Landing gear down and segments?
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Landing gear down and segments?
Hi pprune!
A young soul here seeking clarification regarding aircraft performance...
When you depart on hot days, and when you keep your landing gear down to cool down, how do you do with the 2nd segment? Is that segment, during performance calculations, delayed? And if so, is that a separate calculation?
If i recall correctly, first segment ends when landing gear is fully retracted and all you have to take into consideration is a positive rate of climb (for a two engine)? In some airports obstacles are very close...My question is how those should be cleared when all you have to do is having a positive rate of climb (instead of, during 2nd segment, 2.4% gross and 1.6% net)?
I might just be young and stupid though...But i do believe in the power behind the question ''why?''.
Thanks!
A young soul here seeking clarification regarding aircraft performance...
When you depart on hot days, and when you keep your landing gear down to cool down, how do you do with the 2nd segment? Is that segment, during performance calculations, delayed? And if so, is that a separate calculation?
If i recall correctly, first segment ends when landing gear is fully retracted and all you have to take into consideration is a positive rate of climb (for a two engine)? In some airports obstacles are very close...My question is how those should be cleared when all you have to do is having a positive rate of climb (instead of, during 2nd segment, 2.4% gross and 1.6% net)?
I might just be young and stupid though...But i do believe in the power behind the question ''why?''.
Thanks!
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interesting point
second segment climb is really important if you have an engine failure.
and there are some times where there are so many obstacles nearby you would want to know the performance
BUT, I think most of us would take off and not retract the gear if you wanted to cool the brakes a bit
BUT if one of the engines quit, then we would retract the gear for performance.
It is pretty rare these days to leave the gear down to cool the brakes, the only time I can think one would do this is if you were in the traffic pattern doing multiple take offs and landings as in a training situation
second segment climb is really important if you have an engine failure.
and there are some times where there are so many obstacles nearby you would want to know the performance
BUT, I think most of us would take off and not retract the gear if you wanted to cool the brakes a bit
BUT if one of the engines quit, then we would retract the gear for performance.
It is pretty rare these days to leave the gear down to cool the brakes, the only time I can think one would do this is if you were in the traffic pattern doing multiple take offs and landings as in a training situation
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Thanks SHFG for that quick response!
If you would retract the gear for performance reasons then you should know the exact point were the obstacles are?
I mean say for ex. that after takeoff from RWY 10 the first (and most limited) obstacle are approx 11ft, 200m from the end of TODA... (11ft/(200/.3048)*100)
That will give you a climb gradient of 1.6764% NET (or 2.4764% GROSS)...
With landing gear down...Can you really clear that obstacle?
Again, i'm more than thankful for your response SHFG, and i will follow this thread with curiosity!
If you would retract the gear for performance reasons then you should know the exact point were the obstacles are?
I mean say for ex. that after takeoff from RWY 10 the first (and most limited) obstacle are approx 11ft, 200m from the end of TODA... (11ft/(200/.3048)*100)
That will give you a climb gradient of 1.6764% NET (or 2.4764% GROSS)...
With landing gear down...Can you really clear that obstacle?
Again, i'm more than thankful for your response SHFG, and i will follow this thread with curiosity!
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Some AFMs or related operational documents will give you data for the consideration.
However, one needs to keep in mind that, if you do your own thing .. you may be called to justify it subsequent to a mishap or other conflict.
Doing the occasional non-standard operation with requirements to do further actions in the event of this and that .. might be setting yourself up for a surprise. I'm sure most of us can recall the odd time the gear has been overlooked for whatever reason and not picked up until after takeoff scan time .. ?
Generally only a concern if you are using very heavy braking .. eg accel stop testing or similar .. when leaving the gear down is the technique used to manage the heat buildup problem.
Another approach is to retract the gear, get a suitable amount of air underneath you and then extend it to address your concerns without terrain worries.
However, one needs to keep in mind that, if you do your own thing .. you may be called to justify it subsequent to a mishap or other conflict.
Doing the occasional non-standard operation with requirements to do further actions in the event of this and that .. might be setting yourself up for a surprise. I'm sure most of us can recall the odd time the gear has been overlooked for whatever reason and not picked up until after takeoff scan time .. ?
Generally only a concern if you are using very heavy braking .. eg accel stop testing or similar .. when leaving the gear down is the technique used to manage the heat buildup problem.
Another approach is to retract the gear, get a suitable amount of air underneath you and then extend it to address your concerns without terrain worries.
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Hi Beirut pilot
It's common that certification requirements are being mixed up with procedural requirements. I am kind of a geek when it comes to this topic, so a rather long reply follows...
Certification requirements:
The different segments, and corresponding gradients, of a take off are certification requirements (FAR 25). Hence, the manufacturer of your aircraft has to demonstrate that your aircraft will met these requirements or your aircraft would never have been allowed to fly.
These are just ways for the authorities to ensure, that the aircraft being certified, is able to get away from the ground somewhat at all. They (FAA originally) deviced these manoeuvres and set the requirements, that needs to be demonstrated, to a level that they decided was to be considered safe.
It has nothing to do with obstacle clearance. They demonstrate that the aircraft has a certain climb performance, nothing more, nothing less!
Procedural requirements:
A complete different authority (ICAO), set a limit for minimum obstacle clearance during (all engines operating/normal/standard/day-to-day) takeoffs. This is described in ICAO Doc 8168: Procedures for Air Navigation Services (PANS OPS), currently 5th edition.
Their assessment of what is safe resulted in a minimum required gradient of 3.3%. For our modern high-performance aircrafts with gradients in the 15%+ range, this is not a problem (remember these requirements were set in the 60'ies and applies to propeller/general aviation aircrafts as well).
What further adds to the confusion, is that previous versions (up to 3rd edition), there was indeed a level segment for acceleration in PANS OPS procedure design. This was because Lockheed Constellations, DC-3s etc. didn't have all that great performance. But still it's shouldn't be confused with the certification requirements in FAR25. A level segment for acceleration is obsolete since 1993 with the 4th edition of PANS OPS.
In short, so even with gear-down and accelerating, your modern aircraft should have a gradient well above 3.3%
Engine failure:
ICAO procedures (PANS-OPS/Doc 8168) are ALWAYS assuming all engines operating:
So if your engine subsequently fails, your brake cooling becomes a secondary issue and you retract the gear. There after you "apply the note", in the quote above = follow the engine failure procedure established by your operator: You and your company are on your own! It's YOUR responsibility to clear obstacles and no agency is guaranteeing you anything.
P.s.
For go-around the same misconceptions exists. The reply above is partly copied from a recent reply I made to that topic in http://www.pprune.org/tech-log/55733...ormance-2.html . Maybe it will interest you to read my replies there too.
It's common that certification requirements are being mixed up with procedural requirements. I am kind of a geek when it comes to this topic, so a rather long reply follows...
Certification requirements:
The different segments, and corresponding gradients, of a take off are certification requirements (FAR 25). Hence, the manufacturer of your aircraft has to demonstrate that your aircraft will met these requirements or your aircraft would never have been allowed to fly.
These are just ways for the authorities to ensure, that the aircraft being certified, is able to get away from the ground somewhat at all. They (FAA originally) deviced these manoeuvres and set the requirements, that needs to be demonstrated, to a level that they decided was to be considered safe.
It has nothing to do with obstacle clearance. They demonstrate that the aircraft has a certain climb performance, nothing more, nothing less!
Procedural requirements:
A complete different authority (ICAO), set a limit for minimum obstacle clearance during (all engines operating/normal/standard/day-to-day) takeoffs. This is described in ICAO Doc 8168: Procedures for Air Navigation Services (PANS OPS), currently 5th edition.
Their assessment of what is safe resulted in a minimum required gradient of 3.3%. For our modern high-performance aircrafts with gradients in the 15%+ range, this is not a problem (remember these requirements were set in the 60'ies and applies to propeller/general aviation aircrafts as well).
What further adds to the confusion, is that previous versions (up to 3rd edition), there was indeed a level segment for acceleration in PANS OPS procedure design. This was because Lockheed Constellations, DC-3s etc. didn't have all that great performance. But still it's shouldn't be confused with the certification requirements in FAR25. A level segment for acceleration is obsolete since 1993 with the 4th edition of PANS OPS.
In short, so even with gear-down and accelerating, your modern aircraft should have a gradient well above 3.3%
Engine failure:
ICAO procedures (PANS-OPS/Doc 8168) are ALWAYS assuming all engines operating:
So if your engine subsequently fails, your brake cooling becomes a secondary issue and you retract the gear. There after you "apply the note", in the quote above = follow the engine failure procedure established by your operator: You and your company are on your own! It's YOUR responsibility to clear obstacles and no agency is guaranteeing you anything.
P.s.
For go-around the same misconceptions exists. The reply above is partly copied from a recent reply I made to that topic in http://www.pprune.org/tech-log/55733...ormance-2.html . Maybe it will interest you to read my replies there too.
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Thank you all for your inputs, especially Cosmo for your detailed answer. I will go through it once again soon, and if i encounter any question i will simply ask here.
It is it actually a published procedure on your type to leave the gear down to cool the brakes, or just something someone thought of?
If we depart and leave the gear down on the 777, we have specific performance data for that configuration.
If it's actually a certified procedure on your aircraft, the performance data should also be published.
It would not be safe to simply decided to raise the gear in response to an engine failure, as you would have already lost performance, and gear retraction is often a high drag sequence.
If we depart and leave the gear down on the 777, we have specific performance data for that configuration.
If it's actually a certified procedure on your aircraft, the performance data should also be published.
It would not be safe to simply decided to raise the gear in response to an engine failure, as you would have already lost performance, and gear retraction is often a high drag sequence.
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In some airplanes you can get an ECAM prompting you to keep the gear down, but in IMC in high elevation field, high temperature, max weight and high surrounding terrain… Could be a bad thing. Also, you may consider following the engine out procedure. That should keep u safe.
In VMC, terrain in sight, you can go on according to what you see. Probably doing well most of the times.
In VMC, terrain in sight, you can go on according to what you see. Probably doing well most of the times.
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It would not be safe to simply decided to raise the gear in response to an engine failure, as you would have already lost performance, and gear retraction is often a high drag sequence.
In VMC, terrain in sight, you can go on according to what you see. Probably doing well most of the times.
On the other hand...
As stated above by Wizofoz, there seem to be some sort of tables for that very special config. Now i want to know how common those tables are? Just curious.
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Well, some manufacturers give that info, others don't, which I take as the L/G DOWN performance not being required by any certification or operation regulations.
Basically you are on your own. My opinion is that there is no problem whatsoever unless you are in a challenging airfield, like I mentioned (BOG in a hot day and the airplane full to the brim). In that case I would feel scared and I would try to stay in the lower terrain area, climbing like a vulture if need be. For that, a special engine out procedure is as adequate as any other option (like visually climbing like a vulture).
In non challenging airports I wouldn't care much, my airplane climbs like a rocket with two engines.
Basically you are on your own. My opinion is that there is no problem whatsoever unless you are in a challenging airfield, like I mentioned (BOG in a hot day and the airplane full to the brim). In that case I would feel scared and I would try to stay in the lower terrain area, climbing like a vulture if need be. For that, a special engine out procedure is as adequate as any other option (like visually climbing like a vulture).
In non challenging airports I wouldn't care much, my airplane climbs like a rocket with two engines.
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They (FAA originally) deviced these manoeuvres and set the requirements
Not quite right.
The original story for the current performance philosophy/requirements is the ICAO Final Report of the Standing Committee on Performance dating back to 1953. One of our posters, a long time colleague and very kindly, passed his personal copy onto me some time ago .. now a valued reference library document on the bookshelf to my side.
Various States then publish their implementation (evolving over the years) of these requirements. Hence we see FAR 23/25 etc.
It has nothing to do with obstacle clearance. They demonstrate that the aircraft has a certain climb performance, nothing more, nothing less!
Not quite right.
(a) you are talking about WAT limits .. which are included in the AFM and represent the Design Standards bottom climb line. Rarely are these the critical path for a takeoff weight calculation in the field. Usually, either runway length or obstacle clearance is more critical.
(b) you are overlooking segment obstacle clearance .. which also is included in the AFM and must be met at planning to establish RTOW compliance.
A complete different authority (ICAO), set a limit for minimum obstacle clearance
Not quite right.
PANS/OPS relates to routine AEO operations, letdowns, etc. Nothing to do with takeoff calculations which are AFM based and OEI.
In short, so even with gear-down and accelerating, your modern aircraft should have a gradient well above 3.3%
Now that depends entirely on the gross weight and how the aircraft is being operated .. a very long bow to draw, methinks.
In VMC, terrain in sight, you can go on according to what you see.
Danger, Will Robinson ...
OEI, the gradients can be so shallow that they defy any perceptual attempt to wing it on the day.
Either you have done the sums and fly to the procedure .. or you are in the lap of the Gods .. and the Gods, generally, don't care a fig, ergo, a high probability of a subsequent CFIT.
Some States have permitted this sort of thing for smaller heavy aircraft .. eg, Australia for under 50,000lb permitted reduced splays in VMC (to allow the F27 some flexibility in the early days). Interestingly, this was metricated to 20T (if the memory serves me correctly) .. which thwarted the original rationale. I protested formally (long ago) and gave up in the face of the usual opposition. I notice that it now has sneaked back up to 22.7T ...
Main concern is that it just is NOT feasible to wing OEI obstacle clearance visually ... requires visual/perceptual discrimination beyond our capability.
Not quite right.
The original story for the current performance philosophy/requirements is the ICAO Final Report of the Standing Committee on Performance dating back to 1953. One of our posters, a long time colleague and very kindly, passed his personal copy onto me some time ago .. now a valued reference library document on the bookshelf to my side.
Various States then publish their implementation (evolving over the years) of these requirements. Hence we see FAR 23/25 etc.
It has nothing to do with obstacle clearance. They demonstrate that the aircraft has a certain climb performance, nothing more, nothing less!
Not quite right.
(a) you are talking about WAT limits .. which are included in the AFM and represent the Design Standards bottom climb line. Rarely are these the critical path for a takeoff weight calculation in the field. Usually, either runway length or obstacle clearance is more critical.
(b) you are overlooking segment obstacle clearance .. which also is included in the AFM and must be met at planning to establish RTOW compliance.
A complete different authority (ICAO), set a limit for minimum obstacle clearance
Not quite right.
PANS/OPS relates to routine AEO operations, letdowns, etc. Nothing to do with takeoff calculations which are AFM based and OEI.
In short, so even with gear-down and accelerating, your modern aircraft should have a gradient well above 3.3%
Now that depends entirely on the gross weight and how the aircraft is being operated .. a very long bow to draw, methinks.
In VMC, terrain in sight, you can go on according to what you see.
Danger, Will Robinson ...
OEI, the gradients can be so shallow that they defy any perceptual attempt to wing it on the day.
Either you have done the sums and fly to the procedure .. or you are in the lap of the Gods .. and the Gods, generally, don't care a fig, ergo, a high probability of a subsequent CFIT.
Some States have permitted this sort of thing for smaller heavy aircraft .. eg, Australia for under 50,000lb permitted reduced splays in VMC (to allow the F27 some flexibility in the early days). Interestingly, this was metricated to 20T (if the memory serves me correctly) .. which thwarted the original rationale. I protested formally (long ago) and gave up in the face of the usual opposition. I notice that it now has sneaked back up to 22.7T ...
Main concern is that it just is NOT feasible to wing OEI obstacle clearance visually ... requires visual/perceptual discrimination beyond our capability.
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dear OP
imagine you are taking off and your landing gear fails to retract
do you: stop, and look at data
or
DO YOU FLY THE PLANE?
It would be really rare, though not impossible, to have landing gear fail to retract and also lose an engine at the same time, so you will probably get away with it.
Now, it may interest you to know there are 4 segments of climb and it is not just about losing an engine.
IN REAL LIFE big airlines have engineering departments that make all sorts of calculations for each airport and each runway so we really don't worry about it too much.
But if we had a takeoff from a non routine airport, we would have to examine things.
Pilots sometime have to just "wing it" or play it by ear.
Flying is an art as well as a science!
imagine you are taking off and your landing gear fails to retract
do you: stop, and look at data
or
DO YOU FLY THE PLANE?
It would be really rare, though not impossible, to have landing gear fail to retract and also lose an engine at the same time, so you will probably get away with it.
Now, it may interest you to know there are 4 segments of climb and it is not just about losing an engine.
IN REAL LIFE big airlines have engineering departments that make all sorts of calculations for each airport and each runway so we really don't worry about it too much.
But if we had a takeoff from a non routine airport, we would have to examine things.
Pilots sometime have to just "wing it" or play it by ear.
Flying is an art as well as a science!
The bottom line is that any pilot worthy of the name would not take off with brakes so hot that the gear need to stay down for cooling if there was any question about climb performance.
Also if you were so heavy you need to worry about second segment climb you would also have to worry about stopping ability with those hot brakes. Academic discussions are fine, but in the real world you need to be a pilot.
Also if you were so heavy you need to worry about second segment climb you would also have to worry about stopping ability with those hot brakes. Academic discussions are fine, but in the real world you need to be a pilot.
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Pilots sometime have to just "wing it" or play it by ear.
Some of us might opine that planning and knowledge is superior ...
Also if you were so heavy you need to worry about second segment climb you would also have to worry about stopping ability with those hot brakes
That doesn't necessarily follow at all .. perhaps you might elaborate for us ?
Some of us might opine that planning and knowledge is superior ...
Also if you were so heavy you need to worry about second segment climb you would also have to worry about stopping ability with those hot brakes
That doesn't necessarily follow at all .. perhaps you might elaborate for us ?
My point to the OP was that he stated
as if it is a generally accepted procedure.
I have operated in some very hot places, and have never heard of this being a common practice. It is included in (as an example) the 777 as a non-normal, but i for one have never actually used it , or know of anyone who has.
So to ask again to Beriuit Pilot, is this idea actually included in your manuals, is performance information available, and what information would trigger you thinking it was necessary on any particular day? People will often end up operating in a particular way because :So-an-so told me too", without it actually being a procedure designed for or approved by the manufacturer.
When you depart on hot days, and when you keep your landing gear down to cool down,
I have operated in some very hot places, and have never heard of this being a common practice. It is included in (as an example) the 777 as a non-normal, but i for one have never actually used it , or know of anyone who has.
So to ask again to Beriuit Pilot, is this idea actually included in your manuals, is performance information available, and what information would trigger you thinking it was necessary on any particular day? People will often end up operating in a particular way because :So-an-so told me too", without it actually being a procedure designed for or approved by the manufacturer.
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Further to the Wiz :
It is usually detailed in the MEL OPS proc for Main gear inop( Airbus) . It indicates that specific Perf has to be done . Also mentions "in case of engine failure case .
Doesn't seem to be any reference for the test pilots to just leave them hanging because they cooked the brakes or its a " hot " day . Never seen this considered even in a region where OAT's reach high 45+ degrees in the summer . If brakes hot " delay takeoff " . Seems clear from the manufacturer's viewpoint .
It is usually detailed in the MEL OPS proc for Main gear inop( Airbus) . It indicates that specific Perf has to be done . Also mentions "in case of engine failure case .
Doesn't seem to be any reference for the test pilots to just leave them hanging because they cooked the brakes or its a " hot " day . Never seen this considered even in a region where OAT's reach high 45+ degrees in the summer . If brakes hot " delay takeoff " . Seems clear from the manufacturer's viewpoint .
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The original story for the current performance philosophy/requirements is the ICAO Final Report of the Standing Committee on Performance dating back to 1953. One of our posters, a long time colleague and very kindly, passed his personal copy onto me some time ago .. now a valued reference library document on the bookshelf to my side.
Various States then publish their implementation (evolving over the years) of these requirements. Hence we see FAR 23/25 etc.
Various States then publish their implementation (evolving over the years) of these requirements. Hence we see FAR 23/25 etc.
It has nothing to do with obstacle clearance. They demonstrate that the aircraft has a certain climb performance, nothing more, nothing less!
Not quite right.
(b) you are overlooking segment obstacle clearance .. which also is included in the AFM and must be met at planning to establish RTOW compliance.
Not quite right.
(b) you are overlooking segment obstacle clearance .. which also is included in the AFM and must be met at planning to establish RTOW compliance.
For a normal take off (with gear down as the example of the original poster), segment compliance is absolutely not an issue, nor a requirement. In fact there are no segments in a normal takeoff. What you have to comply with during a normal takeoff is the procedural climb gradient. See below...
A complete different authority (ICAO), set a limit for minimum obstacle clearance
Not quite right.
PANS/OPS relates to routine AEO operations, letdowns, etc. Nothing to do with takeoff calculations which are AFM based and OEI.
Not quite right.
PANS/OPS relates to routine AEO operations, letdowns, etc. Nothing to do with takeoff calculations which are AFM based and OEI.
A complete different authority (ICAO), set a limit for minimum PROCEDURAL obstacle clearance (standard and minimum 3.3%).
I.e., they set the standards for what they considered to be a safe clearance of obstacles for design of instrument procedures.
And... EXACTLY... they have nothing to do with an engine out scenario. See above...
In short, so even with gear-down and accelerating, your modern aircraft should have a gradient well above 3.3%
Now that depends entirely on the gross weight and how the aircraft is being operated .. a very long bow to draw, methinks.
Now that depends entirely on the gross weight and how the aircraft is being operated .. a very long bow to draw, methinks.