[jhb_airlines] Re: Article

  • From: "Bones" <bones@xxxxxxx>
  • To: <jhb_airlines@xxxxxxxxxxxxx>
  • Date: Thu, 25 Nov 2004 00:52:40 -0000

Ah.. This is something different.

The Missed Approach Procedure is always based on QNH. For those of us =
who
fly an approach using QFE it means we check on final that one altimeter =
is
set to QFE and the standby altimeter is set to QNH. On starting the =
missed
approach we therefore use the standby for initial height guidance until =
we
get to the checklist item and then switch the primary altimeter to QNH =
also.

In this context it simply means that if the crew choose to use QFE for
landing then one dial stays on QNH. It doesn't suggest that QFE is
mandatory. I can add to that too and say that ATC do not pass QFE unless
specifically requested. Nor is it found on an ATIS broadcast - simply
because most weather is airfield related but QFE is specific to each =
runway
(based on threshold elevation).

Looking at an old Aerad plate before I see the DH was shown in both =
height
AMSL and AAL so I'm thinking the QNH guys use the former and the QFE =
guys
use the latter..

bones

-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of gwinsk@xxxxxxx
Sent: 24 November 2004 22:01
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Re: Article=20


Perhaps a clue lies in a recent accident report. A flight doing a missed
approach ran into=20
high ground. It was found that both altimeters were on QFE "Not having =
been
reset after=20
the overshoot". Apparently one is supposed to be set on QNH, if the =
other
has been set=20
to QFE, which more or less confirms they have a decision height QFE on =
one=20
instrument?

Gerry Winskill
gwinsk@xxxxxxx



On 24 Nov 2004 at 19:33, Bones wrote:

> Astute question. I was going to write back and say "yes" but then I=20
> had =3D to pause and think for a bit.=3D20
>=20
> You see, the UK airlines almost all used QFE up until a few years ago=20
> =3D and then most migrated to the US policy of remaining on QNH.  If=20
> landing QNH then ATC don't pass the QFE value - and so Decision Height =

> can't be QFE related. Or so the logic told me, but it also sounded=20
> wrong.
>=20
> Looking up the DH of 27L at Heathrow gives a value of 250ft and this =
=3D=20
> must be a QFE value (height above airfield) as Heathrow is about 202ft =

> AMSL. =3D That would mean a DH of 452ft QNH.
>=20
> I had two thoughts here. One was that pilots add their DH to the =3D=20
> airfield elevation and the other was that they set DH on the Rad Alt.=20
> In fact it seemed logical that the latter was the sensible route but=20
> then I worried about sloping ground affecting Rad Alt readings. I had=20
> to resort to a =3D web search and found evidence at=20
> http://av-info.faa.gov/terps/Policies1/TIL00005Aatt.PDF that DH is not =

> =3D used with the Rad Alt unless the pilot knows the height of the=20
> terrain at the =3D DH location and adjusts for the difference between=20
> threshold elevation.
>=20
> I conclude, for the moment, that DH is indeed set on the altimeter and =

> =3D that the crews must have a QNH as well as QFE value on their =
plates=20
> to set. =3D I'll have to look further as a read through the UK AIP=20
> hasn't provided any clues.. Just accept that the CAA plates avoid any=20
> reference to DH or MDH =3D and therefore aren't quite as good as =
getting=20
> Aerad or Jepp plates..
>=20
>=20
> bones
>=20
>=20
> -----Original Message-----
> From: jhb_airlines-bounce@xxxxxxxxxxxxx=20
> [mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of gwinsk@xxxxxxx
> Sent: 24 November 2004 17:09 To: jhb_airlines@xxxxxxxxxxxxx Subject:=20
> [jhb_airlines] Re: Article=3D20
>=20
>=20
> Presumably Decision Height relies on QFE? If memory serves me right, =
=3D=20
> We're only=3D20 given QNH by FPI controllers........
>=20
> Gerry Winskill
> gwinsk@xxxxxxx
>=20
>=20
>=20
>=20
> On 24 Nov 2004 at 5:10, Bones wrote:
>=20
> > Panel
> > I honestly don't know what the cockpit is from on that first photo =20
> >but I have a sneaking suspicion it's the much modified NASA Boeing =20
> >737. =3D20
> > MCP
> > Yep, MCP is indeed Master Control Panel. You can take this as the
> > block =3D3D of switches on the default FS aircraft covering the HDG, =
=3D
> ALT,=3D20
> > Speed, VS, =3D3D APR, BC buttons etc or as the Go Flight MCP unit. =
As=20
> > =3D
> most=3D20
> > add on aircraft =3D3D have a similar bank covering these functions - =

> > and =3D
>=20
> > the article was beginning to dive into slightly deeper waters - it=20
> > was =3D
>=20
> > necessary to start using more exact terminology to avoid =20
> >generating=3D20 confusion. =3D20
> > Speed control
> > Speed behaviour in FS is pretty accurate and you hit the same
> > problem =3D3D found in the real world. In fact slowing down in the
> > descent =3D
> becomes=3D20
> > a problem even down to GA levels once you get a fairly =20
> >streamlined=3D20 aircraft. A Cherokee or C172 does not have any =20
> >problem but move up to=3D20 the PA24 =3D3D Comanche or PA31 Navajo =
and =20
> >you get a shock. =3D20
> > The basic dilemma is that sleek aircraft cannot descend and slow
> > down at =3D3D the same time. Even with much reduced throttle many
> > aircraft=3D20 remain close to cruise speed when descending and so =
you
> > are in the=3D20 trap of foregoing one =3D3D for the other - it is =
either
> > rate of descent =3D
>=20
> > or airspeed that you opt for. =3D3D You can't do both.
> >=3D20
> > The trick is to ignore the book figures for descent rate for the =
=3D3D =20
> >aircraft and use something less. In the PA31 we used a 500 fpm =20
> >descent =3D
>=20
> > rate at =3D3D 180kts as this is easy to calculate. If up at FL100 it =
=3D
> would=3D20
> > take 20 min to =3D3D descend to sea level and at 3nm per minute this =
=3D
> would=3D20
> > mean starting down some =3D3D 60nm from destination. Also, at =
500fpm,=20
> > we =3D
>=20
> > had a bit of flexibility as we =3D3D could still slow down a bit or  =

> >we=3D20 could increase ROD. =3D20
> > For the bigger jets I'd ignore the default 1800 fpm rate set by the
> > autopilot and use 1500 fpm. You would have to check each aircraft
> > to=3D20 see what ROD they use so the above is just a guideline. At
> > the=3D20 shallower =3D3D descent rate the autothrottle would =
probably
> > have a bit =3D
> of=3D20
> > power on and so you'd have a small degree of control over speed=3D20 =

> > settings. An example is one of =3D3D the default aircraft (747 or =
737
> > - =3D
> I=3D20
> > can't recall) that won't peg at 250 kts during normal autopilot=3D20 =

> > descent but stays up nearer 270/280kts. Reducing =3D3D ROD will =
bring=20
> > =3D
> the=3D20
> > aircraft back under the autothrottle envelope.
> >=3D20
> > Admittedly this will entail a longer descent profile and so you =20
> >should =3D3D plan for this. Alternatively use FSNav to compute the =
top =20
> >of =3D
> descent
> > - but =3D3D make sure you change the ROD in the aircraft's =
profile=3D20 =20
> >first.=3D3D20 =3D20
> > Speed brake is the ultimate option and should be used if ATC ask for
> > an expedited descent or if you know you've miscalculated the bottom
> > of =3D
>=20
> > =3D3D descent point. Flaps are generally no help but again this=20
> > varies=3D20 with aircraft =3D3D type - I think the 747 has a high =
figure=20
> > of 270kts =3D
> for=3D20
> > first stage setting =3D3D and there are probably others too. =3D20
> > Spoilers
> > I've had a look at both the PMDG 737 and IFDG A320 air files and it
> > is possible the spoiler drag is in Section 1101 <36h>. I'd play with
> > this =3D
>=20
> > carefully though as the former only has a value of 15 in that box =20
> >=3D3D=3D20 whereas the latter has 123! The default 737 is even higher =
at =20
> >261.. =3D20
> > Missed Approach Procedure and Decision Height/Minimum Descent Height
> > These used to be shown on AIP approach plates a while back but
> > they=3D20 have been removed as they are now considered company =
minima.
> > The=3D20 Jepp/Aerad charts still give the data (airlines then factor
> > this for=3D20 local use) but =3D3D you don't have to resort to =
searching
> > these out. I=3D20 will explain..
> >=3D20
> > A few years ago the CAA was criticised for not stipulating minima
> > =3D3D because this allowed non company aircraft (business or private
> > aircraft) to =3D3D approach in far worse conditions than the =
airlines
> > or =3D
>=20
> > charter aircraft (which =3D3D were legally bound to publish minima=20
> > for=3D20 their pilots). A lot of other =3D3D countries had already=20
> > produced State =3D
>=20
> > Operating Minima and the CAA eventually did =3D3D the same. =3D20
> > To dig this out requires a bit more digging into the AIP. Ignore the
> > approach charts and open up the Textual Data page for the airfield.
> > =3D
> =3D3D=3D20
> > Scroll down to Section 2.22 Flight Procedures and look for sub=20
> > section =3D
>=20
> > 6 - Aerodrome Operating Minima for Non Public Transport Flights. =20
> >This=3D20 should give you the basic data you can go on. =3D20
> > For example at EGNS it gives for the ILS/DME 26 approach a DH of
> > 250ft =3D3D and minima of 700m RVR. If the glidepath is U/S and you
> > are flying =3D
>=20
> > the Localiser/DME approach the DH is raised to 400ft and RVR to=20
> > 1200m. =3D
>=20
> > A =3D3D radar approach (SRA) has a much higher limit - 600ft - =
because=20
> > =3D
> it=3D20
> > is deemed a =3D3D non precision approach, as are NDB or VOR =
letdowns.=20
> > If =3D
>=20
> > you look at Heathrow =3D3D (and almost all other airports) the =
limits=20
> > =3D
> are=3D20
> > much the same - 250ft for an =3D3D ILS, 400ft for a Loc/DME and =
600ft=20
> > =3D
> for=3D20
> > most others.
> >=3D20
> > The Missed Approach Point is shown on the approach plate but not for =
=20
> >an =3D3D ILS approach as it is redundant. This goes back to =20
> >definitions =3D
> so=3D20
> > bear with =3D3D me whilst I explain again.
> >=3D20
> > An ILS is defined as a Precision Approach. Because of this the =3D3D =
=20
> >terminology is slightly different in that the point at which the=3D20 =
=20
> >approach is =3D3D terminated is called the Decision Height. Non =3D
> Precision=3D20
> > Approaches (VOR, NDB and Localiser only) use a different point =20
> >called=3D20 the Minimum Descent Point. There are subtle differences.=20
> >=3D20  With the ILS the aircraft is allowed to descend to the DH=20
> >(usually  250 =3D3D ft) and, if the crew don't see the runway or=20
> >approach lights  they=3D20 HAVE to execute a missed approach. In =
other=20
> >words there  isn't a MAPt=3D20 for this procedure because it is the=20
> >same point as  the DH.
> >=3D20
> > For Non Precision Approaches the aircraft can fly down to the MDH
> > but =3D3D then it is allowed to level off and remain at the MDH =
until
> > it =3D
> gets=3D20
> > to the =3D3D MAPt - only then does it go around. So, a MAPt (I'm=20
> > adding=3D20 the little T because =3D3D the charts now show it as =
MAPt=20
> > rather than =3D
> MAP)=3D20
> > is only necessary and shown =3D3D for non precision approaches. =
=3D20
> > If you are wondering about the oddity of the non precision approach
> > then =3D3D let me explain. In the old days prior to DME a VOR or
> > NDB=3D20 approach was flown =3D3D on timings only - pilots didn't =
have
> > an =3D
> distance=3D20
> > information to show how =3D3D close they were to touchdown. This=20
> > still=3D20 applies to airfields without DME too =3D3D - it isn't a=20
> > historical issue =3D
>=20
> > (look up the NDB plate for Cranfield).=3D3D20
> >=3D20
> > The approach procedure was based on flying over the beacon at a set  =

> >=3D
> =3D3D
> > height and flying outbound for several minutes - the exact =
timing=3D20=20
> > depending on =3D3D your approach speed. You then turned inbound =
and=3D20=20
> > descended to the MDH. If you =3D3D got it right this would almost be =
=3D
> like=3D20
> > an ILS and you would reach MDH fairly close to the runway. However,=20
> > if =3D
>=20
> > the wind was strong or unpredictable it could muck up the descent=20
> > and=3D20 you could easily find yourself at MDH with =3D3D a mile of =
so=20
> > to go -=3D20 hence the need to stay at that height until the MAPt. =
=3D3D=20
> > You could =3D
> play=3D20
> > safe and reduce the descent rate to stop this happening but =3D3D=20
> > you=3D20 could then be faced with the opposite problem in that you=20
> > might still=3D20 be coming down to MDH as the airfield appeared in =
the=20
> > murk below you - =3D
>=20
> > with =3D3D you too high to effect a landing.
> >=3D20
> > So the MDH rule still applies to non precision approaches even =20
> >though we have the luxury of DME to show us exactly how close we are  =

> >to an =3D
> =3D3D=3D20
> > airfield. This makes such approaches much more safe and accurate=20
> > and=3D20 you would =3D3D think the DH rule could be applied to them =
but=20
> > there is=3D20 one more factor for keeping the MDH. Autopilots can=20
> > track and ILS and=3D20 they can be programmed =3D3D to flag the DH =
and=20
> > alert the pilots to land =3D
>=20
> > or go around. This still can't =3D3D be done with a non =
precision=3D20 =20
> >approach. All you can do with a NPA is use the autopilot to fly =20
> >the=3D20 correct inbound heading but it can't be given any descent =20
> >guidance.=3D20 Therefore you just dial up the MDH and let it take you =
=20
> >down to that=3D20 height. =3D20
> > I think I'd better add that to the page...
> >=3D20
> > bones
> >=3D20
> > -----Original Message-----
> > From: jhb_airlines-bounce@xxxxxxxxxxxxx
> > [mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of
> > gwinsk@xxxxxxx Sent: 23 November 2004 14:08 To:
> > jhb_airlines@xxxxxxxxxxxxx Subject:=3D20 [jhb_airlines] Re:
> > Article=3D3D20
> >=3D20
> >=3D20
> > John,
> > Having read and re read the "Article", and learned a lot from it,
> > may I =3D3D ask a few=3D3D20 questions?
> >=3D20
> > Very important. What's the aircraft featured in the first
> > photograph? =3D3D I'm thrown by the=3D3D20 presence of what look =
like
> > sidesticks, on =3D
> to of=3D20
> > a central control =3D3D column?
> >=3D20
> > What is the Autopilot MCP? I know the answer is going to be =3D3D =20
> >embarrasingly obvious? Is=3D3D20 it Master Control Panel? =3D20
> > Not in the article but arising from it. I find that some of the FS
> > jets =3D3D are reluctant to slow,=3D3D20 entailing a need to start
> > the=3D20 decelleration way ahead of the 10,000' =3D3D point, or any
> > other=3D3D20 =3D
> speed=3D20
> > control point. If the first stage of flaps can't be deployed=20
> > until=3D20 down to 220kias,=3D3D20 then that just leaves the =
spoilers.=20
> > On the IFSDG =3D
>=20
> > A320, the braking =3D3D effect of the spoilers=3D3D20 is minimal. =
I've =3D
> looked=3D20
> > through Aircraft.cfg and used AirEdit on the =3D3D .air file, but =20
> >can't=3D20 find=3D3D20 a way of increasing the spoilers' drag. Any =20
> >ideas? =3D20
> > I was sure I'd preserved your words of wisdom on the subject but
> > can't, =3D3D now, find them.=3D3D20 The info I'm seeking is on =
Decision
> > =3D
> Height=3D20
> > and MAP differences and determination.=3D3D20
> >=3D20
> > Something else is sure to hit me, so I may be back. Meanwhile, off =20
> >to =3D3D see whether=3D3D20 Werner Schott's Checklists can be chopped =
=20
> >down =3D
> and=3D20
> > stuck onto file card. =3D3D I'm
> >=3D20
> > disappearing under paper and can't find the thrust lever! =3D20
> > Gerry Winskill
> > gwinsk@xxxxxxx
> >=3D20
> >=3D20
> >=3D20
> >=3D20
>=20
>=20
>=20
>=20




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