undflyboy06

Thanks Texandrvr for finding those figures for me.

mistarose

Maybe it depends on how you define "normal rate" and "normal maneuvers?"

The FAA and Tower want you to land safely no need for clearances to leave MDA, they cancel IFR - nothing said as you know. Tower also will clear you to land before you even see the runway. I am unclear what you meant when you said "the tower clears you to continue VFR."

On a circling approach, I think the point made earlier about being able to see the obstructions says it all. You are cleared to land; you can see the airport environment and obstructions around the airport. Once you descend below MDA you definitely responsible for your own obstruction clearance even when you are within 1.3 miles radius protected (or whatever category/distance applies). If its too rainy and gusty down there then you execute the missed approach; however, if you feel you can safely avoid obstructions and make a landing on the appropriate runway then do it, if you like to be at the normal TPA altitude to make the landing "easier" since most pilots are used to doing so, then go for it.

I believe the 91.175 is interpreted many different ways, yet when it really comes down to it, PIC has final authority. Great discussion - keep it up!

mistarose

After posting I thought of something else:

This is out of 91.175:

(c) Operation below DH or MDA. Where a DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, at any airport below the authorized MDA or continue an approach below the authorized 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: (the airport)

When you are at TPA (after leaving MDA), and have these three requirements met - you are legal. I feel this small section spells it out, am I wrong?

Texandrvr

You're right. IF you have those 3 requirements met. Descending below the MDA and leveling off at TPA and then continuing the circle does not meet the first condition. It means when you can make a normal descent to land i.e. the base turn, final turn, it depends on your altitude and aircraft. But if you are nowhere near your final descent to landing then you are supposed to maintain MDA. The original question was about the LEGALITY and not the common sense thing to do. Obviously if you are familiar and you are VMC and you can see the obstacles then it would be safe to descend to TPA. Also realize that this is an abnormal situation. The normal HAA for circling approaches is 450' and the normal civilian TPA is 1000'. Of course there are exceptions to every rule though. If the circling MDA is above TPA it is because there is an obstacle within the final approach corridor or the circling radius. There is no secondary area for circling approaches, so the obstacle is within the area, not close to it. By studying the varying MDAs, knowing the various circling radii, and the HAAs you can sometimes determine the height of the obstacle and how far from the field it is. I have taught many a student that this is the most dangerous type of approach we do for a reason.

We all know that tower/approach will not use the words "clear to proceed VFR" because VFR is not a clearance. But legally you have to cancel IFR in order to deviate from your approach clearance. Descending below MDA before in a position to make a normal descent to landing is a deviation from that clearance. Remember a circlilng approach just like a visual approach is an IFR maneuver.

For the post that referenced the density altitude. Approach categories are based on IAS. But you can always use a higher category. So it is very prudent to be aware of your TAS and use the higher MDA if your TAS goes into the next category.

N261ND

if you have the airport in sight while doing an instrument approach, you should call it; "have the field in sight", and the tower will usually clear you for the visual approach. you then may proceed directly to the end of the runway (no pattern necessary), unless the tower instructs you "enter left downwind." If you don't have the airport in sight, stay at the MDA, period

Texandrvr

Absolutely. Good input.

mistarose

One thing that must be understood is that, to my knowledge the FAA doesn't say what you can and cannot do after you have legally descended below MDA. 91.175 says what criteria must be fulfilled to descend below MDA - there is no part of the regulation that says what criteria must be fulfilled while below MDA.

Except that if you get back into the clouds and can't see the runway then you should probably go missed with the initial turn being towards the runway environment.

I found an interesting article http://www.casa.gov.au/fsa/2001/sep/34-39.pdf

It is not for the US, its Australian rules as far as I can tell. But they do mention what conditions must be met to "descend within the circling area."


A pilot may descend below the MDA if:
• By night or day, the aircraft intercepts a
position on the downwind, base or final leg of
the normal landing traffic pattern, and,from this
position, can complete a continuous descent to
the landing threshold using normal rates of
descent and angles of bank. The aircraft must
maintain an obstacle clearance along the
flightpath not less than the minimum for the
aircraft performance category until the aircraft
is aligned with the runway.
• By day only, the pilot can maintain visual
contact with obstacles along the intended
flightpath and maintain an obstacle clearance
not less than the minimum for the aircraft
performance category until the aircraft is
aligned with the landing runway.

It’s nothing that different, but it does more clearly emphasize obstacle clearance and that you must make a CONTINUOUS descent to landing. My interpretation of this is that you may not level off at a TPA or anything like that, stay up there until you can descend continuously on one of the legs of the pattern to the intended runway. If you can level off at TPA during the day? I don’t know.

To summarize, in their regs - they specify that in the day, you may descend at your discretion whenever (possibly to TPA). Yet at night, you MUST stay at or above MDA until you are established on downwind, base or final and in a position in which you can continuously descend to land (not leveling off). Its all about obstacles and whether you can see them or not.

Texandrvr

Although interesting, Australia's rules obviously don't apply. The second rule actually makes circling less restrictive in Australia. The first rule is exactly the same as FAA. 91.175 says that you cannot descend below MDA until continuosly in a position from which a descent to a landing can be made at a normal rate of descent. That means that if you are not in a position to start your FINAL descent to landing you cannot descend below MDA. A normal rate of descent does not include a level off. If you are circling and you're midfield downwind you cannot safely start a descent to landing, so you can't legally descend below MDA.

Doing a quick google search gave FAA man 8400.10 which is the checkride criteria for ATP checks. The paragraphs on circling may clarify some.
"...The airplane must not descend below MDA until the runway environment is clearly visible to the applicant, and the airplane is in a position for a normal descent to the touchdown point"

Many people have died, in everything from a 152 to a 747, while circling while below the wx after commencing the circle, presumably in a position to see and avoid the obstacles.

BTW do you have an IAP in mind where the circling MDA is above the TPA?

mistarose

http://www.airnav.com/depart?http://...11/00130VB.PDF

I have done this approach several times, just an example.

Texandrvr

That is a good example. Obviously there are alot of obstacles in the area and the controlling obstacle doesn't appear to be in the circling radius, but either in the final segment or the MAP corridor. It's a good example of when, if you are very familiar with the field, you may be able to descend out of MDA early in a safe manner. But that does not make it legal or the safe thing to do for someone unfamiliar.

If you have access to past "IFR Refresher" articles I'll refer to the TERPS Review articles in issue 97 11 and 96 01. They go into good detail on how circling approaches are created and how they can and should be safely/legally flown.