hsi heading?

[Conure]

Hey all,

 

Just a question to satisfy my curiousity really..

 

When I approach an airfield to land, particularly with ils I set my heading on the hsi. For the sake of simplicity let's say I am landing.on a runway 27 with an exact heading of 270 degrees...why then does that 270 degree steer me exactly onto the runway? Isn't 270 degrees a heading relative to me rather than a universal heading? For example a heading of 270 from where I am in london is certainly not the same as 270 for somebody in mexico, I would imagine?? Why then does this heading work so well at lining me up with a runway?

 

I may have worded this so poorly that no one will understand!

 

Cheers

[Barrakooda]

magnetic variation

 

I watched a vid somewhere explaining that when airport runways were given their designation you have to factor in magnetic variation changes over the years

as it shifts with tme

 

i.e. say the runway was given the designation 27 (270) 20 years ago it probably was an exact bearing at that time but due to the shift in magnetic variation its now actually 272 or something but the runway keeps the 27 desigantion.

 

I hope that makes sense

[hassata]

These charts provide more accurate runway heading info for purposes of landing:

 

http://www.virtual-jabog32.de/index....t=37&file=1200

http://forums.eagle.ru/showthread.php?t=60370

[FlyingBrick]

Think of your airfield as the center of a compass, draw a line bearing 270 away from the runway. As long as you intercept and navigate that line, no matter how far away, you should be aligned with the runway.

 

You can navigate to any steerpoint like this whether it's a airfield destination or a regular mission waypoint.

[FlyingBrick]

Yeah, I didn't explain that very well.

 

With the other posts though he should get the idea.:D

[Conure]

Thank you all very much, makes perfect sense now :) I presume the heading that ATC give you is the heading which perfectly places you in a position to intercept the (eg, 270o) to land on the runway?

 

Thanks again :)

[LostOblivion]

This would be that line FlyingBrick was talking about. Forgetting about magnetic/geographic heading for a second, this is where that perfectly straight line would go around the earth from an initial heading of 300 starting in New York.

[Fish]

Way I look at it is this.

 

Get yourself on the threshold of the runway and find out what the heading is when you are ready to take off. That's what your compass should be showing when you are on approach. To get this accurately, while waiting to takeoff (make sure you are aligned perfectly down the runway.), turn the course heading knob, so that the big arrow inside the compass rose, points at 12oclock. Now read the course digital heading above it. That's the 'course heading' you need to be on on approach. You can use the same course indicator to help with your approach.

 

But its not the whole story, You need to be 'pointing' to the runway, while on that heading. Cause like you said, lots of people may be looking or heading in the same direction, but few will also be pointing to the threshold of the runway you wish to land on. Your mark 1 eyeball is good for this if you are close enough, or you could setup the approach using tacan, or ILS, if you can't eyeball it.

Edited June 12, 2011 by Fish

[bluepilot76]

Im not sure I am following this thread, but am going to stick my 2p in and see what happens!.

Runway headings are magnetic headings, rounded to the nearest 10degs and with the last 0 knocked off.

Your compass in the aircraft is also giving magnetic headings. If your magnetic heading is 310 degrees, and you are pointing towards runway 31, you will have it in line in front of you. If your magnetic heading is 310 degrees but you are not pointing towards the runway, you will pass the runway by. Parallel to it. Assuming no wind of course.

Tacans, VORs, ILS, are all magnetic headings.

 

Your true heading would depend on magnetic variation and compass deviation. a true heading of 315 would be the same in Mexico as it is in Kiruna. it is 315 degrees clockwise from the local line of longitude.

[bluepilot76]

OK I really dont want to be a smarty pants, but in the case of an ILS it doesnt matter what you actually have set in the course selector of the HSI, the localiser bar will only centralise when you are on the localiser, obviously its a lot easier to interpret if it is lined up correctly though and everybody would do this in reality. This is not the same as the VOR (TACAN) useage where it will only centralise when you are on the radial that your HSI is set to. So it sort of depends what navigation equipment you are using which is being displayed on the HSI.

[arriflex]

Fish, fantastic videos. Great quality with clear and understandable explanations of why and how the procedures work. Looking forward to more.