Vectoring to final is one of the more labor intensive tasks associated with air traffic control requiring a great deal of attention by both the pilot and controller. The requirement by ATC is that they shall inform pilots to "expect vectors" as soon as practicable. This is the big clue that you will be vectored to intercept a portion of the the approach, more often that not the final approach course. Regardless, the controller should inform you where you're going to be vectored. 95% of the time it's something like this: "MTN199, expect vectors, ILS Runway 3-4 right final approach course." Immediately my job as a pilot is to locate and analyze the approach chart labeled "ILS or LOC RWY 34R" at KSLC. Let's take a second and review it:
There is A LOT of information on there to a new pilot, but over time you'll get to know what most of it means. First let's talk about the lateral approach profile. Every approach has an initial approach fix (IAF). Look at the graphical portion of the approach and you will identify only two, BOAGY and FFU. They are clearly labeled as IAFs. So when being vectored you can expect you will likely NOT be flying over an IAF, but rather vectored inside these fixes. So looking at the two routes from BOAGY and FFU, they share a common route from PLAGE, ATANE, SCOER, BESBE, GITBE. See all these fixes? OK, let's assume you're coming up from the south and your told to "expect vectors ILS Runway 3-4 right final approach course." The next instruction may be something like this, "fly heading 3-5-0, vector final approach course." Pretty obvious what's happened here. So a couple minutes goes along and you now receive a lengthy clearance like this:
"MTN199, 5 miles from SCOER, maintain 9-er thousand until established on localizer, cleared ILS Runway 3-4 right approach."
Some controllers may complicate it somewhat by adding a heading to fly, too, like this:
"MTN199, 5 miles from SCOER, fly heading 3-5-0, maintain 9-er thousand until established on localizer, cleared ILS Runway 3-4 right approach."
Regardless, it is clear of four things:
1) You are required to fly the last assigned heading and
2) You are required to NOT descend below a specific altitude UNTIL
3) You intercept the final approach course THEN
4) You descend along the descent profile.
Let's take a look at the descent profile for this approach (lower-righthand corner of approach plate). Typically ATC is going to vector you outside the fix they reference in the approach clearance, so SCOER in this example. At SCOER, the minimum crossing altitude is 9500 feet. But remember ATC permitted you to fly down to 9000 feet? This is because ATC utilizes minimum vectoring altitudes (MVAs) to get you BELOW the glideslope of the approach. Now, let's assume you've flown the aircraft to intercept the final approach course and you're heading straight-in on the 341 degree localizer, you've just passed SCOER, level at 9000 feet, but the glideslope is NOT active. What do you do? The best thing is to reference the descent profile. It clearly displays that you can descend to 7100 feet until intercepting the glideslope. Note that the glideslope on the chart is displayed by the gray shading. Once you reach 7100 feet, do NOT descend any lower until you intercept the glideslope. Once intercepted, begin your descent down the approach.
Now, let's take a look at final approach. First you need to know which category of aircraft you are. For brevity, most smaller props are Category A, most large turboprops and slow jets are Category B, most airline jets (B738, CRJ2) are Category C, and most "heavies" are Category D. Let's assume today you're flying a Category C aircraft. Look at the extreme lower-right corner to see what "minimums" are. There are two possible approach profiles:
1) S-ILS 34R = Straight-in ILS 34R
2) S-LOC 34R = Straight-in ILS (Localizer only, no glideslope) 34R
Assuming the glideslope is in operation, the S-ILS 34R fits our profile. Now this approach is boring (for learning purposes) in that minimums are the same regardless of category of aircraft, so minimum descent altitude (MDA) is "4422" feet, or as it states "200" feet above the runway surface. The reference to "1/2" means that visibility must be at least 1/2 mile for this approach to be flown. Notice that if the glideslope was inoperative you'd be utilizing the "S-LOC 34R" profile which in a Category C aircraft only permits you to descend to "4620" feet, but still only requires "1/2" mile visibility. But had you been flying a Category D aircraft the minimums were raised to "3/4" mile.
Next you either a) land the aircraft, or b) declared "missed approach" and fly the missed approach procedure unless otherwise instructed by ATC. Pretty simple. Sometimes in flight-sim we take it to the limit and keep descending below minimums, but in reality that is not permitted and is blatant breech of regulations. Anyway, that's about it. Hope you've learned something from this little exercise. There is quite a bit more information provided on the approach plate but this provides an example of what to expect when told to "expect vectors."
See you up there, Chad
NOTE -- Off topic, but related. The closest an ATC is permitted to vector you to the final approach course is defined as "1 mile outside the gate." The gate is defined as "2 miles outside the final approach fix (FAF)." The FAF is depicted on approach plates with a maltese cross. Therefore, with this repsective approach the absolute earliest point you'll ever be vectord by an ATC is 8.5 miles from touchdown (BESBE + 2 miles + 1 mile). By request a pilot can request to be vectored "inside the gate," but ATC is still prevented from vectoring inside BESBE + 2 miles. Not much of a savings. This explains why most of us get vectors 10 miles BEYOND an airport before turning back to final.
MTN199 Chad