Enroute Climb Limit Weight

[Igor Batiashov]

Does anybody know how to apply penalties to Enroute Climb Limit Weight. (According to MEL/CDL). And what this weight mean itself? B737

[Dave Therhino]

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

[Jim_A]

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

[JABBARA]

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).

[8che]

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

[JABBARA]

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.

[8che]

With respect. It’s actually the only way to accurately and simply apply the correct weight penalty to the aircraft for all enroute possibilities including drift down, otherwise you will not be in compliance with the regulations governing CDL use so to suggest its not relevant is bonkers. Having a lovely flight plan but not tell the FMC ? How is a performance supplier going to help you with the engine failure off the designated route due to weather deviation when your weight is not the same as the flight plan ? The FMC will do it perfectly but only if you tell it about the CDL first. Regulations are actually there for practical reasons not the other way round.

[JABBARA]

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.

[john_tullamarine]

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 ?

[JABBARA]

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.

[john_tullamarine]

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 ?

[Dave Therhino]

Originally Posted by john_tullamarine

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?

[john_tullamarine]

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.

[8che]

So what’s the poster going to do if he is 6 miles off track ?

Could I suggest complying with planning regulations is only part of dealing with a CDL/MEL.

Increase that ZFW otherwise you are not applying the CDL to the aircraft. Or are we the type of pilot that just likes to see the paperwork look correct.

[Dave Therhino]

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.

[BleedingOn]

8che is talking about increasing ZFW in the FMC after departure. OPT (since we’re talking about Boeing) will take care of takeoff performance calculations

[8che]

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"...!.

[oggers]

.........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.
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).

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.

[Tomaski]

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.

[8che]

Oggers, drift down speed change from the FMC is a very minor issue compared to wanting to know from the FMC what the drift down and OEI altitude capability is. Himalayas, N America, Iran etc. Boeing have expressed an aerodynamic degradation in terms of weight because that’s simple but it is still an aerodynamic problem and as such having a slightly higher speed from the FMC would be entirely correct and conservative when dealing with aerodynamic degrade issues.