I am trying landing on Paro, Bhutan. I am studying the cloud break procedure VOR DME like on

https://www.tropicairvirtual.com/company/twoballs/Carte/VQPR_CHARTS.pdf

on page 10.

I am trying to make sense of the altitudes, like at the VOR PRO why am I supposed to be at 13500 and why does it say 6167 under that. Apparently you should be there at 6167 feet above airport altitude? That is a lot, being only 6.7 miles away from the airport.

Am I correct?

Really interesting and dangerous approach!

A cloud break it's not a straight in approach, you must circle to land for landing.... now if you obtain visual conditions with enough distance, in that case, you can discontinue approach and increase your rate of descent and try to a direct landing following the river, for RWY33.

1 hour ago, Rene_Feijen said:

I am trying landing on Paro, Bhutan. I am studying the cloud break procedure VOR DME like on

https://www.tropicairvirtual.com/company/twoballs/Carte/VQPR_CHARTS.pdf

on page 10.

I am trying to make sense of the altitudes, like at the VOR PRO why am I supposed to be at 13500 and why does it say 6167 under that. Apparently you should be there at 6167 feet above airport altitude? That is a lot, being only 6.7 miles away from the airport.

Am I correct?

Really interesting and dangerous approach!

Yup, you are correct, it's a steep approach and you have to be up that high because there is a peak which rises to 12,825 feet off to your left, so at 13,500 feet although you are 6,167 feet above the airfield, you're only around 1,500 feet above the terrain directly below you and it is often in cloud in real life.

But there are actually two reasons why it's invariably a steep approach into such places: The first is pretty obvious - it's to get you over the nearby mountains at a safe clearance as you come in - the second is that there is often a steep wind gradient in such terrain and quite often updrafts and downdrafts on the sides of the mountain peaks as well. So if you come in steep, you pass quickly through wind gradients and are better able to maintain a safe airspeed because of this. It's a pretty standard way of landing on a hilltop site too incidentally for much the same reason, i.e. it gets you quickly through the danger zone with a bit of airspeed to spare which you can lose in the flare. 

Because of this, you want to be careful with your flap settings even though using all your flaps might seem like a good idea in order to 'brake' your descent a bit; the reason you might not want full flaps is that although they do cause a lot of drag which will slow your descent, if you hit a pocket of air which reduces your forward airspeed, your aeroplane will accelerate slower with all that drag from the flaps at a time when you need it to speed up quickly to maintain your desired safe margin of airspeed and thus your rate of descent. This is why you invariably use less flaps in windy settings even at most normal airports. Be aware too that when you are at 6,000 feet above the airfield, you are actually at a much higher pressure altitude of 13,000 feet above sea level, so your wings and engines are slightly less efficient, which will probably mean a higher Vref speed.

As you say, it's a fairly challenging approach compared to most places and so it's a good idea to have the Missed Approach Procedure set up on radios and instruments and have briefed it well so you are ready to go missed if things don't look great.

 

Thanks for the clear  answer!

22 hours ago, Chock said:

You are actually at a much higher pressure altitude of 13,000 feet above sea level, so your wings and engines are slightly less efficient, which will probably mean a higher Vref speed.

IAS is always IAS, regardless of altitude. TAS will be higher, and groundspeed, (and subsequently vertical speed). But it should not alter vref.

On the other hand, you will correct Vr (rotation speed at takeoff) for high altitude airports.

37 minutes ago, SAS443 said:

IAS is always IAS, regardless of altitude. TAS will be higher, and groundspeed, (and subsequently vertical speed). But it should not alter vref.

On the other hand, you will correct Vr (rotation speed at takeoff) for high altitude airports.

True, I shouldn't have wrote Vref as it will indeed remain the same, but since going faster for the same IAS will alter the actual speed over the ground of Vref, the penetration through the air mass changes, and in situations where there is the possibility of windshear, a bit more speed helps too.

Edited February 16, 20215 yr by Chock

You might want to look up how to read a Jeppesen chart. Altitudes are written out in normal text and heights are written in (italicised brackets). Know the difference between QNH (altitude: distance above sea level) and QFE (height above runway) pressure settings.

edit to add: This isn't your typical airliner ILS approach or even non-precision approach that's designed to put you on a 3 degree glideslope. It's a cloudbreak for a circle-to-land: this is intended to get you close enough to the airfield for you to complete the approach visually.

 

Look at the box on the plate with CIRCLING OCA(H) at top left. That's the descent vertical profile. You start from the highest point in that box and work your way across, so for this approach you fly yourself to TAKTI and leave it at 16,000ft QNH.

The main chart above the box says that from TAKTI you fly a course of 360 degrees to Paro VOR. Look again at the vertical profile: when you arrive at the VOR it says you should be level at 13,500ft (6,167ft QFE). This means you'll need to descend 2,500ft in 15nm. Easy. It's worth arriving at 13,500ft (6,167ft) a couple of miles before the VOR so you have time to level off and retrim.

Once you reach Paro VOR you turn left onto outbound radial 328, which you should be established on by 1nm away from the VOR. That's the D1.0 waypoint on the main chart. You stay at 13,500ft (6,167ft) until you reach D1.0.

At that point, while maintaining R328, you begin descending to your minimum descent altitude, 12,500ft (5,167ft). The MDA is found in the bottom right box of the plate (approach minima, in this case circle-to-land) and is also on the briefing strip along the top. If your aircraft has a radar altimeter or you reset QFE instead of QNH before the final descent, your minimum decision height (MDH, above ground) is 6,167ft. Note also the 3,100m in the approach minima: that's your minimum visibility for the procedure. If it falls below, you're supposed to go land somewhere else.

As the chart says, by the time you reach D5.0 from PRO you must be visual with the runway. If you become visual at any point during the final descent, break off the published approach and circle to lose height for a safe landing. You will see from the vertical profile box that the runway is at an altitude of 7,333ft so some simple maths tells you that by following the approach you will end up about 5,000ft above the airfield and 1.7nm from the threshold.

If you are not visual with the runway by D5.0 PRO you start the missed approach. The missed approach is shown on the chart by the dotted line. The instructions are in the box titled MISSED APCH.

 

Edited February 17, 20215 yr by lambourne

Thanks for the extended answer! Most of it I figured out, but MDA MDH and the meaning of the number altitude vs height were not clear to me until now.

Also I thought I read it wrong because descending 6167 feet within 6.7 NM seemed too steep for me, but that is the challenging thing about this approach 🙂

Precise meaning of circle to land I also have to learn.

I have the Air Pilots Manual Part 3 Air navigation and Part 5 Radio navigation and instrument flying (old versions year 2000) btw, but it has an overwhelming amount of information in it.

Google is sometimes useful... 😉

https://en.wikipedia.org/wiki/Instrument_approach#:~:text=Circle-to-land is a,required visual reference to the

...jim

 

That clarifies it. Circling to land sounds like fun.