PDP's

[NDPILOT]

I saw this acronymn on either an ACA or Skywest interview gouge.?.

The person who interviewed mentioned the importance of knowing what a VDP is and also a PDP.

Anyone have any idea what a PDP is? - i assuming it's something similiar to a VDP..?..

I haven't been able to find anything on it.

Thanks for any input.

nd

 

[midlifeflyer]

I've only heard the term in the context of "Personal Descent Point" or "Pilot's Descent Point".

If there's no VDP o the approach, the idea is to calculate your own.

 

[80/20]

One use is: PDP = Pre Determined Point, which is used to reduce the required fuel on long range flights by the use of re-release.

 

[bigsky]

An acronym can mean different things to different people however in the context of VDP I would wager it is a planned descent point. A VDP is a charted point where a PDP is basically the same idea however just made up by the pilot.
Ill give you my theory so take it whats its worth and modify it to fit your needs.
Ideally you want to be established on a 3 degree glide path for landing - correct? Also FARS say at DA you need to have reqd visual ref, visibility, and continuously in pos to make a landing in tdz.
When all else fails , especially in darkness, and poor visibility which can be very disorienting this is critical!
If tou devide the HAT by 300 you get pretty close- Por Ejemplo
lets say tdze is 100 feet and MDA is 750 feet msl- your height above hat is 650 that you need to lose from mda to touchdown.
I suggest planning on crossing threshold at 50 feet so really only need to lose 600 feet Divide this by 300 and you come up with 2.
That is 2 Miles from the threshold where one should leave the mda and if you maintain your normal descent rate(approx 5 x GS) and you should be well established.
If timing were used to figure this vs DME then you use a similar formula. For exaple if in a plane that has approach of 120 kts divide by 10. (600 divided by 10= 60 seconds) 60 sec before map one should be at pdp.
In large or wide body ac instaed of dividing by 300 I would use 325( a 3 bar vasi-upper path is 3 1/4 ) for wide bodies
Finally in faster planes I would also incorpoate a push over point
SAy we have a vdp at 2 miles and we wait till exactly 2 miles to start descent we will be at about 1.8 before we begin our descent so now we are high-- I generally have a push over point about .2 miles previous to my pdp-- ( this is probably only necessary at speeds above 120)

 

[willis]

This may help

For Non-precision Approaches only!!


At the FAF, desend at an appropriate rate to arrive at MDA PRIOR TO THE VISUAL DECENT POINT (VDP). VDP is the point from which a normal descent from MDA may begin. If a VDP is not published for an approach, a pilot descent point (PDP) may be calculated. There are two methods for calculating PDP's:

Timed method (assuming MAP is @ runway)
Subtract 10% of the HAT from the calculated time to MAP.
eg HAT is 500 feet AGL Subtract 50 seconds from time inbound


Distance method
Divide HAT by 300.
eg HAT is 450 feet AGL PDP will be 1.5nm from runway
Peace out,
Willis

 

[willis]

SORRY BIGSKY

$hit I'm sorry bigsky I posted before I read what a fine job you did explaining this crap
Willis

 

[GeorgeTG]

what is a PDP

close close but no cigar...

PDP = Planned Descent Point

Basic Idea:
CANPA = Constant Angle Non Precision Approach.

Concept:
PDP allows for a constant angle descent (typically 3 deg path) from the FAF crossing altitude to touchdown.

This way you can fly the non-precision approach in the same manner as a precision approach with a fixed rate of descent all the way down.

The angle remains the same and for a 3 degree path your descent rate is approximately 5 times your Groundspeed.

Obviously you will need some type of DME or GPS distance information or a GS readout to correct for any Head or Tailwind component.

The VDP - by definition - is located at the point this descent path crosses the MDA.

Some charts show a VNAV path and the PDP attemps to create a similar path.

Be careful because unlike the DA, the MDA is not a "decision" altitude but a "minimum descent" altitude. You will need to make a decision PRIOR to reaching MDA to account for reaction time and aircraft inertia.

As previously stated you can approximate a 3 degree path by applying the 60:1 rule. For every NM of distance you will descend approx. 300 ft

Example:
FAF at 2600 ft
TDZE of 500 ft
2100 ft to loose divided by 300
7 NM distance required

If the FAF is 7.3 NM from touchdown
the PDP is .3 NM after crossing the FAF

At a groundspeed of 120 Kts you will need 600 ft/min rate of descent.

Cheers
George

 

[willis]

WOW

CANPA = Constant Angle Non Precision Approach.


Now that's an impressive accronym. Did you come up with that on your own? Sounds like a CFII d0u(he bag type of word.

PDP Planned descent point/pilot descent point/Pre Determined POint/ Who gives a $hit? It means the same thing.

 

[80/20]

Re: WOW

CANPA = Constant Angle Non Precision Approach.


Now that's an impressive accronym. Did you come up with that on your own? Sounds like a CFII d0u(he bag type of word.

PDP Planned descent point/pilot descent point/Pre Determined POint/ Who gives a $hit? It means the same thing.

CANPA is used by many major airlines that frequently fly non precision approaches. The Flight Safety Foundations suggests that this is the best way and that it could have prevented many controlled flight into terrain accidents. It's a great technique - in my opinion.

 

[100LL... Again!]

It is a great idea - especially for larger aircraft. It does require a FMS or GPS designed to use the approach in that manner.

Check out John Deakin's articles (two of 'em) on AVweb for more info.

 

[bigsky]

NDPILOT: For interview purpose I would guess they are looking for the first answer.
Obviously both techniques are doing the same thing(pdp/Canpa)
Although I would say PDP is better explained as I tried before( perhaps in a few less words) It is the same as a VDP although many charts dont have a vdp so we make up our own=pdp.
The jepp definition of vdp is normal descent from the MDA(not the FAF altitude) may be commenced.
First off I dont know too many major US airlines who do many non-prec approaches( most no longer have NDB in their op specs)
Second it has been my observation that when it comes to airlines the FAA is very slow to approve of some of the new technology often used by many of the corporate pilots.

The idea of canpa is doing the very same thing utilizing a constant descent angle and with fms the computer can constantly monitor ground speed and adjust the the recommended descent to give a glide path similar to and ILs
I personally do not know of many operators(airlines )who are approved to conduct approaches using this- Not saying there arent any!
They are both adjusting the descent point until the airplane is on the proper glide path---same idea -- all I am saying is most airlines still motor down to mda and level off momentarily.
I recently did my md-11 type rating at Delta and in that airplane they use profile all the way down(the FMS will basically build it own glide path) Again the problem I have noticed is a NON prec is not as accurate as an ILS. If the ceiling is low and you go to mda and see the ry you will a little time to line up, however if using the campa method you may not be below the cloud deck till short final and it is difficult and unstabalizing to make large correction in close to ry.