I have been taught that you go missed approach if at any time you are inside the FAF and have a 3/4 or full scale deflection on the CDI. Is there anyplace that this is published or is it just considered good procedure?
I haven't heard that before. I go missed on a full scale deflection. I'm pretty sure that's in the AIM somewhere, but I can't quote you the exact chapter and verse. Look in the AIM and you'll find that.
If you're inside the FAF with 3/4 scale deflection, then you'd better either be correcting and getting back on course and glideslope, or considering going missed. The FAA Instrument Rating practical test standards, which are not regulatory (but represent a minimum standard of performance for a given level of certification) allows for up to full scale deflection prior to the final approach segment. However, after entering into th final approach segment, allows for only 3/4 scale deflecton. This is a rough, bare minimum standard, allowable at the Private Pilot level, on up.
The Airline Transport Pilot certificate practical test standards require the holder to adhere to the limits of 1/4 scale deflection. Does this mean that the holder of an ATP certificate must execute a missed approach at 1/4 scale deflection? Of course not. However, it is reasonable to expect that the holder of the ATP should be able to consistently do this. In the event of a deviation or enforcement action (or accident/incident), the pilot who failed to maintain that level of performance will come into question...especially if ourside those parameters, and not correcting or executing a missed approach.
The FAR doesn't specify that a missed approach will be executed at less than full deflection. However, one should seriously consider going back to try it again if performance has degraded to the point that the course or glideslope has escaped to that degree. Especially inside the FAF, attempting to correct back for gross errors may constitute an unstable or destabilized approach, and the best answer to lack of stability is the missed (in most cases).
The only refernece to going missed in 14 CFR 91, is 91.175(e), as follows:
(e) Missed approach procedures. Each pilot operating an aircraft, except a military aircraft of the United States, shall immediately execute an appropriate missed approach procedure when either of the following conditions exist:
(1) Whenever the requirements of paragraph (c) of this section are not met at either of the following times:
(i) When the aircraft is being operated below MDA; or
(ii) Upon arrival at the missed approach point, including a DH where a DH is specified and its use is required, and at any time after that until touchdown.
(2) Whenever an identifiable part of the airport is not distinctly visible to the pilot during a circling maneuver at or above MDA, unless the inability to see an identifiable part of the airport results only from a normal bank of the aircraft during the circling approach.
Notice that it does not indicate a percent of scale, or any deflection value. It makes reference also to subparagraph (c), which speaks only to operation below MDA/DH (now DA).
Full scale deflections are permitted unless specifically not authorized. Some approaches will specify that the user may not allow full scale, for example. However, as in most things, what is legal is not necessarily safe. What is safe is not necessarily legal. It must be both legal, and safe, or it is not acceptable. Sometimes it's prudent to simply execute the missed approach.
Learn something new everyday. Anyway here is my .02
i agree full scale go mist is a must. however the closer you get to mins the tighter you need to be with that.
on hard approachs, like when you have thick fog clouds to the ground and vis is at mins. If you reach the mins and you have even 1/4 deflection you most likely won't make it. you need to be precise as possible especially in the lower vis approachs and even then sometimes you don't get in.
I was thinking about this and came to this conclusion:
You cannot descend on your approach until you are established. If you go full deflection, you are no longer established because who knows what full deflection means .. you could be 12 degrees off or 25 degrees off. The needle is no longer accurate at full deflection as to how off course you are. You can no longer descend and must go missed to re-established yourself.
Just something I came up with because I am too lazy to walk 10 feet and look through my books for the answer.
If the needle is at 3/4ths and isn't moving back in, you can expect the controller to begin yelling at you so you might as well make the first move and go missed.