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ILS approach RWY 23R in HECA


Goshob

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Hi Guys,

Here below I will try to start a discussion concerning an ILS approach to Rwy 23R in Cairo, Egypt. The charts of IRAC 1801 will be used and a picture from my ND. Have to mention first that I am using AS A320 in all my flights, same for this one. I would like to express my strong expectation that this will become a really useful discussion, except a simple request for reading the step-by-step manual. I have to state in advance, that such subject is not in it.

Let me start with the chart first:

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What it says is that the plane should fly on 3500 ft till reaching CAI D1.4, than descend to 2000 ft and turn right on heading 90 deg on D 5 CAI. Fly app. 2.5 nm on that heading keeping altitude of 2000 ft, and turn left heading 270 deg. After app. 1 nm the plane has to turn another left on heading 225 deg and accept the localizer. The glide slope will be available at point P or D5.5 ITTR, which is on 5.3 nm from the runway. Here the final approach and GP has to be started in order to reach the runway safely and as per the applicable procedure.

All this is very good to be true, as every theory from similar sort. Why I am saying that will be shown below.

Here is how the navigation computer of the bus interprets all the above. I have to state once again that all this is as per the Navigation computer of AS A320. No idea how the real A320 does it:

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Everything up to CAI 05 is as per the chart. The altitude is 2000, which is OK. There is a right turn on heading 90 deg till point 0004, which is OK also, but up to here. The left turn is to INTCPT, which unfortunately is away (more left) from localizer direction 225 deg. The plane than has to fly to D5.5 ITTR as a mandatory condition of the route. Following such it enters into an angle of app. 30 deg to the glide path, has to change the heading to 225 deg to  accept the localizer and unfortunately the GS is missed or big VS corrections have to be made for accepting it.

My questions are: Is there something, which can be done for correcting the position of INTCPT if someone flays without ATS, following the FW on the autopilot only? Is this something related to imperfection of the charts, navigation computer or simply a way of interpretation for simplifying the software?

Thank you in advance!

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  • Deputy Sheriffs

One of the problems in this case is that the decel point (the magenta D) lies in the intercept turn. Normally you would fly with a speed of around 180kts, Flaps 2 in this altitude. 

 

Try to fly the procedure with the approach phase activated and the speed selected at 180 with F2. Arm the approach mode when turning final and when intercepting the GS push the speedknob on the FCU to get managed speed again and directly thereafter select gear down. Continue with F3 and F Full and you should be perfectly stabilized for the landing. 

 

Let us know how that works out. If 180kts is still too fast you could also try a slower speed to make the turn tighter. 

 

Cheers

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Hi Frank,

Thank you for the answer. I made several experiments during the weekend following your advises, but unfortunately all were unsuccessful. I was too busy changing speed, heading, etc. and forgot to take pictures. However I will try to explain in writing. The major stipulation here is that all experiments were made in fair weather conditions, just for a trial.

I strongly feel that the speed is not the main issue in the situation. I am always using (trying to be close to) an old rule, which a friend of mine was teaching his students. According to this rule the approach speed (in ideal conditions, or fair weather) depends on the distance from the runway. It is easier to illustrate this with figures: 10 nm - 200 knt, 9 nm - 190 knt, 8 nm - 180 knt, 7 nm - 170 knt and so on. Hope you can follow the logic of the middle digit. I think I had seen something similar in some of the aviation videos also. In the best of my attempts, I was approaching ITT55, which is 5.5 nm from the airport, with 160 knt flying on 2000 ft as per the procedure.

What I think and correct me, if I am wrong is that the main reason for missing the approach is how the navigation computer interprets the chart. The plane fly from 004 to INTCPT on a 270 deg ark. Than it goes to ITT55 on heading of 195 deg, at least as per the interpretation of the computer. It doesn't actually cross ITT55, but fly another right turn to heading 225 deg, which is normal. This final ark is enough to miss either the localizer or the glide slope because both of them are coming at the same time. In other words, the plane comes at an angle of app. 30 deg (225 - 195 = 30) to a point where the glide slope should be executed already. This point is actually after ITT55. I do not know why, there should be a valid reason for sure, the computer needs to establish on the localizer first and may or may not follow the glide slope, but it has to be captured after the localizer for sure. This is what exactly happens in this case - the localizer is captured, but the plane is above the glide slope already and only fast manual descend can capture it, which is not so easy. There is always an option for manual landing or go around, but this is not what we are discussing here. Something else comes to my mind while writing this and I will definitely try it. To divert the plane from INTCPT to CAI05 and ITT55 after that. Both of these two points (CAI05 and ITT55) are on one line and there might be time for accepting the localizer first and glide slope after that. The entire idea is that the actual chart is different from the actual computer interpretation and such "trick" may help.

Would be curious to know your and some other opinions also.

Thank you!

 

 

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Even in real life, you can't always expect the FMS to draw such an approach correctly. At this point it becomes a guide or representation, and you should use the chart and fly a course that will lead to a successful localizer and glideslope intercept. I'll respectfully disagree that speed is not a problem with such an approach, as the faster you're going the wider your turns are going to be and this can certainly through the aircraft off enough to miss a successful localizer and glideslope intercept. I agree with Frank that a slower speed (160 or 165 knots) would be far better for what appears to be only a 1.5 mile radius turn.  Your friends rule of thumb would work on a straight approach or a circle to land that does not have such a tight turn radius.

 

Best wishes!

 

 

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  • Deputy Sheriffs

Hi Goshob,

 

I just flew the procedure with the latest beta. With this version an ILS23R intercept is no problem when flown with 160-180 kts. The intercept was flown a lot better than shown in your pictures but it was not 100% as it should be and I filed a bug report for the devs to look it over. So the good news is that the Prof version will fly it but the old v1.31 probably not. As I do not have the old version installed anymore I can unfortunately not test the scenario. 

 

I know this is not exactly the answer you where hoping for. With regard to the old rule you explained. This might be ok for straight in approaches but as Dave already said when doing procedure turns and the lot, speeds around 160-180 are a better choice instead of speed vs distance. 

 

If I get permission from Mathijs I will post the beta test video of the approach later on.

 

Cheers

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Hello Gentlemen,

Thank you very much for the answers and the support. Appreciated! Let me make some notes also.

I actually posted all this because I was very curious how such approach can be flown, if left on the autopilot only. Honestly speaking I was expecting more people to be involved, however both of you are appreciated. Biggest part of my curiosity was based on what presumptions the FMS calculates the position of INTCPT point? This is obviously an artificial, computer generated point, which is not part of the chart and in the particular case determines the type of approach, i.e. at an angle or whatsoever. Quoting the chart, we have to admit that it was made in such a way to assure straight approach to the runway. In case the FMS was following strictly the chart all of my questions and doubts could never be raised. Most important of those doubts was how the computer is actually interpreting the charts? What will the real FMS show on the ND in this particular case?

Here is the time to say, that I fully agree with Dave, whom I always consider as my mentor, that FMS is impossible to always give an exact interpretation of the chart. However current chart is straight forward and only the position of one point, generated by the computer anyhow, can completely change the entire situation. The speed is also a factor, which definitely has its impact, but I said that it was not so important in my previous post simply because I flew the approach after INTCPT with F2 and speed of 160 knots and could not establish on the glide slope. Hope my thoughts in the previous post were clear enough.

Fact is that my flight to Cairo with the VA was under VATSIM and the ATC gave me straight path to the runway and there was enough time for accepting the localizer and glide slope. I decided to open this topic after seeing the path drown on the ND and asking myself how could I fly it without ATC. Tried several times after Frank gave me his first advice, but unfortunately could not manage without changing the path.

Anyhow and if someone from AS considers that all these talks are with no use or belong to a different section of the forum, I am ready to accept the Administrators either to delete or move the topic. Alternatively we can continue going deeper into the technicalities of similar situations, which are existing. 

It would be very interesting also if Frank receives necessary permission for sharing the clip, which he mentioned and concerning the new pro version of the bus.

Thank you!

 

 

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I flew the HECA Runway 23R ILS Approach last night.  Following the altitude constraints, I flew into the CAI VOR at 180kts, descended to 2000 ft and slowed to 160 by D5.0, executed a right turn to heading 090 and soon after to heading 270, then to course 225.  I flew this in the Aerosoft Airbus Professional A319, and the aircraft was in excellent position to intercept the ILS.  I did create a video, however it was 1.2GB so I wasn't able to upload it.  We live the Airbus from time to time at www.twitch.tv/ovpa and www.twitch.tv/ovpa1 should be like to see it.

 

NOTES The Nav Display Waypoints shown in the first post are not correct (they do not match either the Navigraph or Aerosoft Charts) and thus displays an incorrect approach.

 

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Best wishes!

 

 

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Hi Dave,

Thank you for the comments! We obviously are coming step by step to what I was trying to say in all my previous posts and mainly to find the reason for it.

On 2/2/2018 at 8:27 PM, DaveCT2003 said:

NOTES The Nav Display Waypoints shown in the first post are not correct (they do not match either the Navigraph or Aerosoft Charts) and thus displays an incorrect approach.

I am using NavDataPro (Aerosoft Charts) annual subscription and FMC is planning based on it. It is regularly updated, for which I am absolutely sure. The Nav Display shown in my first post was based on AIRAC 1801 and I am also saying that the points drawn are not matching with the chart. The questions here are WHY and WHAT CAN BE DONE

My current Airbus version is 1.31 and unfortunately I have no access to the Pro version, which Frank also stated that fly the approach much better.

 

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  • Deputy Sheriffs

The why and the what can be done are easy. 

 

Why doesn‘t the AS bus fly this procedure like IRL? Because it was not modeled correctly. 

 

What can be done? You can fly the procedure in heading mode like Dave did. This is the way we do it IRL when the AFS does not do what we want. What else can you do? Nothing, I reported this bug to the devs and hope they will fix it. If they fix it it will be in the professional edition not V1.31. 

 

Here an example of how it should look like. „That other company“ did a fabulous job and the AFS flew the procedure like I would expect the RW bus to do it. I have been to CAI a lot IRL and normally we always get vectors so I never flew this procedure there IRL.

 

 

ps, look at that huge nav drawing bug before the procedure is actually flown ;) 

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Hi,

Thank you for the explanation and nice video! Summarizing all the above, I feel that following can be concluded:

1. There seems to be a bug in AS bus, V1.31, which prevents it drawing / flying some specific or complicated approaches as the discussed one. The bug will be eventually corrected in the future pro version.

2. There is nothing wrong with published charts, but with their interpretation by the FMC.

3. Good way for flying approaches where the drawn on ND is strongly deviated from the chart is better fly it on heading mode as Dave did.

4. Best way for this particular and any other difficult approaches if an ATC is available who can give vectors (I had a chance for such in one of my SIM flights to Cairo and there was no problem). 

However, I am happy with what we discussed above and strongly feel that it was a good "brain exercise". It answered me some questions, which not being a professional in aviation, were concerning me for some time. Hope it had some value for the others who read all this also.

 

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4 hours ago, Goshob said:

There seems to be a bug in AS bus, V1.31, which prevents it drawing / flying some specific or complicated approaches as the discussed orne.

 

Certainly true, but as Frank eluded to, most flight simmers would be surprised to know this type of thing happens with the real FMSs as well (not just the ones in the Airbust but many different types) and when it does occur the people use either the heading mode or hand fly the approach.  From this perspective, it adds to the realism of simulating normal operations!

 

This is one of many great explanations why we need pilots driving rather than just a computer!

 

Thanks for bringing it to our attention though, never hurts to improve things!

 

 

 

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