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Old 16th Jul 2007, 13:50   #1 (permalink)
 
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Climb gradients

What is the relation between the minimum SID climb gradient, usualy 3,3%, and the standart 2,4% and 1,2% of the initial climb the limit our take off weight?
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Old 16th Jul 2007, 14:11   #2 (permalink)
 
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Oi Becker Junior -
xxx
I see you mention 2.4% and 1.2%. These are the second and third/final segment of climb for a 2 engine turbojet aircraft, such as B-737 or MD-80...
If you study the "critical segment" (the 2nd segment) of 3 engine turbojet airplanes, such as a B-727 or a MD-11, it is 2.7%...
And the 2nd segment for a 4 engine turbojet plane, like the B-747 is 3.0%...
xxx
The SID/climb gradient you mention is the actual climb that must be observed for you to comply with a departure. Should you have an engine failure, you will not be able to comply with that departure. Your airline probably will publish engine-out (engine failure) departures routings, should you have a problem to climb on a SID.
xxx

Happy contrails
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Old 16th Jul 2007, 17:13   #3 (permalink)
 
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No special procedure

HI and thanks for the reply.

I dont think they are based on the same thing. I do fly the 737 thats why i mentioned the 2,4/1,2%. And almost every SID I fly everyday is based on 3,3% and there are no special procedure published.
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Old 16th Jul 2007, 20:50   #4 (permalink)
 
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Oi Che -
xxx
The climb segments come from Part 25, which is a certification standard for the airplane. As an example for the 737, your first segment must be a "positive climb" (no gradient specified) until your gear is retracted. Then start your second segment, 2.4% until 400 feet above your liftoff reference point where you reduce engine to max continuous thrust. then start your third/final segment at 1.2% required, until 1,500 above liftoff reference, where you can accelerate and retract flaps.
xxx
Your SID 3.3% is not a certification segment, it is a climb required to clear obstacles for the departure route. Obvious if you lost an engine at V1, you could not comply with that SID.
xxx
Receba um abraço do seu amigo.
xxx

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Old 17th Jul 2007, 03:52   #5 (permalink)
 
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To reinforce the comments made by BelArgUSA, the SID requirements (e.g. 3.3%) are to be met under PANS-OPS / TERPS rules for AEO (All Engines Operating).

The 2.4% (Gross) and 1.2% 4th Segment (and overall) are to be met by FAR 25 (and it's equivalents) for OEI (One Engine Inoperative).

The 2 sets of rules have virtually nothing in common, especially in terms of vertical and lateral clearance of obstacles.

For each and every Takeoff, the aircraft must be at such a weight that the FAR 25 OEI requirements may be met, and the routing and Altitude requirements RARELY agree with the normal SIDS, thus, Special Procedures (sometimes called OEI SIDS) have to be developed. If you don't carry these, then you should!!!!!!!

Depending upon the quality of the service provider, these are sometimes transparent. For example, one major service provider beginning with a J who operates from Denver and Frankfurt, does not provide any EOSID if OEI can be accomodated with maintaining Runway Track, even though the Minimum Acceleration Altitude may be well above the normal 400 feet (which, to me, makes it a special procedure). Their data also carries a longitudinal limit, usually 30 miles, after that, you're on your own - A pox on their system!

A full explanation of this would require the use of Danny's entire bandwidth, that should do for now.

Regards,

Old Smokey
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Old 18th Jul 2007, 12:45   #6 (permalink)
 
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thanks

Thanks a lot for your considerations. It is right to say then that if you are departing limited by climb in weight, you wont have performance to fly the SID with more than 2,4% on 2nd seg.

Grande abraço, BelargUSA
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Old 23rd Jul 2007, 11:52   #7 (permalink)


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Lightbulb

The minimum design gradient for a SID is 3.3%, from a minimum of 35 feet over the Departure End of the Runway (aka the DER) until the point at which the SID ends. If the end point impinges on your 2nd segment, which is invariably the case, you have to be able to maintain at least 3.3% net climb or there's a chance that you will not clear an obstacle. OS is right, as usual, in that if your aeroplane will not climb at or above 3.3% in the OEI case, under any specific conditions, your company really should provide an emergency escape route procedure.
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Old 23rd Jul 2007, 13:08   #8 (permalink)
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.. a few additional thoughts ..

(a) the design certification figures (ie 2.4 gross etc ..) are WAT (maximum Weight for Altitude and Temperature) limits (for the various segments) and are intended only to make sure that the certification animal is able to climb at a (very) modest gradient (think just how shallow 2.4 really is) after an engine failure according to the Hp and OAT .. if you prefer, the WAT limited weights avoid the need for climb to be dependent on the curvature of the earth. WAT limits have nothing to do with obstacles or anything else .. they are pure and simply minimum free air climb gradient requirements ..

(b) the SID requirements are procedural .. and, often, very much obstacle driven ....

(c) heed OS and OzEx re making sure that you can get the OEI gradient above the SID to avoid the bumpy bits ..

(d) for a twin under critical conditions .. it is not unheard of for the net flight path to extend upwards of 50 miles ...

(e) all in all .. if the airport is not excessively benign .. then one is well advised to leave the number crunching to the ops engineers and fly the OEI escape procedure as prescribed ..
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Old 23rd Jul 2007, 18:16   #9 (permalink)
 
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Another important point to bare in mind is that the climb gradients are invariably posted as 'gross' limitations'. The charts in the AFM generally denotes gross climb. Knock off 8% for net. Many FAR 23 certified aircraft really only have 3 climb segments. Most, if not all FAR 25 aircraft (please pardon my lack of knowledge....I may not be 100% correct....it's been a long time) have 4 segments of climb. The reason I say 3 is that positive rate, in some schools of thought, is not considered climb, hence 3.
The first is the 'clean up', ie flaps, at 400' unless the company is using tabulated data and that info alone will denote the clean up altitude. At this point the aircraft is accelerated to VYSE and any additional power modes are activated, ie water meth (again FAR 23 aircraft). Very few aircraft have this option, the TPE331 comes to mind. And there are limitations on the use of meth. 5 minutes from memory. At 1500' AGL the last of additional power (3rd segment) comes into play (reserve power for instance) and then it's a case of following the SID, or the escape procedure as documented in the tab data, to avoid terrain.

Jets are a little different as they mostly stay at TO power until Max Continuous is selected in the EO situation and you just do your best but essentially clean up at acceleration alt and vyse or Vclean until clear of terrain.

Again it's been a while since I worked this stuff but essentially it's good to know. Knowing the percentages is one thing but when you're in the shit and fighting with an aircraft thats down on an engine the procedure to get the thing above the terrain is the most important thing to know. SOP will 9.9 times out of 10 have you home at the end of an otherwise ordinary day.
Not sure if this will help. Hope it does.

Regards
D

Last edited by Defenestrator; 23rd Jul 2007 at 18:31.
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Old 24th Jul 2007, 18:02   #10 (permalink)
 
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Defenestrator,

I think that I'll add your early remark to my wish list. Did you really mean 8% delta between Gross and Net Climb Gradients? If only it were true, a typo perhaps? Methinks you meant 0.8%

There is an element of discomfort for most pilots in discounting any climb capability (for a twin) in the 1st segment, with the regulations merely specifying that the gradient need only be positive. In truth (at least for most aircraft) the Delta between 1st and 2nd segments ACTUAL gradients rarely exceeds 1%, thus, if you meet the Net 1.6% Net minimum requirement (as you must), the ACTUAL 1st segment is usually of the order of 0.6% or so. Hardly startling performance, but a darned sight better than just "positive". Of course, there may be some 1st Segment "dogs" out there that kill this comfort level.

Hmmm, a bit of discomfort in placing reliance on SOPs getting you home at the end of the day. For good operators with thoroughly developed EOSIDs, yes, that's true. Sadly, I know of more than a few operators whose SOP following engine failure is to maintain Runway Track, and that's it. NOT recommended at Albury 07, Canberra 17, Townsville 19, Alice Springs 30, Hobart 30, Adelaide 05 or 12...... just to name a few Australian nasties seeing as your monika says you're from Australia. These are a few very obvious 'nasties', the seemingly benign 200 foot hill at a mile from the runway end that seemed so innocent in day to day All-Engines Operations, is really going to spoil your day when one quits at V1.... just a 3.3% gradient to meet Vs the 1.6% Net that SOPs provided for (even the full 2.4% Gross won't beat that one).

No criticism of a good post, just putting a few things into perspective.

Regards,

Old Smokey
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Old 24th Jul 2007, 19:32   #11 (permalink)
 
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Old Smokey,
It was indeed a typo. And I agree with your valid points on climb gradients. Many are unaware of some of the finer points of EO performance (or lack thereof). A good thread.

.......Given further reflection and perusing of your post you've reminded me of some very important considerations. As I mentioned in my post, it's been a while since I was instructing newbies, and indeed some not so new, on this important subject. It's troubling that many operaters of FAR 23 and 25 aircraft don't accord with the benefits of tabulated data. All companies I've worked for have seen the benefit of it and indeed (please correct me if I'm wrong) it's a CASA requirement for RPT ops. In the absence of SIDS, properly designed EO procedures for every airfield departed are of great benefit, albeit absolutely essential.

A good refresher for all. Again, a most worthy thread.
Regards and Thanks

D

Last edited by Defenestrator; 24th Jul 2007 at 21:08.
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Old 25th Jul 2007, 04:53   #12 (permalink)
 
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Defenestrator,

Yes, indeed a good thread. It is indeed true that CASA do require full EOSID analysis for RPT operations, so, in speaking to an Australian, I'm preaching to the already converted. CASA are not alone in demanding a high standard of operators in this area, there are many other high standard regulatory authorities, but sadly, there are numerous regulators and operators around the world who merely pay 'lip service' to meeting these requirements with little auditing of conduct of operations in this area. Tick in the box stuff!

Regards,

Old Smokey
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Old 26th Jul 2007, 07:41   #13 (permalink)
 
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Becker asked:
Quote:
What is the relation between the minimum SID climb gradient, usualy 3,3%, and the standart 2,4% and 1,2% of the initial climb the limit our take off weight?
Old Smokey replied:
Quote:
The 2 sets of rules have virtually nothing in common, especially in terms of vertical and lateral clearance of obstacles.
Thats about it really.

Consider this: Most of the time SIDS are flown by transport category aircraft. But SIDS are not exclusive to transport category ops. SIDS are available to all IFR operations. ATC could issue a SID to an IFR Cessna 182, or the IFR rated PPL could elect to do a SID when departing from an AD OCTA.

SID is IFR, not Performance.

If the standard 3.3% SID gradient relates to anything it is more likely to relate to a general IFR requirement -- haven't had the time to check it, but a 2.5% gradient requirement for IFR obstacle clearance in missed approach plus 0.8% factor rings a bell.........
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