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Old 15th Dec 2012, 12:45   #1 (permalink)
 
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Missed Approach Climb gradient and missed approach requirements

Missed approach (standard) requirement, taken from pans ops 8168 vol.2 : 2.5%



Missed Approach Climb gradient single engine = 2.1% (twin engine)


Question: If you go around single engine and follow the published Missed Approach (2.5% gradient), you will fly below it (2.1%)--> You could hit an obstacle!

Am I missing something?
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Old 15th Dec 2012, 13:57   #2 (permalink)
 
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You are correct. That's why savvy operators have performance engineers assess the obstacle environment for each authorized runway end and provide one engine inoperative "escape" flight paths, where necessary.

There are other locations where a 1% gradient (or even less) will clear all obstacles on a missed approach.
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Old 15th Dec 2012, 14:16   #3 (permalink)
 
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Looking at the text in the Aerad supplement that reproduces this diagram, it states:

"It must be emphasised that not all aircraft can achieve this gradient with an engine out, at a maximum certified gross weight. This 2.5% gradient is assumed to extend up to a point at which the aircraft can fly level for 6nms to accelerate and clean up."

So in essence, the answer would be that you could hit something.

I looked at a couple of example charts also from Aerad, which has a MISAP towards a big hill. These give tracks to clear the terrain but do not provide % climb gradient required for the MISAP. Therefore it would fall into the 'operator responsibility' per EU Ops.

Trying to find the definition of what calculations are done for max landing weight by our performance service provider. I suspect that it is weight limit for factored LDA, and also the landing climb, but right now I cannot recall if landing climb is done OEI or not. I suspect not, as it'll be weight to achieve the required % per the certification requirements.

Does your FMS provide the climb % gradient available at your landing weight? That gives you a warm feeling of what the aircraft will do with OEI.
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Old 15th Dec 2012, 15:11   #4 (permalink)
 
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Ops 1.510

"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."
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Old 15th Dec 2012, 16:38   #5 (permalink)
 
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Missed Approach Climb gradient and missed approach requirements

We're mixing things here. 2.1% is a certification req as per EASA CS-25.
Operationally we should comply with EU-OPS and PANS OPS doc 8168 which prescribes 2.5% as procedure design gradient unless otherwise noted.
The requirement is always for One Engine Inoperative.
Note that from PANS OPS revision 4 onwards the level acceleration segment (6nm@800ft HAA I believe) has been deleted. This means now that 2.5% gradient must be assured OEI until MSA/go around altitude. I.e OEI acceleration must be delayed...
Some states such as France have, despite having constructed i.a.w. PANS OPS 4/5, catered for a level acceleration segment i.a.w. chart note. E.g. No level accel prior to xxxx ft.


Rgds
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Old 15th Dec 2012, 16:52   #6 (permalink)
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Quote:
The requirement is always for One Engine Inoperative.
Any IAP is laid out for normal configuration e.g. all engines operating. It's an operators' responsibility to cater for contingencies. Having said that, a twin on STD ISA can achieve on average 5% climb gradient with MLW but for the acceleration segment has been deleted, following published MA SE till MSA or the MA level off alt. might or might not be possible.
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Old 15th Dec 2012, 17:03   #7 (permalink)
 
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Missed Approach Climb gradient and missed approach requirements

Yes you're right. What I was getting at is that very few operators consider an OEI routing in missed app. Hence the PDG of 2.5% has to be complied with OEI in these cases.

Atb
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Old 21st Dec 2012, 16:05   #8 (permalink)
 
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Thanks guys, really appreciate the responses!
merry xmas
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Old 21st Dec 2012, 17:14   #9 (permalink)
 
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As a 737-800 operator we have accounted for all this although its based on an MFRA at roughly 1000 aal. Under the new rules are we now saying that we we have to climb at T/O flap to MSA OEI? That's going to interesting in the summer....
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Old 21st Dec 2012, 17:20   #10 (permalink)
 
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original post states EO climb is 2.1%..

2.5% is gross
2.1% is net

all engine....
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Old 21st Dec 2012, 20:30   #11 (permalink)
 
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Quote:
original post states EO climb is 2.1%..

2.5% is gross
2.1% is net

all engine....
So technically you shouldn't have any problem, as long as you go-around at or before minima, if you do after, for whatever reason, it might be a serious problem.

FB

Last edited by Fullblast; 21st Dec 2012 at 20:30.
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Old 25th Dec 2012, 01:53   #12 (permalink)
 
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Quote:
So technically you shouldn't have any problem, as long as you go-around at or before minima, if you do after, for whatever reason, it might be a serious problem.
It might be if you didnt check your go around climb gradient capability in case of engine fail before starting the approach.
If you started an approach with your actual gradient (one engine toga and flaps in GA position) below the required gradient you are not legal and Yes If you need to GA and then lose engine as you do so,you are in serious

I believe there is a 3.2% balked landing gradient (2engines/twin) that must be statisfied also.(speed VREF,gear down,both engines toga).

Last edited by de facto; 25th Dec 2012 at 01:55.
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Old 25th Dec 2012, 21:58   #13 (permalink)
 
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During actual flight testing of engine out procedures, it was interesting to note just how difficult it is to make the climb and not violate the missed approach surface, especially if you are configured for landing, and near the 140kts CAT C speed....
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Old 26th Dec 2012, 02:43   #14 (permalink)
 
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Quote:
Any IAP is laid out for normal configuration e.g. all engines operating.
Yes, they say that but it doesn't mean anything. If you can maintain the minimum missed approach climb gradient then that's all that matters. It doesn't matter if you've lost one engine or two engines or you're flying a rocket or you fire a cannonball - the object (whatever it is and whatever happens to be propelling it at the time) will not hit any ground object if it can maintain the minimum missed approach climb gradient.

The only reason a designer will say that it's only laid out for normal operation of the airplane is so that they cover their ass for whatever litigation they might encounter from an incompetent company or pilot who decides to sue because it didn't say on the plate that they should double check their performance if they want to attempt the approach single engine.
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Old 26th Dec 2012, 10:44   #15 (permalink)
 
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2.1% is minimum certification (CS/FAR/AP-25) value. For instrumental approach according to 8168 you have to have 2.5%. If there are some significant obstacles, ACG should be bigger, than 2.5%. However MDA(H) must be povided for ACG = 2.5% as well as for bigger one. No gross/net flight path definitions for approach path as well as for other flight phases, describes in 8168. "Net" for abnormal (engine-out) only.
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Old 26th Dec 2012, 13:36   #16 (permalink)
 
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I think we have been through this more than once in other threads.

A departure or missed approach climb gradient is a constant slope.

A OEI takeoff or missed approach path is a "staircase."

Only a performance engineer can determine whether the "staircase" will fall below the constant slope of normal IFR departure or missed approach procedures.
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Old 26th Dec 2012, 16:28   #17 (permalink)
 
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Well, one has to remember, that a procedure design, has to take into account all of the worst case factors...
MLW, max bleeds, dirty engine, low end of the CAT approach speed, initiation of missed, pilot/aircraft reaction time...and especially temperature/met conditions.

The plates will likely have one missed approach shown for all CATS as well...

From a design engineer perspective, considering all of the above factors, I find that few twins meet the missed approach climb requirements when EO....

even during actual flight tests of procedures, with an engine at idle to sim EO, it was creative not to violate to missed approach surface (unless you wanted to design an unreasonable DA/MDA...)

If the plates had EO taken into account, you would see some very unreasonable DA/MDA's...if the DA/MDA is near the 200' OCH, ie 250HAT (200' OCH + 50' momentary descent) I would really see little chance of an EO twin not extending into the OCS...

Note the origin (original post) of the missed approach surface..it is NOT end of runway, it is TCH....

Last edited by FlightPathOBN; 26th Dec 2012 at 16:48.
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Old 26th Dec 2012, 20:30   #18 (permalink)
 
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Quote:
Well, one has to remember, that a procedure design, has to take into account all of the worst case factors...
MLW, max bleeds, dirty engine, low end of the CAT approach speed, initiation of missed, pilot/aircraft reaction time...and especially temperature/met conditions.
FlightPath...

Procedure design has nothing to do with how an airplane is flown. As I mentioned in my earlier post, it doesn't matter if the plane is being flown on 1 engine or 8 engines, as long as it can maintain the minimum climb gradient and carries out the proper rate one turns and maintains the airplane within the allocated distances associated with the category, the airplane will be safe!

One quick point before moving on: categories (A, B, C, D, E) are based on indicated airspeeds. You are supposed to fly according to the minima associated with the category in which you're flying the maneuver at. For example: if you're flying a circling procedure at 140 KIAS then you're supposed to adhere to Cat C minima and the circling distance of 1.7NM. But, I think it should be understood that it does not matter what airspeed you fly your maneuver at, if you maintain within the limits prescribed for that category, you will be safe. If you fly 300 KIAS while circling and keep it within 1.3NM then you could go to category A minima and be safe. If you're flying at 140 KIAS while circling but would like some extra room to maneuver, you may go to the category D minima and keep it within 2.3NM instead of the 1.7NM for category C.

I think it needs to be remembered that there is a HUGE difference between procedure design and airplane performance.

As for the determination of procedure design, there are certain factors for wind and imperfect turning that is applied to the flight path to ensure protection up to a certain limit. The worst case is not the low end of the category approach speed, it is the high end. If you're at the high end you will require a greater turning radius thus requiring larger protection limits while maneuvering. I agree that they they add a fudge factor for pilot/aircraft reaction time, and temperature/met conditions such as wind - however, I don't agree any consideration is taken for MLW, max bleeds, dirty engine, etc. Those are all specific airplane performance factors.
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Old 26th Dec 2012, 21:04   #19 (permalink)
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a modern twin in EO condition and ISA with MLW will achieve on average 5% MA climb gradient.
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Old 26th Dec 2012, 21:38   #20 (permalink)
 
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a huge difference between a procedure design and performance?

I would think they are directly related.

I have worked out many, many missed approach performance profiles, for all kinds of aircraft, in all kinds of conditions, trying to balance weights, airport altitude, and temperature limitations...

on procedures, you get calls all of the time when the temperatures go up...

9.g..perhaps 5% eventually....I would not count on a 5% climb EO at the missed approach point, and the momentary descent EO is significant...
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