Full Length v Intersection Departures

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This slide shows occurrences by phase of flight. Not surprisingly, approx 90% occurred during takeoff/inital climb. Conversely, approx 10% did not...

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Now for the good stuff:

This slide shows that during the study, there were a total of 130 uncontained failures in ALL HB engines (1st and 2nd gen), during those 9.2E7 flights. All other malfunctions are clearly not in the scope of our discussion.

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Finally, the last slide shows the failure rate of HB engines per 100 MILLION flights:

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According to this, you have less than a 1 in 775,000 chance of experiencing an engine failure in a modern high-bypas turbofan engine (like the ones used on the aircraft in the OP) regardless of the selected thrust. Even IF (still debatable) you could do something to further mitigate this "risk", do you really think it would make a significant contribution?

I found it interesting that the study chose to ignore the correlation between power selected and the failure rates. I assume they had the information (considering it was THEIR engines). I can only infer that they found no useful correlation...

And since Chewbacca is a wookie, you MUST acquit !!!

In closing, I can think of several good reasons to take a full length vs an intersection. This just doesn't sound like one of them. Most of the ones I know that do are also in the same camp as those who add extra gas "for the wife n kids" and call out "minimums" 100' high....

The defense rests...
 
I might be bad at reading, but that data is for uncontained engine failures, not ALL engine failures. Engines stop working for all sorts of reasons. Maybe the fuel pump decides to knock off for the day, or maybe the oil is French and decides that it's time to become liberated from the engine.

I don't know that either of the engine I've flown have EVER had an uncontained engine failure where parts grenade out of the engine.
 
JustinS said:
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.
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Every jet I've flown has had a high bypass engine on it, even the venerable EMB-145.
 
jtrain609 said:
I might be bad at reading, but that data is for uncontained engine failures, not ALL engine failures. Engines stop working for all sorts of reasons. Maybe the fuel pump decides to knock off for the day, or maybe the oil is French and decides that it's time to become liberated from the engine.

I don't know that either of the engine I've flown have EVER had an uncontained engine failure where parts grenade out of the engine.
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The details are in the full report (110 pages). All the "other" failures either weren't pertinent to our discussion (engine separation, pretty sure that was going to happen regardless) or were in such insignificant numbers that the bottom line is unchanged. Check it out...
 
jtrain609 said:
Every jet I've flown has had a high bypass engine on it, even the venerable EMB-145.
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I stand corrected. Yeah while looking things up, I realized even the CRJ has a high bypass turbofan. There's really no middle ground. You have things in the neighborhood of 5-6:1, and then there's the JT8D with a 1-1.7:1 ratio depending on the engine variant.
 
thevideographer said:
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.
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I try to be a good neighbor. Especially since I live in the neighborhood. I don't appreciate the supersonic tips at 3am, especially when you actually make more thrust with them subsonic. The initial prop speed is to get on step on the water, not for climb out. You really should reduce the rpm at like full throttle plus 5 seconds.
As far as CHTs, well, from repeated attempts, my engine runs 80-100F cooler taking off at ~23" MP than 30". And since at full power it takes ~300ft to take off and at that reduced power we're talking all of 500ft on a 2000ft+ runway it's not a big issue. If length might be and issue, sure full forward on the yoke, full power, 1/2 flaps, etc. But that isn't the norm. Also I have issues of the preheat only getting the oil to 100F or so, which at full takeoff power will take the oil pressure up near 100psi which is the red line.
As far as a place to land in case of an engine failure, you're really just better staying on the ground if you want to think of that. You might survive the landing, but you're still going to die.
 
Finally, to the OP: I have done 17R/G in KAUS many times in the Airbus. As long as we have the numbers, works good, lasts long time...

We've also chosen to go full length many times for various reasons. It's all good...
 
thevideographer said:
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.
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CHT is the wrong indicator anyway, EGT is where you'll see the difference. And no, the last 1/2" of throttle isn't mixture only, its mixture and power.

Power enrichment has far less to do with CHT than it does with:

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.
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I know some pistons that would disagree with you. Lets not forget that certification is done with new engines with good rings and in test cases.
Real engines have weak oil rings, slightly warped valves, carbon buildup, and timing that's a little off, and people do crazy stuff like add marvel mystery oil to their fuel to "prevent lead fouling." And install plugs that they found in the garbage.

Detonation has little to do with CHT anyway, its a function of load in terms of RPM and pressure, it may be affected by temperature hot spots like the spark plug electrode but generally the spark plug firing begins the detonation event anyhow. I've experienced detonation at a very low cylinder head temp due to a broken oil ring lowering the effective performance rating of the fuel. Mixture full rich stopped it long enough to get back to the ground.

A low stressed engine may not detonate without some kind of major problem... But the size of the engine and the airplane its mounted on aren't a good indicator of that. Stock 152 compression ratio is 8.5:1, sparrowhawk 152 is 9.7:1.

So what's a good way to increase your detonation margin? Rich mixture. 100LL is a brand name, it's really 100/130 with minimum lead content. The second number is the rich mixture rating.

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.
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It probably won't, but definitely could and that's not a universal statement I'd make for all aircraft and all engines.

The nice thing about having a throttle is that we get to decide how to use it.

What's best for economy isn't always best for longevity, what's best for longevity isn't necessarily best for low altitude survivability.

I certainly would at least start with the manufacturer recommendation of how to operate, contrary to what so many strangely untrusting people say, they generally know what they're talking about.

Sent from my XT1254 using Tapatalk
 
z987k said:
I try to be a good neighbor. Especially since I live in the neighborhood. I don't appreciate the supersonic tips at 3am, especially when you actually make more thrust with them subsonic. The initial prop speed is to get on step on the water, not for climb out. You really should reduce the rpm at like full throttle plus 5 seconds.
As far as CHTs, well, from repeated attempts, my engine runs 80-100F cooler taking off at ~23" MP than 30". And since at full power it takes ~300ft to take off and at that reduced power we're talking all of 500ft on a 2000ft+ runway it's not a big issue. If length might be and issue, sure full forward on the yoke, full power, 1/2 flaps, etc. But that isn't the norm. Also I have issues of the preheat only getting the oil to 100F or so, which at full takeoff power will take the oil pressure up near 100psi which is the red line.
As far as a place to land in case of an engine failure, you're really just better staying on the ground if you want to think of that. You might survive the landing, but you're still going to die.
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I do know that on the TIO540 the quicker you get from takeoff power to climb power the lower your CHT stays.
 
trafficinsight said:
CHT is the wrong indicator anyway, EGT is where you'll see the difference.
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True, but EGTs aren't what people normally look at to determine engine health. Engines are usually limited by their CHT - under 400º typically.

trafficinsight said:
Real engines have weak oil rings, slightly warped valves, carbon buildup, and timing that's a little off, and people do crazy stuff like add marvel mystery oil to their fuel to "prevent lead fouling." And install plugs that they found in the garbage.
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All of that stuff (well - minus the marvel mystery oil) would reduce compression and reduce the likelihood of detonation wouldn't it? Hot spots are the one thing I'll give you.

trafficinsight said:
Stock 152 compression ratio is 8.5:1, sparrowhawk 152 is 9.7:1.
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But my last car was an 11:1 compression ratio and it took 93 octane. I could run it up to 6400rpm and never get detonation. How would a relatively low-compression aircraft engine running much higher octane fuel ever detonate in normal operation?
 
thevideographer said:
True, but EGTs aren't what people normally look at to determine engine health. Engines are usually limited by their CHT - under 400º typically.
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Think of EGT as "how much heat am I putting into the engine parts" and CHT as "how well am I dissipating heat."

You likely won't see any immediate CHT change with a given change in EGT.

All of that stuff (well - minus the marvel mystery oil) would reduce compression and reduce the likelihood of detonation wouldn't it? Hot spots are the one thing I'll give you.
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Carbon buildup increases it, valve warp may or may not decrease it but mainly affects how well the face of the valve cools, timing doesn't affect compression at all but has an effect on combustion pressure, hot spots usually cause preignition, which isn't the same thing as detonation. Marvel mystery oil comes from snakes. ;)

But my last car was an 11:1 compression ratio and it took 93 octane. I could run it up to 6400rpm and never get detonation. How would a relatively low-compression aircraft engine running much higher octane fuel ever detonate in normal operation?
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Your car precisely controls fuel mixture and timing to prevent detonation and if it was built in the last decade includes a sensor which detects detonation so that it knows when it occurs and keeps it right on the edge of it for efficiency's sake. If you've ever driven a car from the 1960's up a steep grade then you have experienced detonation.

The aircraft engine is not so smart. Also, until detonation gets severe you may not notice that it's even happening.

Sent from my XT1254 using Tapatalk
 
Toobdrvr said:
Finally, to the OP: I have done 17R/G in KAUS many times in the Airbus. As long as we have the numbers, works good, lasts long time...

We've also chosen to go full length many times for various reasons. It's all good...
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Did you have to ask for it, or was it offered? I just don't really see the point of taking the intersection there and leaving thousands of feet behind you. No doubt its legal, but to save a few min of taxi time, it doesn't seem prudent to modify the standard departure point of the runway IMO.
 
Toobdrvr said:
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.
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Guess what that RPM increase is after you raise the flaps? :stir:
 
Kingairer said:
Did you have to ask for it, or was it offered? I just don't really see the point of taking the intersection there and leaving thousands of feet behind you. No doubt its legal, but to save a few min of taxi time, it doesn't seem prudent to modify the standard departure point of the runway IMO.
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What is the point of V1?
What is the point of the ASDR? (I'm not sure if we're using the same perf system, ours give it back on the PERF page)

Point being, in a part 25 jet, you don't fly it like a GA Stinson 108-1
<<<<<
 
Kingairer said:
Did you have to ask for it, or was it offered? I just don't really see the point of taking the intersection there and leaving thousands of feet behind you. No doubt its legal, but to save a few min of taxi time, it doesn't seem prudent to modify the standard departure point of the runway IMO.
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1. We usually ask for it.

2. Because it's proven to be SAFE
Because it's LEGAL
Because it's EFFICIENT
When the above three are met, my company encourages me to do it.
And it's their jet.
 
As I said before, if any of my teammates are uncomfortable doing it, it's not a big deal to go full length. I just don't think the level of safety is increased anywhere near as significantly as they believe...
 
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