Can you descend below DH or MDA??

[atpcliff]

Can you descend below DH or MDA??
I was reading the requirements for descending lower than the DH and MDA, am I correct to assume you must have:

1) Stabilized approach
I don't think this is a reg at all, but company policy about when you have to be stabilized or not.

2) Runway enviornment in sight
No. On an ILS you can have the approach lights in site at 200' AGL and continue. At 100' you need to have the runway lights/environment in site to continue.

3) Visibility greater than published for the approach
No. You have to have this visibility prior to the FAF, or whenever the final segment of the approach starts. If the reported vis goes down after this, you can continue the approach. You do have to have the "Flight Visibility" at DH/MDA, but not the "Published Visibility".

Also, you can leave MDA (and this applies to the DH also) to land when you have the runway environment in site, but you may later lose site, as in going into a thick cloud, and you may then have to go around at that time. In this case, in a C-172, your gear MAY hit the runway during the go around.


Correct me if I am wrong........

cliff
ABQ

 

[A Squared]

Can you descend below DH or MDA??
I was reading the requirements for descending lower than the DH and MDA, am I correct to assume you must have:

1) Stabilized approach

I don't think this is a reg at all, but company policy about when you have to be stabilized or not.

There is a requirement that you have to ba able to get tot he runnwasy using normena descent rates and manuvers. This isn't the same as a stabilized approach but it's probably where the confusion starts.

2) Runway enviornment in sight

No. On an ILS you can have the approach lights in site at 200' AGL and continue. At 100' you need to have the runway lights/environment in site to continue.

Actually, you may do the same on a non-precision approach also, although without vertical guidance there is more opportunity for screwing it up , as the guys in the Jetstream at Kirksville found out.

3) Visibility greater than published for the approach

No. You have to have this visibility prior to the FAF, or whenever the final segment of the approach starts. If the reported vis goes down after this, you can continue the approach. You do have to have the "Flight Visibility" at DH/MDA, but not the "Published Visibility".

Well, actually, his answer is correct, although it is useful to clarify that it's flight visibility you must have to descend below MDA, not reported visibility.

Requiring visibility to proceed past the FAF is a 121 thing, andh the question was a general one. That doesn't make it incorrect, but it should be noted that under part 91 only, there is no visibility requirement to begin an or continue an approach past the FAF. You make a distinction between "flight" visibility and "published" visibility which at best is confusing. The "published" visibility is the minimum visibility for the approach. To descend below the MDA or continue below DA, the "flight" visibility must be at or above the published minimum. To proceed past the FAF (or to even begin the approach under part 135) the "reported" visibility must be at or above the published minimum. "reported" visibility is used becuse obviously you can't determine flight visibility at the airport from 5-10 miles away, unless you can see the airport from there in which case visibility probably isn't a big issue.

 

[A Squared]

For the misinformed still out there, I happened across this. ​

Section 4 of the AIM (Arrival Procedures)​

4. Chart Terminology
(a) Decision Altitude (DA) replaces the familiar term Decision Height (DH). DA conforms to the international convention where altitudes relate to MSL and heights relate to AGL. DA will eventually be published for other types of instrument approach procedures with vertical guidance, as well. DA indicates to the pilot that the published descent profile is flown to the DA (MSL), where a missed approach will be initiated if visual references for landing are not established. Obstacle clearance is provided to allow a momentary descent below DA while transitioning from the final approach to the missed approach. The aircraft is expected to follow the missed instructions while continuing along the published final approach course to at least the published runway threshold waypoint or MAP (if not at the threshold) before executing any turns.

That's good. in fact it is spot-on, and doesn't leave a lot of room for argument. However. I'm suspect that it isn't going to change some minds. I suspect that the reaction even if not posted is going to be something along the lines of:

I don't care what the TERPS says or what the AIM says, or what the regulations say, or what you guys who do this for a living say! I was taught XX decades ago that you never descend below DH/DA so G0ddamnit, that's what I'm going to teach to my students!!!

Sad when someone gets so set in their ways that they lose the ability to consider that thier way may be incorrect.