Missed approach point?
08-16-2008, 12:50 PM
#11
Organizational Learning
Joined APC: Nov 2005
Position: Directly behind the combiner
Posts: 4,948
There are two points depicted inside the Final Approach Fix -- the Visual Descent Point (VDP), and the Missed Approach Point (MAP). Each has a distinct purpose, and the two should not be confused.
When one reaches the VDP and determines that he cannot make a normal, safe descent to land, he might decide that a Missed Approach is the appropriate course of action. He may even begin a climb in association with the Missed Approach Procedure. (He can climb at any point on the approach, for that matter. He doesn't have to wait for the MAP or the VDP.) However, he cannot commence any turns attendant to the Missed Approach Procedure until he reaches the MAP.
The MAP is the point at which the Missed Approach Procedure commences. Obstacle clearance is calculated based on commencing the procedure here, and any climbs commenced prior only enhance the obstacle clearances. The decision to execute the procedure may have been made prior, but the procedure itself must be commenced at the point.
If flying this particular approach as a non-precision approach (LOC), one must have DME to determine the MAP. It would appear, then, that "DME" should be included in the title, i.e., "ILS or LOC/DME RWY 15". The absence of that terminology leaves one to wonder if the notation was omitted, or a timing block was omitted. Only a conversation with the agency that designed the approach would answer that question definitively. In the meantime, we're left to fly the approach as an ILS or with DME as a LOC.
So, it's like maddogin said in Post #2 -- the MAP is IISM (not ISM) DME 1.2.
.
When one reaches the VDP and determines that he cannot make a normal, safe descent to land, he might decide that a Missed Approach is the appropriate course of action. He may even begin a climb in association with the Missed Approach Procedure. (He can climb at any point on the approach, for that matter. He doesn't have to wait for the MAP or the VDP.) However, he cannot commence any turns attendant to the Missed Approach Procedure until he reaches the MAP.
The MAP is the point at which the Missed Approach Procedure commences. Obstacle clearance is calculated based on commencing the procedure here, and any climbs commenced prior only enhance the obstacle clearances. The decision to execute the procedure may have been made prior, but the procedure itself must be commenced at the point.
If flying this particular approach as a non-precision approach (LOC), one must have DME to determine the MAP. It would appear, then, that "DME" should be included in the title, i.e., "ILS or LOC/DME RWY 15". The absence of that terminology leaves one to wonder if the notation was omitted, or a timing block was omitted. Only a conversation with the agency that designed the approach would answer that question definitively. In the meantime, we're left to fly the approach as an ILS or with DME as a LOC.
So, it's like maddogin said in Post #2 -- the MAP is IISM (not ISM) DME 1.2.
.
08-25-2008, 07:18 AM
#13
Line Holder
Joined APC: Dec 2007
Position: CFI
Posts: 82
to calculate a VDP take the Height above terrain (HAT) of the MAP altitude compared to the touchdown zone (basically this is just the AGL height) and divide that by 300, it will give you a distance in nautical miles FROM THE END OF THE RUNWAY that your VDP should fall at.
To review
HAT/300 = VDP in NM from end of runway. Its fairly conservative but is useful in some of the steeper non preceisions, if a VDP is depicted by the charting authority than use that because there have been inclusions for terrain, obstacles, performance, etc.
To review
HAT/300 = VDP in NM from end of runway. Its fairly conservative but is useful in some of the steeper non preceisions, if a VDP is depicted by the charting authority than use that because there have been inclusions for terrain, obstacles, performance, etc.
08-25-2008, 12:12 PM
#15
Gets Weekends Off
Joined APC: Apr 2008
Posts: 117
Many missed approach procedures contain instructions such as "climbing right turn to xxx degrees". An early turn could conflict with terrain (think RNO landing south). Therefore you are required to continue to the MAP prior to starting any turns, even though you may have decided earlier, such as at the VDP, that you will not be landing out of this approach. There are also some rare approaches that have maximum altitudes on them for crossing traffic at another airport(OAK landing east crosses under SFO landing south), and some where the missed approach has a final altitude that is below the outer marker crossing altitude. So in case of an early missed approach decision you can't always start an immediate climb, and in the case of ATC speed restrictions you may not even be able to accelerate to your flap retract speeds. You will of course request relief immediately from ATC, but it is simetimes hard to get a word in edgewise, and when you catch him by surprise his response is likely to be "fly the published miss". I know that some people will say that this clearance removes the speed restriction, but since the speed restriction may have been for seperation with the traffic ahead, speeding up may create a traffic conflict.
Joe
Joe
08-27-2008, 07:22 AM
#17
Gets Weekends Off
Joined APC: Mar 2007
Position: Cessna 150 Left seat
Posts: 430
Hi Guys,
Still bit confused by the whole VDP procedure.
-Is VDP used to determine when you can recieve a Visual approach from a tower? any connection between the two?
-So not knowing your VDP, can you not descend below MDA even when you have the airport in sight??? or can you go below MDA only after VDP?
-How does pilot comply differently with published VDP or non-published? Can a pilot ignore VDP if it's not published and go below MDA having airport insight?
-Lastly, any other source to read/learn about VDP besides AIM?
Thanks!
Still bit confused by the whole VDP procedure.
-Is VDP used to determine when you can recieve a Visual approach from a tower? any connection between the two?
-So not knowing your VDP, can you not descend below MDA even when you have the airport in sight??? or can you go below MDA only after VDP?
-How does pilot comply differently with published VDP or non-published? Can a pilot ignore VDP if it's not published and go below MDA having airport insight?
-Lastly, any other source to read/learn about VDP besides AIM?
Thanks!
08-27-2008, 09:43 AM
#18
Gets Weekends Off
Joined APC: Feb 2007
Position: A-300 F/O
Posts: 281
-Is VDP used to determine when you can recieve a Visual approach from a tower? any connection between the two?
No and no connection.
A visual approach is an IFR operation (you keep the IFR clearance and traffic separation criteria afforded by ATC, except where you are visually separating from traffic to follow) conducted in VFR/VMC conditions when traffic, cloud clearance and visibility criteria allow pilots to follow other aircraft to the airport or proceed visually such as base turn to 3 mile final and avoiding vectors to join final outside the FAF to save time and expedite traffic flow.
The VDP is the point where the MDA altitude intersects a 3 degree glidepath, and if there is a VGSI, this should be a 3 deg to a touchdown abeam the PAPI/VASI.
-So not knowing your VDP, can you not descend below MDA even when you have the airport in sight??? or can you go below MDA only after VDP?
-How does pilot comply differently with published VDP or non-published? Can a pilot ignore VDP if it's not published and go below MDA having airport insight?
You always go below MDA at your own peril, just as flying is a risk. Going below before VDP means you are below the 3 deg glidepath.
The big thing to know is you don't know why there is no VDP published. Sometimes the person building the approach just did not calculate one. Sometimes there are obstacles in the close in area that don't allow one to be created. If there is a VGSI to the runway, then lack of VDP on the plate should be due to approach/TERPS dude not putting one down.
If there is no VDP and no VGSI info available, use self calculated VDPs with caution. You have probably calculated to the threshold not a point 1000' down the runway and if not in daylight conditions at an unfamiliar airport; you have no idea of what close in obstacles may exist close to the runway.
This is what the AF instrument book AFM 11-217 says about VDPs: It may be absent from an IAP due to an obstacle that penetrates a 20:1 surface, or the TERPS specialist simply did not calculate one. According to 11-217, if the visibility required for the approach is less than 1 mile, then there should be no obstacle penetrations of the 20:1 surface. If the procedure says N/A at Night or if the visibility requirement is greater than 1 mile, then there is a penetration of the 20:1 surface.
I try to impress upon my students the ideas of not doing the dive and drive so as not to spend a long time at MDA by calculating a descent rate based on groundspeed and desired feet/nm to arrive at the MDA about a 1/2 mile prior to VDP (published or self calc'd). This gives about 15 seconds to evaluate the visual cues available in the form of the runway environment, while not yielding to the temptation of beginning an auto descent just because they broke out of the weather. Then at a published VDP, set whatever pitch and power you use on an ILS Glideslope to begin the descent while cross checking the VGSI, and at a self calc'd VDP to take another potatoe or so to evaluate all the visual cues, also gets you another 1000' of forward travel, then set the aircraft's ILS pitch and power setting which should start you down on a 3 deg to a point 1000' down the runway.
-Lastly, any other source to read/learn about VDP besides AIM?
Jepps Commercial Instrument Manual should have some good stuff on VDPs
Free stuff in the FAA Instrument Handbook
http://www.faa.gov/library/manuals/a...-H-8261-1A.pdf
No and no connection.
A visual approach is an IFR operation (you keep the IFR clearance and traffic separation criteria afforded by ATC, except where you are visually separating from traffic to follow) conducted in VFR/VMC conditions when traffic, cloud clearance and visibility criteria allow pilots to follow other aircraft to the airport or proceed visually such as base turn to 3 mile final and avoiding vectors to join final outside the FAF to save time and expedite traffic flow.
The VDP is the point where the MDA altitude intersects a 3 degree glidepath, and if there is a VGSI, this should be a 3 deg to a touchdown abeam the PAPI/VASI.
-So not knowing your VDP, can you not descend below MDA even when you have the airport in sight??? or can you go below MDA only after VDP?
-How does pilot comply differently with published VDP or non-published? Can a pilot ignore VDP if it's not published and go below MDA having airport insight?
You always go below MDA at your own peril, just as flying is a risk. Going below before VDP means you are below the 3 deg glidepath.
The big thing to know is you don't know why there is no VDP published. Sometimes the person building the approach just did not calculate one. Sometimes there are obstacles in the close in area that don't allow one to be created. If there is a VGSI to the runway, then lack of VDP on the plate should be due to approach/TERPS dude not putting one down.
If there is no VDP and no VGSI info available, use self calculated VDPs with caution. You have probably calculated to the threshold not a point 1000' down the runway and if not in daylight conditions at an unfamiliar airport; you have no idea of what close in obstacles may exist close to the runway.
This is what the AF instrument book AFM 11-217 says about VDPs: It may be absent from an IAP due to an obstacle that penetrates a 20:1 surface, or the TERPS specialist simply did not calculate one. According to 11-217, if the visibility required for the approach is less than 1 mile, then there should be no obstacle penetrations of the 20:1 surface. If the procedure says N/A at Night or if the visibility requirement is greater than 1 mile, then there is a penetration of the 20:1 surface.
I try to impress upon my students the ideas of not doing the dive and drive so as not to spend a long time at MDA by calculating a descent rate based on groundspeed and desired feet/nm to arrive at the MDA about a 1/2 mile prior to VDP (published or self calc'd). This gives about 15 seconds to evaluate the visual cues available in the form of the runway environment, while not yielding to the temptation of beginning an auto descent just because they broke out of the weather. Then at a published VDP, set whatever pitch and power you use on an ILS Glideslope to begin the descent while cross checking the VGSI, and at a self calc'd VDP to take another potatoe or so to evaluate all the visual cues, also gets you another 1000' of forward travel, then set the aircraft's ILS pitch and power setting which should start you down on a 3 deg to a point 1000' down the runway.
-Lastly, any other source to read/learn about VDP besides AIM?
Jepps Commercial Instrument Manual should have some good stuff on VDPs
Free stuff in the FAA Instrument Handbook
http://www.faa.gov/library/manuals/a...-H-8261-1A.pdf
08-27-2008, 11:06 AM
#19
Gets Weekends Off
Joined APC: Jul 2008
Position: 747 Captain (Ret,)
Posts: 806
The Op-Specs of many 121 operators require that the crew not descend below MDA until passing the VDP, if published. This doesn't (yet) apply to Part 91 operators. I don't know about Part 135, or fractionals.
Joe
Joe
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