Why are you getting your instrument rating? Probably because it's a stepping stone to a commercial or maybe even a CFI certificate. Maybe because you own your own airplane and are looking to gain some extra flexibility when it comes to cross country flying. Whatever the reason, gaining an instrument rating will increase your confidence and accuracy of flight by reference to the instruments. One of the largest benefits being the ability to conduct instrument approaches.
Now instead of canceling your flight because of low visibility or low ceilings, you will be able to utilize an instrument approach and land hassle free. What comes from your training with a flight instructor in preparation for this rating will be basic attitude instrument flying, tracking and intercepting of navigation aids, holding, and instrument approaches. Along with the flying portion of your new rating, there are a lot of new applicable regulations to be familiar with.
Of the regulations, one in particular stands out as a common misunderstanding and is one often misinterpreted. 91.175(c) talks about operating an aircraft below the published minimums for an instrument approach. In order to continue flight below these minimums there are several conditions you have to meet.
First and foremost is keeping the aircraft in a position that will allow a normal landing using normal maneuvers and normal rates of descent. The FAA doesn't want you to arrive at the missed approach point, directly over the runway threshold at 800 feet, and attempt to land the aircraft on the 3500 foot runway. Consider that you will be in low visibility conditions, making a rapid descent to a runway that could potentially 'disappear' at any time in the low visibility or cloud layers.
Next they require that the visibility is not less than the prescribed minimums on the approach procedure. It's important to also keep in mind what they don't mention here. Ceiling. There is no mention of a ceiling requirement. Often times students believe that the minimums include visibility and the ceiling. If the MDA or DA is 200' and the ceiling is at 100', there is no legal restriction as long as you have at least the minimum visibility required being reported.
Now we get into the tricky part of this easily confused regulation. I often posed this question in oral exams to students. “What can I do if I arrive at DA on an ILS and I have the approach lights in sight, but I can't yet see the runway?” Often times I heard a recital of all the items listed that are required to be visible and distinctly identifiable. Threshold, threshold markings, threshold lights, runway end identifier lights, etc. They recited this list from rote memory because they were taught that if they don't see one of those items from the list, they have to execute a missed approach.
The truth is, if you arrive at DA or MDA with the approach lights in sight, you are legally allowed to continue a descent to 100 feet above the published touchdown zone elevation using the approach light system as a reference. Now if you begin your descent below the DA or MDA and begin to identify the runway, or any listed item, you can continue to land. Think of the approach light system as an aid in the transition from instrument flight to visual flight. They are the link between the two, and should be used as such.
Now a caveat to that is also mentioned in the regulation. It says you may descend to 100 feet above the touchdown zone UNLESS the red terminating bars or red side row bars are also distinctly visible and identifiable. What does that even mean?
What it should say is: If the runway the approach is serving has an ALSF-I or ALSF-II approach light system, visual contact with the red side row bar or red terminating bar authorizes you to continue the descent to land. You do not have to stop at 100 feet above the touchdown zone. Currently the only two approach light systems in the US that include the red side row and red terminating bars are the ALSF-I and the ALSF-II. Keep that in mind when you brief the approach, look at the approach light system so you know what to look for, and so you know what you will do when you get to DA or MDA.
You are getting your instrument rating to increase your ability to complete flights in lower than VFR weather conditions, complete understanding and application of this regulation will help you meet that goal.