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VEJ
24th Apr 2002, 08:26
I'am looking for the definition of an coupled approach.

Reason:
The airplane that I am flying now (DHC-8 315) has a limitation on the autopilot for single-engine coupled approaches and for an coupled back-course approach.

Now do I want to know if an coupled approach only applies to precision approaches or also to non-precision approaches.

(If possible a link to an "official" website)

Thanks for the help,

VEJ

FlapsOne
24th Apr 2002, 09:44
VEJ

You cannot couple to a Non-Precision approach because there is no vertical guidance.

A fully coupled approach requires precision guidance in both azimuth and elevation.

You can use the autopilot to execute a non-precision approach with azimuth guidance (VOR or LOCALISER) coupled, but the descent will be controlled by the the chap driving.

If you want, I am sure there are many folks out there with planet sized brains who can go into far more technical detail than I have enthusiasm for.

Tinstaafl
24th Apr 2002, 14:08
limitation on the autopilot for single-engine coupled approaches and for an coupled back-course approach.

A LOC Backcourse approach doesn't have vertical nav. guidance but has been included in the prohibition.

It seems that in this context the A/P manual is using the term 'coupled approach' to refer to any instance of A/P using navaid input.

Most GA A/P that I've used use the term 'coupled' just to mean 'receiving & responding to input from a navigation system' and not 'receiving & responding to both vertical & horizontal navigation guidance'.

VEJ
24th Apr 2002, 19:00
It seems that in this context the A/P manual is using the term 'coupled approach' to refer to any instance of A/P using navaid input.

Yes, and that is the problem I'am having.

Because in the company manual the backcourse (coupled) line is not mentioned but in the official Bombardier Dash-8 flight manual it is mentioned. :confused:

Intruder
25th Apr 2002, 07:53
It is possible the airplane is capable of a coupled approach (e.g., VNAV and LNAV), but the company and/or FAA don't allow it. For example, our 747-400s are not allowed to do VNAV final approaches due to FAA Operations Specifications limits. However, we CAN do coupled approaches down to certain limits (not to landing) using LNAV and Vertical Speed (e.g., VOR, LOC, or NDB/GPS overlay approaches).

Carnage Matey!
25th Apr 2002, 15:09
I know the newer A320 series can perform coupled VOR and NDB approaches but I think the guidance may be augmented by GPS. Not sure of the full technicalities because the CAA prohibit us from doing them.

OzExpat
27th Apr 2002, 18:42
Funny that ... I've only been developing instrument approaches for about 15 years and have always seen a need to have a start point at an Initial Approach Fix/Waypoint. This is because the approach is predicated on a specific maximum IAS, so we need to make sure the pilot has slowed down the aircraft as necessary, before passing the IAF/IAWP.

I think some companies might be playing games to suggest that the approach only starts at the FAF/FAP/FAWP. Certainly, that's when the approach gets really serious, complete with further speed reduction, reduced terrain clearance, etc., but in most countries that I'm aware of, clearance for an approach is given before passing the IAF/IAWP.

That said, I know there are instances where ATC will vector an aircraft onto the approach just prior to the FAF/FAP/FAWP. But this is simply a convenience issue and won't apply at every airport for every type of approach.

OzExpat
28th Apr 2002, 07:19
Thanks for that BIK... I live and learn. Still, it DOES seem like a bit of a worry that, while JAR seems to be heavily into stuff like theory, it allows the practical flying skills to deteriorate. I s'pose that even sim checks cost companies a lot of money...

My eyes have now been well and truly opened... :eek: