Hi,

Thank you for your posts.
I don’t have any specific aircraft or runway in my mind. I just wanted to have a general idea about takeoff limitations for airliners in the majority of runways. But it seems there is no single answer to my question.

Mutt, it will be nice if you can give more details.

I am wondering if takeoff thrust time limit is limiting factor on takeoff.

Let say an engine fails on takeoff and for some reason (missed approach) the pilot makes a go-around during air turn-back to the departure airport. Using takeoff thrust twice in such period of time may affect the reliability of the engine especially that most of engine failures occur at high thrust.
In such situation can pilot disregard the go-around and land as soon as possible, or perform the around and land? I am assuming the engine failure doesn’t affect the safety of aircraft like engine fire.

It’s true that internet made the world small town, but still members on this forum live all over the world. While I am sleeping in the States other member in the other part of the world is working. I assume many active members in this forum (Tech Log) are pilots: they might be out of town, out the country, or even in other continent. Other people are busy and they have their own schedule to check this forum. So I gave them time to answer and also sometimes it takes time to understand something that I didn’t understand, or ask the next question, or ….

It seems you want to intrude your own rules in this forum, but fortunately there is a moderator here. I am grateful to all members for their responses and also for their previous posts when I use “search function). I am grateful to you “Intruder” if you post useful and technical posts regarding the subject of my post. But if you don’t like my posts or you are “allergic” to my posts just disregard them.

Thank you and feedback appreciated
Regards

If the OP is gone, and the heavy hitters are here......maybe this thread can move off of the kid stuff...and discuss the logic of reduced thrust departures a little bit.

And there is a problem with reduced thrust take-offs?

GF

Johns7022:
The primary logic is to extend engine life substantially with no decrease in safety provided they are done correctly.

When I have more space available than I need at full thrust I can reduce the thrust to the point that the space I need equals the space available.

FE Hoppy:
That's the balanced runway part. The reduced thrust also needs to meet, or exceed the Part 25 takeoff path unless an engine fails after V1 in which case you then need to advance the good engine(s) to max takeoff thrust.

Hmm. now we really are getting into interesting territory. I know a little jet with an ATTCS that will do that for me and I'm not allowed to go if it's inop. I also know quite a few big jets where my performance after Vef is predicated on the assumed temperature thrust and I need not advance the thrust levers.
I also know a jet where advancing the thrust lever on the good engine could well cause me to loose shall we say "control on the ground".

If we swap my "space" for the more commonly used " performance" then I think it covers the whole concept quite nicely.

Oh yes, I detest "balanced fields" and never use them.

FE Hoppy:
No doubt that almost any lightly loaded transport jet could perform the profile with reduced thrust after an engine failure. But, that is simply not the categorical case. (weight, performance, etc.)

No doubt, if below takeoff power VMCg. But, no competent performance engineer would permit that to happen.

I don't understand what you are saying.

That is not an option for commercial operations in the U.S. It's "nice" that you as an individual get to make that determination.

When I have more space available than I need at full thrust I can reduce the thrust to the point that the space I need equals the space available.

Qantas was one of the leading lights in the reduced thrust development process. Wal Stack, at the time the boss ops engineer (and a thoroughly nice bloke as well as having a flying history), took the view that he would leave around a 1000ft accel stop pad for his crews, mum and the kids. I still think that that was a good strategy rather than going to the limiting case for the sake of a few extra kilos.

That's the balanced runway part.

Confusing two concepts I fear.

in which case you then need to advance the good engine(s) to max takeoff thrust.

Never the case. While the pilot retains the ability to advance thrust up to the relevant rating, reduced thrust is based on the philosophy that there is no need or requirement to do so. The caveat is that, should the pilot chose to advance the throttles, he/she should do so SLOWLY.

I also know a jet where advancing the thrust lever on the good engine could well cause me to loose shall we say "control on the ground".

Not only a problem with jets. I was involved in the investigation of a turboprop fatal in which our conclusion was that the pilots pushed up the throttles with an overshoot leading to a Vmca departure and the ensuing fireball ....

But, that is simply not the categorical case. (weight, performance, etc.)

Time for you to produce evidence to support such a statement ?

But, no competent performance engineer would permit that to happen

Said competent performance engineer is presuming that the pilot is NOT going to push up the throttles ...

Balanced Field Length

.. should always be optional other than for those aircraft which only have BFL AFM data (DC9 for instance, as I recall)

John tullamarine,

You are correct my post #3 was written too quickly,I meant Vmca will INCREASE and your actual aircraft speed will be below Vmca.

....But, no competent performance engineer would permit that to happen

Said competent performance engineer is presuming that the pilot is NOT going to push up the throttles ...

Nicely put...
If i misspell your name,apologies Im again on the run:sad:

I think it should follow that if airlines can run engines on condition untill they show wear, rather then TBO...GA aircraft should be able to do it as well..

And while we are at it, in our corporate operations, just like the airlines, we hire our own mechanic to determine engine condition...

Something tells me though...with the boss in the back, being sold on the idea of never having to pay for engine overhauls, might rethink this is I pull up right at the fence(because I calculated balanced field into the overrun)..

(Sorry just saw 'Flying Cheap' on Frontline)

de facto:
If the aircraft is at V2 (or slightly greater) Vmca is not a factor with an engine failure. If the takeoff flight path is obstacle limited then not increasing the power after an engine failure will limit payload, or perhaps cause the takeoff flight path to fall below minimum regulatory requirements. V1 must be above Vmcg and V2 must be above Vmca, otherwise the takeoff flight performance calculations are bogus.

Actually it applies to ALL FAR 25 aircraft as it is determined by FAR25.1001 (IIRC) The aircraft must be able to meet approach/landing climb criteria 15 minutes after takeoff with or without a fuel dumping system. The MD11 AFM actually has a section detailing the weights associated with this limitation.

Sorry but you are incorrect, we operate a WIDE range of aircraft, most are permitted to use DERATE/ASSUMED/FLEX thrust, ONLY ONE OF THEM is required to advance the throttle following an engine failure, and that is the aircraft that FE Hoppy is talking about.

We operate under FAR91/121/135, we operate some aircraft with BALANCED FIELD, some without.

Believe it or not, I was able to make that determination :):) Based upon the aircraft's capabilities and payload advantages.

Most of our corporate fleet that has the option of DERATE/ASSUMED/FLEX thrust use it. It increases the blade life on some of our engines by 12%, which translates into a financial saving, much to the bosses pleasure.


Aero tech, some of our aircraft are limited to 5 minutes takeoff thrust, some to 10 minutes, some to 5 minutes but 10 minutes in the event of an engine failure. And yes you were right, some of us are on the road hiding out in strange hotels :)

Mutt

aterpster -

If the aircraft is at V2 (or slightly greater) Vmca is not a factor with an engine failure

If the speed schedule is V2min limited (generally at minimum weight, say a short ferry flight), then Vmca might not be too far below V2. Mishandle the failure by banking the wrong way and it might get interesting - depends on CG etc on the day but not something to be dismissed as you appear to be doing I suggest.

If the takeoff flight path is obstacle limited then not increasing the power after an engine failure will limit payload

In general that is not so as the reduced thrust takeoff has already considered the obstacle profile (and all the usual things which go into determining the RTOW).

Also, if you have commenced the takeoff, which appears to be a prerequisite to having an engine failure consideration, then how can pushing up the throttle increase your payload at the time you have the failure during the takeoff ? .. or am I missing something obvious to you but mystifying to me ?

perhaps cause the takeoff flight path to fall below minimum regulatory requirements

Likewise, not so as ALL the regulatory requirements have been considered in determining the reduced thrust RTOW data.


I think that we need to call your bluff and ask you to cite some authoritative data to support your claims ?

Now, mutt and I are experienced ops engineers and I don't think we have knowledge of such generic problems ....

Mutt:
So how do you avoid 91.605, 121.189, or 135.379?

john tullamarine:
I am not a performance engineer, I am a TERPs sort of guy. When I used to be a real pilot (TWA) required us to increase power on the remaining engine (s) in the event of an engine failure after achieving V2 speed.

They also taught at the school house that payload was predicated on reduced thrust with all engines operating and with takeoff power in the event of an engine failure.

Wouldn't be the first time they taught bum scoop.

Having said that, at an airport where obstacles limit the flight path, I would be on a fool's errand if I did not increase thrust on the remaining engine (s) rather than hope to clear that ridgeline 7 miles away by 35 feet. :rolleyes:

TWA also did not assess more than 300 feet each side of the takeoff flight path (beyond the airport boundary), which was another reason for advancing to takeoff power in the event of an engine failure.

Increasing power on the remaining seems like good sense. Until you have to deal with fixed derates and the associated effects. Are you sure your full thrust Vmca is below your fully derated V2? If not you certainly will live (very short) in interesting times after advancing the remaining engine to full thrust. Boeing advised us that using the Boeing performance calculation tool we should not advance any thrust levers until we go to MCT if using fixed derates, which we do nearly every single take off (combined with assumed temperature of course).

Denti:

When I did this we changed V1 for derated thrust, but V2 was never changed.

Well, that explains that. Today we play around with all parameters, including V2 which can vary by as much as 40kts for the same conditions depending what you allow the program to calculate.

Denti:
V2 varied greatly by weight, but not by power setting.