unstable approach

[alpergokgoz]

what is an unstable approach ? what makes a circling approach unstable ??:):)

[5LY]

To be stabilized is to be on speed, on profile, fully configured, checklists done, by a certain height, usually 1000 feet. If any of the required elements of a stable approach are not met by the required altitude, then a missed approach should be flown.

A circling approach, by it's nature can take you outside of normal stabilized approach perameters. Some airlines don't alllow them. Those that do, accept that where a procedure requires it, you can plan the approach considering and expecting certain deviations and then do it.

The whole philosophy of stabilized approaches is to give you a bench mark from which to measure your progress. If you do it the same way each time, you'll see any deviations quickly and correct back to profile.

Lots more can be said on this, but that's the basic idea.

[capt. solipsist]

re circling approaches, only the sink rate is allowed to deviate from the NORMAL stabilized parameters, and only till 500' (which you are allowed on VMC anyway), plus you gotta do a specific brief on that. :}

[aterpster]

alpergokgoz:

what is an unstable approach ? what makes a circling approach unstable ??


It depends a lot upon the height above airport (HAA) of the circle-to-land MDA. Where there are only low obstacles TERPs requires the HAA to be not less than 450' for CAT C and 550' for CAT D. The circling maneuvering area (TERPs) is 1.7 miles for CAT C and 2.3 miles for CAT D.

So, you must remain within the circling maneuvering area whether the MDA is 450 or 550, or whether it is, for instance, 2,200 HAA. Those circumstances create very different maneuvering requirements, and both are potentially very dangerous, whether the final approach is offset from the runway by only a relatively few degrees or whether you have to circle to land in the opposite direction.

In the case where the final is lined up, or nearly light up, with the runway but only circling minimums are charted, you have a high descent rate issue facing you. That is just one of many traps in CTL minimums.

That is why "TERPs is Traps." :O Well, that and the fact that trapezoids are used to design some of the protected airspace. PANS-OPS provides much more reasonable areas of airspace for the CTL maneuver. TERPs has new, much better circling criteria approved after 20 years of battle, but certain vested interests are delaying implementation.

[bfisk]

Well, that prompts the question "what is a stabilised approach"? You will find this will differ from operator to operator, but in general something like that:

-The aircraft is on the correct approach path
-The aircraft has the correct energy level (airspeed/altitude)
-The aircraft is configured for landing
-The checklists are completed
-The trend is neutral (ie the thrust, sink rate and trim are within limits).

How this is interpreted, practically, will vary.

Ie; while some will interpret the first one as being on the extended centerline, some may say within 1/2 scale deflection (and that will be a different absolute value for an ILS contra a VOR approach), and some will leave it up to judgement. We have a requirement to be within half-scale deflection on straight in approaches, wings level at 500RA on a visual approach, and wings level at 300RA on a circling approach. There are some circling approaches where that will not be possible (look up ENHV for instance), and then a special briefing must be made.

There are also differences with regards to vertical speed. Many consider 1000fpm the norm, while other operators may allow up to 1500fpm as nescessary to comply with steep approach procedures (ie a 4,5 degree approach requires 900fpm with 120 kts, that leaves very little leeway if the limit is 1000fpm.

For your specific limitations, consult your operations manual. What applies to someone else may not necessarily apply to you.

[bfisk]

official
Now THAT's an interesting word.

I would very much like to see an official stabilised approach concept, as set forth by a regulator. I honestly have never seen one, that might be bad on my part, but is there really such a thing?

I've looked a bit into your FSF link, and I think what is said there makes good sense, and I'm not disagreeing with you on the fact that thrust/min.power setting should be a factor, my bad for forgetting to include that.

However it is my understanding that the FSF is no more "official" than you or me or anyone else -- they have more credibility for sure, but that doesn't make it official.

My two cents are still that whatever stabilised concept your company/operator has determined in it's ops manual, is approved by the appropriate authority, is the only thing valid for you. And it will vary from operator to operator.

[411A]

re circling approaches, only the sink rate is allowed to deviate from the NORMAL stabilized parameters, and only till 500' (which you are allowed on VMC anyway), plus you gotta do a specific brief on that.

Specific briefing for this and that...rubbish.
Circling approaches in our ops manual are very clearly laid out, and line pilots are expected to conform.
And...they do.

The 500 hours guys...and the 3000 hour Senior First Officer types.
Rocket science, it ain't.

And besides...el Capitan is there to correct for any difficiencies on the part of the younger folks.

We use the 'quiet concept FD' scenario...the less said, the better.
This forces the younger guys to actually read and understand the ops manual, and fly accordingly.

And...they do.
OMG, what an absolute surprise....shock, horror.:}

[bfisk]

Thank you! I didn't know that (honestly). :)