Limiting Factors For Takeoff
Hi,
By order of importance what are the limiting factors for takeoff on majority of runways. Through some posts the climb gradient for second segment is the number one, but one of the guru in this forum said it's not necessearily true. Feedback appreciated. Regards |
The ability to stop is a fairly important limiting factor!
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Hi there,
Many factors are taken into account for Takeoff performance and most pilots are aware of it.(low Qnh,runway contamination,aircraft limitations...) However on B737s, emergency turns at V2 banking into the failed engine may be fatal if unaware of spoiler turn assist problems. Not banking into the good engine may drastically reduce the Vmca on which V2 minimum is calculated from. So if you have the choice,turn into the good engine as it is how Vmca was calculated in the first place.(3-5 degrees). Most crews are unaware of Missed approach climb gradient performance limitation for their aircraft,which should be known before dispatching the flight...:eek: 1)Runway(lengh/width) limit 2)0bstacle limit 3)Climb limit 4)Aircraft/weather/Crew limit |
The question is moot...any factor that limits your ability to get off the ground is not more or less important, it's simply a go/no go decision...
You might be smart and simply start at the most restrictive factor that day, then move backwards...but ALL limiting factors have to be calculated, addressed, solved, so they aren't limiting any more.... |
Pardon?
Not sure what AeroTech means on this one. What does second segment mean? On most runways I'd of guessed Max T.O. weight was the basic limit.
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Aero Tech, there is no single answer, it depends on the aircraft and airport. For example:
B747-300 Surabaya is field length limited, the B747-400 is 2nd segment climb limited. B747-300 Madinah is Obstacle Limited, the B747-400 is 2nd segment climb limited. And if you really want an interesting one, look at a MD11 from a hot/high airport and you will find that it is limited by its ability to dump fuel :) Mutt |
Your max take off weight is going to be limited by any one of:
Structural Limit Field length All engines Field Length One engine inop Climb 1st segment Climb 2nd segment Climb 3rd segment Climb final segment Climb missed approach Tyre speed Vmbe Vmc Obstacle clearence Something else I've probably forgotten They all have equal importance as which ever is most limiting is limiting! Which is most common depends on aircraft type and runway and no two are the same. So there is no answer to your question in it's current form. |
Not banking into the good engine may drastically reduce the Vmca on which V2 minimum is calculated
increase, perhaps ? Air Tourer Have a look Hetfield, I suggest that you bin whatever book you got that dreadful sketch from ... riddled with confusion. TOD - to 35ft first - to end of gear retraction second - to beginning of level acceleration third - acceleration and flap retraction fourth - final climb (for most types) fifth - final climb (for some types) FE Hoppy add ASD, TOR, LW plus burn and, if you list Vmc, then Vmcg as well, perhaps .. likewise, I've probably missed a few as well |
May I suggest a better graphic?
http://i48.tinypic.com/2i7sl4y.png
Interesting to know that some aircraft have a 5th segment. What would be the difference then? |
@JT
Yep, sorry it's a simplification on the fast run;) |
For the most recent types I have flown, the most common restriction has been MTOW. In second place, say 20% it is MLW and third place at say 5%, is performance (with the exception of LCY ops, when virtually every takeoff was performance limited). However, for my current type (E190), performance has never been a restriction. To date it has just been a case of turning the wick up to lift the given payload.
PM |
Hi AeroTech,
the limiting factors for takeoff on majority of runways We hardly ever have to use full T.O.thrust (normally use flex power reduction) so it's not very often a TODA / ASDA restriction. |
Interesting to know that some aircraft have a 5th segment. What would be the difference then?
Only seen the one I can recall at the moment (AW650 Argosy - Britain's Queen of the Skies) .. allowed for a final acceleration to enroute climb. Pugachev Cobra Much better diagram .. however, one trusts that the originator intends the aircraft to be several seconds off the ground before selecting wheels up ? The original question is interesting but has no definitive answer .. very much a case of "it depends" ... |
Can't forgest about landing weight next station and enroute climb limit weights when routing takes you over mountainous terrain?
Some older jets are effected by pressure altitude and temperature limits too. |
The original question is interesting but has no definitive answer .. very much a case of "it depends" ... When someone posts a question like that, then does not participate in the ensuing discussion, I consider the person a troll and not worthy of future responses. i can understand a newbie or 3 coming on with a question AND a lack of knowledge of the SEARCH function, but those are relatively rare. This particular OP has supposedly been here for 5 years, so he knows better... |
Then again, it probably doesn't matter all that much .. if the question, regardless of the motives of the poster, is interesting, it will attract responses .. if not, it will die a quick death and sink into the fetid archival abyss.
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Thanks
Thanks fellas, I expected a flogging, but I learn't something even from the first sketch. And I certainly didn't know about a leveling off in a 3rd segment. As for searching, I can never get the right words. As for the O.P. he got plenty to think about. John L.
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leveling off in a 3rd segment
applicable to heavy aircraft .. with a caveat that, for many of the overpowered twins around, the application is a shallow climb to match acceleration to flap retraction times. For lighties the takeoff is much simpler - distance to screen and a climb gradient requirement for initial climb and then you're on your own ... |
In order of importance..
(You'll first need a runway that is sufficient:) Take off Distance Available (TODA) Take off Run Available (TORA) wet runway limitations for accelerated stop distance runway slope/gradient .... and also as mentioned: Structural Limit Field length All engines Field Length One engine inop Climb 1st segment Climb 2nd segment Climb 3rd segment Climb final segment Climb missed approach Tyre speed Vmbe Vmc Obstacle clearence |
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. And if you really want an interesting one, look at a MD11 from a hot/high airport and you will find that it is limited by its ability to dump fuel . 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 is much less interesting considering the fact that the OP posted 2 similar questions then disappeared. When someone posts a question like that, then does not participate in the ensuing discussion, I consider the person a troll and not worthy of future responses. I can understand a newbie or 3 coming on with a question AND a lack of knowledge of the SEARCH function, but those are relatively rare. This particular OP has supposedly been here for 5 years, so he knows better... 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.
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And there is a problem with reduced thrust take-offs?
GF |
Johns7022:
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. |
discuss the logic of reduced thrust departures a little bit. |
FE Hoppy:
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. |
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:
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. |
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:
....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 ... |
And if you really want an interesting one, look at a MD11 from a hot/high airport and you will find that it is limited by its ability to dump fuel . But, that is simply not the categorical case. (weight, performance, etc.) 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. might rethink this is I pull up right at the fence(because I calculated balanced field into the overrun).. 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:
We operate under FAR91/121/135, we operate some aircraft with BALANCED FIELD, some without. |
john tullamarine:
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 .... 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).
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Denti:
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). |
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.
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Denti:
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. |
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