Unless the overweight matter is discussed in the AFM/crew operating manual (by whatever name), this is an abnormal situation, outside the rule book. The sensible pilot/operator will have some ops manual guidance for the crews to provide for an appropriate level of corporate oversight. The AFM, in general, will provide more than enough stuff for the PE folk to run some suitable sums to come up with useful numbers.

Please do note that there is nothing unbelievably difficult with this stuff; plenty of pilots have trained up to be competent PE workers.

If you have some difficulty at a higher flap setting, then you look at a lower setting which should provide you will a better set of climb numbers albeit, usually, at a slightly higher IAS.

What folk seem to be missing, or confusing, is that there exists two sets of related but different criteria. The certification stuff is WAT-limited basic line in the sand sort of stuff and provides the initial maximum performance weight limits which may reduce the permissible weights below the TC (ie AFM) maximum figures. Then we have to look at all the other stuff which may well require us to reduce the weight on the day. Generally, these considerations are operationally driven (ie Part 121) rather than design certification (Part 25). At the end of the day, ALL the various limits have to be considered and addressed with the MOST RESTRICTIVE ending up being the figure which you have to observe on the day.

On another tack, I get the feeling that some folks don't catch the difference between approach and landing climb WAT requirements. The former is to provide for a miss during the approach phase OEI/approach flap/gear up, while the latter looks at a miss from the final approach AEO/landing flap/gear down - a miss initiated OEI in the landing configuration (unless you are VERY light) is not going to end happily. Generally, we want to get back to the approach configuration without too much delay during the miss so that we are set up for the (probably very remote) possibility of losing a motor during the miss. Post the ICAO PAMC, the usual SOP was to conduct OEI landings with approach flap ... and not expect much in the way of going up until the gear was retracted.

Ansett had an unfortunate F27 hull loss at Launceston (March 1965). The upshot was an engine shutdown due to system problems and, at that time, the aircraft Type certification hadn't been revised to accord with the ICAO PAMC on performance which came out around that time (I would have to dig my copy out to check dates). No-one worried about the performance mismatch between OEI and gear down/landing flap. Joe Waxman's (a lovely chap) experience that day put it all very clearly into strong relief. The Type certification was revisited in line with the ICAO paper and, subsequently, OEI approaches and landings were executed in what become known as the approach configuration which gave the dynamics a fighting chance of accomplishing a miss rather more successfully than Joe and his crew managed on the day.

Some URL links may be of interest

Crash of a Fokker F27 Friendship 200 in Launceston | Bureau of Aircraft Accidents Archives

71f90ddffbe649ffb24978c0a80949cb.pdf

Accident Fokker F-27 Friendship 200 VH-FNH, Wednesday 17 March 1965

Origin of "Scheduled" Performance - PPRuNe Forums

Thanks John!

One aspect I’m still trying to reconcile is why Boeing does not explicitly reference MACG in the overweight/NNC landing logic.

For example, at a given landing weight I may be below the approach/landing climb-limited weight, and therefore, per Boeing guidance, select a higher landing flap and corresponding GA flap. However, with that weight and flaps, it seems possible that the aircraft may not achieve the published MACG for a particular procedure.

By the way, this isn’t a question about how MACG can be calculated, the EFB provides that capability and we use it to calculate landing performance.

What I’m trying to understand is whether, in overweight or OEI go-around scenarios, crews are expected to go beyond Boeing’s climb-limited weight and configuration guidance and independently ensure MACG compliance, or whether Boeing’s logic assumes that obstacle clearance is addressed elsewhere?

I would really need to look at the same paperwork as you have to make sure I have my head around it properly.

However, might it just be the case that Boeing is referring to the WAT limits ? The WAT limits are permanent line-in-the-sand stuff. The obstacle gradient requirements will be either the Part 121 things or whatever is specific to a particular runway, ie highly variable.

Hey John, maybe a simplified example shows what I’m trying to reconcile.

Here’s a photo from an EFB landing performance calculation I recently ran:


https://cimg1.ibsrv.net/gimg/pprune....aa3b984e3.jpeg


So for example, if the aircraft landing weight is 235,000 kg (above MLW which is 192,776 kgs), we would still be below the approach climb limited weight (238,181 kgs). Note: even if the aircraft were above that weight, Boeing guidance still allows the approach to continue using a lower flap configuration (i.e., Flaps 20 for landing and Flaps 5 for go-around, instead of Flaps 25 / Flaps 20).

However, my question relates to the following situation:

At that same weight (235,000 kgs) the aircraft would be above the go-around limited weight (230,031 kg) based on the required MACG.

So in that case the aircraft would satisfy Boeing’s climb limits but still not meet the procedure’s required missed-approach gradient.

That’s the part I’m trying to reconcile. In this scenario, since the aircraft weight does not satisfy the required MACG for that runway, we would not be permitted to continue the approach. Is that correct?

The approach can definitely be performed because:

1. The GA climb gradient used in the calculation is based on one engine inoperative (for a two-engine aircraft). However, during a normal approach we have both engines operating. You can also notice that the landing climb gradient is already quite high; therefore, if we perform a go-around with both engines, the climb performance would be even better.
2. Even if we were left with only one engine and attempted the approach, I think it could still be done (no better choice) , but we might not be able to follow the published missed approach procedure. In that case, we would need another option if a go-around is required, such as following an engine-out SID or another suitable procedure.

As far as I understand, the GA climb gradient is indeed based on one engine inoperative. However, I think the fact that both engines are normally operating during the approach is not really considered in the performance calculations.

My understanding is that all landing climb limits (approach climb and landing climb) are evaluated assuming OEI. For example, in the Overweight landing NNC, the crew is asked to check the approach climb/landing climb limited weights to determine the flap setting, even though both engines are actually operating.

I may be mistaken, but I thought the aircraft must be able to meet the missed approach gradient OEI at the landing weight. Do you happen to have a reference for the statement that the approach could still be performed if that gradient cannot be met?

Thanks

I would need some AFM data to come up with anything definitive.

However, the normal deal is that you must be compliant both with the OEI approach climb AND the AEO landing climb requirements, both of which are line-in-the-sand WAT limits and not of much relevance to an actual miss in an environment which involves any obstacles of note (that is to say, you must always be not more than the WAT limits). In this latter case - where you are concerned with a "normal" ops engineering missed approach calculation and procedure - that, usually, will be predicated on an OEI sequence in a manner not overly dissimilar to a takeoff escape procedure. The fact that, near invariably, all motors will be turning and burning is just money in the bank for you, as Captain Speaking.

Quite a few folks confuse the line-in-the-sand nature of WAT limits (which give you a fighting chance of getting some air between you and the earth spheroid) and a design procedure matched to a particular runway (which should give you a very good chance of surviving the episode - often at a quite significant weight penalty compared to the WAT limit). For references to this stuff, have a looksee through Part 25 and Part 121 for starters.

Ok… In my earlier post I gave an example from an EFB calculation, but maybe I didn’t explain my question clearly. I understand that we have to comply with the WAT limits (approach climb OEI and landing climb AEO), which is also why Boeing asks us to check them in the overweight landing NNC.

What I was really trying to understand is the MACG part. If the aircraft meets the WAT limits but cannot achieve the required missed approach gradient for the procedure (say 2.5% or whatever is published), what would the operational decision normally be? Would the approach need to be avoided, or is there another consideration?

(Hopefully I’m not just missing something obvious here, I feel like I may be repeating the question but I still haven’t quite cleared it up).

Once you have checked the WAT limits, you can forget all about them. Now you move to the obstacle profile. If you can't meet the gradient then you are too heavy. Either you reduce weight (a bit late for that) or you increase your missed approach height to get around the problem (ie from a higher miss, you can run with a lower gradient). However, in general, that is going to require an ops engineering procedure. No other options I can see ....

If we speak according to the regulations ,you are correct — the requirements are based on one engine. What I am explaining is that if it cannot be achieved, there must be alternate means related to that procedure, so it can still be conducted.

According to EASA RULE

MISSED APPROACH GRADIENT

(a) Where an aeroplane cannot achieve the missed approach gradient specified in AMC2 CAT.POL.A.225, when operating at or near maximum certificated landing mass and in engine-out conditions, the operator has the opportunity to propose an alternative means of compliance to the competent authority demonstrating that a missed approach can be executed safely taking into account appropriate mitigating measures.

(b) The proposal for an alternative means of compliance may involve the following:

(1) considerations to mass, altitude and temperature limitations and wind for the missed approach;

(2) a proposal to increase the DA/H or MDA/H; and

(3) a contingency procedure ensuring a safe route and avoiding obstacles.

The same applies to takeoff. If the SID requires a climb gradient higher than the OEI capability,(due to obstacles) we can still accept that SID as long as we have an engine-out procedure. It does not mean that we cannot fly that SID at all.

However, if the higher climb gradient is not related to obstacle clearance, then an engine-out SID is not necessary — for example, if it is required for noise abatement or due to ATC requirements.

All of these are excellent subjects for discussion with your Fleet’s Technical Manager who will describe your operator’s policy. Some options available are:

- A bespoke procedure for operations at high weight
- Additional speed limitations or delaying acceleration on the published missed approach
- Flying the engine out on takeoff procedure for the runway you are flying an approach to

Additionally, there may be a type/company specific procedure for a go around below decision altitude.

Every performance approved destination should have been analysed and this procedure carried out by a type-qualified performance engineer.

The answer will (should!) be in your airline’s performance manual.