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# 3xheight at high altitude airport

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# 3xheight at high altitude airport

30th Apr 2019, 12:06

Join Date: Dec 2013
Location: Milan
Posts: 30
3xheight at high altitude airport

Hi everybody!

I’d like to ask a quick opinion. In my previous job I was not really used to fly at high altitude airport, so it was something I accounted marginally by just taking out couple of miles.
Yesterday I flew to a high altitude airport, as I’m used since my beginning to monitor my descent using 3xheight and adding miles to account for deceleration I did also there the same, however I got a little bit confused on initial approach as “I felt like a mad scientist” by taking out miles, adding etc.
in those high alt airport like 3/4000ft, what do you do to keep math simple while allowing for deceleration?
do you do 3xheight and remove immediately airport elev or whatsover?

thanks for your help in this silly question
30th Apr 2019, 14:50

Only half a speed-brake

Join Date: Apr 2003
Location: Commuting home
Age: 41
Posts: 2,290
One way is to use the FAP for all the calcs at all times. Just as an overrun does not start by the edge of the tarmac, an unstable approach begins much sooner than the threshold.

I find it helpful to check my gates earlier, and easily discover what goes and what goes not while you still have time to salvage the approach or abandon without the tunnel vision.

PROG page REF FIX to the G/S intercept point (worth checking WELL which FMS wait it actually is) and then

for instance: distance to FAP = 20 NM —>> you can kill 6000 ft.
FAP at 4000 feet <<==>> 10000 would be good. Compare to present ALT and see where you are.

That removes all ELEV guesswork, and works irrespective of the direction of your arrival relative to runway landing course. I.e for straight in you will need 3x to thr, if the opposite runway is in use then 5000 ft + 3x to thr is required mostly: all this becomes unnecessary with the g/s intercept point method. Sorcerer level 2: estimate the track miles to FAP, not just the direct line from REF FIX page.

As well, it gives a good understanding of what is the worst case short vector scenario. And if you are ok, then ask for it

Mentioning the energy difference between 320, 280, 250 and 210 kt is unnecessary here, same for the wind effect.

On 737 you could just use the VNAV (-300 ft), but on the Airbus - I find it not fit for the purpose.

2c.
30th Apr 2019, 23:54

Join Date: Mar 2006
Location: Ormond Beach
Age: 44
Posts: 32
Originally Posted by easymxp
Hi everybody!

I’d like to ask a quick opinion. In my previous job I was not really used to fly at high altitude airport, so it was something I accounted marginally by just taking out couple of miles.
Yesterday I flew to a high altitude airport, as I’m used since my beginning to monitor my descent using 3xheight and adding miles to account for deceleration I did also there the same, however I got a little bit confused on initial approach as “I felt like a mad scientist” by taking out miles, adding etc.
in those high alt airport like 3/4000ft, what do you do to keep math simple while allowing for deceleration?
do you do 3xheight and remove immediately airport elev or whatsover?

thanks for your help in this silly question
I don't see what difference airport elevation makes in this instance. My 3:1 mental math is based on AGL, not MSL, so whether it's Miami or Telluride is not terribly material.
2nd May 2019, 14:27

Join Date: Dec 2013
Location: Milan
Posts: 30
Originally Posted by FlightDetent
One way is to use the FAP for all the calcs at all times. Just as an overrun does not start by the edge of the tarmac, an unstable approach begins much sooner than the threshold.

I find it helpful to check my gates earlier, and easily discover what goes and what goes not while you still have time to salvage the approach or abandon without the tunnel vision.

PROG page REF FIX to the G/S intercept point (worth checking WELL which FMS wait it actually is) and then

for instance: distance to FAP = 20 NM —>> you can kill 6000 ft.
FAP at 4000 feet <<==>> 10000 would be good. Compare to present ALT and see where you are.

That removes all ELEV guesswork, and works irrespective of the direction of your arrival relative to runway landing course. I.e for straight in you will need 3x to thr, if the opposite runway is in use then 5000 ft + 3x to thr is required mostly: all this becomes unnecessary with the g/s intercept point method. Sorcerer level 2: estimate the track miles to FAP, not just the direct line from REF FIX page.

As well, it gives a good understanding of what is the worst case short vector scenario. And if you are ok, then ask for it

Mentioning the energy difference between 320, 280, 250 and 210 kt is unnecessary here, same for the wind effect.

On 737 you could just use the VNAV (-300 ft), but on the Airbus - I find it not fit for the purpose.

2c.
Thank you very much Flight Detent for your great tips. I’d never thought to use FAP in the PROG Page instead of rwy thresold. There are definitely significant advantages, and I’ll give a try on my next flight.

QUOTE=flyboyike;10460157]I don't see what difference airport elevation makes in this instance. My 3:1 mental math is based on AGL, not MSL, so whether it's Miami or Telluride is not terribly material.[/QUOTE]

Yes, I agree with you. I was used to use MSL (as reduced menthal calcs) and then adjust removing some couple of miles for higher than MSL airports. But definitely it was quite rare for me to visit places higher than 1000ft....
2nd May 2019, 17:05

Only half a speed-brake

Join Date: Apr 2003
Location: Commuting home
Age: 41
Posts: 2,290
a. Estimate track miles to FAP, using any method you could find
b. [NM x 3] + FAP ALT = 3° profile, check where you are compared to that
c. use Ground-Speed / 20 to find out, what V/S will give you 3 deg trajectory and check what descent rate is being achieved

E.g

Track miles to FAP 26
FAF ALT 6000'
IAS 290 kt, GS 370
actual V/S 2200 fpm

What do you think? My answer after yours.
3rd May 2019, 10:06

Join Date: Dec 2013
Location: Milan
Posts: 30
Originally Posted by FlightDetent
a. Estimate track miles to FAP, using any method you could find
b. [NM x 3] + FAP ALT = 3° profile, check where you are compared to that
c. use Ground-Speed / 20 to find out, what V/S will give you 3 deg trajectory and check what descent rate is being achieved

E.g

Track miles to FAP 26
FAF ALT 6000'
IAS 290 kt, GS 370
actual V/S 2200 fpm

What do you think? My answer after yours.
Firstly the great thing is that from whatever position this distance is correct, by using the THR depending on the position (fe downwind expected vs long final) my result could be from very low to very high, so a correction would be needed.

In the above example to be on profile I should be approximately 13800’ so around 1200’ high without accounting for deceleration from 290. Accounting for deceleration I’d consider myself around 2200/2500’ high (if the FAF alt had been lower I’d accounted for more deceleration).
Looking at the VS I’m descending slightly steeper than 3° (required approx 1900). In this scenario if cleared to maintain 290kt I’d probably continue without using S/brakes and reassess the profile at around FL120/FL100 and every 1000s below FL100.
Then about 2000’ above FAF alt I’d start decelerating from 290kt and from there see If I need a bit of S/brakes or not. All of this provided ATC allows 290kt below FL100 otherwise I’d used some S/brakes above FL100 before deceleration to 250 (and maybe during) to go back on a 3° profile.
3rd May 2019, 16:31

Only half a speed-brake

Join Date: Apr 2003
Location: Commuting home
Age: 41
Posts: 2,290
Mine:-
(1) -> 26x 3 = 7500 (approx) + 6000 G/S intercept =>> 3 deg profile is 13500'
(2) -> the A/C is 1500' above
(3) -> 370 /20 = 1900 fpm is required to keep a 3 deg descent
(4) -> with present sink of 2200 we're slowly regaining the profile from above.

This arithmetic gives a good understanding of
- where you are (2)
- where you will be (4) based on GS, the effect of wind is already accounted for.

Obviously, with deceleration towards 250 knots coming soon that nice, steeper-than-3° trajectory won't last for long.

Personally, I do not make any mental calculation adjustments for the decel segments (250 / 210). I just run the (2) and (4) again and again, as many times as required. Anticipation notwithstanding!

---------------
The above example is quite critical, me thinks.
- With platform at 3000' and 270, it would be "rather efficient"
- With platform at 3000' and 290, I'd say daring,
- With platform at 6000 and 270, it looks borderline,
But 6000 and 290, with 1500 above already? The (vertical) room to slow down, which needs to be done soon to 250 and then almost immediately to 210ish, is just not there.

Choice of weapons depends. My present operator requires 250 below 10k AFE, so A/P off and full speed-brake for us
--------------------
3rd May 2019, 20:09

Join Date: Dec 2013
Location: Milan
Posts: 30
Originally Posted by FlightDetent
Mine:-
(1) -> 26x 3 = 7500 (approx) + 6000 G/S intercept =>> 3 deg profile is 13500'
(2) -> the A/C is 1500' above
(3) -> 370 /20 = 1900 fpm is required to keep a 3 deg descent
(4) -> with present sink of 2200 we're slowly regaining the profile from above.

This arithmetic gives a good understanding of
- where you are (2)
- where you will be (4) based on GS, the effect of wind is already accounted for.

Obviously, with deceleration towards 250 knots coming soon that nice, steeper-than-3° trajectory won't last for long.

Personally, I do not make any mental calculation adjustments for the decel segments (250 / 210). I just run the (2) and (4) again and again, as many times as required. Anticipation notwithstanding!

---------------
The above example is quite critical, me thinks.
- With platform at 3000' and 270, it would be "rather efficient"
- With platform at 3000' and 290, I'd say daring,
- With platform at 6000 and 270, it looks borderline,
But 6000 and 290, with 1500 above already? The (vertical) room to slow down, which needs to be done soon to 250 and then almost immediately to 210ish, is just not there.

Choice of weapons depends. My present operator requires 250 below 10k AFE, so A/P off and full speed-brake for us
--------------------
Really interesting, thank you Flight Detent for your wonderful contribution.
I agree with you regarding 6000’/290kt with the restriction of 250 below FL100AFE is definitely tight, without is achievable, probably with a bit of S/brake.

I’ve always used an arithmetic approach in flying. Some colleagues think I’m overcomplicating but I like to run 3x rule as much as possible especially getting closer.
I used to make an allowance for deceleration from 250/210 and I found pretty useful especially in some places where due to traffic/ATC I was left higher than platform. Eg with FAP 3000/9nm and stuck at 5000’ I knew that I could keep 210kt no more than closer than 18Nm then maybe better going managed and select F1. I found this arithmetic approach always reliable and a huge help maintaining awareness.

Definitely next flight I’ll try your tips as I think are definitely better and easier

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