View Full Version : Hsi - Missed Approach

7th Aug 2007, 13:34
On the Missed Approach and to the right of the centre-line, with the airport now behind and the runway inbound track still set on the course selector, does the Bendix King KI-525A HSI give a 'fly left' command to regain the centre line, or is a reverse command given i.e. 'fly right'?

The reason I ask is that the version of Radio Aids Navigation Tutor (RANT) I have, when to the right of centre-line on Bournemouths R/W26 on the missed approach, gives a 'fly right' indication.

I know the chances of Mr Oddy slipping up here are very low but it is something I want to confirm (not least because having done a few missed approaches for real, I am rather embarrassed to realise that I had never asked myself the question before, instead happily following runway heading, never having been subject to large crosswinds).


7th Aug 2007, 16:13
In all cases, for all ILS approaches, both front course and (seen very seldom now) backcourse, the HSI course selector should be set to the inbound front course QDM.
At some airport locations, the ILS front course can be switched from one runway to the opposite end, the frequency being the same as well as (most times) the identifier, and in all these cases, the HSI course selector would/should be set to the inbound front course.
Having said this, for the HSI instrument to function, it does not matter at all whether you set a course or not, as with a localizer (quite unlike a VOR) it makes no difference whatsoever, however, for the presentation to appear properly to the pilot, the course selector is always set as I have indicated.

Capn Bloggs
7th Aug 2007, 16:26
Should be QFU, me thinks. Otherwise, good post, 411A! :ok:

(Bloggs now stands by for a :ouch:)

7th Aug 2007, 17:24

Cheers for replying.

I am inclined to disagree with your statement regarding whether or not you set a course on the course selector. Imagine you have the inbound course set on a standard front course (I don't want to deal with back courses....ever!) and are following runway heading. At the moment you are sitting 1.25 degrees off the centre line, shown by a half scale defection on the CDI bar. Now, whilst I agree rotating the course selector will not present any instantaneous change to the CDI indication, by continuing the turn through 180 degrees the command given by the CDI bar is now in the wrong sense ( I believe this is why, when flying back courses, autopilots have a B.C. button that MUST be pressed). Thus I believe you should always set the inbound track with the course select pointer. I shall qualify this by stating that I am basing my assumptions above on the aforementioned RANT navigation aid simulator, as I haven't flown yet with the kind of crosswind that would cause me reason to ensure I know the answer.

Anyway I'm flying tomorrow so I'll hopefully have a strong enough crosswind to find out what kind of indication my HSI's CDI gives on the missed approach.

If anyone out there can give a definitive answer on whether an aircraft that flies a localiser slightly to the right of centre line all the way down and continues right of centre line on the missed approach is given different commands from the CDI before and after the missed approach , or the same throughout the whole procedure, I'll be grateful. Ideally I'd like a reference to back up what is said, but I don't want people not to give input if they cannot provide one.

7th Aug 2007, 18:00
The commands continue in the correct sense on the missed approach. Only if you fly the missed approach backwards (i.e. a backcourse approach) will the sense be reversed.

7th Aug 2007, 22:30

I have dug a little deeper and found a book that confirms what you say, that the command sense doesn't change on the missed approach, which means that RANT can't have been programmed correctly for the missed approach indication. However, this is the first fault I have found with RANT, and I still recommend it to anyone wishing to sort out their needle work - also, the version of RANT I have is rather old so the newer version may have the correct indications in it.


7th Aug 2007, 23:15
Should be QFU, me thinks.

Oh well...coming from the USA I'm surprised I know anything about Q's as we don't use 'em here in civil aviation, at least not in everyday usage.