Missed Approach Climb Gradient question?

[Balkanhawk]

Hi all,

I will shortly start to fly a twin turbine performance class B aircraft and I have a couple of questions that you most wise of professionals may be able to answer!!

During an IFR approach with two different DA(H), one for a 5.0% and another for a 2.5% missed approach climb gradient, do I have to use the 2.5% on the assumption that I may loose an engine? It will not do 5.0% single engine.

Is there any document that I can find the stipulation that you must use the single engine climb gradient for selecting IFR approaches?

What happens if there are only minimums for a 5% climb gradient? Do i have to calculate an increased DA(H) that will allow a 2.5% climb gradient?

Any help is much appreciated.

[FlightPathOBN]

A multi-variant question indeed...

First off..the criteria assumes all engine for the missed. EO procedures are custom. There are NO calculations assumes with any criteria for EO.
Not sure what you reference is, either FAA or ICAO...but neither address EO in design criteria.

EO procedures are emergency only.

Remember, and most forget, these are MINIMUMS. If the chart states an MDA, then you must calc you DA depending on your real time performance.

[aterpster]

As flight path states, those gradients are for all-engines operating only. With all engines operating you have to determine whether your aircraft can comply with the steeper climb gradient. If not, you are required to use the higher minimums predicated on the less demanding climb gradient.

With an engine inoperative you need to have a one-engine inoperative "escape route."

As to normal ops, no one provides the performance data so it is mostly an exercise in politics rather than performance.

A lesson in aircraft instrument flying procedures: It is a lot easier for the government lackies and manufacturers to determine how an airplane will descend on an instrument flight procedure than climb on an instrument flight procedure.

[low n' slow]

You assume that you will be flying the MAP with one engine and therefore you need to know your OEI climb gradient to be able to choose which minima to use. If you have an escaperoute for departure from the same runway, perhaps once in a while it could be accepted to use that procedure and then use a lower minima, but remember that the GA performance calculations and TO performance calculations differ in their requirements and that it is not (in a strict world) possible to just decide to use normal departure procedures for GA.

We had this problem in Sarajevo when I flew there. In bad weather it was more advantageous to be as light as possible to get a better climb gradient to be able to choose a lower minima. One good way to keep track is to ask the performance calculating company to produce a speedbook with the gradients stated for each weight.

Edit: I see the two previous posters say that the performance is based on all engines operating. Perhaps it is so for Perf Class B, so be it, I'm only familiar with performance class A. In any case, I for one would not want to be below minima if I didn't have single engine performance to get me out... All takeoffs are based on it so why not have the same reasoning for go arounds?

[ATP_Al]

The reference you are looking for is EU OPS 1, subparts G & H.

There is no specific requirement to ensure that a performance class B aeroplane can meet the requirements of a non standard (i.e. greater than 2.5%) missed approach gradient. This requirement only applies to class A aeroplanes.

Class B aeroplanes are only required to demonstrate an arbitary minimum level of go around performance. This is a steady gradient of 0.75% in the approach climb (going around from 1500ft with one engine inoperative, gear and flaps retracted), and 2.5% in the landing climb (a baulked landing from below DA/MDA with the gear and landing flap extended). For a twin engined class A aircraft, the required gradients are 2.1% in the approach climb and 3.2% in the landing climb. Note that single engine performance is not necessarily guaranteed in either class, even on a standard missed approach.

So using the 5.0% minima is not expressely prohibited, but I would seriously question the wisdom of doing it without checking your aircraft's performance manual first. As 2.5% is the standard missed approach procedure gradient, airfields with a steeper gradient will always publish higher minima for aircraft unable to meet it. If in doubt use the 2.5% minima.

[Balkanhawk]

Cheers for the pointers.

I just found the below paragraph in EU Ops for performance class A aircraft.

OPS 1.510
Landing — Destination and alternate aerodromes

(b) For instrument approaches with a missed approach gradient greater than 2,5 % an operator shall verify that the expected landing mass of the aeroplane allows a missed approach with a climb gradient equal to or greater than the applicable missed approach gradient in the one-engine inoperative missed approach configuration and speed (see applicable
requirements on certification of large aeroplanes). The use of an alternative method must be approved by the
Authority.

My understanding is that for performance class A if the climb gradient is greater than 2.5% then you must check that you can achieve it OEI, would that be correct?

I then found this for Performance class B aircraft
OPS 1.545
Landing — Destination and alternate aerodromes
An operator shall ensure that the landing mass of the aeroplane determined in accordance with OPS 1.475
(a) does not exceed the maximum landing mass specified for the altitude and the ambient temperature expected for the estimated time of landing at the destination and alternate aerodrome.

It looks as if there is no requirement to consider a OEI missed approach climb gradient with performance class B aircraft. That seems odd....

[ATP_Al]

Balkanhawk,

Yes that's the way I understood it. What makes even less sense is that for performance A the minimum approach climb gradient for certification is 2.1%, yet the standard MAP gradient is 2.5%, there is no guarantee in either class that you'll be able to achieve the MAP gradient with one engine inoperative. That said, these figures are certification minimums and the performance of your aircraft could be considerably better - there are some performance class B aircraft with higher performance margins than some performance class A aircraft.

The point I'm trying to make is, study the performance data for the aircraft you'll be flying and understand what it can do, especially if you'll be flying into somewhere performance limiting.

[low n' slow]

You are correct Balkanhawk (funny name, in the balkans this discussion highly relevant).

Performance class B aircraft have relaxed performance requirements in take off and as it seems, also in go around. With this in mind, most things will be legal but I would seriously question going into lets say Sarajevo in ****ty weather and going below the 2.5% minima. If it doesn't work out and you net to get yourself out of there, it's a long way up to MSA if your flying a piston twin on one engine...

But that was perhaps not the question. Anyhow, take care.

[FlightPathOBN]

That is why all OEI procedures are all custom. Nothing in the criteria supports OEI, especially the obstacle clearance surfaces.

Even if you can make 2.5% OEI, you still must have a custom procedure design approved by the regulator.

[aterpster]

FlightPath:

That is why all OEI procedures are all custom. Nothing in the criteria supports OEI, especially the obstacle clearance surfaces.

Even if you can make 2.5% OEI, you still must have a custom procedure design approved by the regulator.

Alas, the regulator in this country is incapable of determining whether the operator's OEI procedure will work. So, it's all in the hands of the operator's performance engineering department.

The FAA does have to ostensibly approve carrier deviations from public departure procedures, which the carrier represents as meeting both TERPs and Part 25 OEI takeoff flight path requirements.

Thank goodness for the reliability of modern jet engines, at least above V1 and for awhile after that.:)

[FlightPathOBN]

Concur!

As actively designing EO procedures, it is certainly enlightening, and a quite a bit worrisome.

as you say..."thank goodness for the reliability of modern jet engines"

[A-3TWENTY]

The operator should provide the pilot with a table with Field Alt vs Temp= LW for several climb gradients in order to comply with approach climb performance.

In the airbus you only can find it until 2,5% for CAT I and 2,1% for CAT II/III.
FCOM 3.05.35

Any climb gradient greater than that , refer to the table that you should be provided.

[theficklefinger]

Of course while everyone is quoting regs, calling their chief pilot, digging though the FARs, the question remains...do you shoot an approach that should you lose an engine you can't outperform the terrain on the missed?

Not sure if everyone here is really solid on the reasons why we fly twins instead of singles.

[galaxy flyer]

Ficklefinger

Many of the posters on this thread are professional procedure designers and performance engineers discussing the "whys and wherefores" of doing what you make sound so simple, pray tell us, how do you determine that every missed approach you fly will result in terrain clearance OEI.

References to ICAO documents, TERPS, Advisory Circulars or Kentucky Windage, greatly appreciated. We use an APG report, by the way.

[theficklefinger]

Galaxy do you fly planes with a flight manual?

[aterpster]

theficklefinger:

Galaxy do you fly planes with a flight manual?

That question doesn't add much to the discussion.

What g.f. is pretty much trying to tell you is that the gradient expressed on either a departure procedure or IAP missed approach procedure is climb performance "apples" and that an OEI profile, whether on a departure or missed approach procedure is climb performance "oranges."

The two appear to some to be related but they are distant cousins, especially when the obstacle environment is critical (aka, "obstacle rich environment" in performance engineering and procedure design parlance).

The obstacle assessment done by the public procedures designers is often of little, or no, use for OEI purposes. It comes down to the specifics of the aircraft you are flying, and the OEI profile your company elects to use. That, in turn, requires a very specific obstacle assessment that is valid for your company's elected profile for each specific type of aircraft.

[theficklefinger]

Your flat out wrong ATERP...you need to see how planes are certified...and how instrument approaches are certified...

Simply put, if your looking at the climb gradient of a MAP or departure, and are responsible enough to your passengers, industry, owner of the aircraft, your family, your profession...then you will pull out the Flight Manual and see if you have the single engine performance to do that procedure.

I don't get how the OEI differs from the IAP procedures...if by that you mean the math that the pilot has to accomplish to get to a climb gradient or feet/nm...that's the pilot's job...

Either way...the numbers need to be crunched if you are actually doing your job.

[FlightPathOBN]

No, FF, you are.

The obstacle clearance surfaces, either Part 77 or ICAO, are analysed for all engine performance. This is all there is, no matter what your performance is, or what you think it is..

http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/07/P773dsurf.jpg

This is all there is for a Part 77 certification on a runway.

Get with the program, NOTHING in the procedure design criteria addresses Engine Out, nothing.

If you really think that you have terrain and/or obstacle clearance Engine out based on either ICAO or Partt 77, ...you are fooling yourself.

[theficklefinger]

You guys need to look up Part 25 aircraft certification.

You've dug yourselves into a hole if you want the world to believe that you can fly jets without having single engine performance that meets the departure and MAP profile.

And even if your not flying a Part 25 aircraft it's irresponsible to be flying twins with such reckless abandon.

If your gonna fly your twins like a single engine aircraft, you need to be flying single engine aircraft, well actually you shouldn't be flying at all...

[aterpster]

theficklefinger:

Your flat out wrong ATERP...you need to see how planes are certified...and how instrument approaches are certified...

I've been around TERPs a bit, Part 25 a bit, and OEI performance engineering a bit.

Your arrogance is only matched by your closed mind.

Best of luck with your operations. You'll need it.

[FlightPathOBN]

Here is an online doc that uses BCOP to analyze the performance climbs for Westjet. http://www.smartcockpit.com/data/pdfs/flightops/navigation/RNP_IN_Daily_Operations.pdf

This climb out perf is all engine. Note how many variants, depending on temperature and altitude, have a climb rate below 2% All engine.
When you look at BCOP and the performance, hot places like Australia, many variants have EO climb gradients on the order of 1%. This offer no protection from the terrain and obstacle assessments, thus a custom terrain/obstacle clearance is needed, or the weights will be severely restricted.
http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/04/climbperf.jpg

You've dug yourselves into a hole if you want the world to believe that you can fly jets without having single engine performance that meets the departure and MAP profile.

Again, nothing in the criteria, including the procedures, addresses Engine out.

thats rather humorous, you telling Terpster he needs to understand how aircraft are certified. :ok:

[galaxy flyer]

Seriously, theficklefinger, you do seem to delight in publicly parading around showing that you would be out of your depth in a puddle.

[theficklefinger]

This isn't a debate...if you can't determine you single engine performance as it relates to the departure or MAP that you have to fly, then your either incompetent or lazy, or both.

[FlightPathOBN]

if you can't determine you single engine performance as it relates to the departure or MAP that you have to fly

so now it is as it "relates'

You've dug yourselves into a hole if you want the world to believe that you can fly jets without having single engine performance that meets the departure and MAP profile.

you stated it 'meets'

incompetent...no doubt you are very familiar with this term.

Does your grandmother know you are using her computer? :=

[galaxy flyer]

Agreed the Ficklefinger then, one question, how do you determine OEI flight path clearance for "close-in" obstacles? Those in the ICA or what used to be termed Zone 1.

[theficklefinger]

In the end when I talk single engine performance, you guys have no clue as to what I am talking about......

[galaxy flyer]

No argument there, after all why should performance engineers and check airman know anything on the subject.

[aterpster]

He sounds like another MSFS troll who has gotten loose on the forum.

[aterpster]

FAA AC120-91 is required reading for anyone who actually wants to understand this issue:

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%20120-91/$FILE/AC120-91.pdf

[theficklefinger]

Aterp - I read it...your point?

[aterpster]

theficklefinger:

Aterp - I read it...your point?

Repeating my previous post:

FAA AC120-91 is required reading for anyone who actually wants to understand this issue.

So, since you presumably read it, you either understand it and your questions are answered, or you don't understand it and nothing anyone can say on this forum will make a difference in that regard.

End of discussion.

[theficklefinger]

Your blowing smoke, if you had a point you would have made it...

[aviatorhi]

Fickle, if you are a pilot (which I highly doubt) I would be surprised if you are able to stay employed anywhere with the attitude that you have. Aterpster is right, but that is beside the point now, you don't belong in any sort of aviation, including simulated.

[rudderrudderrat]

Hi ficklefing,
you guys have no clue as to what I am talking about......
Correct. Please rephrase your question.

[theficklefinger]

You guys are idiots...no offense, but if you can't figure single engine performance...forget being a pilot, you shouldn't be on a technical aviation forum.

I suspect that we can survive without this poster's erudition - JT

[rudderrudderrat]

Hi ficklefing,
You guys are idiots...no offense - but I do take offence at that remark.
but if you can't figure single engine performance...
er...... I must have missed something, how many engines did you start with?

[westhawk]

I suspect that we can survive without this poster's erudition - JT

I suspect JT is correct.

But I appreciated the opportunity presented to review AC 120-91 again aterpster. :)

This is probably the single most misunderstood and misapplied operational requirement I've encountered in my experience as a part 135 pilot. The very few pilots who do seem to grasp the concept are grossly outnumbered!

Anyway, it's been a treat!

[aterpster]

westhawk:


But I appreciated the opportunity presented to review AC 120-91 again aterpster. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif

This is probably the single most misunderstood and misapplied operational requirement I've encountered in my experience as a part 135 pilot. The very few pilots who do seem to grasp the concept are grossly outnumbered!

Anyway, it's been a treat!

If nothing else AC 120-91 sends a strong message that Part 121 and 135 operators that operate Part 25 birds really do need the expert assistance of performance engineers.

[john_tullamarine]

For routine performance work, the work is relatively straighforward and the ops engineer doesn't need a great deal of anything other than

(a) a good understanding of what he/she is endeavouring to achieve

(b) good housekeeping and general attention to detail.

What is a problem is the (generally) pilot who views the work as being a lot more simplistic than it is. Perhaps this sort of view develops as a consequence of using the typically very simply presented RTOW tables in routine line operations ?

[FlightPathOBN]

a pilot should be required to spend time in Operations with the people doing the loading plans..

[airbus757]

Other than being a little rude I can't see where ff has gone wrong. All he is saying is that a pilot should ensure that the A/C meets or beats the one engine out performance requirements for a departure or an arrival with a missed approach.

As to how all these requirements are developed, I don't think that was his argument.

The way i read the circular it seems that One engine out performance is considered in the missed approach.

[john_tullamarine]

theficklefinger's technical concerns and inferred questions were fine.

However,

(a) his comments were suggestive of a lack of detail knowledge as to how things can be done and a lack of interest in pursuing technical discussion on the same

(b) there comes a time when gratuitous insults thrown in the face of folks who are endeavouring to help out gets to the point of being a tad over the top

(c) there are other forums where such combatant behaviour is more welcome than here

[airbus757]

Fair enough.

I got the impression that some posters were suggesting that one engine out performance was not considered when developing missed approach procedures. The way I read the posted circular suggests that it is.

Show me the error of my ways.

Thanks.

[john_tullamarine]

I got the impression that some posters were suggesting that one engine out performance was not considered when developing missed approach procedures

I think that's precisely what some posters were suggesting. FlightPathOBN, aterpster, and others, such as OzExpat (who hasn't spotted this thread yet) are expert in the procedures discipline and I defer to their expertise.

The OEI case is left to the airline operator and, for other operations, (quite inappropriately) the poor old pilot who has next to no real chance of figuring it out on the run.

OPS 1.510 goes some of the way to a sensible protocol but is still rather lacking, especially for the twin fraternity.

Checking the OEI gradient capability (for which configuration ?) is false comfort and doesn't consider performance capability with respect to reconfiguration during the miss.

Attempting to use the takeoff escape procedure for a miss carries with it a number of uncomfortable problems, potential and real.

For a difficult terrain runway, the only sensible way to approach the OEI problem is to have the ops eng folks do a relevant study for the miss. Any suggestion that the pilot can wing it on the day works only for benign terrain situations.

theficklefinger, having ventured into subject material in which his/her knowledge appears to be a little lacking in detail then received a bit of a friendly bollocking from the residents - goes with the territory in technical discussions and is something one needs to be able to withstand.

The post grad student has a far more intense time of it when defending his/her thesis.

[whenrealityhurts]

Sorry JT...

It comes down to this...your either planning/recognizing for single engine performance to exceed any all obstacle and navigational aspects of your flight...or your not.

It's immaterial whether you can figure it out, or whether it's required, or whether your told to do it.

Simply put, if you can't meet Part 25 specs to fly around on one engine at any phase of flight, then you shouldn't be there.

[airbus757]

AC No: 120-91


17. MISSED APPROACHES, REJECTED LANDINGS, AND BALKED LANDINGS.

a. General.
(1) Parts 121 and 135 do not specifically require an obstacle clearance analysis for one-engine-inoperative missed approaches or rejected landings. While it is not necessary to perform such an analysis for each flight, dispatch, or landing weight limitation, it is appropriate to provide information to the flightcrews on the safest way to perform such a maneuver should it be required. The intent is to identify the best option or options for a safe lateral ground track and flightpath to follow in the event that a missed approach, balked landing, rejected landing, or go-around is necessary. To accomplish this, the operator may develop the methods and criteria for the analysis of one-engine-inoperative procedures which best reflect that operator’s operational procedures.

(2) Generally, published missed approach procedures provide adequate terrain clearance. However, further analysis may be required in the following circumstances:

(a) Published missed approach has a climb gradient requirement;

(b) Departure procedure for the runway has a published minimum climb gradient;

(c) A special one-engine-inoperative takeoff procedure is required; or

(d) There are runways that are used for landing but not for takeoff.
NOTE: Operators should incorporate procedures for converting required climb gradients to required climb rates in pilot and dispatcher airplane performance sections of their approved training programs.


Gents. This tells me that OEI climb gradients are considered.

Also one can refer to FCOM 3.05.35 Approach Climb Gradient (%) to determine any odd %, other than the standard 2.5%.

[mutt]

Simply put, if you can't meet Part 25 specs to fly around on one engine at any phase of flight, then you shouldn't be there. What people are trying to point out to you is that Part 25 has nothing to do with TERP's/PAN OPS..... The aircraft is certified to specific Missed Approach Criteria, (all engine and one engine inop) as detailed in Part 25.

Prior to the AC, there was no FAA guidance telling airlines to do anything apart from clear all obstacles in the takeoff flight path. For Missed Approach procedures there was even less information.

I find it disappointing that the FAA have only issued an Advisory Circular, as they are there for information, you don't have to adhere to them. I would much prefer to see the word "MUST" used rather than "SHOULD". (Its the same with AC-91-6A regarding contaminated runways!)

Airbus757, even before the AC, we were reducing landing weights to comply with Missed Approach Climb Gradients in certain airports, even though this had a significant commercial impact on the operation.

[john_tullamarine]

Good development of the discussion in my view.

[First, for those who may not be aware, Mutt is (was ?) an ops engineering specialist (in his previous life and looked after this sort of stuff for a fairly large operation).]

Second, the problem which is being missed a little is that there are two supposedly complementary (but, often, in opposition) things in play -

(a) Design Standards - eg FAR 25

(b) Operational Standards - eg FAR 121, 135

The Design Standard gives you an aeroplane which is certificated to be compliant with a bunch of requirements and capabilities specified in the Standard. In general, however, it doesn't address much about what, when, where and how the operator might or should go about doing operational things.

The Operational Standard addresses what the Operator is required to do as a minimum.

For performance, one generally uses the data output from (a) via the AFM to figure out how to meet the requirements of (b). It helps if (a) and (b) are compatible and, while this usually is the case, one often sees the odd case of the left and right hands not knowing what the other is doing.

your either planning/recognizing for single engine performance to exceed any all obstacle and navigational aspects of your flight...or your not.

Considering OEI one should certainly be doing. The relevant question is how do you go about doing that ? FAR 25 gives you some data but not much in the way of tools. FAR 121/135 spells out some requirements but doesn't give you much in the way of how to meet them. Enter ops engineering (or those pilots who have made it their task to get up to speed on the ways of doing performance work).

It's immaterial whether you can figure it out, or whether it's required, or whether your told to do it.

I'm not sure that I understand where you are going with this comment. Figuring it out is mechanistic, requirements are in the Regulations or follow from sensible governance considerations and "told" is a combination of airmanship and corporate/regulatory governance.

Simply put, if you can't meet Part 25 specs to fly around on one engine at any phase of flight, then you shouldn't be there.

Not quite the case but near enough for government business. However, FAR 25 only gives you some data - it doesn't bridge the gap between data and not bending the aeroplane.

do not specifically require an obstacle clearance analysis ... it is appropriate to provide information to the flightcrews on the safest way to perform such a maneuver should it be required

Now I'm only a dumb PE with a bit of airline flying experience - just how does one provide information on the safest way to perform such a manoeuvre without doing some analysis ? Sounds like black magic mumbo jumbo to this little black duck.

To accomplish this, the operator may develop the methods and criteria for the analysis of one-engine-inoperative procedures which best reflect that operator’s operational procedures.

I suspect that that goobledegook means "do some analyses" ?

Generally, published missed approach procedures provide adequate terrain clearance

they left out the bit which says "for minimum terrain requirements and AEO operations"

Published missed approach has a climb gradient requirement

this might require a reduction in weight but still only is considering AEO

Departure procedure for the runway has a published minimum climb gradient

if nothing else this alerts everyone to the idea that we have some serious terrain here ..

A special one-engine-inoperative takeoff procedure is required

often this will have little to do with the missed approach ?

There are runways that are used for landing but not for takeoff

the "why ?" is important but the inference still suggests the need for a closer looksee at things.

Gents. This tells me that OEI climb gradients are considered

ah, no, not at all. Main shoot down is how do you consider OEI for twins, three holers, and quads simultaneously without specifying a lot of information ?

Also one can refer to FCOM 3.05.35 Approach Climb Gradient (%) to determine any odd %, other than the standard 2.5%.

How do you intend to account for the progressive clean up from the landing configuration to the missed approach configuration to the enroute configuration .. with varying gradient capabilities throughout ? Not to mention the hills here and there and the possible need for turns ?

[rudderrudderrat]

Hi JT,

How do you intend to account for the progressive clean up from the landing configuration to the missed approach configuration to the enroute configuration .. with varying gradient capabilities throughout ? Not to mention the hills here and there and the possible need for turns ?

In my company, if the published MAP climb gradient is >2.5%, we are required to calculate the "Approach Climb Gradient" (from the lap top) using Estimated Landing weight, Airfield conditions, Landing Config. If we can't make it - then we have to use the higher published minima.

If we can satisfy the required OEI climb gradient, and we suffer an engine failure then we raise the acceleration altitude to MSA or 1st published stop Altitude or level acceleration Alt (when published).

[galaxy flyer]

To add a bit to mutt's comments, FAR 25 deals only with certification while Tprocedures drawn using TERPS, PANS-OPS or any national standards differing from them (unusual, granted) are designed to achieve the lowest reasonable minimums and compatibility with the ATC structure. Many procedures, especially SIDs are drawn, not to optimize payloads or to minimize climb gradients, they are drawn to meet ATC needs. The procedure designer cannot anticipate the performance characteristics of each plane using the procedure, he assumes AEO operations. It is up to the operator to plan for the engine failure case, not the designer. Meeting FAR 25 OEI climb gradients is irrelevant to DP or MAP and to achieving optimum gross weights may not happen by using the published procedure and using the published procedure may not (likely not, in many cases) provide the greatest margins in the event of OEI.

It is, in many cases, erroneous to plan meeting the specified climb gradients means the operation is being done in the safest manner. Many think planning to fly the SID or MAP using OEI performance data is best, many would be wrong.

[airbus757]

How do you intend to account for the progressive clean up from the landing configuration to the missed approach configuration to the enroute configuration .. with varying gradient capabilities throughout ? Not to mention the hills here and there and the possible need for turns ?


On the airbus these figures are presented on three charts. For a missed approach we select TOGA, gear up, and move flaps up one step to conf 3, conf 2, or conf 1+F. From their respective charts we can see the expected climb gradient and as long as it is equal to or greater than the required gradient all is good. This required gradient is listed on lido charts. It is 2.5% or a non standard requirement. Also if a turn is required we must allow for 0.9%. We maintain that configuration until the missed approach altitude is reached where we level off and clean up to hold or enroute speeds.

As with most things there is more than 1 way to skin a cat. Other options are available if required gradients are not attainable.

[aterpster]

mutt:

Prior to the AC, there was no FAA guidance telling airlines to do anything apart from clear all obstacles in the takeoff flight path. For Missed Approach procedures there was even less information.

I find it disappointing that the FAA have only issued an Advisory Circular, as they are there for information, you don't have to adhere to them. I would much prefer to see the word "MUST" used rather than "SHOULD".


If AC 120-91 stated "must" or "shall" then instead of being an advisory circular, it would be a de facto amendment of F.A.R. 121.189 and related regulatory sections. The FAA cannot make rules via ACs. If they tried to do that, it would likely throw the entire issue into a "full press" rule-making process, including formal public hearings, etc. Simply put, there are marginal operators that do not wish to be bound by AC 120-91. Rather, they use a very sharp pencil to "comply" with the 600 foot wide 121.189 OEI path beyond the airport boundary.

Having said that, for benefit of the lurkers, a very good example of the missed approach case, and how it bears absolutely no relationship to FAR 121.189 is KBIH, Bishop, California. Bishop has a good RNP AR IAP to Runway 30, but Runway 12 would not qualify. So, two LNAV IAPs were developed to Runway 12, one with very low straight-in minimums for this airport and a climb-gradient missed approach, and the other with a missed approach that is 40:1 clear and, thus, with much higher minimums. These IAPs are strictly TERPs. The procedures folks who designed them know nothing about performance engineering, nor should they. They are making normal ops IAPs for every conceivable type of airplane, from a well-performing light airplane to an Airbus 320 or Boeing 767.

Low minimums with climb gradient:

http://aeronav.faa.gov/d-tpp/1108/05737RZ12.PDF (http://aeronav.faa.gov/d-tpp/1108/05737RZ12.PDF)

High minimums with 40:1 clear missed approach (assumes not less than 200 feet per mile CG):

http://aeronav.faa.gov/d-tpp/1108/05737RY12.PDF (http://aeronav.faa.gov/d-tpp/1108/05737RY12.PDF)

As you can readily see the missed approach flight track for either of these IAPs, particulary the "Z" (low minimums) approach is very likely where the performance engineer would not want to send his airplane in the event of an engine failure at, or near, MDA. He might rather continue down the valley, where there are airspace and steeper terrain problems, nonetheless a fairly wide valley for 70 miles, or so.

What makes this airport and, in particular, Runway 12 very interesting is that IFR takeoff minimums are not authorized because of the close proximity of terrain to the D.E.R. (This issue is avoided with the IAPs by having the MAP prior to the runway threshold, plus even being at the lower MDA, you have a "running start" as opposed to an engine failure just above V1 on takeoff).

KBIH takeoff minimums (you have to scroll down a bit to located Bishop):

http://aeronav.faa.gov/d-tpp/1108/SW2TO.PDF (http://aeronav.faa.gov/d-tpp/1108/SW2TO.PDF)

Now, let's say the missed approach engine failure occurs after turning east into the "merry go round" missed approach track. Do I want to continue around towards higher terrain or do I want to escape through the saddle into the valley to the east? Only performance engineering tailored to the specific airplane type can make that determination. Because engines can fail at varying points from MDA (or even prior to MDA) to infinately varying points along the missed approach flight track, is the very reason why AC 120-91 states that more than one OEI missed approach path may have to be provided for a given runway at a location as complex (terrain rich) as Bishop.

Another aspect, if the decision is to continue with the missed approach path back to BIH VOR because of an engine failure fairly late in the game, does holding have to be considered? Of course not, the holding pattern is what drives the 13,000 final altitude. Proceeding OEI up the valley to the north could result in a less demanding OEI path.

What is very apparent to the trained person is that none of this bears any relationship to TERPs, other than the performance engineer may elect to continue with the charted missed approach flight track, albeit without TERPs containment assessments.

In my considered opinion AC 120-91 should be regulatory and it should be updated to provide RNAV and even tight RNP OEI flight path options. But, this is a classic case of the "tombstone factor" at the FAA when something as critical as payload politics is involved. If the day comes when a marginal operator who does not use AC 120-91 pastes a bird on a mountain side while OEI then that would get things moving. :)

Finally, I can come up with many airports with OEI issues every bit as demanding as Bishop. And, as we know, these types of airports exist throughout the world. Latin American is rich with them.

Note: The URLs provided here will expire on August 25. But, the same charts would be available after that with a bit more searching at:

Digital Terminal Procedures/Airport Diagrams (http://aeronav.faa.gov/index.asp?xml=aeronav/applications/d_tpp)

[aterpster]

Adding to the specifics of my Bishop message a better overview of the topography is provided by an overlay of the missed approach flight track on the 1:500,000 San Francisco visual sectional aeronautical chart:

http://tinyurl.com/3j338o9

This clearly shows the option to design the OEI flight path down the Owens Valley instead of encountering the mountains overflown in the TERPS missed approach procedure. If the engine failure occurred between MDA and PULIE, it very well may be better to have the OEI flight path depart the TERPS track at, or prior to, PULIE and continue down the valley.

Or, if the engine failure occurred well after PULIE it might be desirable to depart the TERPs track between TEVOC and NEBSE and proceed over lower terrain to the valley to the northeast.

The OEI assessment, just like a TERPs assessment, should be done on the best available topographic data. In the case of the US this is the USGS 1:24,000 topographic map. (I have found to my distress that some performance engineering entities do not use topographical data this good).

To the USGS topo map the procedures designer (for TERPs) or the performance engineer (for OEI) must plot and add all antennas or other structures of record. In the U.S. all such structures of 200' height or greater are recorded (lower heights close to the airport in accordance with the FAR 77 model).

The FAA has all of this high-fidelity and recorded structures in an automated system. And, they have all the TERPs design criteria semi-automated. Designing an OEI procedure in the U.S. would be far easier if the performance engineer had access to this FAA system (known as IAPA).

Here is a portion of the Bishop missed approach track at 1:24,000:

http://tinyurl.com/3l7jwsn

[Zeffy]

Airbus757

On the airbus these figures are presented on three charts. For a missed approach we select TOGA, gear up, and move flaps up one step to conf 3, conf 2, or conf 1+F. From their respective charts we can see the expected climb gradient and as long as it is equal to or greater than the required gradient all is good. This required gradient is listed on lido charts. It is 2.5% or a non standard requirement. Also if a turn is required we must allow for 0.9%. We maintain that configuration until the missed approach altitude is reached where we level off and clean up to hold or enroute speeds.

Yes, it is possible for a pilot to make a few spot checks of expected climb gradients in various configurations and compare them to the overall gradient required by a Missed Approach.

But doing so is not the same as a full performance analysis computed by the professional engineering entities.

As you are no doubt aware, airplanes do NOT climb along linear paths -- aka "gradients".

During climb (all engines or OEI) thrust is decaying, time limits for power settings are reached, acceleration segments are required for cleanup, etc.

Our actual climb paths are anything BUT "gradients".

[FlightPathOBN]

In my considered opinion AC 120-91 should be regulatory and it should be updated to provide RNAV and even tight RNP OEI flight path options. But, this is a classic case of the "tombstone factor" at the FAA when something as critical as payload politics is involved.

Payload politics for sure...
In working with these performance profiles, it really is very difficult given the number of variants, engines, configurations, bleeds, etc that is would be difficult for the FAA to regulate how this is accomplished.
For the most part, when the carrier is shown the EO performance, it is usually a bit of a shock with the weight limits or temperature limits. Many regulators then default to EO as 'emergency operations' and let it go at that, again, thank goodness for the reliability of todays engines.

For the most part, the people back at Ops are using BCOP or something similar, to load the aircraft, with assumptions for the destination, as well as departure.
The pilot should do a quick check on approach to make sure the assumptions are close to real time conditions, namely temperature and weight, and adjust if necessary.

[FlightPathOBN]

Here is a test example.

Input

http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/07/Capture03.jpg

Resultant performance...note the difference even between same aircraft type, F30 vs F40, and add icing makes a huge hit...or temps above 30.

http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/04/climbperf.jpg

[FlightPathOBN]

terpster,

in answer to your very well presented case...

in regards to the OE path following the published missed, or an EO departure following anything published, 2 points...1. Cant do it the 70% answer...2. Dont even think about it.. 30%

[john_tullamarine]

and we suffer an engine failure then we raise the acceleration altitude to MSA

We maintain that configuration until the missed approach altitude is reached where we level off and clean up to hold or enroute speeds

That gets us out of the configuration change/gradient problem. However, given that thrust for GA generally is the same as/similar to TO, do we give any concern to time limits at GA thrust ?

Also if a turn is required we must allow for 0.9%.

Good (although a tad higher than I might have expected) but how do we account for turn radius/terrain ?

[aterpster]

and we suffer an engine failure then we raise the acceleration altitude to MSA

Policies like that are why a full-route OEI path is needed where radar services are not available. The MSA may be several thousand feet higher than is necessary.

[Zeffy]

rrrIf we can satisfy the required OEI climb gradient, and we suffer an engine failure then we raise the acceleration altitude to MSA or 1st published stop Altitude or level acceleration Alt (when published).

How well would that method work in the example procedure provided by aterpster?

http://i202.photobucket.com/albums/aa92/zeffy_bucket/KBIHRNAV12.png

MDA = 4580

First published altitude = 13,000

Would the company have us going all the way from 4580 to 13,000 in an approach climb configuration? :ouch::ouch:

MSA = 15,500

And as JT noted, we probably shouldn't omit to take into account the time limit at GA thrust...

:hmm: :hmm:

[FlightPathOBN]

This plate is a basket case....

The * on MDA notes that you must climb to 11000, if able...that altitude makes sense with the controlling obstacle listed, and the mountainous ROC.

climb to 13000 direct KUPLE...this is about a 500' DA...so one goes from 4580 to 13000 for the missed? Where the heck does that come from?

3.68 GPA???? CAT C...wow...VGSI and GPA not coincident...no ****...

one has to love the FAA exempting themselves from the criteria...

[aterpster]

FlightPathOBN:

This plate is a basket case....

The * on MDA notes that you must climb to 11000, if able...that altitude makes sense with the controlling obstacle listed, and the mountainous ROC.

climb to 13000 direct KUPLE...this is about a 500' DA...so one goes from 4580 to 13000 for the missed? Where the heck does that come from?

3.68 GPA???? CAT C...wow...VGSI and GPA not coincident...no ****...

one has to love the FAA exempting themselves from the criteria...

It's a good procedure that provides access to high-performance birds that previously has not been available. It is an LNAV only procedure, thus the desent angle; this is normal TERPs. A vertically guided procedure would not qualify because of GQS problems. Otherwise, this runway would have had an RNP AR IAP.

The minimum holding altitude in that valley is 13,000 feet, thus the climb to 13,000. If there were no hold the missed approach would still have to go to 12,500 to 13,000.

Did you check the "Y" procedure for the average performing aircraft?

Obviously, this procedure is impractical for other than turbine airplane.

[aterpster]

j.t.,

and we suffer an engine failure then we raise the acceleration altitude to MSA

We maintain that configuration until the missed approach altitude is reached where we level off and clean up to hold or enroute speeds

That gets us out of the configuration change/gradient problem. However, given that thrust for GA generally is the same as/similar to TO, do we give any concern to time limits at GA thrust ?

Also if a turn is required we must allow for 0.9%.

Good (although a tad higher than I might have expected) but how do we account for turn radius/terrain ?

All factors in why more than one OEI route is required for a complex location, as recommened in AC 90-121.

Using the Bishop RNAV RWY 12 "Z" IAP as the case study:

1. If the engine fails at MDA the OEI path should depart the missed approach path at ROCOS and proceed down the valley on a preplanned database RNAV OEI route. Clean up would be complete at 1,500 feet with acceleration to enroute climb and a left turn out of the valley perhaps many miles later when terrain on the east side of the valley could be safety overflown.

2. If the engine failure doesn't occur until PULIE and if we are adhering to the normal ops climb gradient we are long since cleaned up, at almost 11,000 and probably 250 KIAS. So, another evaluation needs to be preplanned at that point as to whether to continue to 13,000 along the missed approach path, or depart into the adjacent valley to the east passing TEVOC.

This can be so easily accomplished with today's state-of-the-art FMS flight plan options. It has indeed been tailored into some air carriers FMS/navigation systems by the likes of Naverus.

Alas, the industry in general is way, way, behind in taking full advantage of the capabilities of their FMS/navigation system.

Sensing an engine failure, the system could offer the crew the OEI RNAV flight path options, depended upon ship's position. The required vertical profile could also be displayed at that time.

[stormyweathers]

Im sorry, but I really think that banning FF was not justified at all. I read these posts, and i know that he must be very experienced and has alot to offer to this discussion. He is the reason the thread evolved to this depth. I like to keep an open mind at all times. I dont think he insulted anyone. Some peoples ego might be so high that they refuse any suggestion that they may be wrong. So you ban him because he is politically incorrect with not much finesse. I can tell that he has alot of common sense and very experienced and is quite intelligent... and you decide to ban him...

My thoughts, you have Approach Climbs requirements (1 engine inop.), you have Landing Climb requirements (all engines), both based on airport altitude. You have Missed Approach requirements which are published on the chart and based on DA or MDA. The chart might specify a gradient, and this gradient must be satisfied. My understanding is that what FF was saying is that this gradient must be MET point. If you cannot meet it because you are performing an overweight landing, or if your engine is out, or your gear is stuck down, you must find an alternate path which operations will work out for you, this alternate path might be the same as the T/O engine inop path. This is what I think FF is saying. You seemed to be all ganging up on him to tell him read this and read that, as if he is illiterate. You insulted him as much as he insulted others. BTW, please dont ban me, i meant no harm...

[john_tullamarine]

I really think that banning FF was not justified at all.

Your opinion is respected.

Some peoples ego might be so high that they refuse any suggestion that they may be wrong.

Not at all a problem if a poster wishes to indicate that he/she considers someone else's comments to be incorrect. If it were not for incorrect opinions sites such as PPRuNe would lose their way, I suspect.

The problem is the manner of so indicating.

BTW, please dont ban me

We don't ban folks for holding opinions.

[MD83FO]

Im not grasping it
Speaking OPS 1, is it a dispatch requirement to limit landing weight based on single engine go around performance at destination?

[stormyweathers]

Thanks for your reply JT.

Some gradient requirements have to do with OBSTACLE clearance, some dont. For example Landing Climb or Approach Climb gradients dont consider obstacles. They are just gradients that must be satisfied.

However, SIDS coinsider Obstacles with a 3.3% gradient. If you cannot meet this 3.3% for ANY reasons whatsoever, you need an alternate path (the companies engine out procedure) otherwise you might fly into an obstacle.

Similarly, the Missed Approach also considers OBSTACLES in the path. If you cannot meet this gradient for ANY reasons whatsoever, you might fly into an obstacle. So whether it considers engine out or not is irrelevant. I dont understand the question. If you follow the missed approach but cannot meet the gradient for obstacle clearance you might fly into something. So yes, if you have to limit your landing weight, but most probably you would simply raise your landing minimums or follow your companies engine out procedure for that runway.

[Non Zero]

If it were not for incorrect opinions sites such as PPRuNe would lose their way, I suspect.

So are you actually admitting that there are correct and/or incorrect opinions ... or ... you are more interested in outcomes?

[john_tullamarine]

So are you actually admitting that there are correct and/or incorrect opinions ... or ... you are more interested in outcomes?

Not quite sure where you are leading.

However, all of the above. Correct/incorrect refers to factual basis for an opinion, in which case some are correct, others incorrect.

If an opinion is a value judgement, rather than a point of fact, then correct/incorrect is not the consideration, rather reasonableness and, to a large extent, that involves peer review.

.. and we should all have a directed interest in outcomes as those are what gets us to the other aerodrome in one piece or find us scattered about the hillside.

[Non Zero]

Not quite sure where you are leading. ... just waiting for your correct answer! And you did ...
reasonableness and, to a large extent, that involves peer review :ok:.. and we should all have a directed interest in outcomes as those are what gets us to the other aerodrome in one piece or find us scattered about the hillside. :ok: