Slick9

Expert 777 pilot help needed @ SKCL (Cali, Columbia)

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Posted (edited)

Morning all –

I’m hoping someone with more skill than me can do me a favor and check out an approach to Cali, Columbia (SKCL) with their PMDG T7.   The backstory on this, I flew this approach this weekend and had to go around three times because I was too high each time.  Finally I flew below the published minimums and landed.

I flew the ULQ2E  STAR then transitioned to the RNAV Z approach to Runway 02.  Following the published altitude restrictions, I crossed KADIT @ 13,000/250, then crossed NIGRU@ 11,000/230,  I arrived @ PALOV @ 8000/180 flaps 5, I turned base and arrived at LOMIN @ 6000/170 and lowered the gear.  Once I crossed KOGLO @ 4800feet, I slowed to VRef+ 5  ~145kts and went flaps 30.  The altimeter at the time was 30.08.  I descended from KOGLO toward the runway  at 700 fpm.  Three times I did this and three times, I was too high to land.  I double checked the altimeter with three different sources and they all matched 30.08, I am using the latest Navigraph, AIRAC 1805.  Once on the ground I checked the altitude readout and it read 3,160feet  with the altimeter setting 30.08, so I don’t think that was the problem.   The only addon  I’m using  is ORBX’s South America scenery with P3Dv4.

So if some of you expert pilots out there could fly this approach and see if you have the same issues or if the problem is with me I would really appreciate it.  I’d like to know what I’m doing wrong.  Thanks!!!

 

Richard Bansa

Edited by Slick9

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Posted (edited)

I wonder where you got the GNSS Z for the 02. My LIDO has only GNSS Z for 20.

Also why don't you fly the ILS at 02 maybe you'll find out what's going on. You could conduct and autoland there.

Edited by 30K

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Hi Henrick,

I'm using the Jeppsen 30 Dec - 16 chart from Navigraph.  Navigraph has 3 approaches for SKCL RWY 02, ILS, GNSS, and VOR I also will try the ILS and see if that explains this situation.

 

Richard Bansa

 

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Posted (edited)

Do that.

My LIDO (1805) says the same but there is no GNSS Z for rwy 02 only for 20 that's what I meant. Anyway your description matches the STAR and GNSS app chart so that is not the source of your complications.

Edited by 30K

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Henrik - you are correct, now i see it's just GNSS, not GNSS Z.  Maybe that speaks to my flying abilities 😃  

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6 hours ago, Slick9 said:

I flew this approach this weekend and had to go around three times because I was too high each time.  Finally I flew below the published minimums and landed.

I'm slightly confused by this.

Looking at the chart, the published descent path takes you to the MDA of 3560ft at 1.1NM from the runway. The final 405 ft from there is a fraction steeper than 3 degrees, but only a hair.

However, I have a feeling you might be misinterpreting how to fly an NPA like this. You're not trying to fly to the missed approach point (RW02 -- the runway threshold) at 3500ft are you?

If you can see the runway, you simply fly visually to it and land! However, you must not descend below the MDA until you can see the runway. If you then reach the Missed Approach Point and still haven't seen the runway, you go around. However, in practice you would fly this as a continuous descent approach rather than a 'dive and drive' -- so if you follow the descent path published on the chart (to 3560 ft at 1.1 NM from the threshold) and don't see the runway at that point you would go around (as clearly you would not be able to achieve a properly stabilised approach if you start your final descent inside 1NM).

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Posted (edited)
15 hours ago, skelsey said:

However, I have a feeling you might be misinterpreting how to fly an NPA like this. You're not trying to fly to the missed approach point (RW02 -- the runway threshold) at 3500ft are you?

Hi Simon,

No, I didn’t fly to the threshold @ 3500ft.  I started a continuous  decent from the final approach fix (KOGLO), and shortly after that the runway was visible so i continued  descending through 3500ft.  But once the runway became visible the papi  lights were solid white, and the sight picture looked wrong, I could tell I was too high.  Since I was flying Vref  +5, approximately 145kts or so, I used a descent rate of approximately 750 fpm.  At that constant rate when I arrived at the runway i was still at  I was several hundred feet above the runway.  When I get some time I’m going to take a Cessna up and fly the ILS approach and see if I can figure out where the problem is.  If the glideslope was steeper than 3 degrees, this would make sense, but it’s a normal 3 degree g/s. 

Richard Bansa

Edited by Slick9

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I am definitely not an expert but why don't you use a descent rate of 800-850fpm? That's what my autolands consistently use for a 3 degree glideslope. Wouldn't that solve the problem?

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Agree with Dugald here.... actual V/S required for 3 deg descent (318 ft/nm) depends on ground speed but in the B777 it will be closer to 850 fpm.  Did you notice the B777 FD can be set up to provide a FPA (Flight Path Angle) in place of V/S?  Also, four whites is not a bad thing and only means than you can descend a little quicker.

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3 hours ago, Slick9 said:

Since I was flying Vref  +5, approximately 145kts or so, I used a descent rate of approximately 750 fpm.

Ah! 

Your rule of thumb for rate of descent is right, but you are using the wrong speed. 

Remember it is ground speed x 5 to give you the approximate rate of descent. Cali, elevation 3162 ft with a temperature as I type of 24 degrees Celsius, is very much a 'high density altitude airfield' ('hot and high').

This means that your TAS (and hence GS) will be a lot higher than if you were landing at a sea level airfield, resulting in higher rates of descent and general energy management issues. 

For example, using today's conditions an IAS of 145 kt would result in a TAS of 156 kt and probably closer to 160 kt on the approach - necessitating a rate of descent closer to 800fpm (bearing in mind also, as Dan says, that GS x 5 is just a rule of thumb approximation and not a perfect mathematical solution so there is some definite 'fudge factor' required).

During your descent were you checking your height against the DME? Ultimately you need to adjust the rate to stay on the charted profile, ie to arrive at 1.1NM from RW02 at 3560 ft. As I say, this is a touch above a 3 degree profile but should be easily recoverable.

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I will give your suggestions a try and report back - I may not get to it till the weekend, but I do appreciate the ideas.  I've flown to SKCL before with no problems, so this was very weird, but I'll try with the increased v/s and see what happens.

 

Richard Bansa

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Various factors gave you those results:

1. At typical hot(ter) temperatures, your true altitude would have been above 4800 feet.

2. The required V/S given your true airspeed was more around 850 fpm (as already mentioned)

3. Although the chart mentions a standard 3° glide path, I am calculating a profile of 329'/nm which is more than 3°

4. The profile view of approach plates is not realistic. There it's an instantaneous descent after KOGLO. Your 777 (or any heavy jet) can not instantaneously give you commanded V/S. It takes awhile to settle, thus getting you above profile from the getgo.

5. There is only 1645 feet on this approach to try and recapture the profile.

 

All these factors contributed to your three approaches 🙂

 

Cheers !!!

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7 hours ago, skelsey said:

As I say, this is a touch above a 3 degree profile but should be easily recoverable.

Simon,

I went out and flew the approach this evening without any problems.

I have thought about writing a brief training module on RNAV approaches based on a recurrent document I have from a while back.  🙂 

I am going to cut some corners and just hit the highlights. 

1. Cross MUKIX at or above 9000 slowing to 210 KIAS. Engage VNAV as early if possible.  

2. Prior to MUKIX set 4800 in MCP.  Go to FIX page and type in KOGLO and ..../3 to set a 3 mile arc around KOGLO.

3. Brief Missed APCH, set heading to 015, set AUTOBRAKE to 1. 

4.  FLAPS 20 and on speed at LOMIN. 

5. Inside LOMIN and prior to KOGLO set MCP to TDZ.  I use 0000, but was taught TDZ. Make sure VNAV is engage and on profile before resetting MCP to TDZ.  

6.  Prior or at the KOGLO 3 mile arc, GEAR DOWN and FLAPS 30. My Vref was 149 KIAS. It is very important the aircraft is on speed and on profile at KOGLO.

7. At KOGLO I call GEAR, FLAPS, SLATS, Cleared to Land.  

8. At 1000 call reset MCP to MAP altitude of 5000.

10. At MDA, disconnect the AP and land.  The VASI was showing one RED which is where I normally fly my approaches.

I thought the RNAV 02 approach was very straight forward and I had no problems with it.  

 

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7 hours ago, Bluestar said:

set AUTOBRAKE to 1. 

Question: 

in the 777 training videos of airline2sim the captain says you would not use autobrakes 1 on the 777 for the reason that the brakes wouldn‘t even get warm enough to effectively brake the airplane and a minimum setting of 2 was required on the 777. (but he also said that you would seldomly land the 777 manually and well... I‘ve watched too many yt videos of the 777 to follow this..) I don‘t want to highjack the topic, but as you‘ve just mentioned the brakes  😄 

Thanks 

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35 minutes ago, Ephedrin said:

in the 777 training videos of airline2sim the captain says you would not use autobrakes 1 on the 777 for the reason that the brakes wouldn‘t even get warm enough to effectively brake the airplane and a minimum setting of 2 was required on the 777. (but he also said that you would seldomly land the 777 manually and well... I‘ve watched too many yt videos of the 777 to follow this..) I don‘t want to highjack the topic, but as you‘ve just mentioned the brakes  😄 

Wilhelm will I'm sure confirm his thinking, but on the 747 at least it would be normal to use brake 1 at hot and high airfields because of the higher ground speeds involved (= more energy to be absorbed by the brakes = more heat).

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Hi Wilhelm,

I will try your steps, I think one of the biggest differences I see between what i did and your method was you went flaps 20 at LOMIN, I was Flaps 5 170 kts.  Also I was hand flying the approach because I was worried that given the tight constraints the automation wouldn't react fast enough.  I was under the impression that you had to be two white two red on the PAPIs through the descent - good to know you can be slightly off.

One interesting thing that I found out about the SKCL is that on the older approach plates when the magnetic heading was 01/19, on the VOR RWY02 approach the GS was 5.2 degrees, on the current plates the same VOR approach for RWY02 is now published at 3.04 degrees. (I know we're discussing the RNAV approach and not the VOR, but I thought it interesting that the GS gradient was changed while the distance from the VOR to the threshhold remained the same).  

 

14 hours ago, xkoote said:

4. The profile view of approach plates is not realistic. There it's an instantaneous descent after KOGLO. Your 777 (or any heavy jet) can not instantaneously give you commanded V/S. It takes awhile to settle, thus getting you above profile from the getgo.

5. There is only 1645 feet on this approach to try and recapture the profile.

Hi Xander,

The proximity of the runway to the KOGLO makes for some very tight quarters, there's not a lot of room to be off profile.

Richard Bansa

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6 minutes ago, Slick9 said:

I was under the impression that you had to be two white two red on the PAPIs through the descent - good to know you can be slightly off.

Richard,

I was told early in my flying career that landing short was a CLM.  🙂

 

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1 hour ago, Slick9 said:

the VOR RWY02 approach the GS was 5.2 degrees

Are you sure it wasn't 5.2%, which, I think, is equivalent to 3 degrees?

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Posted (edited)
34 minutes ago, dmwalker said:

Are you sure it wasn't 5.2%, which, I think, is equivalent to 3 degrees?

Dugald you are 100% correct - it was 5.2%.  What's the rule of thumb for the conversion from % to degrees?  

 

Richard Bansa

Edited by Slick9

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Posted (edited)

I'm afraid my rule of thumb is to Google it but I may have seen this specific correlation in the Navigraph Airport Chart Manual or an equivalent guide from Jeppesen. Anyway, it's simple trigonometry and you can find websites which can convert. Can I mention one: The Engineering Toolbox? A vertical drop of 1 in a horizontal run of 19 comes out pretty close to 3 degrees and 5.2%.

Edited by dmwalker

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Posted (edited)
1 hour ago, Slick9 said:

Dugald you are 100% correct - it was 5.2%.  What's the rule of thumb for the conversion from % to degrees?  

 

Richard Bansa

The rise over the run ratio is the sine of angle, and the gradient in percent is simply the rise over the run.  The basic numbers are 5.24% = 318.436 / 6076.12; and sin-1(0.0524) = 3 deg.  Not much trig involved here, just basic geometry.

Edited by downscc
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Posted (edited)
8 hours ago, skelsey said:

Wilhelm will I'm sure confirm his thinking, but on the 747 at least it would be normal to use brake 1 at hot and high airfields because of the higher ground speeds involved (= more energy to be absorbed by the brakes = more heat).

but a higher groundspeed also results in a longer landing distance and therefore an even higher brakes setting would make sense again, in combination with max reverse (or at least higher then idle)..

When the brakes setting becomes science.. lol.

 

Edited by Ephedrin

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16 minutes ago, Ephedrin said:

but a higher groundspeed also results in a longer landing distance and therefore an even higher brakes setting would make sense again, in combination with max reverse (or at least higher then idle)..

When the brakes setting becomes science.. lol.

 

Sure, engineers had to solve problems like this in their sophomore year.

The higher the autobrake setting, the greater the deceleration rate and one would think that the longer you decelerate the more heat you get. This is not true. In fact, the opposite might be true in most cases.  The amount of heating of the brake and wheel assemblies is only a function of how much energy is absorbed/converted and the effects of time are negligible. The deceleration rate you dial in with the autobrake switch is achieved with the combination of braking (heat), and other factors including reverse thrust, rolling resistance and aerodynamic drag.  The higher the deceleration rate, the less time there is for the other factors to contribute to the deceleration leaving more of the total braking energy to be converted to heat.  The lowest braking temperatures will be at the lowest deceleration rate, the usual constraint being runway landing distance.  I am not aware of any operational or technical reason to not use autobraking 1 if there is sufficient landing runway.  So while I agree that higher landing speeds may warrant a higher deceleration rate, the decision should normally be to select the lowest possible deceleration given the distance if heat is a determinant.

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37 minutes ago, Ephedrin said:

but a higher groundspeed also results in a longer landing distance and therefore an even higher brakes setting would make sense again, in combination with max reverse (or at least higher then idle)..

When the brakes setting becomes science.. lol.

Dan is correct -- lower brake energy is generally achieved with lower autobrake settings as other factors can assist in the deceleration (and certainly one would want to consider partial or full reverse in a brake energy limited situation). Because the autobrake targets a deceleration rate and not a constant brake pressure, use of a low autobrake setting in combination with reverse (and the other effects less under the pilot's control such as aerodynamic drag and rolling resistance) may result in very little if any brake application, particularly in the early stages of the landing roll where reverse and aerodynamic effects provide their greatest contribution. Obviously at lower speeds the wheel brakes will gradually "take over" but of course by then the total energy remaining to be converted to heat is much less (Ek = 1/2mv2). This leads on to...

6 minutes ago, downscc said:

I am not aware of any operational or technical reason to not use autobraking 1 if there is sufficient landing runway.

The reason as I was always lead to believe is that this to do with carbon brake wear.

Carbon brake wear is directly proportional to the number of applications. This is significantly different to traditional steel brake wear, which is heavily linked to brake temperature.

As such, with very low autobrake settings (i.e. 1) the autobrakes are liable to cycle on and off repeatedly during the landing run as the target deceleration rate may be very close to that achievable through aerodynamic/rolling resistance means alone. This increases carbon brake wear significantly, whereas using brake 2 with the resultant higher target deceleration rate is more likely to provide a single smooth automatic application of the brakes (but resulting in higher brake temperatures).

So for normal ops with carbon brake equipped aircraft, brake 2 results in lower brake wear overall. However, brake 1 results in lower temperatures and therefore is useful in hot and high/brake energy-limited situations.

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5 minutes ago, skelsey said:

Carbon brake wear is directly proportional to the number of applications. 

Hmmm.... , really?  I suspect that that is a generalized presumption.  I am pretty sure that any wear calculation is going to be based primarily on materials and friction conditions, velocity and duration of friction.  This also leads me to suspect that any linkage to brake temperature as a determinate of wear is probable only when temperatures are high enough to effect the materials in such a way that alters friction conditions.  I just did a quick scan of technical articles on line related to brake wear and of course they address the automotive disc brake but the aviation disc brake, while configured differently, would seem to have the same physics I suspect.

Simon, you have a source for this number of application relationship to wear?  Is it possible it presumes each landing is sufficiently the same as far as velocities and time?

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