobdrvr]

Okay, for the Jet crowd, here 'goes:

This is the link for the full report (again).

http://www.faa.gov/aircraft/air_cert/design_approvals/engine_prop/media/CAAM2_Report.pdf

Lots of good stuff in there if you're interested. I have searched around and this really seems like the most comprehensive report on engine malfunctions in the free world.

This is who participated in the study:

These are the aicraft studied:

This slide shows the sample size. Note: they looked at "9.2E7" (that's 92 MILLION) total flights of aircraft using 2nd generation high-bypass turbofan engines, which is defined in note 6. Pretty much every HB engine in use in modern aircraft, including all current Boeing and Airbus products...