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Turkish A330 incident, Kathmandu

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Turkish A330 incident, Kathmandu

Old 10th Mar 2015, 22:08
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Originally Posted by silvertate
>>RAIM outages.

RAIM is real-time monitoring of the satellite constellation. You cannot determine RAIM outages by NOTAMS. Or are you telling me that the NOTAMS know exactly when the next satellite will be hit by some space debris, or lose its IRS stability system?
Wait what? So what exactly is this RAIM prediction feature that the local airways services outfit provides on it's web based flight planning/NOTAM service all about then? Or for that matter, the RAIM calculation built into many GPS units (Garmin 430/530, G1000 etc)???

I'll think you'll find that RAIM prediction is very much possible due to the "fixed" nature of the constellation, and being able to calculate if there will the appropriate number of satellites available to facilitate the use RAIM at a given place at a given time.

Obviously, the RAIM in the onboard system will then make sure everything is working nicely, "in realtime", when you actually get there... And provide the appropriate "RAIM unavailable" type warnings should anything be amiss (like a satellite getting hit by debris in the interim etc)
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Old 10th Mar 2015, 23:15
  #142 (permalink)  
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Silver:

Sorry, but did you read that Powerpoint link? It says (p10), quote...
Indeed, many times. Did you note ANP? RNP is a performance minimum. ANP is much better on RNP AR approaches or alerting will require the pilot execute an extraction.

As to IRU drift, on any airframe approved for RNP AR of less than 0.30, there are generally three IRUs, with blended position updated continuously by GPS/GNSS. So, if an alert is received that requires extraction, the IRU position is the same as the GPS position was when the alert is received. From that point on (which is very rare) the IRUs begin drifting. This drift is accounted for very conservatively in RNP AR missed approach criteria.

RNP AR is presently the term used for this type of approach throughout the world. The U.S. stopped using RNP AAAR several years ago.
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Old 10th Mar 2015, 23:25
  #143 (permalink)  
 
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Originally Posted by Silvertate
>>TCAS assisted incidents.

The Swiss collision would not have happened without TCAS. It was a total system usage error that had not been fully thought through and promulgated to all airlines and crews before the incident.
Rubbish; the TCAS was going to save them; the Russians didn't follow the TCAS instructions like they were supposed to. Don't blame the (pretty simple) technology for human incapacity.

Originally Posted by Silvertate
And the multiplicity of notation does not help. The USA might have RNP-AR, but in Europe we generally have RNAV GNSS. EPKT Katowice in Poland or EGBB Brum in the UK are GNSS approaches. There are a few around. LTBS Dalaman GNSS in Turkey is more pertinent to this thread, as it goes through the hills and is offset.
Come on. Working out the difference between RNAV GNSS and RNP-AR is pretty basic stuff. Surely you don't just call up an approach in the database and say "gee this looks good, let's give it a go!"?. That Turkey approach is a bog-standard RNAV (GNSS) that the world has been doing for years and is "tiger moth" stuff compared to an RNP-AR. It has got a minor kink early on but is dead straight from 3000ft down. Offset? Yes, and that is much less desirable than that RNP-AR at Kathmandu. As pointed out earlier, RNP-AR has an aligned final. You seriously need to get into Google and understand what you're talking about before carrying on here.

Originally Posted by Silvertate
The satellite constellation is fixed, while the Earth rotates inside it. Thus the number of satellites you can see, and the declination and azimuth of those satellites, will change during the day (and with your location). Some locations and times are better than others - especially if there is a satellite outage in your area.
You can't be serious...

Originally Posted by Silvertate
>>IRS backup.

Worse than useless. As I said before, our IRS fix can easily be a couple of miles away from the GPS fix, and the VOR/DME is not much better in mountainous terrain. So if you lose the GPS on the approach, and the FMC position reverts to IRS fix position, you get a rapid 2nm map-shift. Ok, so the nearest mountain peak is only a couple of nm away, and the autopilot is trying to recapture the new IRS trackline which is 2nm away - your move, as they say...
I now see why you're so worried about the "mystical" GPS. If you "lose the GPS" and have a sudden 2nm map-shift your outfit shouldn't be doing GPS approaches, period. Sounds like a bunch of cowboys trying to do the good stuff with totally unsatisfactory gear.
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Old 11th Mar 2015, 01:07
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The satellite constellation is fixed, while the Earth rotates inside it. Thus the number of satellites you can see, and the declination and azimuth of those satellites, will change during the day (and with your location). Some locations and times are better than others - especially if there is a satellite outage in your area.
To expand on Capt Bloggs useful remark...

Global Positioning System - Wikipedia, the free encyclopedia

The satellite constellation can be varied, and the satellites do rotate around a rotating earth if you believe Wikipedia (at twice the earth's speed). The satellites are not fixed in space relative to the earth, if that's what you mean. Their altitudes are about 3 times the diameter of the earth, so this helps coverage greatly. The official websites do say that 6 should be available almost anywhere on earth, but if you read some websites, it says that these satellites should be "above the horizon". If you're in a deep valley or flying below the top of a mountain range, your horizon may well be limited. With a satellite out, perhaps GPS coverage could get pretty sparse. However, depending on your navigation system, your map position shouldn't suddenly start moving sideways to the pure IRS position when you lose your GPS. The nav system should maintain a constant bias towards the previous radio-based position until you reacquire a new radio position or the system is reset. The difference is not (normally) suddenly washed out.
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Old 11th Mar 2015, 02:49
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So do any of you guys have any info relevant to this KTM accident, was there in fact some issue with how the Turkish pilots flew the RNP approach on that day, or are you just having a willy waving contest over who knows the most intricate knowledge of RNP / RNAV?

It's all very interesting but I'll bet my bottom dollar it's completely irrelevant to this accident. The approach was fine until the point where they actually had to look out the window and determine if they could see the bloody runway or not.

It doesn't matter what kind of high tech you have on board, what approvals you have, or what kind of approach you do, if you elect to continue below minima without sufficient visual reference.
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Old 11th Mar 2015, 05:04
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Not willy-waving, Luke, education.
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Old 11th Mar 2015, 05:13
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Luke, for what happened, see my last post.

May not be word for word but is how it was described by someone on the radio at KTM at the time
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Old 11th Mar 2015, 05:15
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I found our OM-C comments re the KTM VOR approach.."in the event of loss of VOR or DME a missed approach is required..."...hmmmm that would have been interesting in our non-GPS 767.
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Old 11th Mar 2015, 05:20
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Educated willy waving then?
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Old 11th Mar 2015, 10:14
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couldn't agree more , willy waving - since this is getting your education on a rumor network instead of your officially backed books.
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Old 11th Mar 2015, 11:22
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So Boeingrestricted, where in his "books" is silvertate going find out about RNP-ARs? Perhaps you don't realise it, but there is a great deal of knowledge put forward by members of Prune. If one is a professional pilot who has a basic handle on things, it is easy to sort the wheat from the chaff and learn a lot.
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Old 11th Mar 2015, 11:53
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The post-crash selfies look as if they were taken in pretty thick fog. Did I miss something...
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Old 11th Mar 2015, 13:13
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I have to agree totally with Luke SkyToddler post


He posted


So do any of you guys have any info relevant to this KTM accident, was there in fact some issue with how the Turkish pilots flew the RNP approach on that day, or are you just having a willy waving contest over who knows the most intricate knowledge of RNP / RNAV?

It's all very interesting but I'll bet my bottom dollar it's completely irrelevant to this accident. The approach was fine until the point where they actually had to look out the window and determine if they could see the bloody runway or not.

It doesn't matter what kind of high tech you have on board, what approvals you have, or what kind of approach you do, if you elect to continue below minima without sufficient visual reference.


The questions I would like to ask are these


What was the reported viz before they commenced each approach, how much fuel did they have left after their second approach and what was their planned diversion strategy ie to where and did they have enough fuel to get there ?
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Old 11th Mar 2015, 13:23
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Actually reported vis is the main point at their approach ban and minima.
Seeing the runway with reported fog may not warrant a safe landing.
Entering the flare and the fog at the same time could lead to obvious difficulties eventhough you saw the runway from a different height/angle.
Respecting given visibility is paramount to a safe and legal approach and landing.
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Old 11th Mar 2015, 21:21
  #155 (permalink)  
 
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GPS constellations

Luke

So do any of you guys have any info relevant to this KTM accident? Or is this willie-waving?
If the KTM A330 was not aligned with the runway centerline, due to an rnp offset as discussed here, it could have contributed to this incident. It is a possibility to consider.

However, having mentioned these innacuracies of the GNS approach system, various critics came out of the woodwork claiming that GNS is a navigational panacea that is never wrong. And they are still claiming that GNS works to the accuracy of the ANP, when ANP is only the performance at this moment in time. Clearly, some operators need to set up training programs to discuss the design, operation and pitfalls of the standard GNSS approach system.

The known inaccuracies of GNSS is why the WAARS and EGNOS augmentation systems are being developed. Why spend all that money on a new augmentation system, if the original GNS is always 100% accurate? Answer - it is not that accurate, which is why it says 95% accurate on the tin.


P.S. Yes, the orbits of the satellites stay fixed, while the Earth rotates underneath them, just as I said. So the azimuth and declination of the satellites is constantly changing - with satellites setting behind the hills as you make the approach.

Below is a nice GPS satellite animation.
Note that the orbits remain fixed, resulting in an ever-changing azimuth and declination of the satellites your receiver is tracking.
The blue satellites are the ones that are visible. Note the changing number of satellites visible, and remember that this number will be less in high terrain.
The green lines indicate the azimuth and declination of each satellite. Note how satellites drop behind the horizon and are then deleted.
Remember that satellites in the zenith (overhead) provide little or no lateral navigation input, while those on the horizon are subject to refraction errors.






ok 465

Actually GLS and WAAS are two different animals.
No they are not. WAAS and EGNOS are both GBAS (ground based augmentations systems) for GNSS approaches.

A GNSS approach plus a GBAS equals a GLS. So they are all part of the same system - a system that will eventually eradicate the errors being discussed here.

Last edited by silvertate; 11th Mar 2015 at 21:37.
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Old 11th Mar 2015, 22:33
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ok465:

Lots of folks don't realize that Hawaii doesn't have WAAS either.
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Old 11th Mar 2015, 23:38
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Originally Posted by Silvertate
The known inaccuracies of GNSS is why the WAARS and EGNOS augmentation systems are being developed. Why spend all that money on a new augmentation system, if the original GNS is always 100% accurate? Answer - it is not that accurate, which is why it says 95% accurate on the tin.
For goodness sake! WAAS gives better accuracy: lower minima eg for LP and LPV approaches! That is all!

GLS same: lower minima, no need for expensive ILS gear.

Do you really think someone didn't think of "hey hang on, that satellite is going to drop out of view! What is a crew going to do then?!" That's what RAIM, FD and FDE is all about.
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Old 12th Mar 2015, 00:43
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WAAS and EGNOS are both GBAS (ground based augmentations systems) for GNSS approaches
I think you'll find that's SBAS (space based augmentation system).
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Old 12th Mar 2015, 01:09
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Gastineau Channel: Alaska Airlines has continued to defy the 95% probability.

Otherwise, they would be out of business because of all the fatal CFITs.
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Old 12th Mar 2015, 07:29
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I understand from the info I have there are no runway centre line lights at this airport.

When i saw this it reminded me of something that happened to me and who knows might have been a factor with the THY.

Thanks to a good co pilot I got away with it.

Landing from minimums with low vis and blowing crosswind, when I broke out of cloud with the aircraft in a crab I got sight of the lights and continued towards what I thought was the centreline however it was the left edge of the runway.

My co pilot called go-around, which at the time I didn't understand but knew he must have had a good reason.

Going downwind he explained and then it dawned on me what I had done. During the approach briefing I had made no mention of no centre line lights and assumed the airport had them.

Landed from the second approach but was shocked how my mind had convinced me of an image that looked absolutely right at the time.

In other words did they line up with the edge lights thinking they were on the centre line?

Last edited by Say Mach Number; 14th Mar 2015 at 17:09.
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