Determination of DA(H)
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I tend to agree with 411 on this one!
For some time I have been wondering why we are being encouraged to use the CDA approach method simply because we now have the kit to do it accuartely. It seemed to me early on that such an approach, when likely conducted to minimums, gives little time for crews to look out and have any chance of getting the required visual cues, especially if MDA(H) is likely to coincide with what will (in effect be) a MAP?
Provided that one adheres strictly to the appropriate step down levels, what is wrong with aiming the descent to conclude at a distance that permits level off at the MDA(H), followed by level flight of a short duration?
Provided one doesn't bust it, the little extra time at the minimum permitted level is likely to give one a better chance of making a successful approach if the conditions permit.
For some time I have been wondering why we are being encouraged to use the CDA approach method simply because we now have the kit to do it accuartely. It seemed to me early on that such an approach, when likely conducted to minimums, gives little time for crews to look out and have any chance of getting the required visual cues, especially if MDA(H) is likely to coincide with what will (in effect be) a MAP?
Provided that one adheres strictly to the appropriate step down levels, what is wrong with aiming the descent to conclude at a distance that permits level off at the MDA(H), followed by level flight of a short duration?
Provided one doesn't bust it, the little extra time at the minimum permitted level is likely to give one a better chance of making a successful approach if the conditions permit.
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To BOAC
... read all text again
The nature of the minima’s, MDA(H) or DA(H):
Part 1 - minimum is MDA(H) - CDFA or non CDFA
The MDA(H) being a minimum descent altitude, no altitude loss below the MDA(H) is allowed during the approach and go-around; this implies to either:
− Level-off at the MDA(H) - step-down / dive-and-drive technique - until visual references are acquired:
− Initiate the go-around above the MDA(H) - constant descent-angle technique - if no visual references are acquired, in order not to “duck under” the MDA(H).
Part 2 - minimum is DA(H) - only CDFA
This is obviously not required when the applicable minima is a DA(H), which is a decision altitude; if no visual references are acquired when reaching the DA(H), a go-around must be initiated at DA(H)
... and more info from JAA
Issues related to DA/H and MDA/H
The application of the CDFA technique requires all NPA operations, to be flown with a decision altitude/height (DA/H). When determining the applicable DA/H, the operator must take account of the missed approach point (MAPt) and the minimum descent altitude/height (MDA/H). While it is quite clear that a missed approach must be initiated not later than at the MAPt, the question of MDA/H is a different matter. Quite a few operators use MDA/H as the DA/H with no height add-on; in fact this is the case with a majority of the largest European operators. This modus operandi has
raised concern that the unavoidable height loss below the MDA/H during a go-around might introduce a safety risk, even if the height loss can be minimised by the use of appropriate operational procedures (call-outs, high degree of on-speed/on-path discipline, training). In order to evaluate the safety of the use of MDA/H as DA/H, the AWOSG has compared the obstacle protection for this type of approach with the obstacle protection for ‘traditionally’ flown non-precision approaches as well as with the protection for approaches with vertical guidance (APV) using the criteria contained within ICAO PANS OPS. The AWOSG is convinced that using the MDA/H as a DA/H offers adequate obstacle protection. Another comparison between the CDFA technique and the ‘traditionally’ flown non-precision approaches indicates that the latter involve several safety traps, such as:
- Early descent with a prolonged flight close to obstacles;
- Multiple step-downs possibly inside the FAF;
- An approach which is, by definition, destabilised;
- Temptation to make a late and steep descent from MDA/H towards the threshold;
-Risk of descending early from the MDA/H;
While there are no records of accidents related to the use of the CDFA technique during approach operations, there are several accidents attributable to the risks listed above.
The matter of using the MDA/H as a DA/H is progressing in the ICAO OCP and OPSP. Until there exists a final result of the work in ICAO, it must be left to the discretion of each Authority to make decisions on the matter. Since the benefits of the CDFA technique are generally acknowledged, the decision is typically whether to require an add-on to the MDA/H to ensure that the height loss does not lead to flight below the related MDA/H during a go-around, based on formal or other reasons. It is not the intention of this NPA to imply that an add-on to MDA/H must be required, but rather an acknowledgement that it is an option. In order to facilitate the decision-making process, the evaluations referred to above can be made available in the form of Power Point slides and working papers. In addition, a short paper by Mr Theo van de Ven (KLM) outlining the safety arguments in favour of using MDA/H as a DA/H is attached at the end of this Explanatory Note (See Attachment A).
At the latest meeting of the ICAO OCP (WG of the whole in Singapore in November 2006, it was recognised that the use of DH in connection with the CDFA technique, could be acceptable from an obstacle clearance point of view and that future work should be referred to the ICAO OPSP, The CDFA uses a DA(H). The DA(H) figure is derived from the OCA(H) for the associated procedure plus any buffer decided by the operator or the authority. MDA(H) is the lowest altitude (height) for the level portion of an approach flown using the traditional dive-and-drive technique, not the CDFA technique. Use of MDA(H) would undermine the philosophy of the CDFA. The AWOSG has undertaken several studies which conclude that the use of MDA as DA is safe (attachment A to this document, WP 9 to OCP WGHL, March 2006 by Mr T v d Ven, NLR-report CR-2000-451 by Mr H.W. Kleingeld and in “A statistical look at the safety of CANPA procedures”, 11 June, 2002 by Capt J Meijer, RLD). If an operator or an authority thinks that mitigation is needed anyway, this can be done by means of a buffer and/or procedures and training. NPA OPS 41 does not prescribe how to decide, but leaves this to the NAAs. Use of the CDFA technique is considered as a significant safety improvement. (Ref to ALARP). It is also important to note that the NPA does not suggest anything that is not already in widespread use by European operators.
... read all text again
The nature of the minima’s, MDA(H) or DA(H):
Part 1 - minimum is MDA(H) - CDFA or non CDFA
The MDA(H) being a minimum descent altitude, no altitude loss below the MDA(H) is allowed during the approach and go-around; this implies to either:
− Level-off at the MDA(H) - step-down / dive-and-drive technique - until visual references are acquired:
− Initiate the go-around above the MDA(H) - constant descent-angle technique - if no visual references are acquired, in order not to “duck under” the MDA(H).
Part 2 - minimum is DA(H) - only CDFA
This is obviously not required when the applicable minima is a DA(H), which is a decision altitude; if no visual references are acquired when reaching the DA(H), a go-around must be initiated at DA(H)
... and more info from JAA
Issues related to DA/H and MDA/H
The application of the CDFA technique requires all NPA operations, to be flown with a decision altitude/height (DA/H). When determining the applicable DA/H, the operator must take account of the missed approach point (MAPt) and the minimum descent altitude/height (MDA/H). While it is quite clear that a missed approach must be initiated not later than at the MAPt, the question of MDA/H is a different matter. Quite a few operators use MDA/H as the DA/H with no height add-on; in fact this is the case with a majority of the largest European operators. This modus operandi has
raised concern that the unavoidable height loss below the MDA/H during a go-around might introduce a safety risk, even if the height loss can be minimised by the use of appropriate operational procedures (call-outs, high degree of on-speed/on-path discipline, training). In order to evaluate the safety of the use of MDA/H as DA/H, the AWOSG has compared the obstacle protection for this type of approach with the obstacle protection for ‘traditionally’ flown non-precision approaches as well as with the protection for approaches with vertical guidance (APV) using the criteria contained within ICAO PANS OPS. The AWOSG is convinced that using the MDA/H as a DA/H offers adequate obstacle protection. Another comparison between the CDFA technique and the ‘traditionally’ flown non-precision approaches indicates that the latter involve several safety traps, such as:
- Early descent with a prolonged flight close to obstacles;
- Multiple step-downs possibly inside the FAF;
- An approach which is, by definition, destabilised;
- Temptation to make a late and steep descent from MDA/H towards the threshold;
-Risk of descending early from the MDA/H;
While there are no records of accidents related to the use of the CDFA technique during approach operations, there are several accidents attributable to the risks listed above.
The matter of using the MDA/H as a DA/H is progressing in the ICAO OCP and OPSP. Until there exists a final result of the work in ICAO, it must be left to the discretion of each Authority to make decisions on the matter. Since the benefits of the CDFA technique are generally acknowledged, the decision is typically whether to require an add-on to the MDA/H to ensure that the height loss does not lead to flight below the related MDA/H during a go-around, based on formal or other reasons. It is not the intention of this NPA to imply that an add-on to MDA/H must be required, but rather an acknowledgement that it is an option. In order to facilitate the decision-making process, the evaluations referred to above can be made available in the form of Power Point slides and working papers. In addition, a short paper by Mr Theo van de Ven (KLM) outlining the safety arguments in favour of using MDA/H as a DA/H is attached at the end of this Explanatory Note (See Attachment A).
At the latest meeting of the ICAO OCP (WG of the whole in Singapore in November 2006, it was recognised that the use of DH in connection with the CDFA technique, could be acceptable from an obstacle clearance point of view and that future work should be referred to the ICAO OPSP, The CDFA uses a DA(H). The DA(H) figure is derived from the OCA(H) for the associated procedure plus any buffer decided by the operator or the authority. MDA(H) is the lowest altitude (height) for the level portion of an approach flown using the traditional dive-and-drive technique, not the CDFA technique. Use of MDA(H) would undermine the philosophy of the CDFA. The AWOSG has undertaken several studies which conclude that the use of MDA as DA is safe (attachment A to this document, WP 9 to OCP WGHL, March 2006 by Mr T v d Ven, NLR-report CR-2000-451 by Mr H.W. Kleingeld and in “A statistical look at the safety of CANPA procedures”, 11 June, 2002 by Capt J Meijer, RLD). If an operator or an authority thinks that mitigation is needed anyway, this can be done by means of a buffer and/or procedures and training. NPA OPS 41 does not prescribe how to decide, but leaves this to the NAAs. Use of the CDFA technique is considered as a significant safety improvement. (Ref to ALARP). It is also important to note that the NPA does not suggest anything that is not already in widespread use by European operators.
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When you fly NPA as CDFA, you may use MDA/H as the DA/H with no height add-on.
"Part 1 - minimum is MDA(H) - CDFA or non CDFA
The MDA(H) being a minimum descent altitude, no altitude loss below the MDA(H) is allowed during the approach and go-around; this implies to either:
− Level-off at the MDA(H) - step-down / dive-and-drive technique - until visual references are acquired:
− Initiate the go-around above the MDA(H) - constant descent-angle technique - if no visual references are acquired, in order not to “duck under” the MDA(H).
Part 2 - minimum is DA(H) - only CDFA
This is obviously not required when the applicable minima is a DA(H), which is a decision altitude; if no visual references are acquired when reaching the DA(H), a go-around must be initiated at DA(H)"
and your note from JAA itself says "The matter of using the MDA/H as a DA/H is progressing in the ICAO OCP and OPSP. Until there exists a final result of the work in ICAO, it must be left to the discretion of each Authority to make decisions on the matter." so I felt your initial words (as quoted at the top) could be misleading. As always, stick to what your company tells you to do.
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BOAC,
How do you determine (by looking at the plate) whether a procedure is a true DA(H) kind, approved by the authority, or just a revised chart format (jepessen says they will only indicate DA(H), even if the original procedure uses MDA(H), and they make no additions whatsoever).
I believe the safest option, until it all clears out, is to add 50ft to ALL NPAs indicating a DA(H) on the plate.
Spiros Chazapis
Athens, Greece
PS Thanks for all the replies guys, they are very appreciated
How do you determine (by looking at the plate) whether a procedure is a true DA(H) kind, approved by the authority, or just a revised chart format (jepessen says they will only indicate DA(H), even if the original procedure uses MDA(H), and they make no additions whatsoever).
I believe the safest option, until it all clears out, is to add 50ft to ALL NPAs indicating a DA(H) on the plate.
Spiros Chazapis
Athens, Greece
PS Thanks for all the replies guys, they are very appreciated
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BOAC,
Hm, I don't think this is very conclusive. First of all, the link points to a "chart clinic" article that is quite old (1999-ish). A lot have changed since.
Then, I believe that it doesn't really apply outside FAA-landia. For instance (extract from this document):
"And the big “IF.” The MDA may be used as a
DA only if there has been a visual segment
obstacle assessment made for the straight-in
landing runway. The FAA has stated that
there has been an obstacle assessment when
the runway has a VASI or PAPI as a visual
guidance system indicator, an electronic
glideslope, or an RNAV approach published
with a decision altitude.
Since an obstacle assessment has been made,
the FAA has authorized the DA since it is
assumed that a momentary descent will be
made below the DA during the execution of
a missed approach.
When there is a VDP, it should be at the point
where the descent angle meets the MDA."
So, no addition to the MDA(H) if the runway has PAPI lights? Also, the point about "momentary descent etc" is clearly in violation of PANS-OPS.
I found a reference to the 50 ft, but not on a regulatory document - it's in an FSF ALAR briefing note (7.2, page 5) that states
"Approaching the MDA(H)
At an altitude corresponding to the MDA(H) plus 1/10 the rate of descent (typically MDA[H] plus 50 to 100 feet), anticipate a go-around decision to avoid descent below the MDA[H], as required by applicable regulations".
I still believe that the safest option on CDFA NPAs is to add 50 feet to all procedures, until there is a positive way to identify DA(H) procedures that originate from the authority and not the charting company...
Spiros Chazapis
Athens, Greece
Hm, I don't think this is very conclusive. First of all, the link points to a "chart clinic" article that is quite old (1999-ish). A lot have changed since.
Then, I believe that it doesn't really apply outside FAA-landia. For instance (extract from this document):
"And the big “IF.” The MDA may be used as a
DA only if there has been a visual segment
obstacle assessment made for the straight-in
landing runway. The FAA has stated that
there has been an obstacle assessment when
the runway has a VASI or PAPI as a visual
guidance system indicator, an electronic
glideslope, or an RNAV approach published
with a decision altitude.
Since an obstacle assessment has been made,
the FAA has authorized the DA since it is
assumed that a momentary descent will be
made below the DA during the execution of
a missed approach.
When there is a VDP, it should be at the point
where the descent angle meets the MDA."
So, no addition to the MDA(H) if the runway has PAPI lights? Also, the point about "momentary descent etc" is clearly in violation of PANS-OPS.
I found a reference to the 50 ft, but not on a regulatory document - it's in an FSF ALAR briefing note (7.2, page 5) that states
"Approaching the MDA(H)
At an altitude corresponding to the MDA(H) plus 1/10 the rate of descent (typically MDA[H] plus 50 to 100 feet), anticipate a go-around decision to avoid descent below the MDA[H], as required by applicable regulations".
I still believe that the safest option on CDFA NPAs is to add 50 feet to all procedures, until there is a positive way to identify DA(H) procedures that originate from the authority and not the charting company...
Spiros Chazapis
Athens, Greece
Last edited by shazapis; 30th May 2010 at 19:41.
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Shaza - the whole thing has been made unnecessarily complicated by the EU authorities. The safest thing for you is to "follow your company procedures" as they should have been approved by your regulatory authority. If those 'procedures' are not clear, ask for a ruling from your Training department. They should have issued you with guidance on how to apply the 'new' minima where they appear. If you cannot get an answer, adding 50 is safe, of course.
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Ok We've been here before. EUROCONTROL issued a Safety Reminder Message back in February:
EUROCONTROL - Safety Alerts Board
EUROCONTROL - Safety Alerts Board
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Thanks LLLK - I could not afford the time to locate that. It is not really much help - what do you do if your company has not adopted (or published) the 'new' procedure? I think elsewhere we were given an implementation date of July 2011? A whole year of fun for some.
"n Aircraft operators are invited to: § Note the issue above specifically with a review of the need to consider the requirement for an add-on factor to account for height loss at missed approach initiation."
Just a little Euro-Woolly!! but again refer to your company, Shaza. If in doubt, add!
"n Aircraft operators are invited to: § Note the issue above specifically with a review of the need to consider the requirement for an add-on factor to account for height loss at missed approach initiation."
Just a little Euro-Woolly!! but again refer to your company, Shaza. If in doubt, add!
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The problem as I see it is that many European operators have been flying stabilised approaches for years and have been following the PANS-OPS guidance that has been there since Pontius: The DA/DH is based upon the OCA/H with an additional margin 'based upon operational consideration of
– category of operation
– ground/airborne equipment characteristics
– aircraft performance
– meteorological conditions
– aerodrome characteristics
– terrain profile/radio altimeter
– pressure error/pressure altimeter
- etc.
And they usually came up with a figure in the region of 50ft - although some decided that no add-on was necessary.
EU-Ops tried to capture all this in the CDFA and RVR sections without much success. EASA is in the process of rewriting EU Ops as IR Ops but it could be some time before that sees the light of day. In the meantime, States have committed themselves to publishing RNP APCHs to LNAV/VNAV minima for all instrument runway ends by 2016 (or thereabouts). If you fly to LNAV/VNAV minima the problem goes away.
I have heard that at least one major European State has taken a similar view to the FAA - if the visual segment has been appropriately assessed for obstacles (it has to be done for RNP APCH to LNAV/VNAV) then MDA=DA. But then if there is an LNAV/VNAV approach published, why fly CDFA on a conventional NPA?
– category of operation
– ground/airborne equipment characteristics
– aircraft performance
– meteorological conditions
– aerodrome characteristics
– terrain profile/radio altimeter
– pressure error/pressure altimeter
- etc.
And they usually came up with a figure in the region of 50ft - although some decided that no add-on was necessary.
EU-Ops tried to capture all this in the CDFA and RVR sections without much success. EASA is in the process of rewriting EU Ops as IR Ops but it could be some time before that sees the light of day. In the meantime, States have committed themselves to publishing RNP APCHs to LNAV/VNAV minima for all instrument runway ends by 2016 (or thereabouts). If you fly to LNAV/VNAV minima the problem goes away.
I have heard that at least one major European State has taken a similar view to the FAA - if the visual segment has been appropriately assessed for obstacles (it has to be done for RNP APCH to LNAV/VNAV) then MDA=DA. But then if there is an LNAV/VNAV approach published, why fly CDFA on a conventional NPA?
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BOAC,
"if those 'procedures' are not clear, ask for a ruling from your Training department."
... that would be me I guess
I am the Stand/Eval officer (something like a flight standards officer of an airline) of a military transport squadron in charge of SOP development. We had a sudden wake up call when CDFA procedures plates for LGSA landed on our doorstep, and I now have to figure out a way out of this mess. Needless to say, our previous SOP manual did not include any specific procedural guidance for CDFA NPAs (just a generic statement that it is the preferred way to do it), although we have been aplying stabilized approach criteria for quite some time now.
To make things more complex, our planes have been recently retrofitted with modern avionics, adding to the complexity of developing standard ops (the steam gauge suite was way simpler...).
Ofcourse we are also talking to other squadrons that share the same problems (military operators are used to getting very little guidance from manufacturers on these issues - thus the delay in implementing procedural changes...)
rgrds
Spiros Chazapis
Athens, Greece
"if those 'procedures' are not clear, ask for a ruling from your Training department."
... that would be me I guess
I am the Stand/Eval officer (something like a flight standards officer of an airline) of a military transport squadron in charge of SOP development. We had a sudden wake up call when CDFA procedures plates for LGSA landed on our doorstep, and I now have to figure out a way out of this mess. Needless to say, our previous SOP manual did not include any specific procedural guidance for CDFA NPAs (just a generic statement that it is the preferred way to do it), although we have been aplying stabilized approach criteria for quite some time now.
To make things more complex, our planes have been recently retrofitted with modern avionics, adding to the complexity of developing standard ops (the steam gauge suite was way simpler...).
Ofcourse we are also talking to other squadrons that share the same problems (military operators are used to getting very little guidance from manufacturers on these issues - thus the delay in implementing procedural changes...)
rgrds
Spiros Chazapis
Athens, Greece
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Aha! I sympathise! Not sure who produces your plates? In the absence of an edict from 'higher command', I think what I would have done in my days as a RAF Command IRE would simply be to issue an instruction that where the plate is annotated DA/H, use it as such, and where it says MDA/H add 50'. If you have that authority, I'm sure that would keep you safe until it is all resolved - and if anyone from command 'bleats' about it say "Well, where were you when I needed you?"
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Sounds like an argument for check airman, people who write SOPS manuals, and chief pilots hoping that the 500 hour FO doesn't bust down to low..
In the real world...50 ft is only there as a place to start leveling out when you don't see the glow, gives you time to push some throttles forward, clean things up....
I don't think anyone really cares if you go 25 below DHA/MDA on a real flight...this whole thread is about check rides and sim sessions....
In the real world...50 ft is only there as a place to start leveling out when you don't see the glow, gives you time to push some throttles forward, clean things up....
I don't think anyone really cares if you go 25 below DHA/MDA on a real flight...this whole thread is about check rides and sim sessions....
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BOAC hi,
We have a MAIP (Military - AIP) that includes only Greek airports. For other airports we use DoD FLIPS, CENOR, UK military FLIPS (RAF No 1 AIDU - produced) and of course Jepessen. Our SOPs are based on Jepessen charts (to describe the standard approach briefing for instance).
Naturally, on issues like this one, the opinion of the operator (the squadron) is very important to HQ - they will almost always approve the squadron's point of view on procedural matters (as long as it is properly justified), so we want to make sure we get this right.
johns7022:
I see your point of view. Nevertheless, I believe that procedures have to be, amongst other things, in accordance with regulations. If a 50 ft requirement is deemed appropriate and is included in a regulatory document, this requirement has to be reflected in the SOPs. What can or may happen during line flights is a different (also very interesting) issue.
Anyway, this has been a very interesting discussion indeed - once more, thank you for all the replies, they are very appreciated.
Regards,
Spiros Chazapis
Athens, Greece
We have a MAIP (Military - AIP) that includes only Greek airports. For other airports we use DoD FLIPS, CENOR, UK military FLIPS (RAF No 1 AIDU - produced) and of course Jepessen. Our SOPs are based on Jepessen charts (to describe the standard approach briefing for instance).
Naturally, on issues like this one, the opinion of the operator (the squadron) is very important to HQ - they will almost always approve the squadron's point of view on procedural matters (as long as it is properly justified), so we want to make sure we get this right.
johns7022:
I see your point of view. Nevertheless, I believe that procedures have to be, amongst other things, in accordance with regulations. If a 50 ft requirement is deemed appropriate and is included in a regulatory document, this requirement has to be reflected in the SOPs. What can or may happen during line flights is a different (also very interesting) issue.
Anyway, this has been a very interesting discussion indeed - once more, thank you for all the replies, they are very appreciated.
Regards,
Spiros Chazapis
Athens, Greece
