Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

NPAs flown using CDFA - deriving DA/H

Rotorheads A haven for helicopter professionals to discuss the things that affect them

NPAs flown using CDFA - deriving DA/H

Old 26th Apr 2020, 22:19
  #1 (permalink)  
Thread Starter
 
Join Date: Oct 2004
Location: HLS map - http://goo.gl/maps/3ymt
Posts: 384
NPAs flown using CDFA - deriving DA/H

Are any helicopter operators under EASA required to add an increment to the MDA/H for an NPA procedure in order to derive a DA/H for a CDFA operation?

AMC3 CAT.OP.MPA.110 doesn't require an add-on to be applied.

AMC1 CAT.OP.MPA.115(a)(5) which applies only to aeroplanes requires operators to establish an add-on to be applied and specified in the OM.

ICAO Doc 9365 doesn't require an add on to be applied unless the state/authority choose to require it.

NPA 2018-06C 'All Weather Operations' suggests this requirement will also be removed for fixed wing if the proposed amendments of GM5 CAT.OP.MPA.110 are adopted "... the safety of the use of MDH as DH in CDFA operations has been verified by at least two independent analyses concluding that CDFA using MDH as DH without any add-on is safer than the traditional step-down and level-flight NPA operation..."

As it stands CDFA is not currently mandated by EASA for helicopters conducting NPAs, but are any pilots required by their OM to add-on an increment when deriving a DA/H? Or when using a Jepp plate where there is no factored margin in the NPA DA/MDA?

Thanks in advance
​​​​​​​

Last edited by Aucky; 26th Apr 2020 at 22:37.
Aucky is offline  
Old 26th Apr 2020, 23:00
  #2 (permalink)  
 
Join Date: Apr 2005
Location: England
Posts: 348
My op doesn't as they leave it to the crews to decide but as long as you don't go below MDA/H (when doing CDFA) during the go around then you're legal unlike a PA where action (movement of controls/AP) has to be made at DA/H and drifting below is not a problem. I generally at 50 ft for a NPA CDFA.
jeepys is offline  
Old 26th Apr 2020, 23:04
  #3 (permalink)  
 
Join Date: Aug 2001
Location: Shropshire
Posts: 611
Originally Posted by Aucky View Post
Are any helicopter operators under EASA required to add an increment to the MDA/H for an NPA procedure in order to derive a DA/H for a CDFA operation?

AMC3 CAT.OP.MPA.110 doesn't require an add-on to be applied.

AMC1 CAT.OP.MPA.115(a)(5) which applies only to aeroplanes requires operators to establish an add-on to be applied and specified in the OM.

ICAO Doc 9365 doesn't require an add on to be applied unless the state/authority choose to require it.

NPA 2018-06C 'All Weather Operations' suggests this requirement will also be removed for fixed wing if the proposed amendments of GM5 CAT.OP.MPA.110 are adopted "... the safety of the use of MDH as DH in CDFA operations has been verified by at least two independent analyses concluding that CDFA using MDH as DH without any add-on is safer than the traditional step-down and level-flight NPA operation..."

As it stands CDFA is not currently mandated by EASA for helicopters conducting NPAs, but are any pilots required by their OM to add-on an increment when deriving a DA/H? Or when using a Jepp plate where there is no factored margin in the NPA DA/MDA?

Thanks in advance
​​​​​​​
Greetings Aucky
I have to confess I haven't seen the NPA but I'm aware of some helicopter operators that have instigated CDFA approaches without considering the requirement to re-calculate the OCA to provide a DH which protects the MDA.
Cheers
TeeS
TeeS is online now  
Old 26th Apr 2020, 23:33
  #4 (permalink)  
Thread Starter
 
Join Date: Oct 2004
Location: HLS map - http://goo.gl/maps/3ymt
Posts: 384
Interesting, in the both the replies so far it is accepted that you must protect the MDA/H associated with the NPA flown as a non-CDFA. Where is this stated?

When flying CDFA you are flying to a DA as per the annex 1 definitions:

(83) ‘non-precision approach (NPA) operation’ means an instrument approach with a minimum descent height (MDH), or DH when flying a CDFA technique, not lower than 250 ft and an RVR/CMV of not less than 750 m for aeroplanes and 600 m for helicopters;

By my interpretation of AMC3 CAT.OP.MPA.110 the minimum available DA/H for a CDFA approach may be limited by the same OCH as that which determines the minimum available MDA/H for non-CDFA i.e. the two figures could be the same. However, when used as a DA you would only be required to initiate the GA at that altitude and some transient dip beneath would be permissible.

Admittedly, in the vast majority of cases the extra 20-50ft will not be the deciding factor on whether you get visual references or not so it becomes academic, it’s more a question of what should be taught from a standardisation perspective, and what is actually compliant.

I’m happy to be proven otherwise but I think adding a margin to the MDA when deriving a DA for CDFA operations may be a fixed wing carry over as that is where CDFA has come from, and they are required to add on a margin under AMC1 CAT.OP.MPA.115. I can’t see anything which prohibits you from dipping beneath the OCH as part of the go around manoeuvre when flying CDFA to a DA. I’m happy to be corrected if someone can point me to something which states otherwise.

Last edited by Aucky; 26th Apr 2020 at 23:54.
Aucky is offline  
Old 27th Apr 2020, 06:09
  #5 (permalink)  
 
Join Date: Sep 2005
Location: Montreal
Posts: 624
Are you looking for a legal loophole to “dip” below MDA, just because you can do it on a PA? Or do you want to look at it practically from an approach designer’s perspective and the application of approach design criteria? The “dip below” is part of the design consideration in a PA and is protected. Not so for a CFDA flown to an MDA. Helicopter/airplane makes no practical difference. If the regulators decide all non-precision approaches shall be designed in a way that the “dip below” when flown CFDA will be protected, then designers will simply raise the MDA ((now a DA) the appropriate amount. Which would you rather have?
malabo is offline  
Old 27th Apr 2020, 08:37
  #6 (permalink)  
 
Join Date: Aug 2001
Location: Shropshire
Posts: 611
Hi Aucky
It's covered in Doc 8168 Volume 1, Part II - Section 5, Chapter 1

1.8.2.3 If the visual references required to land have not been acquired when the aircraft is approaching the MDA/H, the vertical (climbing) portion of the missed approach shall be initiated at an altitude above the minimum descent altitude/height (MDA/H) sufficient to prevent the aircraft from descending through the MDA/H. At no time is the aircraft to be flown in level flight at or near the MDA/H. Any turns on the missed approach shall not begin until the aircraft reaches the missed approach point (MAPt). Likewise, if the aircraft reaches the MAPt before descending to near the MDA/H, the missed approach shall be initiated at the MAPt.

1.8.2.4 An increment for the MDA/H may be prescribed by the operator to determine the altitude/height at which the vertical portion of the missed approach shall be initiated in order to prevent descent below the MDA/H. In such cases, there is no need to increase the RVR or visibility requirements for the approach. The RVR and/or visibility published for the original MDA/H should be used.


Cheers
TeeS
TeeS is online now  
Old 27th Apr 2020, 09:32
  #7 (permalink)  
 
Join Date: May 2006
Location: UK
Posts: 171
If one follows the notional glidepath that the designer envisaged when drawing that particular 2D approach (i.e. by following the altitudes v distance to go as depicted on the plate), one should arrive at DA (MDA) before the MAPt. In this case, initiating a MAP at DA hence "ducking under" DA (MDA) as the aircraft transitions from a descent to a climb, would probably permit adequate terrain separation (OEI) during the missed approach segment.

If, on the other hand, one was less than diligent in following the notional glidepath, and arrival at DA (MDA) coincided with the MAPt, it is clear that one would now be following a path on the missed approach segment that was below the designed path. Terrain separation is now not assured. This therefore would have to be taken into account when deciding when to initiate the missed approach procedure i.e. earlier than DA (MDA).

There has been no redesign of the 2D approach in order to derive a DA. The procedure design is based on MDA. For example, the OCA for the NDB/DME RWY 27 approach at EGBJ was 600 ft in July 2005. The DA (MDA) today is also 600 ft.

I would have thought it unwise to brief different minima depending upon how close to the MAPt one may end up at DA (MDA), hence our company DA is published CDFA DA + 30 ft.
Mustapha Cuppa is offline  
Old 27th Apr 2020, 09:53
  #8 (permalink)  
 
Join Date: Aug 2001
Location: Shropshire
Posts: 611
Hi Mustapha
The limiting obstacle could be before or after the MAPt so 'ducking under' earlier rather than later is not in any way a safer action. Also, the procedure designer does not take one engine inoperative performance into account, that is up to you, as the operator, to consider.
Cheers
TeeS
TeeS is online now  
Old 27th Apr 2020, 10:55
  #9 (permalink)  
Thread Starter
 
Join Date: Oct 2004
Location: HLS map - http://goo.gl/maps/3ymt
Posts: 384
Originally Posted by TeeS View Post
Hi Aucky
It's covered in Doc 8168 Volume 1, Part II - Section 5, Chapter 1

1.8.2.3 If the visual references required to land have not been acquired when the aircraft is approaching the MDA/H, the vertical (climbing) portion of the missed approach shall be initiated at an altitude above the minimum descent altitude/height (MDA/H) sufficient to prevent the aircraft from descending through the MDA/H. At no time is the aircraft to be flown in level flight at or near the MDA/H. Any turns on the missed approach shall not begin until the aircraft reaches the missed approach point (MAPt). Likewise, if the aircraft reaches the MAPt before descending to near the MDA/H, the missed approach shall be initiated at the MAPt.

1.8.2.4 An increment for the MDA/H may be prescribed by the operator to determine the altitude/height at which the vertical portion of the missed approach shall be initiated in order to prevent descent below the MDA/H. In such cases, there is no need to increase the RVR or visibility requirements for the approach. The RVR and/or visibility published for the original MDA/H should be used.


Cheers
TeeS
Thanks TeeS - this is exactly what I was looking for, an unambiguous statement on the issue.

I have also just spotted that ICAO Doc 9365 states in section 3.4.4 'The missed approach following a CDFA operation must be initiated so that the aircraft does not descend below the MDA/H or OCH...' I had missed this section.

Thanks for your input
Aucky is offline  
Old 27th Apr 2020, 11:11
  #10 (permalink)  
 
Join Date: Aug 2001
Location: Shropshire
Posts: 611
Glad to help Aucky
TeeS is online now  
Old 27th Apr 2020, 12:35
  #11 (permalink)  
Thread Starter
 
Join Date: Oct 2004
Location: HLS map - http://goo.gl/maps/3ymt
Posts: 384
On a Jepp plate, when an approach is charted as CDFA with a 'DA/MDA(H)' the explanatory information on Aerodrome Operating Minimums says:
"For non-precision approach minimums based on CDFA, the descent label is shown as DA/MDA(H). This DA/MDA(H) value does not include any add-on to compensate for height-loss. If the State requires or suggests a specific height loss, a note will be added to indicate this situation.

A DA(H) is shown on non-precision approaches only if published as such on State-provided procedure source. In this case it is assumed that the State of the Aerodrome has incorporated a height loss value.

An MDA(H) is shown on all non-CDFA non-precision approaches, or if the State published an MDA(H) value on procedure source."
In the case of EASA (EGBJ NDB27 beneath) there is no such note, presumably because EASA don't 'specify or suggest a specific height loss'- it could easily be interpreted that no additional factor is required. The EASA regulations (AMC3 CAT.OP.MPA.110) allow the minimum CDFA DA to be at the OCH which would not protect against descent beneath the MDA unless you have 0ft height loss. It seems odd that following the standards set in ICAO Docs 8168 / 9365 they wouldn't add a line to say that when determining a DH for a CDFA approach height loss shall be factored to prevent descent beneath the published MDA?

To reiterate - I'm not trying to chip away at minimums and will happily add a height loss factor when determining a DA from an MDA - it seems entirely logical, it was more a question of how the DA is to be applied as read off a Jepp plate, to remain compliant with EASA regs.

Aucky is offline  
Old 27th Apr 2020, 14:18
  #12 (permalink)  
 
Join Date: Aug 2001
Location: Shropshire
Posts: 611
Aucky, it would be interesting to know why Jepperson add 'CDFA' and 'DA' to the plate when they say "A DA(H) is shown on non-precision approaches only if published as such on State-provided procedure source. In this case it is assumed that the State of the Aerodrome has incorporated a height loss value." as there is no mention of these, that I can see, in the AIP.
Cheers
TeeS
TeeS is online now  
Old 27th Apr 2020, 15:41
  #13 (permalink)  
 
Join Date: Jun 2003
Location: Omnipresent
Posts: 397
Slight tangent but I was recently informed of an ATO enforcing CDFA as an EASA requirement. Is this correct as it appears not to be from comments above. Can anyone provide exact wording?
Hedski is offline  
Old 27th Apr 2020, 16:19
  #14 (permalink)  
 
Join Date: Aug 2001
Location: Shropshire
Posts: 611
Hi Hedski
CAT.OP.MPA.115 Approach flight technique - aeroplanes
States that CDFA technique shall be used for all non-precision approaches (with some caveats); however, this only applies to commercial air transport in aeroplanes. I have never come across any similar requirement for helicopters or non-CAT aeroplanes. It may be that the ATO saw the above sentence but missed the paragraph heading.
Hope that helps.
TeeS
TeeS is online now  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.