Tabulated Data

[747CLASSIC]

Something that I have always wondered; How do the charts and graft information found in the Commercial Aircraft Flight Manual that come with the aircraft get into the user friendly Tabulated Data in the Performance Manual used by the airlines?

Classic

[Old Smokey]

The charts and graphs found in the AFM originate from numerous data plots from flight testing. As these are not always nicely ordered, and a few 'wild cards' have to be eliminated, a process of 'curve fitting' either by hand, suitable algorithyms, or computer generation are used, with all due consideration of 'break-points' (which are numerous and highly significantt if interpolation is to be used).

This 'curve fitted' data is then broken down into millions of data points at small intervals, for use in Computerised applications.

Data points at much more 'pilot useable' intervals are taken from these. Where the performance engineer has to exercise extreme caution is to ensure that linear interpolation will yield at least, accurate data, and at worst, conservative data. In numerous cases, worst case assumptions must be made where graphic or algorythmic data is simply far too complex to put into a 'daily use' pilots manual.

For the reasons of the necessary conservatism mentioned, manually prepared data by the pilot will inevitably be conservative. I've done considerable work in applying 'pure' performance manual data to the process of RTOW creation following airport analysis, this applies all of the bends and twists in the real data with accuracies down to a fraction of a Kg. The general 'day to day' charts for the same aircraft I've created for pilot use, make many conservative and general assumptions. Be assured that if you find a better weight from the general data than the computer generated RTOWs provide, you've made a big mistake. At best, they should just be equal.

[mutt]

747Classic,

Boeing produce a number of computer programs:

INFLT produces all inflight data in a user friendly format.

Mark7 produces takeoff and landing data.

SCAP produces takeoff and landing data for newer aircraft and is becoming an industry standard.

Most manufacturers will have a similiar range of programs.


Mutt.

[john_tullamarine]

If I may put a different spin on Old Smokey's comments.

(a) the AFM data generally originates from various mathematical models developed from first principles (although, in practice, one starts with any of the "standard" sets of equations). The windtunnel and flight test programs are used to validate these models .. which often involves the need for adopting fudge factor fixes to make the equations fit the observations.

Once an acceptable model is developed (and accepted by the regulatory authority) that model is used to build whatever AFM charts might be desired.

(b) if an operator chooses not to use the manufacturer's models for some reason, then the operator can go through the exercise of setting up extensive lookup tables or doing the regressions to derive a large set of equations to represent the AFM carpets. The result of either is a workable PC system to punch out RTOW data. Doing the work manually .. ie direct from the AFM .. is VERY labour intensive and only really suitable for a small aerodrome network

[747CLASSIC]

Thanks for the responses! Your answers have created more questions.

Old Smokey;
Performance Engineers, are they employed at the airline level to accomplish this conversion? If so, do smaller airlines have them on the payroll?

Mutt;
Can you elaborate more on, INFLT, Mark 7 and SCAP? I have never heard of them.

Question; How can the "tab data" from one company be different from the "tab data" at another company? All variables being equal.
I am looking at V1, VR and V2 for a B747-100 at the lower weights where VMCG may be a factor.
For example;
A 440,000 aircraft, 0 press alt and temp between 32-44C.
The speeds for one company are; 114/114/131 and the other company the speeds are; 112/115/131.
What gives? Thanks.

Classic

[mutt]

Classic747, I'm not really surprised that you havent heard of these programs, but combined with TOPAZ/OPAL from Douglas and Performance Engineers Programs (PEP) from Airbus are used to produce all performance related data within airlines.

While J_T and Old Smokey have told you about tabulating the AFM data, this is very unusual in an airline. Technology has taken us beyond that requirement.

As for the difference in V1, check the date of the AFM source. I have found similiar differences between Boeing AFM values and Operations tabulated values.

Mutt.

[Old Smokey]

747Classic

Yes, many airlines do have Performance Engineers on staff, or use a sub-contractor. This is particularly so in Australia where local regulations are close to, but not entirely equal to FAR25 / JAR-Ops requirements. In other cases, the AFM data is so 'user unfriendly', that the local authority has stipulated presentation of data for operating crews derived from the AFM.

Up to a point, I agree with Mutt that "Technology has taken us beyond that requirement", Boeing for example is now producing much more 'crew friendly' data. The cr@p still delivered from some other manufacturers still meets all of the certification requirements in full, but would require much much crew manipulation to be daily useable. (I would like to sincerely thank these cr@p providers, they've kept me in a good second income).

The instance you cite of Company derived differing speeds for the same aircraft PROBABLY arise from the (non-Boeing) performance engineer adapting Boeing supplied AFM data to either accurate and/or conservative interpretation as I've alluded to earlier. Both are probably correct (one is more correct) with the more conservative simplified case leading to performance penalties that the operator finds acceptable.

[mutt]

Old Smokey,

PROBABLY arise from the (non-Boeing) performance engineer Remove the work "NON" and i will agree with you. :)
Boeing have sent us a lot of incorrect data over the years, it just gets shipped right back to them!


Mutt.

[Old Smokey]

Mutt,

Consider (non-Boeing) removed, the original post left unedited so that subsequent comments remain relavent.

I think we agree (in different words) on one point, the cr@p data keeps a certain number of us in a job, be it sending it back, or making it useable.

Smokey

[747CLASSIC]

Gentlemen,
Please forgive me. I do not have as deep the techno background that I preceive you to have.
If I understand you correctly, you are telling me that we are all reading from the same sheet of music and are coming up with different tunes. Is that basically correct?
I can't see the Feds buying this and also, if there was an incident where there was a rejection right AT V1 and something happened there could be a lawsuit involved.

Can I get some names and contact info of some of the sub-contractor that do this Performance Engineering.

Thanks,
Classic

[Old Smokey]

747classic,

A well turned phrase, "Reading from the same sheet of music", it sums it up quite well, but the resultant tunes should sound very similar. I used an example where the Australian authorities required deeper interpretation of Flight Manual / Performance Manual data for compliance with the rules there. Before the disappearance of both, Ansett and TAA / Australian Airlines operated identical aircraft over several decades, but the company produced Operations Manuals looked very different.

The bottom line in "Company Derived Data" is that, for acceptance by the relevant authority, it must be shown to be DERIVED from AFM / Performance Manual data. Development of this data is prohibited, and referral will have to be made back to the manufacturer if new data outside the scope of existing data is required (as opposed to that within the scope of existing data). The various authoritys have rules for proving of these data. This will include such things as making available for their assessment computer programmes used for RTOW calculation.

If directly derived from AFM / Performance Manual data, there should be no legal problems following an incident / accident so long as the data is demonstrably in line with AFM, or more conservative. That is, after all, what operating crews do each day, operate in accordance with, or more conservatively than the AFM.

A fairly simple example of data 'derived' from the AFM / Performance Manual. One aircraft I had the task to interpret for the Company Operations Manual had no Engine Inop Ceiling / Drift-Down data available in the AFM. The AFM / Performance Manual DID have a very good table of engine inop gradients for a very comprehensive range of Weights, Pressure Heights, and Temperatures, as well as good data for Referred Fuel Flow at MCT. A table of engine inoperative ceilings was obtained by extracting where, for a particular weight and temperature, gradient was zero. Integration of a series of Gradients, Speed, Fuel Flow (and thus decrementing weight) enabled calculation of the Drift-Down locus, and a table of Time / Fuel / Distance for drift-down to operational ceiling. A quite simple task for a novice performance engineer, but a nightmare in the cockpit if the information was quickly needed. All data emanated from the AFM and Performance Manual, without any 'development'.

To suggest sub-contractors, it will first be necessary to know on which country's register the proposed operation will be. Some sub-contractors (including some very well known ones) have difficulty in acceptance in certain countries, or the sub-contractor is unwilling to take work in a particular country.

[747CLASSIC]

Thanks Gentlemen for trying to explane this to a non-techno person but, I don't think you are understanding me correctly.
ALL the V1, VR and V2 speeds are spot on the same between the two companies data for the weights from 800,000 lbs down to aprox 520,000lbs and below (depending on temp). Then down to 400,000 lbs this gets into the shaded area of the tab data chart where the note states, "shaded area indicates performance affected by minimum control speed." In the shaded area is where the speeds don't match. I can understand what you are telling me with two different people trying to split hairs the the speeds varing a knot either way, but I would think that would be consistent through-out the chart, not just at the lower weights where VMCG may be a factor. Am I explaining myself correctly?

Thanks,
Classic

[mutt]

You will find that someone has read the VMCG charts incorrectly and has limited the V1 speeds accordingly. I can show you two Boeing supplied V-speed tables for the same aircraft with this error.

What model and engine are you talking about? We presently operate all 5 versions of the B747.

Mutt.

[john_tullamarine]

..Mutt and I belong to the club of OEM post-beta testers ....