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Backcourse

Jamie4590 Guest

What is the purpose of a backcourse apoproach? Is it to avoid the opposite steering that can occur and to make it easier for the pilot?

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

Jamie4590 wrote:

What is the purpose of a backcourse apoproach? Is it to avoid the opposite steering that can occur and to make it easier for the pilot?

Sorry, I don't know what you mean by opposite steering.

The idea of a backcourse approach is to use the lateral part of an ILS system at the opposite end of the runway. Imagine for a moment, that runway 09R is ILS approach equipped. Thats all well and fine for an approach into runway 09R in IFR conditions with winds of 270/10 but what if the winds were 090/10? Its unlikely that you'd want to make an approach into runway 09R due to decreased control surface efficiency and reponse, especially if its a big jet.

The most favourable option, is to carry out an approach on runway 27R i.e. the opposite end, but shock horror, it doesn't have an ILS system installed. The next best thing would be to carry out a backcourse approach (which is a non-precision approach by the way) which allows you to use a beam from the ILS system of runway 09R (the lateral beam, not the glideslope beam) so you have the desirable winds on approach with a lateral navigation system as to where the runway is. You would then need to descend on your own to the runway threshold.

Another crude diagram courtesy of MS Paint:

I hope that helps a bit 😉

Jamie4590 Guest

Thanks mate indeed it does. So given that a backbeam approach is non precision would it only be used when there is no alternative?

In the scenario you've illustrated would ATC have to be advised of anything special. Is landing a heavy with no glideslope an emergency situation or are pilots so used to it that they can descend to the runway threshold using judgement alone?

Referring to the diagram again so if I approach 27R using the ILS frequency for 09R will the steering be affected unless I activate the backbeam autopilot switch? I thought in this scenario, becasue I'm following the ILS localiser from the opposite dirrection unless I use the backbeam then when I steer left although the aircraft will steer left the HSI will show right steering and vice versa? Is it the backbeam switch that elimiminates this confusing instrument behaviour?

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

Jamie4590 wrote:

Thanks mate indeed it does. So given that a backbeam approach is non precision would it only be used when there is no alternative?

A lot of approaches are non-precision such as VOR, NDB, ADF approaches which aren't used that often. It is the norm in commercial aviation that visual approaches are used (normally with the aid of the PAPI) or an ILS approach is used, depending on the weather conditions.

Jamie4590 wrote:

In the scenario you've illustrated would ATC have to be advised of anything special. Is landing a heavy with no glideslope an emergency situation or are pilots so used to it that they can descend to the runway threshold using judgement alone?

To be honest, I don't think that backcourse approaches are all that common. Most runway approaches for aircraft will either have head winds or cross winds. If there is a small tail wind, then it really isn't anything to panic over. A lot of runways at major airports have more than one ILS system installed aswell so there is little need for them

Far from it. It is unusual that a pilot of any aircraft (unless your flying GA in the middle of nowhere) will be flying solely by visual cues, but there is certainly no reason why this cannot be done. Most runways have PAPIs or VASIs which aid the pilots descent. If not, then radar vectoring might kick in, where an approach controller may guide you in giving you headings and speeds and descent rates. This certainly happens in an IRS failure.

Jamie4590 wrote:

Referring to the diagram again so if I approach 27R using the ILS frequency for 09R will the steering be affected unless I activate the backbeam autopilot switch? I thought in this scenario, becasue I'm following the ILS localiser from the opposite dirrection unless I use the backbeam then when I steer left although the aircraft will steer left the HSI will show right steering and vice versa? Is it the backbeam switch that elimiminates this confusing instrument behaviour?

Yes it can get quite confusing. On a backcourse approach, left is right and right is left. On a conventional ILS approach, if you drift right, the needle goes left, telling you, you need some left aileron and rudder to become centered. On a backcourse approach if the indicator goes left, you need to turn right to center it and if it goes right, you need to go left to center it. I think you have it the wrong way around. The backcourse is the more confusing method because it is the less common method.

By the way, some localiser backcourses have a glideslope indicator as well and are called Localizer Back Courses with Glide Slopes which only adds to the amounting confusion, as up means down and down means up, whilst left means right and right means left.

I hope thats what you meant by steering.

Tee Hee Wacko

Jamie4590 Guest

It is yes and thanks for the input. I think the moral of the story is to avoid backcourse approaches where possible! 🙂)

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

Jamie4590 wrote:

It is yes and thanks for the input. I think the moral of the story is to avoid backcourse approaches where possible! 🙂)

I would rather do a backcourse approach over a VOR / ADF / NDB approach (especially if it involves an arc) any day of the week! 😳

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