MDA
Thread Starter
Join Date: Dec 1999
Posts: 115
Likes: 0
Received 0 Likes
on
0 Posts
MDA
Apologies if this has been discussed before.
Does anybody out there believe that it is permissible to go below MDA when not visual and conducting a missed approach from a NPA?
I am aware that many operators add an amount (around 50') to the published MDA and treat it as a DH. In this case the aircraft will not go below the actual MDA.
I am also aware of at least one operator that states in its ops manual that you can initiate the missed approach at MDA. This clearly results in the aircraft going below it.
Just to clarify this question relates only to a "traditional" NPA not a LNAV/VNAV approach with a DA published.
An authoritative reference showing the acceptability of this practice would be appreciated.
Does anybody out there believe that it is permissible to go below MDA when not visual and conducting a missed approach from a NPA?
I am aware that many operators add an amount (around 50') to the published MDA and treat it as a DH. In this case the aircraft will not go below the actual MDA.
I am also aware of at least one operator that states in its ops manual that you can initiate the missed approach at MDA. This clearly results in the aircraft going below it.
Just to clarify this question relates only to a "traditional" NPA not a LNAV/VNAV approach with a DA published.
An authoritative reference showing the acceptability of this practice would be appreciated.
Join Date: Jul 2007
Location: The Netherlands
Age: 40
Posts: 81
Likes: 0
Received 0 Likes
on
0 Posts
A traditional NPA (some of them still have that option) has a step down procedure. In this case you level off and continue to the MAP, where you decide to go around or not. In this case you would not loose ALT, so you won't go below your MDA. With these CDAs of nowadays it gives you the possibility to shoot a NPA faster, easier and with less noise. Only problem is, that you will not level of towards the MAP. When you initiate the go around you will indeed go below the MDA.
As it stands for MINIMUM DECENT ALT, you can not bust it unless you continue with the approach. The 50' is a safe buffer.
As it stands for MINIMUM DECENT ALT, you can not bust it unless you continue with the approach. The 50' is a safe buffer.
When you initiate the go around you will indeed go below the MDA.
If you procedures are such that you intend to fly level to the MAP you also should not descend below MDA without the required visual reference.
This has previously been extensively discussed on Pprune - suggest you do a search!
I have flown for airlines that didn't specify 50' addition for a constant descent approach.
The MDA is the MDA, and the tolerance specified was +100', and -0' ... it was left up to the pilot's skill to meet that tolerance, rather than specify any particular figure.
The MDA is the MDA, and the tolerance specified was +100', and -0' ... it was left up to the pilot's skill to meet that tolerance, rather than specify any particular figure.
Join Date: Oct 2002
Location: In my seat
Posts: 822
Likes: 0
Received 0 Likes
on
0 Posts
MDA on NPA's is slowly being replaced by DA at a lot of EASA member-state airports, sometimes resulting in slightly higher minima's.
In some cases, 50' makes the difference of becoming visual or doing a G/A. This is why I am not a fan of VNAV NPA approaches combined with an MDA in marginal weather. Use the V/S and put the MDA in the MCP. Keep slightly low in order to ensure level flight at the Decision Point. (Decision Point is the point where on a normal ILS, you would end up at minima considering a standard glide angle of 3°). If no contact, go around. (and NO there is NO requirement to fly level up to the MDA, this is a big misunderstanding by some collegues).
HOWEVER, and this I must emphasise: FOLLOW your COMPANY SOP. This is a personal note and in my present company VNAV NPA's are not done.
In some cases, 50' makes the difference of becoming visual or doing a G/A. This is why I am not a fan of VNAV NPA approaches combined with an MDA in marginal weather. Use the V/S and put the MDA in the MCP. Keep slightly low in order to ensure level flight at the Decision Point. (Decision Point is the point where on a normal ILS, you would end up at minima considering a standard glide angle of 3°). If no contact, go around. (and NO there is NO requirement to fly level up to the MDA, this is a big misunderstanding by some collegues).
HOWEVER, and this I must emphasise: FOLLOW your COMPANY SOP. This is a personal note and in my present company VNAV NPA's are not done.
Join Date: Oct 2007
Location: Hong Kong
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
No you can't
MDA means Minimum Descent Altitude. You cannot descend below this altitude unless adequate visual reference is achieved.
DA means Decision Altitude. This is the altitude that the decision is made to go around. You will descend slightly below this altitude in a go around.
In my company, when conducting a NPA there is an auto call-out of "Hundred above" when there is 100 feet to go to the MDA. We count to two seconds and if not visual, push the thrust levers forward and go around. From the call of "Hundred above" and two seconds thereafter, we ensure that at no time we descend below the MDA.
DA means Decision Altitude. This is the altitude that the decision is made to go around. You will descend slightly below this altitude in a go around.
In my company, when conducting a NPA there is an auto call-out of "Hundred above" when there is 100 feet to go to the MDA. We count to two seconds and if not visual, push the thrust levers forward and go around. From the call of "Hundred above" and two seconds thereafter, we ensure that at no time we descend below the MDA.
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
Keep slightly low in order to ensure level flight at the Decision Point. (Decision Point is the point where on a normal ILS, you would end up at minima considering a standard glide angle of 3°). If no contact, go around. (and NO there is NO requirement to fly level up to the MDA,
Join Date: Mar 2011
Location: engineer at large
Posts: 1,409
Likes: 0
Received 0 Likes
on
0 Posts
On charts, the movement is towards MDA for non-precision approaches, DA for precision approaches.
You have to add your momentary descent to the MDA to get your DA.
No you do not, never....
You have to add your momentary descent to the MDA to get your DA.
When you initiate the go around you will indeed go below the MDA.
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 4,497
Likes: 0
Received 0 Likes
on
0 Posts
Actually MDA is the "old fashioned" way and there is a movement towards DA for all approaches including NPAs. As far as i know it is even a requirement in EASA-land to convert to DA for NPAs.
Join Date: Mar 2011
Location: engineer at large
Posts: 1,409
Likes: 0
Received 0 Likes
on
0 Posts
If you note the Jeppeson charts, many have just recently been converted to an MDA. ICAO RNP 9905 uses MDA, while FAA 8260.52 uses a DA.
It is not due to precision, but multi-variant performance considerations. With RNP baro-vnav, the approach can be anywhere from 2.5 to 3.1 degrees on a 3 degree approach, hence an MDA...
RNP transition to GBAS final, uses of course, a DA.
It is not due to precision, but multi-variant performance considerations. With RNP baro-vnav, the approach can be anywhere from 2.5 to 3.1 degrees on a 3 degree approach, hence an MDA...
RNP transition to GBAS final, uses of course, a DA.
Last edited by FlightPathOBN; 26th Jun 2011 at 18:44.
Join Date: Jan 2006
Location: Airplane
Posts: 133
Likes: 0
Received 0 Likes
on
0 Posts
When conducting approach other than ILS, there is no need to add 50ft to MDA as long as a CDA is being used. This is relatively new proc at my current company. We were doing it 15 years ago at my previous company.
7
7
Join Date: Mar 2011
Location: engineer at large
Posts: 1,409
Likes: 0
Received 0 Likes
on
0 Posts
That is completely wrong. You can not go below the MDA on a missed approach.
SKYbrary - Minimum Descent Altitude/Height
SKYbrary - Minimum Descent Altitude/Height
