[jhb_airlines] Re: Tonight's FPI

  • From: "Bones" <bones@xxxxxxx>
  • To: <jhb_airlines@xxxxxxxxxxxxx>
  • Date: Thu, 1 Sep 2005 16:55:53 +0100

Back in the 1960's there were a few civil airfields with full PAR equipment
and the controllers could talk down aircraft with both azimuth and glide
slope displays. Easier for the pilot as all he gets is left/right and
up/down instructions. This all changed when a B727 ploughed in at Gatwick
and the AIB findings pointed at slight PAR discrepancies that could have
been a contributing factor. The CAA's action was immediate and all PAR
equipment was withdrawn immediately. The last PAR I remember was over at
Dublin - it soldiered on for a few years after the UK stopped using them but
eventually it also went.

Nowadays we are left with just a standard radar display so guidance is only
possible for directional control. With no glideslope data the only action
possible is to give advisory heights for distance from touchdown - usually
at half mile intervals. I know we have your actual height on SSR but that is
not really useful - things are happening too fast to use this data. If you
should be at 1750 ft and I see you at 1870ft I can tell you are above the
glide path but there just isn't time to work out the differential, do the
same calculation for the next half mile point and see if your deviation is
getting better or worse. With the vertical element in the PAR you could
instantly see if an aircraft was above or below the nominal slope, how great
that deviation was and, most importantly, the actual descent path of the
aircraft. The latter was the essential bit as you could instantly see if an
aircraft's rate of descent became excessive - something that frequently
happened just as an aircraft started to break through a scuddy cloud base as
the pilot would lower the nose to get visual just a little bit sooner.

An SRA is more difficult than a full autopilot driven ILS but it is very
similar to a Loc/DME only approach. You can still use HDG mode to fly the
headings but rate of descent has to be constantly watched and adjusted - you
have to start thinking. The trick here is to use G/S x 5 for ROD and at
120kts this means starting off with 600fpm and seeing how it looks. Varying
wind strength as you descend means constant reassessment of your ROD and you
can rarely set it at one value from the start to the finish of the SRA.

In real life pilots like SRA's as they find then the easiest of all
approaches other than an AP driven ILS. It's easier than a manual ILS and
much easier than an NDB or VOR approach. The difference between FPI and the
real world is that real pilots will, from time to time, have to fly a VOR or
NDB approach and so they have more experience here. These approaches are
hard to learn and a lot of the initial IR training is centred on them. I
think I only ever flew one full ILS approach during training but the
instructor gave me a lot of VOR and NDB approaches to fly and a lot of
Localiser only approaches - but he was a particularly evil instructor
<vbg>.. He always said his granny could fly an ILS so it wasn't worth
wasting training time on.

In FS things are the wrong way round and pilots usually learn to fly an AP
driven ILS first - and many never try to fly a VOR or NDB approach. It is
this lack of experience that limits the airfields we can use in FPI as we
are aware that the ones we pick HAVE to be ILS equipped. Picking a non ILS
airport is tricky because we can't always assume that the weather will be
good enough for a pilot to make a visual approach - exactly what happened
last night at Plymouth with the wind being wrong for their only ILS runway.

At this stage I think it is tricky to reverse the problem of lack of
training. Real pilots would have been taught VOR and NDB tracking first and
then moved up to a VOR approach and then an NDB approach. Most of this would
have been manual flying too. With FS I suspect it would be best for pilots
to reverse the normal training and move from ILS down to a VOR and then to
an NDB approach. A VOR is much like a Localiser/DME approach where you are
using the DME to give you distance and work out the appropriate heights
(normally shown on the approach plates). Again you can let the AP fly the
headings and concentrate on descent profile only. The only headache here is
when the VOR is not actually on the airfield - some are 4nm away and these
take a little more skill to master.

The NDB approach is the hardest because you have to calculate your own
headings as well as descent profile. AN NDB/DME is better but without the
DME you can only fly the approach by following the full published procedure
and base your descent point on stopwatch timings. Headings also have to be
constantly watched to take wind drift into account - the mental arithmetic
here being one reason why pilots dislike NDB approaches! The equipment on
the aircraft makes a great difference too. The basic ADF on the Cessna is
the hardest to master but life is a lot easier if the aircraft is fitted
with an RMI where the ADF needle is on a gauge also giving heading


-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
Sent: 01 September 2005 08:27
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Re: Tonight's FPI

Weather permitting, it's something I'd look forward to repeating. I
wrongly referred to it as the old GCA, wot our setup was devoted to, at
St M. I fact it was the Search Controlled  Landing that they used, when
on 13, When on 31, the GCA runway, the Precision tube, complete with
glidepath cursor,  meant they didn't use advisory heights just "above"
or "below" glidepath. That would be an easier procedure for an MP pilok. I
must admit to using a technique that wasn't available in 1960. I
controlled descent with the A/P, setting alt at airfield level and
varyinf rate of descent to suit the advisories. In the Q400 I use a %
throttle gauge, since the Autothrottle is like a fiddlers elbow. Since I
managed to nail airspeed on 120 the ROD didn't need much changing. I
suppose the AP twist is offset by the fact that the realworld pilot had
someone else to look out of the window, trying to spot the runway. It
was probably having to do both that made the talkdown seem to pass in
almost seconds.

Off to chop down the AG trees that grow across the UK2000 13 threshold.

Gerry Winskill

Bones wrote:

>It's sad that the server glitch spoilt the beginning of the session - I
>saw quite a few flight plans for aircraft that must have subsequently
>given up through not being bale to contact ATC. Full marks (not) to the
>Lufthansa 1120 pilot who flew from London to Guernsey squawking 7700
>all the way and lit up all our tubes.
>Once Stefan rebooted the servers it got better and most (not all)
>aircraft then started picking up ATC.
>I hadn't intended dealing with Plymouth traffic but Alan and Andrew
>didn't show up tonight (or couldn't log in) and this left the airport
>empty. With real weather forcing the use of 13 I had no option but to
>give inbounds an SRA - I doubt an NDB approach would have been very
>appealing. The only omission from a proper SRA was that I only gave 1nm
>height checks instead of 0.5nm checks - but it became rapidly obvious I
>was too rusty to try the full talkdown patter. The other problem was
>that the non ILS runways don't have any runway centrelines on the
>screen. At least I remembered how to nail the wind drift - I think it
>was only Mike who was slightly off the centreline a tad.
>Good fun though..
>-----Original Message-----
>From: jhb_airlines-bounce@xxxxxxxxxxxxx
>[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
>Sent: 31 August 2005 22:03
>Subject: [jhb_airlines] Tonight's FPI
>Well, having survived the server problems, that was very enjoyable. It
>was probably even more difficult for the controllers. Did anyone else
>find that the VFR Database's AG trees are planted plumb on the
>threshold of Plymouth's rwy 13?
>Very enjoyable GCA talkdown, too. I've long wanted to try one. I was
>amazed how quickly the last 8 miles sped by, in comparison to a normal
>ILS approach; even a manual ILS. The weather couldn't have been better
>for the talkdown. I didn't see the runway unti;l approaching Decision
>Height. Off for a lie down.. Gerry Winskill

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