[jhb_airlines] Re: IAP Tutorial

  • From: "bones" <bones@xxxxxxx>
  • To: <jhb_airlines@xxxxxxxxxxxxx>
  • Date: Fri, 21 Sep 2007 15:26:03 +0100

Wind is a constant variable and can be a headache. If you are put in a stack
and slowly get dropped down in this as aircraft at the bottom get fed off to
the ILS the wind will usually back and decrease.

Wind drift to a VOR is easy as you just have to subtract the radial (your
track) from your heading. That assumes you are nicely stabilised on the
radial though and not still chasing the needle. If you were on the correct
285 radial to VANIN then a 286 heading would only give one degree of drift..


-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
Sent: 21 September 2007 14:43
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Re: IAP Tutorial

I'll fly it again, now that you've pointed out that the Vanin leg
headings are IOM related. Now why didn't I think of that.
There was a significant crosswind this morning but my gauge takes quite
a bit of hassle out of that. With a heading of 286 being followed the
Magnetic Track line shows me what actual track I'm following, as the
result of the wind component. If it's 12 degrees less then I just
increase  the heading by 12 degrees.

Forunately the next surprise didn't surface until I'd left Vannin on the
306 Carnane heading. Suddenly there was  a big wind shift and I found
myself  tracking about 10 degrees beyong my initial path!

Who started this game?

Gerry Winskill

bones wrote:

>Many fixes have been introduced since GPS became an accepted navigation
>tool and the trend is to create airways that are pure GPS navigation -
>they can't be flown by an aircraft with basic VOR and NDB kit. This
>will continue because airways can be very easily created now they are
>freed from the restraints of building ground based aids.
>If we switch from the en route phase to the approach phase then fixes
>are different. Fixes used as holding patterns are almost always aligned
>with a VOR radial - which is why the VANIN hold is aligned to the IOM
>VOR rather than on a heading to CAR NDB.
>For the hold you have two essential bits of information. One is the
>holding pattern's inbound heading and the second is the DME distance to
>mark the fix. In the case of VANIN you should already be tracking to it
>on 285 (established on the 105 radial from IOM) and you enter the hold
>as DME hits 26NM. Make sure you keep your OBS on 285 so that the needle
>allows you to intercept the radial again as you finish the hold.
>You start the hold as I have described with a Rate 1 turn outbound. The
>outbound leg should be flown  on a heading of 105 (no wind) but in real
>life you need to calculate the drift angle and apply 3 x this to the
>heading. You fly this heading for one minute but, just to be really
>accurate to RW procedures, you also have to take into account and
>headwind or tailwind and increase or decrease the time by 1 sec for
>every knot of wind.
>This is the complexity we face in real life and I wanted to avoid it in
>FS as it cannot be explained in a few sentences on a web page.
>Assessing drift in a hold or when flying an NDB procedure is tough
>work, needs complete understanding and a lot of practise - it's the
>point at which you need serious help and need to start reading the
>Well before we start holds in real life our I/R training goes right
>back to basics and we learn to fly to (and from) a VOR on a specific
>radial - and most of you can do that. I wonder how many of you watch as
>the autopilot tracks into the VOR and you make a note of your drift
>angle? We also learn to track an NDB on a specific heading - much
>harder - and learn to correct for wind from observing the rate of
>drift. This takes a lot of mental calculation and older pilots have
>been doing this since WW2.
>Without these skills (tracking an NDB and adjusting for wind in a hold)
>you have to accept that your holds will remain rudimentary and it will
>be a matter of luck if your stopwatch hits the 4 min mark as you cross
>the fix again. Despite this it is still worth doing because as you
>practise you will develop a feel for the procedures and will begin to
>sense what wind is doing to you.
>Back to the VANIN hold. You have turned outbound and fly the outbound
>leg on a calculated heading for a calculated time. At that point you
>turn inbound again and if you have the wind hacked you should turn in
>right back on the 105 radial. Now this is the important bit - during
>the turn watch for the needle and intercept the radial as you would for
>an ILS. Don't just dial in a Rate 1 turn and watch it happen as it
>takes you past or short of the radial - start working to hit it.
>The whole purpose of the hold is to be back on that radial as you
>finish the procedure. It's a feather in your cap if you can do this in
>exactly 4 min as you then have the skills beloved of hoary old pilots
>like Gann and Bach - but things are changing. Nowadays they publish a
>distance at which to start the inbound turn (DME 31 for VANIN) and this
>means the old four minute hold is no longer as crucial in timing as it
>once was. I am just grateful I learned these skills as I can relate to
>how the old pilots flew.
>So establishing on the inbound radial is very important but a four
>minute pattern is not as critical as it once was.
>I once flew the BEL VOR hold in a PA28 when there was a 45kt crosswind.
>That produced a 25 degree drift angle - which meant that I should have
>flown the outbound leg at 3 times that. That is impossible and the max
>limit for the outbound offset is pegged at 45 degrees. When I started
>the turn back into the VOR it was inevitable that we would be blown
>right through the inbound track and I needed far more than a Rate 1
>turn to capture it. Flying holds in a light aircraft without autopilot
>is about as hard as you can get - their slower speeds mean bigger drift
>angles and the manual flying coupled with the mental workload can be
>I guess I should add the above to a final web page on the subject but I
>fear it would frighten people off. It's not meant to but I think you
>should fully appreciate the forces that are at work when it comes to
>even basic VOR or NDB procedures.
>-----Original Message-----
>From: jhb_airlines-bounce@xxxxxxxxxxxxx
>[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
>Sent: 21 September 2007 10:14
>To: jhb_airlines@xxxxxxxxxxxxx
>Subject: [jhb_airlines] Re: IAP Tutorial
>That reads very well; thanks.
>This morning I tried the proceedure for 26, via Vannin. I was surprised
>how quickly each minute in the Vannin hold goes! Coping with the wind
>was made easier using my drift gauge but I still failed to overfly the
>Vannin start point, for my second orbit. I'm forced to ask how they
>managed before the advent of GPS? Or have Vannin, Kelly and other fixes
>only been included post GPS?
>I used the Dreamwings ERJ145, which is good apart from in one area.
>Down at the correct Vref, on the glideslope, it requires almost full
>lock corrections, with anticipatory opposite lock, to cope with its low
>speed wallowing tendency and get correctly lined up. Any idea whether
>tweaking the Aircraft.cfg's Roll_Stabillity value might improve this?
>Gerry Winskill
>bones wrote:
>>Hopefully this is now finished and I invite questions and comments
>>about either the pages or about flying these procedures.
>>I can't do justice in just four pages to these procedures but there's
>>plenty of further information online - even Wiki has a decent section
>>on them. All I have done is condense the basics into the pages. The
>>disadvantage of doing this is that it may seem daunting as a few
>>sentences can suggest a lot of new concepts and ideas - but taken
>>slowly the pages can be worked through gradually and, hopefully, the
>>concepts will start falling into place.
>>This is not an overnight exercise - it takes a lot of practise and
>>possible frustration. You may get part of the way through a procedure
>>and suddenly have no idea what comes next. This is normal so just keep
>>plodding at it and the information will slowly assimilate - you learn
>>a little more each time. Gradually your mind will absorb the added
>>mental thought processes needed and it will all start falling into
>>John Woodside

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