Circling approaches

mryan75

Pattern Altitude
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mryan75
Hey folks,

When you are making a circling approach, and you have the field in sight prior to reaching the MDA, can you then descend below the MDA on the approach while making the circling maneuver to the landing runway? Like at my home field, the circling MDA on the ILS or LOC runway 33 (at KRME) is 1140. So I'm on the circling approach, ILS 33 circle to land 15, I see the field prior to reaching 1140 feet, I can then descend below that altitude, and stay below that altitude, so long as I can still see the field, correct?
 
Hey folks,

When you are making a circling approach, and you have the field in sight prior to reaching the MDA, can you then descend below the MDA on the approach while making the circling maneuver to the landing runway? Like at my home field, the circling MDA on the ILS or LOC runway 33 (at KRME) is 1140. So I'm on the circling approach, ILS 33 circle to land 15, I see the field prior to reaching 1140 feet, I can then descend below that altitude, and stay below that altitude, so long as I can still see the field, correct?

Nope, you shouldn't descend below MDA until you are on the final for the runway you are landing on. The MDA protects you from obstacles, and on an MDA once you see the airport you are supposed to keep it in sight. Most MDAs are well below pattern altitude, so not sure why you would need to be any lower until you are lined up to land. At your airport that MDA is about 600 feet agl, that's pretty low.
 
Or, if you want to legally, but not necessarily safely, then just ask for the visual once you are VMC
 
Nope, you shouldn't descend below MDA until you are on the final for the runway you are landing on. The MDA protects you from obstacles, and on an MDA once you see the airport you are supposed to keep it in sight. Most MDAs are well below pattern altitude, so not sure why you would need to be any lower until you are lined up to land. At your airport that MDA is about 600 feet agl, that's pretty low.
This is exactly what I was wondering, thank you. And yes, it is pretty low, it's weird making a pattern that low. I'm basically wondering for the checkride, but I realized that I've never seen this specific question addressed.
 
doesn't a circling app only provide 300' obstacle clearance?
 
Nope, you shouldn't descend below MDA until you are on the final for the runway you are landing on.

Correct me if I'm wrong, but I believe it's "when in a position to land" or some such.

I've seen some circling minimums that are pretty high. At least higher than I'd want to be on final that close to the runway.

Edit: Better wording...

"In a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers"
 
Or, if you want to legally, but not necessarily safely, then just ask for the visual once you are VMC

I get what you are saying but so the OP is clear, I believe you must have VFR minimums to cancel while airborne. (If he was at 2000'agl and saw the airport, no problem)

P#2 poses that the MDA is 600'.
What I am thinking of is if he was in the pattern at 610' agl, I believe that would not be vfr minimums anywhere; and I have heard of violations for 'being nice to the guy behind/trying to get out' by canceling when airborne but the vis/ceiling was below vfr minimums.
Corrections welcome, I need to learn this better too.
 
Correct me if I'm wrong, but I believe it's "when in a position to land" or some such.

I've seen some circling minimums that are pretty high. At least higher than I'd want to be on final that close to the runway.

Edit: Better wording...

"In a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers"

Yeah, that's probably more accurate, thanks.
 
91.175 is rather clear on this.

b) Authorized DA/DH or MDA. For the purpose of this section, when the approach procedure being used provides for and requires the use of a DA/DH or MDA, the authorized DA/DH or MDA is the highest of the following:

(1) The DA/DH or MDA prescribed by the approach procedure.

(2) The DA/DH or MDA prescribed for the pilot in command.

(3) The DA/DH or MDA appropriate for the aircraft equipment available and used during the approach.

(c) Operation below DA/DH or MDA. Except as provided in §91.176 of this chapter, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—

(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;

(2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and

(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.

(ii) The threshold.

(iii) The threshold markings.

(iv) The threshold lights.

(v) The runway end identifier lights.

(vi) The visual glideslope indicator.

(vii) The touchdown zone or touchdown zone markings.

(viii) The touchdown zone lights.

(ix) The runway or runway markings.

(x) The runway lights.
 
I can then descend below that altitude, and stay below that altitude, so long as I can still see the field, correct?

What altitude are you looking to descend to, where [on the approach]?

The word continuously is the tricky part to 91.175. Just when are you "continuously" in position? If there's only 1 runway are you "continuously" in position even when off to the side for the entire downwind for the circling approach or are you only in position when on base or final or abeam the point of intended landing?

Second to that is what constitutes a "normal" maneuver or descent. Is a power-off 180 a "normal" maneuver? It's supposed to be, its supposed to be an energy management maneuver with as normal a pattern as you can make it though most instructors teach it as more of an emergency engine failure maneuver since on a checkride you wouldn't be allowed to add power back in (and since the most common complex trainer available prior to the rule change last year was the Piper Arrow with its Hershey Bar wings which sink like a rock, you usually didn't have a very square pattern and had one continuous turn downwind-to-base-to-final)... so that's usually how I see it practiced and even then most people dont regularly practicing the maneuver outside of practice for their commercial so I wouldn't consider it a "normal maneuver" for most people. Similarly a forward or side slip both are regularly considered normal maneuvers but you may have to reject on "stable approach" criteria if you're having to slip it in too much. There are places where a penetration approach is considered not only "normal" but required (granted GA pilots aren't likely to encounter them).

For most circling approaches, these considerations are pedantic and overkill
Looking at KRME, it falls into that category. The field elevation is 500 ft so an MDA of 1150 is going to give you 650' agl. That's a base leg altitude. I wouldn't descend below that on a visual approach until base at which point I think you can easily make the argument you are "continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers." 600 ft seems to be about the average for a circling approach which is probably why alternate minimums for a non-precision approach are 800ft-2miles, it gives you 200 ft below the clouds at MOST airports with a circling non-precision approach.

That being said, there are some outlier airports. The VOR approach into KPSP has minimums of 2300 and the runway is at 474 ft. That's puts me at 1825 ft AGL over the airport which is 825ft above pattern for a non-turbine, small-piston plane such as myself (and 325 ft over pattern for a turbine). Its easy to see why; KPSP is nestled into a valley with rapidly rising terrain in pretty much all directions except to the Southeast and while the airport is 474 ft the VOR for PSP (which is about 4 miles to the NorthEast of the field) is at 1687 ft with other higher obstacles to the North and West of the field.

Still being at 1825ft AGL on a day at minimum visibility in a Category A/B approach (1 SM) and having to circle to land on 13 would make for an awfully tight and steep pattern even if I were to execute a power-off 180 and throw my flaps out full early in the approach (since my engine hasn't actually failed I'm not as concerned about the additional drag and actually want it in this situation since I'm high). Just doing the math, abeam the threshold of 13 on a 3/4 mile pattern would give approximately 2.25SM (2NM) to descend right on the very edge of (actually a little past due to the angular path) visibility on the downwind-to-base turn with the threshold at the 45-degree point (.75^2 + .75^2 = 1^2). Coming down 1800ft in 2NM works out to a 9-degree glide slope, almost certainly above "normal descent" and "stable approach" criteria. In this case I would argue a "normal maneuver" with "normal descent" is a traffic pattern and would descend to 1474/1000ft AGL and execute accordingly. Just be ready to cram and climb the second you lose visibility of the field.
 
Hopefully on all circle to land approaches with visual approach lighting you don’t descend until you see the light and determine you are not below the visual glide path.
 
Hopefully on all circle to land approaches with visual approach lighting you don’t descend until you see the light and determine you are not below the visual glide path.
Unfortunately those lights don’t curve around onto downwind or base.
 
Just about all the time WX will be enough above circling mins one can just transition to a visual type pattern at the appropriate time, that may be 800-1000’ AGL. Of course if on a checkride or the WX is actually near mins, adjust as needed.

As posted above I wouldn’t be in any hurry to start down until you have to.
 
The Check ride answer....
IR.VI.D.S5 Establish the Approach and landing configuration for the situation and maintain altitude +100/-0 until a descent to a normal landing can be made.

IMO that means once you go below the MDA you should continuously be descending in a normal manner until you round out for the flare.


Brian
CFIIG/ASEL
 
Best advice! Cancel IFR then proceed below MDH. There are several “Gotchas” that are rarely enforced but can be used against you in a (you get the picture)!


Sent from my iPhone using Tapatalk
 
Next time you do a circle to land see how quickly they do come into view on base.

AIM:

The visual glide path of the VASI provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4 NM from the runway threshold. Descent, using the VASI, should not be initiated until the aircraft is visually aligned with the runway.

If you wait that long, you may be too high to initial a normal landing using normal descent rates and maneuvering.
 
AIM:

The visual glide path of the VASI provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4 NM from the runway threshold. Descent, using the VASI, should not be initiated until the aircraft is visually aligned with the runway.

If you wait that long, you may be too high to initial a normal landing using normal descent rates and maneuvering.

Stop and think about this. A difference between a straight in approach course and the extended runway centerline can be 30 degrees. The reg says you may descend below the MDA when you have the visual approach indicator.
 
Just to check, this pertains to instrument flying, not VFR?

In the real world, we’re allowed to look outside before the MDA and the MAP. We also have various levels of circling approaches. Some may just be a 40 degree offset, the next may be to the opposite end of the approach runway. Of course the weather at the time factors in, as to what’s possible.

For just about every rule, one can find an exception.
 
I don’t get that far from the threshold in a VFR pattern...why would I do it on a circle to land?

I don’t know because on a typical VFR traffic pattern I can always see the visual indicator well before I turn final. If you can’t maybe your patterns are a bit tight.
 
I don’t know because on a typical VFR traffic pattern I can always see the visual indicator well before I turn final. If you can’t maybe your patterns are a bit tight.
I can see it before I turn final, but I’m always descending before that, VFR or IFR.
 
Stop and think about this. A difference between a straight in approach course and the extended runway centerline can be 30 degrees. The reg says you may descend below the MDA when you have the visual approach indicator.
Same for you. The 30 degrees is for straight-in approaches, not circles. For offset straight-ins, see figure 3-3-3 in TERPS.
 
When you are making a circling approach, and you have the field in sight prior to reaching the MDA, can you then descend below the MDA on the approach while making the circling maneuver to the landing runway?
This is very tempting to do under certain circumstances, and quite lethal. Breaking out, seeing the runway and descending in order to stay visual below a sloping cloud deck on a straight-in approach killed people in a Merlin a long time ago at KCGF. It also wiped out the Marshal State football team at Morgantown, WV, IIRC.

My advice: Maintain MDA until turning final and until you HAVE to start down, not before.
 
There's no requirement for an obstacle identification surface in that area you're descending. Only on final, see TERPS figure 3-3-2. Could be problematic at night. Just sayin'..
It’s a visual descent from MDA to the runway. I can see outside. I don’t see that it’s more problematic than descending out of pattern altitude VFR before turning final.
 
You are allowed 1.3 nm from the threshold, use it.

You’re given a distance based on the required turn radius of an aircraft at the maximum speed for the category of the approach. The category of approach is determined by your Vref speed or 1.3x Vs0 speed, in the case of 1.3NM we’re talking a Cat B approach with a Vref of less than 121 kias.

If you’re using all 1.3 NM and flying at a speed well under 121kias you are not only flying a significantly wider pattern than you need to/should but are going to have a heck of a time transitioning to anything faster especially if you intend to remain in the same category.

Of course there are other problems with the way they determine the radius...

The turn radius is based on Vref or Vs0 which is an indicated speed and does not account for winds or pressure altitude (important more at higher altitude airports on Cat C/D approaches where the error is more significant) which can increase your turn radius.

Also, the minimums are often less than the radius often by a rather significant margin (1SM=0.87NM so radius is 50% wider than visibility) which means at certain speeds, especially near the maximum for the category, it may not be possible to complete the approach as you are unable to turn in a smaller radius and you’ll lose visibility of the runway in the turn.


Stop and think about this. A difference between a straight in approach course and the extended runway centerline can be 30 degrees. The reg says you may descend below the MDA when you have the visual approach indicator.

Approach indicators are usually around 1,150 ft down the runway (top of the 1000’ markers). Approach indicators permit you to descend below 100’ AGL (measured from TDZE) to land but there are several other indicators that you can also use to descend to land such as REIL lights that will come into view much earlier.

To descend to 100’ AGL from TDZE you need only have the runway environment in sight, which is most often the approach lighting but could also be the runway.

If you wait to have the Approach Indicator lights in sight to descend from MDA at visibility minimums of 1SM on an approach such as the one in to KPSP, you could descend at 900fpm at 60kts (an unstable approach and 9 degree glide slope) and you would land with less than 1000’ remaining of a 9000’ runway.

5,280’ visibility - 1250’ approach indicator displacement = start of descent 4030’ before runway.
4000’ + 9000’ length of runway = 13,030 ft available for descent.
12,152 ft = 2 NM. 1825 ft AGL / 2NM = 912 feet per nautical mile and 60 kts is 1 nm/min meaning 912 fpm to land with 848’ left.

That’s at 60kts. At 120 for Cat B, you’re talking 1800fpm and decelerating from 120 to 0 in 8 seconds experiencing -0.68g. Above 120? Pretty sure you’re bracing for an overrun

I’d advise you begin your descent below MDA before the visual approach indicators come into sight as this still ignores the fact that you might not have the approach indicators for another 320ft if flight visibility is 1SM (slant distance vs horizontal) and the response delay both human and mechanical from acquiring the approach indicators to actually descending.
 
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You’re given a distance based on the required turn radius of an aircraft at the maximum speed for the category of the approach. The category of approach is determined by your Vref speed or 1.3x Vs0 speed, in the case of 1.3NM we’re talking a Cat B approach with a Vref of less than 121 kias.

If you’re using all 1.3 NM and flying at a speed well under 121kias you are not only flying a significantly wider pattern than you need to/should but are going to have a heck of a time transitioning to anything faster especially if you intend to remain in the same category.

Of course there are other problems with the way they determine the radius...

The turn radius is based on Vref or Vs0 which is an indicated speed and does not account for winds or pressure altitude (important more at higher altitude airports on Cat C/D approaches where the error is more significant) which can increase your turn radius.

Also, the minimums are often less than the radius often by a rather significant margin (1SM=0.87NM so radius is 50% wider than visibility) which means at certain speeds, especially near the maximum for the category, it may not be possible to complete the approach as you are unable to turn in a smaller radius and you’ll lose visibility of the runway in the turn.




Approach indicators are usually around 1,150 ft down the runway (top of the 1000’ markers). Approach indicators permit you to descend below 100’ AGL (measured from TDZE) to land but there are several other indicators that you can also use to descend to land such as REIL lights that will come into view much earlier.

To descend to 100’ AGL from TDZE you need only have the runway environment in sight, which is most often the approach lighting but could also be the runway.

If you wait to have the Approach Indicator lights in sight to descend from MDA at visibility minimums of 1SM on an approach such as the one in to KPSP, you could descend at 900fpm at 60kts (an unstable approach and 9 degree glide slope) and you would land with less than 1000’ remaining of a 9000’ runway.

5,280’ visibility - 1250’ approach indicator displacement = start of descent 4030’ before runway.
4000’ + 9000’ length of runway = 13,030 ft available for descent.
12,152 ft = 2 NM. 1825 ft AGL / 2NM = 912 feet per nautical mile and 60 kts is 1 nm/min meaning 912 fpm to land with 848’ left.

That’s at 60kts. At 120 for Cat B, you’re talking 1800fpm and decelerating from 120 to 0 in 8 seconds experiencing -0.68g. Above 120? Pretty sure you’re bracing for an overrun

I’d advise you begin your descent below MDA before the visual approach indicators come into sight as this still ignores the fact that you might not have the approach indicators for another 320ft if flight visibility is 1SM (slant distance vs horizontal) and the response delay both human and mechanical from acquiring the approach indicators to actually descending.

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It’s a visual descent from MDA to the runway. I can see outside. I don’t see that it’s more problematic than descending out of pattern altitude VFR before turning final.
I'm not saying the starting altitude might be problematic, the lack of lighting might be because lighted obstructions are only required on final.
 

Shame on me for not reviewing/confirming all reference material before posting. I should know better by now.

Yes, expanded circling minimums account for Pressure Altitudes. They still dont account for winds and more importantly while the FAA did develop expanded circling maneuvering radius and update TERPS, they did not mandate all circling approaches be redesigned/re-evaluated for compliance with the new radii.

I also note the minimums for such approaches are still much shorter than the maneuvering radii which is actually made worse under the expanded circling maneuvering radii standards. A Category B approach still generally can be done with 1 SM of visibility but has an expected pattern that takes you 1.7NM from the threshold.

Even if you were to do a downwind to final turn in Cat B at 120 Kts and 25 degree angle of bank you would need a pattern that is .888 NM wide (turn radius in NM = velocity^2 / ((11.26 * tan ( 25 ) and you need to make 2 such turns to make a full 180). 0.888 NM gives you no base leg to speak of and visibility minimums of 1SM or .87NM are still ever so slightly off (about 100 ft short).

I also realize I mis-stated Category B approach radii as 1.3NM which are now 1.7NM and were 1.5NM under the old radii. This doesn't really affect any of the points I made but they would have been stronger made without the inaccuracy.
 
Shame on me for not reviewing/confirming all reference material before posting. I should know better by now.

Yes, expanded circling minimums account for Pressure Altitudes. They still dont account for winds and more importantly while the FAA did develop expanded circling maneuvering radius and update TERPS, they did not mandate all circling approaches be redesigned/re-evaluated for compliance with the new radii.

I also note the minimums for such approaches are still much shorter than the maneuvering radii which is actually made worse under the expanded circling maneuvering radii standards. A Category B approach still generally can be done with 1 SM of visibility but has an expected pattern that takes you 1.7NM from the threshold.

Even if you were to do a downwind to final turn in Cat B at 120 Kts and 25 degree angle of bank you would need a pattern that is .888 NM wide (turn radius in NM = velocity^2 / ((11.26 * tan ( 25 ) and you need to make 2 such turns to make a full 180). 0.888 NM gives you no base leg to speak of and visibility minimums of 1SM or .87NM are still ever so slightly off (about 100 ft short).

I also realize I mis-stated Category B approach radii as 1.3NM which are now 1.7NM and were 1.5NM under the old radii. This doesn't really affect any of the points I made but they would have been stronger made without the inaccuracy.
You make some interesting points. For an ol' guy like me, the old circling radii still stands. I had it memorized whereas the new ones I'd need to refer to a chart. Never had a problem staying inside the old ones anyway. As for the vis limit and staying closer than that, well, it helps to pick a homing landmark 1/2 mile off the approach end of the runway, so if you DO lose sight of the threshold, temporarily, you still know where you are. If the legality of that is concerning, I suppose you could ask for a contact. I'd rather keep my mouth shut.
 
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