departure proc gradient

[vikena]

A 2 Eng a/c needs to be able to acheive a 2nd segment gross grad of 2.4% with one enine out

A depature procedure requires an all engines op gradient of 3.3%

If i'm very light then I know that on one engine I can acheive 3.3% so then I could follow the SID and know that I'll clear all obstacles

But how can I quantify this precisely?

If I had a table of temp. head wind component a/c weight and climb gradient then I could formulate a much clearer plan of what to do rather than just climbing straight ahead to 1500ft or following an EOSID

Can airbus help me here or anyone

Thanks

VIKENA

[Old Smokey]

vikena,

A lot of what you say is feasible, but there are a number of important considerations that you must make. Here's a few -

(1) "A depature procedure requires an all engines op gradient of 3.3%", OR MORE if required for the depature routing.

(2) There is 0.8% 'fat' built into the SID 3.3% gradient, so you would need to extract performance data applicable to 2.5% Net Gradient, or the SID Gradient minus 0.8% if higher than 3.3%

(3) The SID gradient commences at the end of the runway, whereas the 2nd segment for OEI performance commences at the end of the 1st Segment. You will have to ensure that the 1st Segment lies ENTIRELY above the Runway and the SID Gradient from the end of the runway. This will mean reducing your Runway Effective Operational Length by a considerable amount. You'll have to do some trigonometry for Runway Slope, SID Gradient, and 1st Segment Length and Gradient. (That's going to be the most difficult part).

(3) You'll need discrete obstacle data within the SID coverage area to ascertain the Acceleration Altitude (3rd Segment), and this is generally not available. If it's not available, you'll have to use the Altitude at which the SID Gradient requirement terminates, or the MSA. If MSA was, for example, 7000 feet, you'd have to use this as the Acceleration Altitude. Do you have enough time to conduct a OEI Climb to 7000 feet, and complete your 3rd segment acceleration to Clean-Up within the 5 or 10 minute limit at Takeoff thrust? Actually, in converting the PANS-OPS obstacle clearance criteria to FAR25 (or it's equivalent) you need not go all the way to the MSA. In this case you can use -

Acceleration Altitude = Airport Elevation + (MSA - Airport Elevation - 1000) X 3.3 / 2.5 + 35.

(4) If you can't make MSA within the Takeoff thrust time limit as specified in (3), then you'll need discrete obstacle data AGAIN to ascertain a suitable 'break-off' point from the SID to an area where the FAR25 obstacle clearance requirements can be satisfied.

There's a 'Starter Kit' for you.:ok:

There are a great number of SIDs that start earlier than what would be desired for optimal obstacle clearance under OEI FAR25 rules (e.g. The SID (3.3%) requires a turn at Runway End, the OEI procedure (2.4%) requires Runway Track to 7.0 DME). This leaves the pilot in a 'Grey' area if suffering an engine failure after commencing the SID. In these cases, it has been necessary for me when developing Engine Failure 'Escape Routes', to provide a second, more limiting' OEI procedure to be followed if the SID is to be followed. With these options, the pilot is then, before Takeoff, commited to either the standard OEI Escape Route at the optimum weight, or the SID, at a reduced weight. In developing these secondary 'SID OEI Escape Routes', all of the factors listed above have to be considered.

Lots of luck with the project,:D

Old Smokey

[vikena]

THanks Old Smokey

Certainly a comprehensive reply

So the 2nd segment obstacle clearance req. starts at Gear up

But the 3.3 % grad starts at the end of TORA.

If I use 10kt tail wind figures then that will guarantee me the best initial performace but then I lose out with induced drag by having a lower V2 hence a higher pitch attitude and also I'll have increased rudder deflection

Can you just explain again where I go from here

Thanks again

[Old Smokey]

I'd love to vikena, but just walking out the door to be at "an airfield not too far from you" for the next few days.

Maybe the erudite John_Tullamarine will come up with a far better response until I can get back.

Regards,

Old Smokey

[john_tullamarine]

Vikena,

Not too sure where the tailwind thoughts came into the equation ?

What my good colleague OS is suggesting (in a detailed way) is that it's "not quite that simple".

The gameplan still requires that the escape procedure has to meet whatever operational airworthiness requirements exist for your AOC. If this can be done with regard to the SID procedure, then that is fine. However, it is not just a matter of making sure that the gradient is OK (presuming that you can push the third segment above the limiting obstacle). One needs to ensure, for instance, that the turning points, turn radii, GFP/NFP, wind drift, trapezoid clearance .. numbers fit with the SID.

What I would suggest is to do what some ops engineers do .. check the SID as an escape using the normal OEI sums and procedures and declare whatever weight limitations etc., might be appropriate for such an escape.

In the majority of cases, it is quite unreasonable to expect the pilot to make escape assessments at the time .. they need to be done in a fairly rigorous engineering analysis approach... one needs to keep in mind that the analysis might need to be defended at a judicial enquiry after the incident/accident ...

[vikena]

thanks JT.

its off to the ops engineers then

been flying for years and only recently realised that i know precious little about perf

[john_tullamarine]

... make 'em earn their money ... that's what they're paid to do.

It's an amazing thing .. most of us have the same sort of experience ... spend 40 - 50 years in whatever disciplines we profess ... become quite expert in one or two things (an expert = one who has had enough time to make many more mistakes in the field than the average chap and, hopefully, learn along the way ...).

Then, eventually, we retire (retirement = when all the other folk have come to the realisation that one is past one's use-by date) and do sensible things like sailing, fishing, etc.

[oldebloke]

VIKENA,just as a rule of thumb remember that 'gradient' is climb.
To figure out a 2.4% simply mulitply the basic figure of 60" per nautical mile as 1%(6000'-mile)..ergo 2.4% is 144' per mile x the grounspeed equals rate of climb required.
144' x 145KNOTS =350'rate of climb(MINIMUM)on 'one engine'
In Canada the SID rate of climb is 200'/mile,as stipulated in the Canada Air Pilot for the edification of questionable departures.
Some carriers depict 'escape routes-engine out'depending on what terrain clearance guidance they utilize..ICAO,or FAA(reduced swath limits)
cheers:ok:

[Old Smokey]

vikena,

I knew that I could count on John_Tullamarine to come up with a worth-while reply during my jaunt.

On reflecting upon your query over the past few dats, I seriously cannot arrive at any solution to your problem other than to follow the steps laid down in my earlier post. OEI procedures and SIDs are incompatible in so many ways.

If you're really determined to see this through, and, seeing as you were speaking of very light 'positioning' weights, there is 1 rather crude, but safe way that you could achieve it.

You could dispense with the need to keep the 1st segment above the Runway / SID Gradient if you could achieve the required gradient all the way to acceleration altitude from 1st Segment performance. 1st segment performance assumes that the gear is down or in transit, and would be very limiting for normal operations, but, at the very light weights that you speak of, might be achievable. Of course, DO pull the gear up in actual operations.

If the MSA was not too high, about 2000 feet, you probably would not have a problem with the 5/10 minute limit at Takeoff thrust. Higher MSAs could see you hitting the limit.

You could use standard Newtonian physics to ascertain the time to V2 at Takeoff thrust and within the runway distance, the distance to Acceleration Altitude at the SID Gradient and TAS at V2 to find the time for the 2nd segment, and access 3rd segment data to ascertain the time to thrust 'cutback' to MCT. The total of these 3 times must be equal to or less than the 5/10 minute limit. Gross, not Net performance may be used for this, but Net performance is still required for obstacle clearance.

A small addendum to my earlier post, the Acceleration Altitude may be the lesser of the actual MSA, or that derived from the formula. The final +35 additive should be amended to +50 if there is a turning manoeuvre involved.

Other than that, I can see no other simplification possible.

At the end of the day, if you are going to operate a flight in accordance with OEI procedures in a SID, such a procedure must be within the constraints and approved procedures of your AOC, otherwise you'd be operating illegaly, even though safety may have been assured.

Regards,

Old Smokey