MDA
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MDA
I am aware that JAA insist on 50ft being added to non precision MDA, VOR/NDB approaches, world wide.
Yet the FAA do not require this safety margin, which I am told is to allow for the interia in the level out.
My Question, is this in the new LASORS, or is it a CAA JAA Circular, or where can I find the reference material.
If it applies to NPA, and then this becomes a circle to land, does the circle then have the higher mins.
Lastly, does any other authority apply this rule: UAE, India, China, Russia...for example.
Many thanks, Glf
Yet the FAA do not require this safety margin, which I am told is to allow for the interia in the level out.
My Question, is this in the new LASORS, or is it a CAA JAA Circular, or where can I find the reference material.
If it applies to NPA, and then this becomes a circle to land, does the circle then have the higher mins.
Lastly, does any other authority apply this rule: UAE, India, China, Russia...for example.
Many thanks, Glf
Last edited by Gulfstreamaviator; 12th Dec 2010 at 01:37.
Hi Gulfstreamaviator
The 50ft addition to the MDA on an NPA is only applicable if you wish to conduct the NPA using Constant Descent Angle (CDA) techniques. I don't think that the JAA (which doesn't exist anymore BTW) insisted on this. If you wish to employ 'dive and drive' techniques, there is no need to add anything. I think it is true however, that the provisions of EU-OPS and the UK CAA strongly recommend using CDA techniques when conducting NPAs (as do the Flight Safety Foundation).
The MDA remains as published, but the CDA technique requires a Decision Altitude (DA), rather than an MDA.
In other words, when you reach the DA, you either initiate a go-around or continue to land, depending on whether or not you have adequate visual reference. With the CDA technique, you do not level off at the MDA and fly towards the MAPt before initiating a GA. This is similar to the DA employed on an ILS approach.
The reason for the 50ft addition now becomes clear: it is there to enable you to make a decision to GA without descending below the MDA during the manoeuvre.
By contrast, if using the 'dive and drive' technique, you plan to level off at the MDA, so no addition is required.
For a 'circle-to-land', again you are planning to level off at the circling minimum, so you don't need to add anything.
Unfortunately, I don't have the EU-OPS reference to hand. I am basing my response on the practises employed by UK PT operators. I don't think this info would be in LASORS either.
When using this CDA technique, it is important to remember that the GA must be continued straight ahead until passing the MAPt, before any turns may be commenced.
Hope this helps,
Eck
The 50ft addition to the MDA on an NPA is only applicable if you wish to conduct the NPA using Constant Descent Angle (CDA) techniques. I don't think that the JAA (which doesn't exist anymore BTW) insisted on this. If you wish to employ 'dive and drive' techniques, there is no need to add anything. I think it is true however, that the provisions of EU-OPS and the UK CAA strongly recommend using CDA techniques when conducting NPAs (as do the Flight Safety Foundation).
The MDA remains as published, but the CDA technique requires a Decision Altitude (DA), rather than an MDA.
In other words, when you reach the DA, you either initiate a go-around or continue to land, depending on whether or not you have adequate visual reference. With the CDA technique, you do not level off at the MDA and fly towards the MAPt before initiating a GA. This is similar to the DA employed on an ILS approach.
The reason for the 50ft addition now becomes clear: it is there to enable you to make a decision to GA without descending below the MDA during the manoeuvre.
By contrast, if using the 'dive and drive' technique, you plan to level off at the MDA, so no addition is required.
For a 'circle-to-land', again you are planning to level off at the circling minimum, so you don't need to add anything.
Unfortunately, I don't have the EU-OPS reference to hand. I am basing my response on the practises employed by UK PT operators. I don't think this info would be in LASORS either.
When using this CDA technique, it is important to remember that the GA must be continued straight ahead until passing the MAPt, before any turns may be commenced.
Hope this helps,
Eck
With the CDA technique, you do not level off at the MDA and fly towards the MAPt before initiating a GA.
The 50ft extra is for those who wish to do the approach like an ILS ie treat the "minimum" as a DA.
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fairly typical responses
Thanks guys, two opposing views, and not one firm reference to quote....
Sorry, not meaning to be critical.
In a CDA approach, the AP will appreciate the MDA, and commence level out to maintain the MDA, in a Slam dunk, (thus usually NON AP), the pilot will have a lot more inertia to convert, and thus more likely to bust the MDA.
If an ILS APP is permitted to go below the DH, due to intertia, (at 200ft), then what is the problem at 450ft (say), on a NPA.
In the case of a CDA, Assuming response 1, then when can one transition from the MDA+50 to the MDA circle.?????
Again, I seek hard copy reference material, to clarify my position to others.
glf
Sorry, not meaning to be critical.
In a CDA approach, the AP will appreciate the MDA, and commence level out to maintain the MDA, in a Slam dunk, (thus usually NON AP), the pilot will have a lot more inertia to convert, and thus more likely to bust the MDA.
If an ILS APP is permitted to go below the DH, due to intertia, (at 200ft), then what is the problem at 450ft (say), on a NPA.
In the case of a CDA, Assuming response 1, then when can one transition from the MDA+50 to the MDA circle.?????
Again, I seek hard copy reference material, to clarify my position to others.
glf
Gulfstreamaviator
In the US, RNAV approaches that have LNAV/VNAV minimums usually are charted with a DA; while most VOR or VOR/DME or NDB approaches have MDA with a note "only authorized operators may use VNAV DA (H) in lieu of MDA (H)". Use of a DA, in these cases, are an OpSpec for FAR 121/135 operators and not addressed for FAR 91 operators. The FSDO will probably shrug their shoulders, if a FAR 91 operator asks for a LOA to use DA.
I don't think there is a regulatory guidance requiring adding 50', just that you cannot go below the MDA, so the 50' is a fudge to prevent going below using a VNAV to guide. While some FMS systems will honor the Altitude Selector (ASEL), others will not. Specifically, the Collins system in VGP mode will treat the VNAV PTH just like an ILS GS and NOT level at the selected altitude, in fact, procedure is to set missed approach altitude like on an ILS.
WRT the ILS, the difference is in the obstacle identification slope. A non-precision appproach, by definition, has a hard floor representing the minimum obstacle height. An ILS obstacle clearance floor is surveyed based on a slope underneath the GS, all the way to TCH or a controlling obstacle. If the mins are above 200', watch out for a close-in obstacle penetrating the 1:34 or 1:20 slopes.
To the pilot's eye, I agree that any altitude loss at a VNAV CDA missed approach would be minimal and probably accounted for. But, until surveyed going below the MDA mins is a no-no.
GF
In the US, RNAV approaches that have LNAV/VNAV minimums usually are charted with a DA; while most VOR or VOR/DME or NDB approaches have MDA with a note "only authorized operators may use VNAV DA (H) in lieu of MDA (H)". Use of a DA, in these cases, are an OpSpec for FAR 121/135 operators and not addressed for FAR 91 operators. The FSDO will probably shrug their shoulders, if a FAR 91 operator asks for a LOA to use DA.
I don't think there is a regulatory guidance requiring adding 50', just that you cannot go below the MDA, so the 50' is a fudge to prevent going below using a VNAV to guide. While some FMS systems will honor the Altitude Selector (ASEL), others will not. Specifically, the Collins system in VGP mode will treat the VNAV PTH just like an ILS GS and NOT level at the selected altitude, in fact, procedure is to set missed approach altitude like on an ILS.
WRT the ILS, the difference is in the obstacle identification slope. A non-precision appproach, by definition, has a hard floor representing the minimum obstacle height. An ILS obstacle clearance floor is surveyed based on a slope underneath the GS, all the way to TCH or a controlling obstacle. If the mins are above 200', watch out for a close-in obstacle penetrating the 1:34 or 1:20 slopes.
To the pilot's eye, I agree that any altitude loss at a VNAV CDA missed approach would be minimal and probably accounted for. But, until surveyed going below the MDA mins is a no-no.
GF
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http://www.skybrary.aero/bookshelf/books/167.pdf
Lots of Gen here.
and here.
http://www.skybrary.aero/bookshelf/books/811.pdf
Lots of Gen here.
and here.
http://www.skybrary.aero/bookshelf/books/811.pdf
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EU-OPS
Here is EU-OPS: http://transportstyrelsen.se/Global/...epslanguage=sv
Page 57-58 are interesting read. It says:
1) All approaches shall be flown as stabilised approaches (SAp) unless otherwise approved by the Authority for a particular approach to a particular runway.
2) All non-precision approaches shall be flown using the continuous descent final approaches (CDFA) technique unless otherwise approved by the Authority for a particular approach to a particular runway. When calculating the minima in accordance with Appendix 1 (New), the operator shall ensure that the applicable minimum RVR is increased by 200 metres (m) for Cat A/B aeroplanes and by 400 m for Cat C/D aeroplanes for approaches not flown using the CDFA technique, providing that the resulting RVR/CMV value does not exceed 5 000 m
Page 57-58 are interesting read. It says:
1) All approaches shall be flown as stabilised approaches (SAp) unless otherwise approved by the Authority for a particular approach to a particular runway.
2) All non-precision approaches shall be flown using the continuous descent final approaches (CDFA) technique unless otherwise approved by the Authority for a particular approach to a particular runway. When calculating the minima in accordance with Appendix 1 (New), the operator shall ensure that the applicable minimum RVR is increased by 200 metres (m) for Cat A/B aeroplanes and by 400 m for Cat C/D aeroplanes for approaches not flown using the CDFA technique, providing that the resulting RVR/CMV value does not exceed 5 000 m
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The "dive and drive" technique is more used with piston planes than it is with jets (correct me if im wrong).
The 737 FCTM asks you to add 50' to the MDA for NPA and VNAV/LNAV.
Speaking of the 737 when doing a GA the aircraft will decend at least 30-40' before it will initially climb away so hence the 50' add on to MDA.
During my JAA IR I was told to add 50' on top of the DA for an ILS which I never understood.
The 737 FCTM asks you to add 50' to the MDA for NPA and VNAV/LNAV.
Speaking of the 737 when doing a GA the aircraft will decend at least 30-40' before it will initially climb away so hence the 50' add on to MDA.
During my JAA IR I was told to add 50' on top of the DA for an ILS which I never understood.
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The EUOPS reference that 172 refers to is the latest legislation. Note there is now no requirement to add 50 ft for any reason. The table for calculating minimum RVR from DH refers specifically to a Constant Descent Angle Final Approach and as stated above if you for any reason don't do a CDFA then add the RVR supplements according to your approch category A,B,C or D).
It is different to the previous JAR rules. You can use most methods of finding distance from the threshold to calculate the constant descent angle ie: DME, GPS, IR's so no real reason not to do a CDFA.
Extract from our approach chrat provider Rules and Regs section EUOPS:
7.9.3 Non Precision Approach (NPA) (EU-OPS)
A Non-Precision Approach (NPA) operation is an instrument approach with a Minimum Decision Height or
Decision Height not lower than 250ft and an RVR/CMV of not less than 750m, unless accepted by the
authority.
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3),
7.9.4 Decision Height (DH) and Minimum Descent Height (MDH) for Cat 1, APV and NPA (EU-OPS)
Decision Height (DH)
An operator must ensure that the Decision Height (DH) to be used for an approach is not lower than:
• the minimum height to which the approach aid can be used without the required visual reference; or
• the OCH for the category of aircraft; or
• the published approach procedure decision height where applicable; or
• 200ft for Cat 1 approach operations; or
• the lowest decision height specified in the Aircraft Flight Manual (AFM) or equivalent document, if stated;
• the system minimum
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3)
whichever is higher.
Minimum Descent Height (MDH)
An operator must ensure that the MDH for an approach is not lower than:
• the Obstacle Clearance Height (OCH) for the category of aircraft; or
• the minimum descent height specified in the AFM if stated; or
• the system minimum
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3)
whichever is higher.
As far as EUOPS and circling goes here is an extract from our approach chart provider, Rules and Regs section:
7.10 Circling and Visual Approach (EU-OPS)
7.10.1 Minimum Descent Height (MDH)
The MDH for circling shall be the higher of:
• The published circling OCH for the aircraft category; or
• The DH/MDH of the preceding instrument approach procedure; or
• The minimum circling height indicated on the EU-OPS Table 10.
For more information refer to:
⇒ Rules and Regulations General Information 7.10.6 Minimum VIS and MDH for Circling vs. ACFT Category (EU-OPS Table 10)
7.10.2 Minimum Descent Altitude (MDA)
The MDA for circling shall be calculated by adding the published aerodrome elevation to the MDH, as determined under paragraph "Minimimum Descent Height (MDH)".
For more information refer to: ⇒ Rules and Regulations General Information 7.10.1 Minimum Descent Height (MDH)
These are all extracted from the EUOPS document and do not refer at any stage to having to add 50ft as previously.
It is different to the previous JAR rules. You can use most methods of finding distance from the threshold to calculate the constant descent angle ie: DME, GPS, IR's so no real reason not to do a CDFA.
Extract from our approach chrat provider Rules and Regs section EUOPS:
7.9.3 Non Precision Approach (NPA) (EU-OPS)
A Non-Precision Approach (NPA) operation is an instrument approach with a Minimum Decision Height or
Decision Height not lower than 250ft and an RVR/CMV of not less than 750m, unless accepted by the
authority.
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3),
7.9.4 Decision Height (DH) and Minimum Descent Height (MDH) for Cat 1, APV and NPA (EU-OPS)
Decision Height (DH)
An operator must ensure that the Decision Height (DH) to be used for an approach is not lower than:
• the minimum height to which the approach aid can be used without the required visual reference; or
• the OCH for the category of aircraft; or
• the published approach procedure decision height where applicable; or
• 200ft for Cat 1 approach operations; or
• the lowest decision height specified in the Aircraft Flight Manual (AFM) or equivalent document, if stated;
• the system minimum
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3)
whichever is higher.
Minimum Descent Height (MDH)
An operator must ensure that the MDH for an approach is not lower than:
• the Obstacle Clearance Height (OCH) for the category of aircraft; or
• the minimum descent height specified in the AFM if stated; or
• the system minimum
⇒ Rules and Regulations General Information 7.9.6 System Minima vs. Facilities (EU-OPS Table 3)
whichever is higher.
As far as EUOPS and circling goes here is an extract from our approach chart provider, Rules and Regs section:
7.10 Circling and Visual Approach (EU-OPS)
7.10.1 Minimum Descent Height (MDH)
The MDH for circling shall be the higher of:
• The published circling OCH for the aircraft category; or
• The DH/MDH of the preceding instrument approach procedure; or
• The minimum circling height indicated on the EU-OPS Table 10.
For more information refer to:
⇒ Rules and Regulations General Information 7.10.6 Minimum VIS and MDH for Circling vs. ACFT Category (EU-OPS Table 10)
7.10.2 Minimum Descent Altitude (MDA)
The MDA for circling shall be calculated by adding the published aerodrome elevation to the MDH, as determined under paragraph "Minimimum Descent Height (MDH)".
For more information refer to: ⇒ Rules and Regulations General Information 7.10.1 Minimum Descent Height (MDH)
These are all extracted from the EUOPS document and do not refer at any stage to having to add 50ft as previously.
Last edited by Torque2; 12th Dec 2010 at 09:47.
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I seem to remember on small twins you had to add 50ft to an ILS, this was published in the AIP (Probably the place to look for this one). I think it was due to performance issues on light twins which couldn't maintain a great Climb Gradient with one engine out.
In the company I work for we recently changed our procedures so that we no longer Add 50ft to MDA if it is described on the Jeppesen plate as a DA, I think this will come down to the individual approach (Offset etc) on whether its classed as an MDA or DA.
I think there is probably some good info in the Jeppesen text manual on this if you can get your hands on it.
In the company I work for we recently changed our procedures so that we no longer Add 50ft to MDA if it is described on the Jeppesen plate as a DA, I think this will come down to the individual approach (Offset etc) on whether its classed as an MDA or DA.
I think there is probably some good info in the Jeppesen text manual on this if you can get your hands on it.
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During my JAA IR I was told to add 50' on top of the DA for an ILS which I never understood.
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EU-OPS 1.430 (d)2 details the requirement for continuous descent non-precision approaches, further information can be found in Appendix 1 (old) or (new) to OPS 1.430 depending which your company is using in the Operations Manual for working out approach minima.
Yet more information is available in TGL44,in particular ACJ OPS 1.430, AMC 1.430 and IEM OPS 1.430.
Ultimately you should work out the minima as defined in your operations manuals.
Obviously the above only applies to those operating under an AOC.
Yet more information is available in TGL44,in particular ACJ OPS 1.430, AMC 1.430 and IEM OPS 1.430.
Ultimately you should work out the minima as defined in your operations manuals.
Obviously the above only applies to those operating under an AOC.
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Gulfstreamaviator:
What you don't make clear is whether JAA requires this only when MDA is being treated as a DA. In that case, as some here have said, the FAA indeed does require adding 50 feet.
If, however, a NPA with MDA minimums is flown in the manner envisioned in criteria, then no additive is necessary, either under TERPs or PANS OPS, because of the minimum in minimum descent altitude.
I am aware that JAA insist on 50ft being added to non precision MDA, VOR/NDB approaches, world wide.
Yet the FAA do not require this safety margin, which I am told is to allow for the interia in the level out.
Yet the FAA do not require this safety margin, which I am told is to allow for the interia in the level out.
If, however, a NPA with MDA minimums is flown in the manner envisioned in criteria, then no additive is necessary, either under TERPs or PANS OPS, because of the minimum in minimum descent altitude.
Capn Bloggs,
I agree that there is nothing stopping them, but one has to ask, why would anyone want to do that? With the exception of a circle-to-land, levelling at the MDA from a CD NPA will automatically put you above the desirable approach path to the runway of intended landing.
My understanding is that the idea behind CD NPA is to try and make the execution of these as similar as possible to an ILS. Hence the use of a CDA, a DA and the lack of a level flight segment prior to the MAP. Although I agree that the use of a CD is beneficial, even if you plan to fly level at the MDA, I really can't see the point of this level flight towards the MAPt (unless circling). It seems to invite the pilot to spot the threshold at a later stage than normal and then make a dive towards the runway. We all know what that can lead to.
Regards,
Eck
Depends entirely on company SOPs. There is nothing stopping anybody flying a CD NPA, even from a database, levelling at the MDA, proceeding to the Mapt and then executing the missed approach.
My understanding is that the idea behind CD NPA is to try and make the execution of these as similar as possible to an ILS. Hence the use of a CDA, a DA and the lack of a level flight segment prior to the MAP. Although I agree that the use of a CD is beneficial, even if you plan to fly level at the MDA, I really can't see the point of this level flight towards the MAPt (unless circling). It seems to invite the pilot to spot the threshold at a later stage than normal and then make a dive towards the runway. We all know what that can lead to.
Regards,
Eck
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exhard:
No approving authority in its right mind would permit treating MDA as a DA and also approve a level off.
My understanding is that the idea behind CD NPA is to try and make the execution of these as similar as possible to an ILS. Hence the use of a CDA, a DA and the lack of a level flight segment prior to the MAP. Although I agree that the use of a CD is beneficial, even if you plan to fly level at the MDA, I really can't see the point of this level flight towards the MAPt (unless circling). It seems to invite the pilot to spot the threshold at a later stage than normal and then make a dive towards the runway. We all know what that can lead to.
Thanks aterpster, my view as well.
I think we're talking about two things here:
what an Approving Authority might authorise; and
how a crew might interpret an approach chart.
Capn Bloggs made the point that a CDA followed by a level flight segment was not precluded, and I agreed. I then tried to make the point that although allowed, this manouevre would result in a possible steep/deep approach and landing.
In the private world (not under an AOC or Ops Spec), the crew may be free to use different techniques to that employed by the airlines. The point I was making is that the use of a CDA and a DA (=MDA+50) gives the best chance of completing the landing without 'using excessive bank and pitch angles or excessive rates of descent' (which is how I believe some of the regulations are worded).
The problem is that Private Operators don't usually need permission or approval to do anything, provided the aircraft and crew are properly certified and equipped.
Anyhoo, I think we agree on the fundamentals!
Regards,
Eck
I think we're talking about two things here:
what an Approving Authority might authorise; and
how a crew might interpret an approach chart.
Capn Bloggs made the point that a CDA followed by a level flight segment was not precluded, and I agreed. I then tried to make the point that although allowed, this manouevre would result in a possible steep/deep approach and landing.
In the private world (not under an AOC or Ops Spec), the crew may be free to use different techniques to that employed by the airlines. The point I was making is that the use of a CDA and a DA (=MDA+50) gives the best chance of completing the landing without 'using excessive bank and pitch angles or excessive rates of descent' (which is how I believe some of the regulations are worded).
No approving authority in its right mind would permit treating MDA as a DA and also approve a level off.
Anyhoo, I think we agree on the fundamentals!
Regards,
Eck
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exhard:
Indeed we do.
In FAA-dom, coverting the MDA to DA has to be on the chart, and is limited to commercial operators that get an FAA blessing.
Part 91 operators cannot obtain this approval, but there is nothing stopping them descending to MDA then trucking on level to the MAP. In a Cessna 182 at KLAX, that would probably work.
Anyhoo, I think we agree on the fundamentals!
In FAA-dom, coverting the MDA to DA has to be on the chart, and is limited to commercial operators that get an FAA blessing.
Part 91 operators cannot obtain this approval, but there is nothing stopping them descending to MDA then trucking on level to the MAP. In a Cessna 182 at KLAX, that would probably work.
Aterpster
As this issue has been discussed many times at recurrent (Global Express), is there an express prohibition on FAR 91 operators using the MDA as DA, IAW the note on the Jepp chart? Where is it?
GF
As this issue has been discussed many times at recurrent (Global Express), is there an express prohibition on FAR 91 operators using the MDA as DA, IAW the note on the Jepp chart? Where is it?
GF
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galaxy flyer:
Most FAA NPAs that have straight-in minimums have the advisory vertical path coded into the procedure's database, RNAV or not (exluding LOC or LDA). Thus, any operator with the requisite avionics can use that vertical path. But, without the stated authorization they cannot treat MDA as DA.
It is a very fine line, indeed.
The requirements for the authorization are contained in some obscure advisory circular and, I believe, is limited to qualified commercial operators.
So, you might ask, why doesn't this IAP simply have a line of LNAV/VNAV minimums with a charted DA? Most likely because the runway's close-in obstacle environment did not pass muster for the FAA glide-path qualification surface (GQS). Also, in this case the descent angle of 3.14 degrees is beyond the limits for Approach Category D.
As this issue has been discussed many times at recurrent (Global Express), is there an express prohibition on FAR 91 operators using the MDA as DA, IAW the note on the Jepp chart? Where is it?
It is a very fine line, indeed.
The requirements for the authorization are contained in some obscure advisory circular and, I believe, is limited to qualified commercial operators.
So, you might ask, why doesn't this IAP simply have a line of LNAV/VNAV minimums with a charted DA? Most likely because the runway's close-in obstacle environment did not pass muster for the FAA glide-path qualification surface (GQS). Also, in this case the descent angle of 3.14 degrees is beyond the limits for Approach Category D.