Performance question TORA

[bultaco]

Hi all,

On page 6 of the performance document CAP 698 it states:

"when no stopway or clearway is available the take-off distance must not exceed 1.25 x TORA"

should this not read that the take-off distance should not exceed 80% of TORA ?


Best,
Bultaco

[Keith.Williams.]

You are correct.

The information in subparas 2.1 b.(2) and (3) is incorrect. The correct information is on page 19.

All of the FTOs are aware of this fact, so if you are doing a recognised course, then your performance instructor should have told you about this problem.

The CAA has been in the process of rewriting these books since 2001!!! But their most recent offerings were errrrrrrrmmm "somewhat problematic".

[john_tullamarine]

While acknowledging the fact that, sometimes, Britain does it differently .... what regulatory process requires this purported requirement ?

If there is no stopway/clearway, then one would expect TODA=TORA.

The statements

(a) "when no stopway or clearway is available the take-off distance must not exceed 1.25 x TORA" doesn't make much sense as it would infer having TODR>TODA

(b) "the take-off distance should not exceed 80% of TORA" likewise doesn't make much sense as it infers that we are not going to use a substantial fraction of the TODA.

.. or is this a misguided way to test knowledge of the airports design process which typically limits the amount of clearway ?

(signed) Confused

[OzExpat]

Good one John! I suspect that you've just encapsulated the problems faced by the UK CAA in rewriting their publication on the subject. :}

[Keith.Williams.]

Hello John,

As I said in my previous post, the statement that the TOD must not be more than 1.25 x TORA is incorrect. The correct statement on page 19 of the CAP 698 is the TOD x 1.25 must not exceed the TORA. this leaves a 20% safety margin.

The correct versions of these factors (on page 19) are not the inventions of the examiners, but come straight from the regulations JAR OPS(1), 1.530. Class B aircraft take-off.

You are correct that this means that the maximum TOD is only 80% of the TORA, (and of the TODA and ASDA with no stopway or clearway).

They are also (some of) the factors that the students are expected to use when they move on to the CPL flying.

I had always assumed that the factors specified in FAR are more or less the same. Are they not?

[bultaco]

Thanks Keith, John and OzExpat for the info. The ATPL course in general is very slow because one has to cross-check every statement and equation due to the amount of errors in the documents and the seemingly ambiguous definitions used. It sometimes appears that the only reliable source of information is PPrune.

[john_tullamarine]

Keith,

As always, I defer to your knowledge of the UK exams ...

I don't work much with JAA operational regs although I am more than familiar with the maintenance side of things so I had best do some homework to see if I can get my head around your observations and the JAA regs but it all seems a tad strange to me at the moment.

A search suggests that CAP 698 is near 13M so I think I'll download it at work tomorrow rather than take all night on the domestic dial up account ...

Found a purported copy of 1.530 at this site (http://www.espania.com/aspa/bibliot/jarops12.htm) which I presume to be correct. If I can spare the time, I'll look up the JAA references on the company site tomorrow at work.

The numeric details differ slightly from what we are used to on this side of the globe, but the intent is the same .. ensure that part of the takeoff flare to screen is over the hard bit toward the runway head. With that additional background I have no difficulty with what you have put to the audience .. particularly when one accounts for the unfactored references .. all's well, good sir ..


Back in due course after I've had a chance to review the CAP ...

[bultaco]

Is it correct that the procedure on page 8 of CAP698 (to figure out FLL TOW) is incorrect ?....If I follow the instructions I get a different weight. I only get the same answer as the example on page 8 if I parallel the obstacle clearance grid on the right side of the graph. But I don't think you do this because the factored ASDA is used and the TODA not equal to TODA.

[Keith.Williams.]

Although the slopes are marked "obstacle height" they are actually your height above the surface. At the left end you are at zero feet, so the aircraft has just lifted-off the ground. The distance to this point is the take-off run (TOR). At the right end of the slopes you are at 50 ft screen height. The distance to this point is the take-off distance (TOD).

Remember that the various factors that you have just to defactorise the TORA, TODA and ASDA, all came from the take-off distance (TOD). So when you use one of them to enter the graph to find the field limited take-off mass, you are at the end of the TOD (at screen height). This means that you must go down the slopes.

It is unfortunate that the quality of the CAP is too poor to see many of the examples given.

[john_tullamarine]

An interesting volume .. I have to admit to an empathy with the CAA which notes that it intends to revise the document by Autumn 2005 ... I guess those good folks have a busy schedule as well ...

So far as the exams go .. just a matter of trying to get the maximum real knowledge you can during your training and then jumping through the exam hoops to get the tick in the box at the end of the exercise. Main thing is to avoid simply training to pass the exam .. same in Oz ... all that does is perpetuate ignorance and OWT in the Industry (generously aided by those "instructors" around the traps who know precious little more than their unsuspecting students) .. I am sure that Keith and I could swap more than a few tales regarding misconceptions which show up in class .. albeit that I have been out of the theory training arena for many years now.

One point to note and that is in respect of definitions. One needs to understand the definition of whatever in the context of the particular discussion. So, for instance, TOR in this context is quite different to TORR in the heavy aircraft side of things. Just something to keep in back of the mind for when things seem to be unduly confusing .. as they can be from time to time.

Main advantage of PPRuNe in these matters is that it gives the student access to a range of knowledgeable folk (= been around a lot longer than the student) and even a few experts (= made enough errors during that longer time to have got to the point where they don't make many new ones ..) who are only too happy to lend a helping hand to the new chums on the block....

Hang in there, guys and gals ... down the track a bit you'll look back on the exam phase with bewildered bemusement ... I recall my first foray into the ATPL performance exam as an aero engineering undergraduate .. looked up the syllabus in the ANOs, got the referenced texts, did the swot, turned up to the exam .. only to discover that the exam had near naught to do with the syllabus .. I then discovered this concept called specimen and past exam papers .. hence my comment to learn the subject first and then worry about figuring out how to pass the exam ..

[bultaco]

Thanks Keith - however, being of simple mind, I don't think I quite understand your last post...I don't think the ASDA is derived from the TOD i.e. if you enter the graph with the value for ASDA then you're not at screen height even with all the surface, slope and regulation factors taken into consideration...Is my logic fuzzy ?

[Keith.Williams.]

Hello John,

I must confess to having been rather perplexed by your original post in this tread. But having thought about it for a while, I concluded that you were probably thinking of the required distances TORR, ASDR and TODR, whereas the original question and my answer to it related to the TOD. When this is increased by the appropriate factors it gives the minimum acceptable TORA, ASDA and TODA. Logically these should be called the TORR, ASDR and TODR, but the author of the CAP chose not to do so. These relationships are some of the things that JAR students are required to know.

I certainly agree with your view that students should learn as much as possible about the subjects during their training. But there is an unhealthy tendency for far too many students to tell themselves that "it is all too difficult to understand, so I will just focus on feedback lists". This situation has not been helped by the fact that bootleg copies of the JAR question bank without any form of explanations, are freely available.

This problem is compounded by the fact that the examiners are far too slow in generating new questions. Students who simply learn the answers often find that 80% or 90% of their exam is made up of questions that they have already seen and memorized. This is great for national pass rates but pretty dreadful for the learning process.

Prior to the introduction of the JAR exams the old CAA performance examination was based almost entirely on the CAP. Any student who could get the correct answers out of the graphs in the CAP would pass the examination. Unfortunately this did nothing to improve their understanding of why aircraft perform the way they do or how they are likely to respond to changing conditions.

When the first students took the JAR exams they found that everything had changed. There were no questions requiring the use of the graphs, very few questions relating to the CAP, and almost all of the questions were based on "applied principles of flight". Needless to say the initial pass rates were pretty dreadful.

The schools quickly retuned their training to cover the "applied principles of flight" in more depth, and paid less attention to the graphs in the CAP. In most cases this meant going through all of the material in the CAP once or twice, but would not involve students doing large numbers of practice graphical exercises. At that stage we were probably producing pilots who had a far grasp of the fundamentals but couldn’t use a performance graph if their lives depended on it.

More recently the examiners have introduced larger numbers of graphical questions, such that there is a more even balance. If they can now vastly increase the rate at which new questions are introduced, we might have a reasonably effective system.



Hello Bultaco,

We need to go back and look at what we have just done.

We started with 4250 TORA, 4470 ASDA, and 4600 TODA. We then divided these by the factors listed in page 19.

This process gave us the de-factorised distances of 3220 based on TORA, 2605 based on ASDA, and 3030 based on TODA.

These are the maximum acceptable values for the TOD. We must not exceed any of these values, so we must use the smallest. This is 2605 based on ASDA.

But although this value came from the ASDA, it is the maximum acceptable TOD. So when we put this into the graph we are at screen height at the end of the TOD.

[john_tullamarine]

Yo, Keith ...

Actually, I was confused by the quite different way the Brits appear to approach things.. to me the process in the CAP is exceedingly convoluted ... although the aim is much the same as the much simpler approach with which we are familiar in this neck of the woods. The related words in the first couple of posts didn't make much sense without the rest of the story's details to fill in the holes in my knowledge of how you guys go about business ..

Once I got my head around the process, the initial confusion associated with the early posts in this thread resolved itself fairly easily ...

Guess I have learned a bit from this thread as to how some things are done elsewhere .. main thing is that folks like you and me continue to toss things around so that the students amongst the readership get to see a broader picture than just the frenetic rush to get the tick-in-the-box pass.

Years ago, when I was actively involved in theory training, many of my students probably hated me intensely for pushing the learning bit at the start .. but, invariably, that made the exam bit a lot easier .. mind you, if the average evening class was scheduled for two hours .. it generally ended up going for three to four ... I just don't learn ... did the same thing with sim training .. if we could scrounge a bit more time from the techs we put it to good use ... recall one keen upgrade crew several years ago .. it was about 0200 and 5-6 hours into the (extended) session .. the fatigue signs cut in and I just had to pull the plug .. they were still as keen as mustard .. but isn't that what makes it all worthwhile for guys like you and me ? ... the real keen student .. doesn't matter whether he/she is a fast learner or not ..

[bultaco]

Yikkes....the penny has dropped. Thanks keith.