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Why do we have take-off segments?

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Why do we have take-off segments?

Old 9th Mar 2013, 12:12
  #21 (permalink)  
 
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Minimum acc ht of 400ft is a regulatory requirement both JAA/FAA and therefore minimum operational acceleration height is 400 ft or higher

Last edited by vilas; 9th Mar 2013 at 12:29.
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Old 9th Mar 2013, 15:31
  #22 (permalink)  
jmn
 
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Second Segment

Hi all,

2.4% minimum gross gradient; can it be increased?
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Old 10th Mar 2013, 10:24
  #23 (permalink)  
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2.4% minimum gross gradient; can it be increased?

Simply by reducing weight which often is required for obstacle clearance.
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Old 10th Mar 2013, 11:35
  #24 (permalink)  
 
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Simply by reducing weight which often is required for obstacle clearance
Before off loading bags,use of improved climb may be used..
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Old 13th Mar 2013, 01:57
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jmn

2.4% minimum gross gradient; can it be increased?


If I may, 2.4% is the minimum net gradient requirement on the 2nd segment for twin engines.

To answer the question:

Increasing V2 and/or reducing flaps setting can be considered if TODA is not limiting.
Otherwise, like already said, mass reduction is the other option.
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Old 13th Mar 2013, 11:13
  #26 (permalink)  
 
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Originally Posted by Feno
2.4% is the minimum net gradient requirement on the 2nd segment for twin engines.
Wrong. It is a gross gradient. It is obtained at the start of the 2nd segment. The gradient of the flight path reduces with height due to the thrust reducing with altitude. Therefore WAT-limit gradient is not equal to the average gross flight path gradient in the second segment.

Originally Posted by hvogt
A lot of confusion arises from the fact that the take-off performance requirements of CS-25 do not define any 'segments' as such.
I think the confusion arises from failure to appreciate the differences between the take-off climb requirements of 25.121 and the gradient of the flight path defined in 25.115.

25.121(a), (b) and (c) contains three minimum steady climb gradient requirements out of ground effect in still air which together define the maximum take-off weight for the altitude and temperature, or WAT-limit. That is an airworthiness limitation that exists independent of the presence of obstacles. It replaces a provision in the predecessor regulation (CAR 4b) that required a minimum rate of climb as a function of the stall speed prior to the age of turbine engines.

In the take-off flight path the gradient is never steady. The ground effect changes with height above the surface. The drag changes when the configuration or speed changes. The thrust changes with ambient pressure and temperature as the airplane climbs, and with changes of airspeed. The take-off flight path is also subject to wind.

25.121(a) takes speed, configuration, and thrust at different points of the 'first' segment:
- speed is at liftoff,
- configuration is at the point of maximum drag in the gear retraction cycle - typically wheel well doors open and the gear half-way retracted,
- thrust is at the point where L/G retraction is begun - typically three seconds after liftoff.

Last edited by HazelNuts39; 13th Mar 2013 at 12:24. Reason: typos
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Old 13th Mar 2013, 16:22
  #27 (permalink)  
 
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HazelNuts

Thx for clearing that up.
The gross ("actual" as per CS 25.115 terminology) and net notions apply as part of the clearing obstacles process by 35 ft, which is a separate issue from the gross 2.4% requirements for which the 0.8 % penalty would not make sens then.
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Old 13th Mar 2013, 22:51
  #28 (permalink)  
 
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Part of the confusion comes from what the rules are written for.

The segments are, initially, for certifying the aircraft. Hence they are spelled out in detail in the FARs. Naturally if an aircraft is certified against certain requirements that manufacturer will have generated the flight test data to prove their case. Thus they can publish this data for the user and if we can fly the same profile and have certainty of the aircraft's performance.

If you are flying an aircraft with marginal performance then you will most likely have to fly the same segments to be able to ensure terrain clearance. If, however, you are blessed with additional performance then you could safely, from a terrain clearance perspective, fly a different profile such as accelerating early or retracting flaps early.

Just to add to the confusion we now take into account crew workload, automation, and noise abatement when designing procedures. So to the casual reader of a company ops manual it may not be clear why events happen at a certain point. Myths and legends then appear that 'you can't' do certain things.

For example, in Australia the requirement is to ensure 35' terrain clearance on departure or 50' in a turning departure. There is no regulatory requirement to fly a segmented climb but most operators have a segmented climb procedure. But this does not stop you flying a profile of your choosing if you maintain the required terrain clearance.
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Old 13th Mar 2013, 23:28
  #29 (permalink)  
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But this does not stop you flying a profile of your choosing if you maintain the required terrain clearance.

quite so .. but how do you establish (ie where are the numbers and hard data for your benefit at the Inquiry) that all is OK before you launch ? The advantage of flying it per the AFM is that the OEM has done all that stuff.

Different matter AEO to keep yourself above the OEI net profile ..
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Old 14th Mar 2013, 00:55
  #30 (permalink)  
 
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Part of the confusion comes from what the rules are written for.
Agreed

It's quite often a certification vs exploitation confusion.
Another example being the GA approach climb 2.1 % climb gradient requirement which is a certification one as opposed to the 2.5 % climb gradient imposed by OPS 1.510 for approaches with Decision Heights lower than 200 ft.
On a side note, about that particular last point, Jeppesen doc seems to use the 2.5% climb gradient requirement as a standard figure for any type of approach, whereas even Cat 1 approaches are not subjected to it (their DH's never being lower than 200 ft). Hence any Company using exclusively jeppesen figures in this particular case potentially penalize themselves unnecessarily.

While I'm at it, here's another one:
About the previously discussed points of take off gross/net/penalty climb gradient in the scope of obstacle clearance, I've failed to find any penalty requirement when it comes to GA obstacle clearance requirements. Just would like to have a clear confirmation that they actually don't exist.
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Old 14th Mar 2013, 01:07
  #31 (permalink)  
 
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Minimum acc ht of 400ft is a regulatory requirement both JAA/FAA and therefore minimum operational acceleration height is 400 ft or higher
Folks,
I would suggest the above is late in the chronology of developments.

Re. the derivation of the original 400', a most interesting piece of information, the first time I saw the results as a certification standard was SFAR 422B (B707 etc). SFAR 422B preceded the establishment of FAR 25, and a JAR was something with jam in it.

Given the T/O power time limits for such as the JT-4 (original B707-300 series), 400' fitted the time limits, with max oil temperature as well as max EGT being an issue.

The general increase to a minimum of 800' for power reduction, acceleration and configuration change was influenced, as I recall, by the loss of a South African Airways B707 departing Windhoek, Namibia.
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Old 14th Mar 2013, 01:43
  #32 (permalink)  
 
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John,

You are quite right that unless you have the data you can't plan your profile in advance. So in practice we end up using profiles very similar to those for certification. My point was a semantic one about what is legal or not rather than the practical application. If you have the data you can legally use a different profile.
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Old 14th Mar 2013, 07:15
  #33 (permalink)  
 
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4.1.3.1. MinimumAcceleration Height

JAR 25.111 Subpart BFAR 25.111 Subpart B

“JAR/FAR 25.111

(c)(2) The aeroplanemust reach V2 before it is 35 ft above the takeoffsurface and must continue at a speed not less than V2 until it is 400 ft above the takeoff surface”


4.1.3.2. MaximumAcceleration Height

The Maximum Takeoff Thrust(TOGA) is certified for use for a maximum of 10
minutes, in case of anengine failure at takeoff, and for a maximum of 5 minutes with
all engines operating.The Maximum ContinuousThrust (MCT), which is not time-limited, can only be selected once the enrouteconfiguration is achieved (i.e. when the aircraft is in clean configuration at green dotspeed). As a result, the enroute configuration (end of the third segment) must be achieved within a maximum of 10 minutes after takeoff, thus enabling the determination of a maximum acceleration height
Reproduced from Airbus document. GETTING TO GRIPS WITH PERFORMANCE

Last edited by vilas; 14th Mar 2013 at 07:17.
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Old 14th Mar 2013, 12:16
  #34 (permalink)  
 
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5 or 10 minutes is engine specific regardless of the generic airbus publication.


On the little ejets it's just a matter of buying the upgrade from embraer.
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Old 14th Mar 2013, 14:35
  #35 (permalink)  
 
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Feno,

Airplanes operating under EU-OPS will have been certified under EU regulations. The EU certification requirements for Decision heights less than 200 ft are contained in CS-AWO (All Weather Operations), which essentially requires the AFM to provide a WAT-limit chart for 2.5 % gradient at the speed used for go-around.

Vilas,

The quote from FAR/JAR 25.111(c)(2) is incomplete. It omits the essential bit which reads:
"... and must continue at a speed as close as practical to, but not less than V2 ...".

Last edited by HazelNuts39; 14th Mar 2013 at 15:02.
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Old 18th Jul 2014, 22:26
  #36 (permalink)  
 
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A little over a year late but I thought I'd post this document here since it explains many of the details that people in this thread are inquiring about.

It's about the history of the regulations and explains some of the reasoning behind the current regulations.

http://flightsafety.org/fsd/fsd_feb00.pdf
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Old 19th Jul 2014, 21:42
  #37 (permalink)  
 
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Wow! This thread has became one of the most interesting and constructive threads I have ever seen on a forum.
Thank you guys
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Old 21st Jul 2014, 16:18
  #38 (permalink)  
 
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This should clear up about first and second segments -

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