Enroute Climb Limit Weight
 

The enroute climb based weight limit is defined by 14 CFR 121.191. Those MEL or CDL weight penalties are applied to that takeoff weight limit. That decremented takeoff weight limit may or may not be the most limiting factor in determining allowable takeoff weight for a given flight. For example, your allowable weight at takeoff could be more limited by takeoff performance if the runway is short.

Sec. 121.191

Airplanes: Turbine engine powered: En route limitations: One engine inoperative.

(a) No person operating a turbine engine powered transport category airplane may take off that airplane at a weight, allowing for normal consumption of fuel and oil, that is greater than that which (under the approved, one engine inoperative, en route net flight path data in the Airplane Flight Manual for that airplane) will allow compliance with paragraph (a) (1) or (2) of this section, based on the ambient temperatures expected en route:
(1) There is a positive slope at an altitude of at least 1,000 feet above all terrain and obstructions within five statute miles on each side of the intended track, and, in addition, if that airplane was certificated after August 29, 1959 (SR 422B) there is a positive slope at 1,500 feet above the airport where the airplane is assumed to land after an engine fails.
(2) The net flight path allows the airplane to continue flight from the cruising altitude to an airport where a landing can be made under Sec. 121.197, clearing all terrain and obstructions within five statute miles of the intended track by at least 2,000 feet vertically and with a positive slope at 1,000 feet above the airport where the airplane lands after an engine fails, or, if that airplane was certificated after September 30, 1958 (SR 422A, 422B), with a positive slope at 1,500 feet above the airport where the airplane lands after an engine fails.
(b) For the purposes of paragraph (a)(2) of this section, it is assumed that--
(1) The engine fails at the most critical point en route;
(2) The airplane passes over the critical obstruction, after engine failure at a point that is no closer to the obstruction than the nearest approved radio navigation fix, unless the Administrator authorizes a different procedure based on adequate operational safeguards;
(3) An approved method is used to allow for adverse winds:
(4) Fuel jettisoning will be allowed if the certificate holder shows that the crew is properly instructed, that the training program is adequate, and that all other precautions are taken to insure a safe procedure;
(5) The alternate airport is specified in the dispatch or flight release and meets the prescribed weather minimums; and
(6) The consumption of fuel and oil after engine failure is the same as the consumption that is allowed for in the approved net flight path data in the Airplane Flight Manual.

Amdt. 121-143, Eff. 6/26/78

The MEL document should say exactly how to apply this penalty, and it is usually done by the dispatcher.

Let me try to explain with my Level 4 English

Similiar regulation which Dave mentions is also at EASA AIR OPS CAT.POL.A.215 En-route — one-engine-inoperative (OEI)

As Take off performance limited weight, take off weight canot not be more than, so that, at resultant climb or cruise weight, airplane one engine inoperative performance is unable to meet this requirement during at any (or most limiting) climb or cruise phase.

For Airbus 330, at old FCOMs VOL 3 in chapter 3.06.20, below the GROSS CEILING WITH SINGLE ENGINE OPERATION CHART page, there was an information table showing correction factors to subtract from GROSS CEILING to calculate NET CEILING. As an example from this table for GE engine, at the point where airplane cruise weight is 210t, NET CEILING is calculated as subtracting 6600 feet from GROSS CEILING (at ISA+10C). However in new FCOMs this table is removed. This is very logical because NET CEILING is a concept to be used at PLANNING PHASE for planned enroute track. What I mean, along the route, as noticing the combination of the height of each obstacle and the planned aircraft weight as approaching these obstacles should be so that, in case of engine failure, the NET CEILING as explained in regulations, should be clearing the most demanding or critical combination. If it is not clearing, then either Take off weight (payload) should be reduced or an escape route should be planned. As seen, this is a very complex calculation. Additionally, if there is also an MEL penalty which is reducing this net ceiling, the calculation becomes even more difficult and only be figured out by a computer calculation. Besides, as AIB Pilot, there is no tool, software, charts or tables in our hand to do all these calculations.

Airbus FlySmart software is only for take off performance calculation, and gives no idea about enroute pergormance. If it is ammended to calculate enroute performance as well ( I hope not), then we have to enter planned enroute track to FlySmart as well.

Therefore, I believe all these calculation (including MEL penalties to NET CEILING) are done (or should be done) by service provider of Computer Flight Plan (LIDO, JEPPESEN etc).

However, at least at the routes which I fly with A 330, even at very unlikley cruise weight around 210 t, with ISA+10 at cruise, without any MEL penalty, according to this old FCOM, net ceiling will be:
Gross ceiling 23500 (at Green dot), minus 6600 feet equals =16900 feet. And there is no terrain in any route which I fly at this elevation (16900 feet).

What a load of waffle..... so to answer the question sticking to Boeing......it’s a fault that affects the aerodynamic properties of the aircraft. OPT takes care of any take off and landing performance penalties.

To apply the the enroute climb penalty, after take off simply increase the ZFW in the CDU by the afore mentioned weight penalty. Then take it off again before landing if you so desire.

Job done

8Che
That's also what I do in A 330 with a concern with the accuracy of shown MAX or OPT ALT in MCDU.
Since performance penalty of a CDL is not detected by FMS, It may be a good discretion on the safe side
However, this addition to ZFW is completely irrelevant with the regulations mentioned, which are also covering Boeing.

8 Che, all correct what you said, but when you are on the plane. Mentioned regulations are for the planning stage.
As you said, actual driftdown altitude for actual conditions are the matter of pilot, but net ceiling info is not the matter of pilot and useless info at this stage for pilot. Therefore AIRBUS removed related info from in- flight operation documents. For the actual conditions I also do what you do. However Net ceiling and the factors whch are deteriorating it (e.g CDL) is the matter of the planner. From planner perspective, Gross ceiling or driftdown altitude is not an issue. And the net ceiling is tried to be calculated according to best available weight and ambient conditions predictions. Planner considers if actual (e.g gross ceiling) is different than planned that is is pilot's problem. The amount of standard deviation between planned and actual shows the quality of operation of that operator; bigger deviation equals to worse operation quality.

Might I suggest that net ceiling is the appropriate expectation in the same way that net takeoff segment climb gradients are. Yes, you might do a little better on the day, and that's real fine, but to expect that is cutting into the certification fat somewhat ?

JT, I am not sure what you mean exactly, but based on the core of thread, the regulations doesn't only cover the requirements for a driftdown from cruise.
I mean, for example, in the case of Engine Failure at take off and need to divert to take off alternate because of weather, the weight at the end of take off flight path, shouldn't be more than so that the net path (in this case a climb path = 1.1% less than gross path for 2 engine airplane) sould be clearing the terrain (e.g mountain, if there is) on the planned track to take off alternate.

We are not (at least me) facing all these requirements because Take off performance Limied weight is usually the most limiting weight of all these phases, at least at the places where I fly.

My concern is that the certification requirements cover the enroute terrain consideration, which can be critical for some aircraft and, if one can't meet that, then the plan ought to be looking at a drift down while avoiding hostile terrain by the usual clearance requirement. Heading off with weights which would/might result in gross ceiling, coincident with hostile terrain, probably isn't a really good strategy.

I may have the wrong end of the stick from my reading of the thread .. in which case, I'll go quietly. Concern is to make sure that folks aren't forgetting the terrain and a need to have a bit of fat for the not-so-good days ?

The regulation I posted above is an operating rule that applies to all air carrier flights of turbojet airplanes, and requires the airplane, with the critical engine out, to be able to either (under (a)(1)) climb when at an altitude 1000 feet above all terrain within five miles of the planned track at all points in the flight, allowing for expected fuel burn-off, or (under (a)(2)) have a bail out path at all points in the flight to a diversion airport that similarly ensures terrain clearance. Credit for fuel jettison is allowed under the (a)(2) option. The engine out cruise altitude at maximum continuous thrust will therefore always be at least 1000 feet above all terrain within five miles of the planned or diversion tracks.

Does that address your concern or did I miss your point?

That's fine. Generally, the cert/ops rules fly in formation, although not always. Main thing is that the aircraft can cruise with an appropriate terrain clearance or run via a driftdown with a generally higher clearance.

You can do that but in some cases it will be overkill. For example, in a case where only the en route climb limit weight is reduced by the CDL item, if you are already runway performance limited to a weight that is even more restrictive, then you don't need to reduce the weight further.

Thanks BleedingOn,

Wheres that icon for head banging against the wall...…..What has a take off performance limit got to do with cruise altitude capability ?

AS previously said OPT takes care of the CDL for take off and landing only. You need to increase the CDU ZFW (after departure) for the "enroute phase" weight restriction. That's why its called "enroute"...!.

Surely the point of the CDL penalty is that you start with normal planning and then simply apply the weight and fuel penalty. That does not need a computer, even though it will be done on one. The penalty is crude and conservative, therefore the penalised aircraft will in reality perform better but less efficiently than one dispatched at normal weight/configuration.

8che has a point. As a function of weight your aircraft with its missing part has more drag than is accounted for in the performance data. The FMC will overestimate your ceiling, and underestimate fuel burn. If you give the FMC an 'assumed' ZFW equal to the actual weight plus penalty, then the ceiling and fuel burn data will become conservative (you will actually do better). But there is a problem because the same is not true for driftdown speed. As the FMC now thinks the aircraft is heavier than it actually is, the computed engine out speed will be too high. Therefore the drifdown speed used should be that which the FMC would compute for your actual weight or which you would get from the tables. Even that will not be perfect because it does not account for the extra zero lift drag of the deviation, but I assume that the weight penalty is sufficiently conservative to allow for it.

As far a MEL/CDL corrections on the 737 go, some of you are overthinking this. The corrections are in the MEL/CDL document and are quite conservative as far as fuel burn and cruise performance goes. There is probably greater potential for performance degradation associated with the weight and balance calculations than there are in the CDL/MEL corrections.

Fuel Penalty application is crystal clear but weight is not. I am not mentioning FMS calcualtion, I am talking about planning calculation. How to use weight penalty for planning purpose? Adding CDL penalty weight to actual weight is not a solution, That only helps to figure out what will be the capability of gross ceiling with this CDL penalty, which new gross ceiling is always less than the actual weight. But this has "NO RELATION" with NET CEILING. This calculation never gives an idea about driftdown NET CEILING path and NET CEILING VALUE, therefore we may not be aware whether this new NEt CEILING path and vaue is conflicting with enroute terrain/obstacles or not.

The net flight path data must be in your AFM (or approved supplement of) because it is the law:

b) Each Airplane Flight Manual must contain the performance information computed under the applicable provisions of this part.......25.123. En route flight paths. The one-engine-inoperative net flight path data must represent the actual climb performance diminished by a gradient of climb of 1.1 percent for two-engine airplanes [etc]

Nobody is saying to add weight. You determine the enroute limit weight using the AFM performance data (for net flight path, it must be there). But you won't be able to achieve that performance given the extra drag of the missing item, so you reduce actual weight by the amount stated in the CDL and your net flight path will still be okay. I don't understand why that is not clear for you.

But I understand why you do not understand, because it is complex

Let me answer again to clarify"
Yes but it is not in the form of pilot usable or pilot friendly and AFM is not an operational manual which normally distrubuted to pilots.

That is the extarct from A 330 AFM:
For en route net flight path (single engine cruise) performance determination, the Performance Engineer's Programs/AFM_OCTO approved FM module at the latest approved revision must be
used. Refer to PERF-OCTO Performance Database.

What I remeber at 90's, the B 737 AFM (which is not distrubuted to pilots but I grabbed one set somehow), used to consist of big, thick 2 or 3 binders (thousands pages) including NET FLIGHT PATH charts as well. But not anymore at least in AIRBUS AFM.


Since as a pilot we cannot reach NET FLIGHT info or enroute limited weight values because it is not available for us (as I mentioned above paragraphs), the above quotation becomes void. I mean "reduce actual weight by the amount stated in the CDL" becomes void. There is no meaning of reducing the actual weight by amount of penalty Suppose our initial Actual TO weight before CDL was 200 t, so what should we do with CDL? Off loading payload by penalty? No way!
The penalty amount should be reduced from Enroute Limiting Weight, but There is no info about that in our hand.

As example A 330 CDL 57-04 FLAP TRACK FAIRING missing penalties

- Fuel consumption is increased by 3.42 %.
- Enroute performance Limiting Weight is reduced by 5 240 kg (11 553 lb)

First one is crystal clear : Example new trip fuel = TRIP FUEL x 1.0342

Second one is not clear: 5240 Kg? To subtract from which value? We do not know that. To find this value, we need the software mentioned in AFM and Route Obstacle Information.



I hope now you understand.

JABBARRA

Yes I understand that you cannot do it because the pilots at your company do not have the information to hand. Nonetheless it remains a fact that knowing how to check your enroute climb limit weight is required knowledge for professionals. Your dependence on a third party to do those calculations is no answer to the question posed by this thread.

If you are given an aeroplane and told to fly from A to B and have nothing but the FCOM, DDG, QRH, etc. then I could see it being an issue. Who does that? Every outfit I’ve heard of that flies large transport aircraft has some sort of flight planning system that takes account of en-route performance (in my case LIDO). If there is a problem with MEL items that compromises MSA, drift down, etc. then it will be flagged up or it simply won’t produce a plan.

From a safety POV, your plan will be OK as long as the correct inputs have been made. Now you want the information presented to you in flight to be representative of operating with the particular defect: a simple way is to add the performance weight penalty to the ZFW in the FMC so things like OEI ceiling are displayed correctly (and probably reasonably conservatively). Job done.

Am I hearing an echo ?

:)

IMO it’s very easy to over-think these kind of things. Yes, as a performance engineer you have to cover all the angles and use the most accurate calculations possible. If you’re operating the aeroplane, especially past the point of dispatch, it’s big-picture stuff...

My interpretation of this thread: As a worst case scenario, you are in the cockpit to fly back to home base but you found out just a new CDL is added to Tech Log Book effecting Enroute Performance Limiting weight with a penalty of 5000Kg; What I can do with this 5000kg?

If my interpretation is incorrect, yes dear Oggers, my answers may not be a solution.
But if my interpretation is correct, then I consider my answers are correct; besides they reveals a factuality: I repeat again, in that scenario 5000kg value is useless in the purpose at which it is given.

However, as advised at previous threads (including mine) and latest by FullWings, adding this value to actual ZFW or Actual weight to optimize FMS calculation is a better than nothing improvisation by pilot (not by any regulation or operation manuals including MEL, as far as I know) and I agree.
But emphasize again this is not the intended usage of 5000kg by CDL, but good enough to see what could be our real performance capability for Max Climb Altitude or related predictions.

That is I mean

Here is My 2 cents worth. the steps are detailed below the chart:
https://cimg8.ibsrv.net/gimg/pprune....721716f10c.jpg

JABBARRA, see the above worked example by gearpins of how easy it is to achieve this task. It is absurd to interpret the question of "how is this done?" as "how is this done if I don't have the net performance data which must by law be provided to the operator and used to accomplish this task".

Oggers, as you make comment you are revealing your ignorance in this issue.

The fake (but better than nothing) solution which was recommended by you was as below and be sure most of the people used to know before you.
This quotation shows, unfortunately, you were not aware, neither the way you mentioned was the real solution nor, in fact, there is a real regulative solution.
However, I have to confess there is some progress: At least now you have learned CDL penalty application is not at the way as you recommended before. And I hope you understand it should be at the way I mentioned or by the way as in gear pins thread.

But still it looks you are away from understanding the real concept as considering it is very simple. No, it is not. Slowly read maybe you can get it.

First of all, that table is not particularly for CDL penalty correction. Theoretically you have to use that table for all flight regardless you have CDL penalty or not, to evaluate the obstacles through the route. I do not know how many pilots are doing this before every flight.

This practical solution advised by the table maybe only good for a short range flight; probably as in the operation area of the Airplane (likely to be Boeing) of the subjected Operator of which the given table belongs (e.g from table: For our operations this penalty is s never limiting)

To visualize what this table means, I write this sample (even without CDL): Consider a scenario; Departing from somewhere in Middle East and reaching TOC (single cruise level) after half an hour, then after another 5 hours crossing Himalayas, then arriving somewhere in Far East. If there is no escape route, Let´s say from a similar table (and with another additional table to calculate drift down fuel) we calculated weight to cross Himalayas should not be more than 190 t. This tables assumes you will be at 190t after only 30 minutes from departure or with another word, 5 hours before Himalayas. Therefore, TO weight should be adjusted as guaranteeing TOC weight should not be more than 190T. I guess in such a scenario, for example A 330, it can be implemented only at a Ferry Flight. Besides, if there is CDL penalty, you have to subtract this penalty (let´s say 5000Kg) from 190T, MTOW is 185t. If all these are digestible, yes calculation, either with CDL penalty or not, is very simple.

Let me detail for you: If you understand, for a route of which the highest obstacle is towards the end of route which maybe thousands NM away, according to this table, you have to limit your initial TOC weight, this table only recommends this. Therefore, simplified way may seriously affect your TOW limit so your payload. Consequently, this may be good only for the kind of operations for table´s owner; as they mentioned e.g For our operations this penalty is s never limiting.

To consolidate what I write above: For a true solution you have to find worst case of multiple weight vs obstacle height combinations as including the earlier obstacles effect. And this is not possible with a single table. Opposite the methodology of table (in fact), along the route, the highest obstacle (let´s say 16000) may be less critical or limiting if its location is towards the end of the route because of less demanding critical combination of weight vs obstacle height, because of reduced airplane weight along the route. As oppose the table recommendation, in this case no need to limit TOC weight.

Besides, an obstacle which lower but at the earlier phase of flight (were airplane is heavier) could be giving a more demanding weight vs obstacle height combination. If you want to be really legal and optimized you have to done this evaluation for all obstacles through the route. In this case that appreciated (and better than nothing ) table solution is not enough.

Additionally, This was from me:

Above the light of all above, since -for example- Airbus is not distributing Net Flight Path data for pilots, then – although my English may not be so good as yours- but I guess, commenting my interoperation like
"how is this done?" as "how is this done if I don't have the net performance data which must by law be provided to the operator and used to accomplish this task"
itself is really absurd.