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

[Slick9 24]

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

[BlueStar 323]

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.  🙂

 

[dmwalker 601]

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?

[Slick9 24]

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 May 9, 2018 by Slick9

[dmwalker 601]

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 May 9, 2018 by dmwalker

[downscc 1,327]

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 May 9, 2018 by downscc

[Ephedrin 418]

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 May 9, 2018 by Ephedrin

[downscc 1,327]

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.

[skelsey 765]

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 (E_k = 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.

[downscc 1,327]

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?

[skelsey 765]

5 minutes ago, downscc said:

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?

Whilst I'm sure that you are correct in that carbon brake wear is likely to be much more complex than just number of applications, this seems to be the general 'pilot friendly' advice from both Boeing and Airbus.

A few useful links:

http://www.boeing.com/commercial/aeromagazine/articles/qtr_03_09/article_05_1.html

https://www.iata.org/whatwedo/ops-infra/training-licensing/Documents/best-practices-for-carbon-brakes-application_Airbus.pdf

https://airlinesafety.blog/2014/04/03/how-to-get-the-most-out-of-carbon-brakes/

http://code7700.com/carbon-carbon_brakes.htm

Happy reading!!

[downscc 1,327]

26 minutes ago, skelsey said:

Happy reading!! 

Thanks, the airline safety blog provides the answer.  Carbon brakes wear the most when cold and brake most effectively when hot.  This leads to operational considerations for taxi (do not lightly tap brakes often, use one heavier application instead of many light ones) and I can see where this leads to the preference for higher deceleration rates on landing.  This is a perfect answer to my linkage to frictions conditions, which in the case of carbon is related to temperature.  The hotter the carbon gets the better..... up to a point.  No one wants to melt the fuse plugs.

[Ephedrin 418]

15 minutes ago, downscc said:

Carbon brakes wear the most when cold and brake most effectively when hot

and this would explain the statement of Cpt. Ashcraft in the tutorial video, why he wouldn't use Autobrakes 1, at least when having carbon brakes... 

Thanks guys, you're amazing! 😄

 

Simon? Back to Beta... 319.. 😛

[BlueStar 323]

16 hours ago, skelsey said:

Wilhelm will I'm sure confirm his thinking,

Simon,

I'm not rated in the B777 so I fly it like I would aircraft I am more familiar.  I almost always use minimum Autobrake and rely more on Reverse thrust when runway length and weather conditions permit.  This approach was a visual to a 10,000 foot runway and my turnoff would have been the same even it I'd used brake 2/3.    

My biggest concern about brake and tire temperatures is on departure.  

I will tell a tale on myself.  At the 80 knot call I always push the yoke forward. I know I'm old and it's no longer necessary but some habits are just hard to break. ROFL

[Slick9 24]

Went back and flew my KMIA - SKCL route this weekend, and using Bluestar's blue print, I was able to nail the landing on 02.  The biggest adjustment I made was to ensure that I was close to Vref/146kts (i was @ 165kts), with gear down, by the time i arrived @ the final approach fix.  I had intended to be @ flaps 30 also but FS2crew must not have heard my command, so I was @ flaps 15 as I crossed the final fix KOGLO.  Once I started the descent I was only descending @ around 600 FPM so I took a quick peak @ my flaps and realized my flaps 30 command had not been carried out.  So i didn't get to flaps 30 till I was around 4000 feet. Once in full landing config she slowed to Vref + 5 very quickly.  At this point I was at 3 white 1 red on the PAPI and it was just a matter of applying a little rudder to counter the slight crosswind.  From there on the landing was uneventful.  

So even though the parameters are pretty tight given the relatively low altitude of the final fix, there is a small margin for corrections to the approach. 

A couple of final questions that i have, is that on this approach and quite a few others I don't get a distance to the runway readout on the PFD.  Does that readout only showup on ILS approaches?  Also what PFD display would you fly an RNAV approach with?  I used the MAP display, should I have switched to the Approach display? (maybe that's why I didn't get the DME display.

Anyway, thanks Bluestar for the tips!!  If you do put an RNAV tutorial together, I would be very interested.

 

Richard Bansa