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WAAS in Europe? (also GPSS / roll steering)

Yes, you can get roll steering on non-SBAS boxes, but it is much smoother and more accurate on SBAS boxes.

Both GNSWs and GTNs can feed (as far as I can make out, equally) smooth roll steering.

GTN will provide Visual approaches to grass runways, provided they are in the AIP.

ESKC does not seem to be in the Swedish AIP?

I am guess that that is also why it can’t be a VNAV target, if there isn’t a verified elevation, but you can always use sea level and add the elevation.

Last Edited by Timothy at 24 May 10:05
EGKB Biggin Hill

Timothy wrote:

ESKC does not seem to be in the Swedish AIP?

Yes it is. But you basically need to know it exists to be able to find it in the AIP.



I was going to suggest that it must have an AD 2 entry to qualify, but then ESOL, which is also not in AD 2, but does have a hard surface, does have Visual Approaches but ESGS doesn’t.

But many UK grass airfields (EGSL Andrewsfield and EGKA Shoreham were the examples I looked at) do.

So, it is not runway surface, it is not AD 2, it is not terrain (ESGS and ESKC are on flatlands) so I am out of ideas.

Ask Jeppesen?

Last Edited by Timothy at 24 May 10:46
EGKB Biggin Hill

Anders wrote:

Yes it is. But you basically need to know it exists to be able to find it in the AIP.

But it is in the GPS database including runway data?

EGTK Oxford

Certainly if the extent of the information in the AIP is that shown in AD 1 above, there is no way it could be coded; for example, there are no co-ordinates for runway ends, but then how do we explain ESOL?

EGKB Biggin Hill

Can someone explain from a technical perspective the difference between an AP performing with roll steering and without it?

How can one sense if his AP is configured to use roll steering without looking at the wiring diagram? From what I’ve heard, it behaves the same, and you can only sense the difference when flying a ‘curved’ path.

Doesn’t the AP fly the plane using ailerons control in both cases? Will the non roll steering one overshoot the turns in a ‘snaking’ pattern, or how becomes one ‘smoother’ than other?


LRIA, Romania

GPSS steering is great. The plane behaves as it should without much pilot input, it will fly a whole flightplan without telling you to change OBS settings e.t.c. It also anticipates turns, can use fly over waypoints e.t.c in procedures and fly holdings and other stuff provided by the GNS box.

Once you have had it, you won’t want to fly without it.

The 60-2 will most probably need the S-Tec GPSS converter installed to use this feature off a 530/430W box, or you can install an Aspen which has it’s own converter. My 55x has it native and it works very well indeed.

Once you have had it, you won’t want to do without it. I certainly don’t.

LSZH, Switzerland

AlexTB20 wrote:

Can someone explain from a technical perspective the difference between an AP performing with roll steering and without it?

Roll steering is an output from an FMS/GPS system that defines a precise bank angle for the autopilot to intercept and track a course. It does not depend on a CDI deflection, but rather the desired track, actual track, ground speed etc. The FMS/GPS generates the bank angle needed to fly the course or procedure. Modern autopilots have a roll steering input, but most legacy autopilots do not. So the KFC 225 and the Stec 55X have a roll steering input, but the KFC200, KFC150 Century III, Stec 60-2, Stec 50, Stec 30 do not. The legacy autopilots can be connected to a roll steering adapter that converts the bank angle into a command input accepted by these autopilots. What is accepted by the legacy autopilots is the heading bug signal that is used to guide the autopilot in heading mode. The heading bug signal is referred to as heading error and is normally generated by the DG or HSI anytime the heading and heading bug differ. Some clever engineers at Stec recognized that the heading error signal generated a voltage proportional to the error and that the heading mode autopilot computer would introduce a bank in proportion to the signal. So if the heading error is 5 degrees, the computer would introduce a 5 degree bank to correct the heading back to where the heading bug is located. A 10 degree error would introduce a 10 degree bank, and so on up to the bank angle or rate limit of the autopilot. Stec came up with a converter that converts a bank angle into a heading error and inserted a switch between the autopilot and one of the two sources for the heading error signal, either the DG/HSI or the GPS/Converter that was driven by the roll steering output. That is why on most legacy autopilots, you set the autopilot into heading mode when you wish to use GPSS or roll steering.

Last Edited by NCYankee at 24 May 14:01
KUZA, United States

This is what will get you going with GPSS on a 60-2 AP:

S-TEC GPSS Converter

As you are asking about replacing your EHSI with something more modern you can actually kill this problem by getting an Aspen. The Aspen has the same functionality inbuilt. All you do is fly the AP in HDG mode all the time you want GPSS and select GPSS on the Aspen.

LSZH, Switzerland

Operationally, what is the difference between having roll steering and not?

I recommend a search with the term

“roll steering” AND kln94

and one thread is here

The benefit is negligible unless you want the autopilot to fly arcs, holding patterns, etc. I would certainly not spend 4 or 5 figures on it.

And LPV depends on where you fly; if you fly out of the UK then all airports you fly to need Immigration (called “Customs” in standard international terminology, though not the same thing) and unless you fly a lot to particular airports and in bad weather you will find they have an ILS anyway. At least, that is what I continue to find, and all the time I continue to find it, I won’t be spending the money

Shoreham EGKA, United Kingdom
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