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Home > Archive > Flight simulator > March 2006 > MDA and DH
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| stevej 2006-03-24, 2:02 pm |
| Hi Guys
Doe's anyone know the difference between MDA and DH ? - I have the Virgin
B747 DVD EGLL-KSFO and on approach the pilots have set MDA 210 and DH 200 on
the PFD, why both ?
Also, does the chart MDA or DH override the standard ILS minima's ?
Cheers
Steve
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| Beech45Whiskey 2006-03-24, 2:02 pm |
| stevej <nopam@nospam.net> wrote:
quote:
> Doe's anyone know the difference between MDA and DH ? -
MDA stands for minimum descent altitude and DH stands for decision height.
MDA is used for non-precision approaches, such as VOR, GPS (non-WAAS),
localizer, and NDB. Normally, these approaches have "step-down" altitudes
and the last and lowest step-down altitude is called the MDA. You would
fly along the MDA until picking up the visual to the airport or reaching
the missed approach point (MAP) along the approach, whatever occurs first.
You will find a DH on precision approaches (approaches that provide runway
centerline and descent guidance to the runway) like ILS, PARs
(radar-controlled precision approaches), and GPS-WAAS approaches.
Think of a DH as the moment you arrive at the decision height while coming
down the glideslope, you must make the decision based on visibility whether
to continue to land or to start your missed approach.
quote:
> I have the Virgin
> B747 DVD EGLL-KSFO and on approach the pilots have set MDA 210 and DH 200 on
> the PFD, why both ?
MDA for non-precision approaches like the ones I listed above and DH for
ILS and other precision approaches (in the case of the sim, just ILS
approaches).
quote:
> Also, does the chart MDA or DH override the standard ILS minima's ?
Yes, the published approach, which you will find as printed charts,
overrides any "standard" altitude you may have memorized, as local terrain
and man-made obstructions dictate these altitudes.
--
Peter
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| Beech45Whiskey 2006-03-24, 2:02 pm |
| Beech45Whiskey <pjricc@ZZgmail.com> wrote:
quote:
> Think of a DH as the moment you arrive at the decision height while coming
> down the glideslope, you must make the decision based on visibility whether
> to continue to land or to start your missed approach.
To clarify the above, you must make *and then act* on the decision to
continue or fly the missed upon reaching the DH.
--
Peter
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| stevej 2006-03-24, 2:02 pm |
| >
quote:
>
> MDA for non-precision approaches like the ones I listed above and DH for
> ILS and other precision approaches (in the case of the sim, just ILS
> approaches).
Hi Peter
Thanks for the info, there isnt a major difference is there..
RE- above maybe they set both then incase the ILS signal failed and it would
save a panic to switch to manual procedures.
Steve
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| Beech45Whiskey 2006-03-24, 2:02 pm |
| stevej <nopam@nospam.net> wrote:
quote:
> Thanks for the info, there isnt a major difference is there..
Sorry if it wasn't clear, but the response to your point above is, it
depends on what your definition of "difference" is.
It is conceivable while on a non-precision approach to step down to the
MDA, then continue to fly for 5 to 10 more miles before reaching the missed
approach point.
This contrasts sharply with flying a precision approach, whereas the moment
you reach the DH you must either continue to land or begin the missed
approach.
Think of the difference this way: A DH on a precision approach is where to
begin the missed approach. As far as the pilot is concerned, the DH is
defined as an altitude along the glideslope, not a distance from the
runway.
Thus, the DH is more like the missed approach point (MAP) of a
non-precision approach rather than the MDA, since the pilot must continue
to land or start the missed upon reaching the MDA, too. Of course, the MDA
is not defined by altitude, but rather as a fixed point along the approach.
--
Peter
| |
| Beech45Whiskey 2006-03-24, 2:02 pm |
| stevej <nopam@nospam.net> wrote:
quote:
> RE- above maybe they set both then incase the ILS signal failed and it would
> save a panic to switch to manual procedures.
Sorry, I missed this in my other post. That could be, since most ILS
approaches will become approved localizer approaches in the event the
glideslope fails.
Whether the airline aircraft can continue as a localizer approach if the
glideslope were to fail during the ILS (as opposed to going missed and then
trying again) would be covered in their airline operating manual.
--
Peter
| |
|
| Peter,
I guess that the airline operating manual will mostly state to continue on a
non-precision (LOC) approach for most of the airlines? Or do you really have
that much different procedures for the different airlines. If yes, that
sounds confusing. For us (military) it was [yes, was, retired :-( ] standard
to continue on puplished non precision approach if precision approach
failed. Even in the case you scre%%$ up and managed to get yourself outside
the beam! Provided you still had the LOC.
Loek
"Beech45Whiskey" <pjricc@ZZgmail.com> schreef in bericht
news:fr9mn2oc137y$.dlg@ID-259643.user.individual.net...
quote:
> stevej <nopam@nospam.net> wrote:
>
> Whether the airline aircraft can continue as a localizer approach if the
> glideslope were to fail during the ILS (as opposed to going missed and
> then
> trying again) would be covered in their airline operating manual.
>
> --
> Peter
| |
| Beech45Whiskey 2006-03-24, 2:02 pm |
| Loek <just.ask@nl> wrote:
quote:
> I guess that the airline operating manual will mostly state to continue on a
> non-precision (LOC) approach for most of the airlines? Or do you really have
> that much different procedures for the different airlines.
Hello, Loek - I don't know the answer to your question with certainty as I
do not have first-hand knowledge of airline operations, just speculation
based on conversations with airline pilots about operating procedures in
general.
I wanted to be sure to include the point that airline operating procedures
most likely do direct the pilot in handling an ILS approach where the
glideslope fails, but how these typical airline procedures handle this
scenario, I don't know.
In reading your post, my speculation is that most airlines here in the
States also all have the same requirement.
--
Peter
| |
|
| Peter,
I guess we speculate on the same thoughts then. Anybody with an answer based
on facts?
Loek
"Beech45Whiskey" <pjricc@ZZgmail.com> schreef in bericht
news:1f4fgwdtuyg7i$.dlg@ID-259643.user.individual.net...
quote:
> Loek <just.ask@nl> wrote:
>
>
> Hello, Loek - I don't know the answer to your question with certainty as
> I
> do not have first-hand knowledge of airline operations, just speculation
> based on conversations with airline pilots about operating procedures in
> general.
>
> I wanted to be sure to include the point that airline operating procedures
> most likely do direct the pilot in handling an ILS approach where the
> glideslope fails, but how these typical airline procedures handle this
> scenario, I don't know.
>
> In reading your post, my speculation is that most airlines here in the
> States also all have the same requirement.
>
> --
> Peter
| |
| Beech45Whiskey 2006-03-24, 2:03 pm |
| Loek <just.ask@nl> wrote:
quote:
> I guess we speculate on the same thoughts then. Anybody with an answer based
> on facts?
Oskar has one, but he appears to be on vacation from the group.
--
Peter
| |
| stevej 2006-03-24, 2:03 pm |
| >
quote:
>
> Oskar has one, but he appears to be on vacation from the group.
>
Hi Peter
Yes I have wondered where Oskar is.
Thanks for your info, I have this clear now.
To answer Loek's question, I would have thought the G/S failure procedures
to be more type specific than airline specific. And perhaps (by accident) we
have stubbled accross the B747 procedure as in my earlier post the MDA is
entered for use if the approaches has to switch to non-precission.
Steve
| |
| Beech45Whiskey 2006-03-24, 2:03 pm |
| stevej <nopam@nospam.net> wrote:
quote:
> To answer Loek's question, I would have thought the G/S failure procedures
> to be more type specific than airline specific.
Perhaps it is type specific, but it will be spelled out in the airline's
operating procedures, which in a way also makes it airline specific.
Airline operating procedures are written, among other reasons, by the
airline to elevate safety beyond that which is mandated in the federal
aviation regulations. In fact, from what I understand, the US FAA
recognizes that the FAA cannot mandate every single aspect of aviation
safety and instead has a catch-all regulation that recognizes the existence
of this airline operating procedure manual.
Hence, this is the reason for Loek's and my speculation about different
airlines perhaps having different requirements for flying an ILS approach
whereby the glideslope fails. This scenario falls right into the
jurisdiction of the airline's operating manual. Is this further broken
down by type of aircraft? Perhaps it is that, too.
--
Peter
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