View Full Version : A-320 AutoPilot Localiser/Radial capture

29th Mar 2006, 17:17
Dear fellow aviators,
I have 2 questions
1.ATC can vector an aircraft upto a maximum intercept angle of 90degrees while making an ILS/localiser approach or a VOR approach.
Is this true or false and reasons/comments please.
2.What is the maximum intercept angle ( if there is) for the autopilot to capture the localiser of an ILS or the radial/course of a V.O.R.
Can the autopilot for example capture the Localiser if is on a far away (lets say 20 nms.) downwind leg to the ILS approach of a runway.

29th Mar 2006, 21:57
I cannot remember the exact angle an A320 will intercept the localizer but it will not track a vor.The vor tracking on an A300-600 is so poor that it is for en-route navigation only, so perhaps Airbus learned their lesson when the minibus was born.

4th Apr 2006, 12:11
Dear Friends,

Can someone please throw some light into Auto-Pilot characteristics when it comes to carpturing a localiser .... How does it do so.....Any recommended site....Am interested in knowing about ILS capture and how autopilots manage to do so....

is there a maximum intercept angle that an autopilot will allow for intercepting a localiser..



4th Apr 2006, 19:34
Cornwallis - The current spec Pegasus boxes on the Airbus will allow VOR tracking, it's in the Dir page and asks for radial in/course out.

Very useful for cleaning the box on arrival or for some departures.

To be exact though, you are following a generated track from a point that coincides with a VOR so it is not true VOR tracking :ok:

5th Apr 2006, 13:10

Try FCOM 4.5.70 page 3 and you'll find a graph and text showing the intercept angle that the autopilot can cope with at various speeds.

It also adds:

Note : ICAO requires loc beam to ensure a normal capture within 10 NM and plus or minus 35 degrees from the course centerline. Some ILS systems just meet the requirement and are subject to false capture outside these limits.

Sorry didn't have any luck posting the picture et al!


5th Apr 2006, 20:04
Javelin,the A300-600 has a vor/loc button.The Fcom states that the vor tracking is for enroute nav only,and has variour other restrictions on speed/intercept etc.In other words it is rubbish!!The A320 was in gestation whilst the A300-600 appeared and obviously the learned men of Toulouse looked at what had come before,realised it was rubbish and binned it.If you have to fly a vor radial use the bird and fly track-then along came the pegasus fmgc and it would do it for you.Maverick what is your interest because on the line you really don't think about it!

6th Apr 2006, 06:47
The aim is to understand the Limits of the Autopilot Capture...Its something like calculating the maximum limits to which the autopilot can function...
for example.....Its more theoritical, like your stall speeds...which you know the limits and the theory behind...but when you are flying at green dot or below , you dont really visualise the airflow going from laminar to turbulent and the C of P moving forward......
Maybe i need to ask the engineers in avionics or some people involved in autopilot programming...
its simply out of an interest in the growing world of 'fly by wire'...
and thank you idg,cornwallis n javelin for your answers :)

6th Apr 2006, 22:22
Maverick ,I locked onto the localizer once at>300kts in a 330.It was quite a sharp turn-on but it coped with it.If ATC give you a bad turn ie through the loc the afs stays in loc* until it recaptures from the other side.The A300 is quite susceptable to loc deviations due to ac on the rwy and departing-Airbus came up with a localizer inertial smoother to sort it out but my company didn't buy it.The quality of the afs has got better as computer technology has improved.On a day to day basis it is impossible to know what mod standard is in the box under your feet you just use it sensibly.:}

6th Apr 2006, 22:45
The intercept angle is more of a energy management thing. 300kt at 90deg would be unachievable for any auto pilot. You would pass right through the localiser beam before LOC green on the A320 series. You might get LOC*, but not full capture. The other problem with a 90deg intercept is that the a/c will not know whether to fly fly a front or back course approach. A 60deg intercept is possible at low speed. Any else would be bad airmanship and an indication of poor planning.

6th Apr 2006, 23:00
Quoting from memory it performs the capture with an initial dot and a bit overshoot then a smaller overshoot the otherway before finally capturing the loc.I was merely trying to demonstrate what the afs was capable of!
A300-605r fcom 2.022.03 p11 shows a maximum angle of 60* at 180kt at 15 nm going to 20* at 6nm at 220kt.This however is for a 1980's autopilot!
Obviously doing this high speed capture will not work close in but then you would not be doing 300kts close in either unless you were at an airshow!:}

8th Apr 2006, 04:17
Airspace requirements in Australia, used to dictate domestic jet aircraft would be at 20 track miles to run at 300kts & 5000'. ATC could further ask for a 'high speed' descent. This involved a 320 ( CFM engines importantly ) being at 5000 plus feet & 340kts and again, 20 track miles to run.

LOC interception at 30 degrees was routine. Anything greater could be accomplished by a combination of slowing down & finessing the intercept in HDG mode. LOC capture assistance function would have managed NAV nicely turning inside a waypoint to facilitate interception.

Can't recall the intercept parameters; they were certainly pushed. Self-recovery by the aircraft in a LOC overshoot was quite good. Better than FCOM 4 I recall. :}

8th Apr 2006, 21:15
well, the idea again, is not for practical flying...its about how you wud get into the depth of undertstanding a particular subject...a hobby perhaps.... having to use up the full stopway and bringing it to a halt just at the end of the runway, might be a debate for poor/excellent airmanship, but still there are people going thru the depth of calculating inertias, V1's and distances with many variables, ( wet, dry, contaminated )....

its to find the depth of the autopilot and master it, coz at the end of the day, the more we know, the more safer we get and the more we enjoy playing the game.....

thankyou dear friends...

well, the real need to know the extents of a system is to be ensure that you don't really misuse it, but to know, and apply your knowledge when you are in a situation. Your in-DEPTH knowledge might actually help you out.......i am not saying that we have to fly at near VMO speeds and high angles of interception, its just about how far can the autopilot cope up with the flight envelopes.......

Its interesting to me and a few people here and I thought it might be nice to learn from the knowlegde and experience of our experienced pilots...