I would like to thank one of our students, Bryan, for submitting the following question. Keep the questions coming!
*Image from FAA Pilot's Handbook of Aeronautical Knowledge, pg.14-22.
Question
Once you turn base, what altitude are you supposed to maintain? Also, on final once you've turned at what point do you want to begin begin your descent?
We can cover this with a pretty simple answer (the short answer), or we can dive deeper into the details (the long answer).
Short Answer
You're going to begin your descent abeam the touchdown point on the runway. Therefore, your descent will begin already on the downwind leg of your traffic pattern. Generally, you'll turn base when the runway is at about a 45° angle behind you. However, this could change depending on the wind or, if ATC is telling you otherwise (i.e. "I'll call your base turn").
Long Answer
Non-Towered Airport, like Hampton Airfield (7B3) - let's say runway 20
Enter the pattern at a 45 degree angle. On the radio: "Hampton traffic, RV 271VA (or "green RV") is on the 45 runway 20, Hampton." You should be at traffic pattern altitude (TPA) when on the 45.
The 45 will take you to midfield downwind. On the radio: "Hampton traffic, RV 271VA is midfield downwind 20."
Abeam the numbers (or your landing point), pull your power back to idle. Hold the nose up (maintain altitude) until you hit your approach speed. Let the nose down until you can maintain your approach speed. Add a notch of flaps. You will continue your downwind leg until you have lost about 300 feet of altitude (TPA - 300').
As you're passing through TPA-300', make your base turn and add your second detent of flaps. On the radio: "Hampton traffic, RV 1VA turning base runway 20, full stop, Hampton." (I like to add "full stop" at the end so the person behind me can plan spacing accordingly. I certainly appreciate it on a busy pattern day so I can extend my downwind instead of do a go-around due to traffic on the runway.) Descend another roughly 300 feet - so now you'll be TPA-600.
As you're passing through TPA-600 (may be more like TPA-500 if you were a little close to the runway on downwind), make your turn to final. On the radio: "Hampton traffic, green RV turning final runway 20, full stop, Hampton." You have two detents of flaps down, you're right on your approach speed, you're in a good place.
Continue your approach on final. Keep in mind that if you planned everything correctly, did your turns at the right altitudes, and judged the wind properly, then you have been at idle power since abeam the numbers on downwind. If you're high, slip it a bit. If you're low, add a shot of power. Remember, pitch for speed and power to control your rate of descent. When it comes down to it, I'd rather have an extra 100 feet of altitude that I have to slip off than not have it and wish I did (in the event of engine trouble).
Note that the above assumes no, or light wind. If you have significant wind, you'll obviously have to make the appropriate corrections.
Towered Airport, let's say Pease runway 34
The towered airport situation could be a little different since ATC may call your base turn, you might need to make a larger pattern to integrate with other aircraft, etc.. Let me walk you through a situation I experienced yesterday.
I'm at 1500' about 5 miles east of KPSM. I pick up the ATIS and call up the tower. They tell me to report a 2 mile left base runway 34. Okay, dandy. Now what?
I always make sure that as soon as I know I'll be in the pattern at Pease (vs just flying through the class D), that I'm at pattern altitude. That's about 1100'.
Now consider that, since airport elevation is 100', you have 1000' to descend to hit the runway. Let's say you want to descend at 500 feet per minute (fpm). That'll take you two minutes to descend 1000' (1000ft/500fpm = 2 min, see below eq1). You may want to consider a 300 fpm descent instead. If so, then 1000ft/300fpm = 3.3min, so about 3 minutes and 20 seconds to descend 1000'. For simplicity, let's stick with the 500 fpm descent for now.
If your speed is 60 kts (nautical miles per hour), then that'll take 2 nautical miles to descend 1000 feet (see eq2 math below). So, if I start a 500 fpm descent when I'm 2 miles out from my landing point, then I'll hit the runway right where I want to. Notice how the units cancel out... I had to change nm/hr into nm/min since I had calculated my descent time in minutes.
Your E6B flight computer will help you with this stuff too, but with practice you can do a lot in your head.
Now, do I do this math in my head every time I go to land? Honestly, no. Once you do the approach enough times and you get to know the airplane, you'll be able to judge your distance from the runway and figure out when you need to start your descent. You'll be able to picture the glide slope in your head.
If you have the luxury of the airport being super quiet and it's just you in the pattern, then you can fly the non-towered airport approach. These are all just tools and they could be used at really any airport. It's your job as the pilot to pick which tool or set of tools you want to use for any given situation.
Additional Resources
You may want to check out some additional resources. Take a look in the Pilot's Handbook of Aeronautical Knowledge (PHOAK for short) chapter 14 - Traffic Patterns. You can also check out the Airplane Flying Handbook (AFH for short), chapters 7 - Airport Traffic Patterns, and 8 - Approaches and Landings. You can also check out the AIM section 4.3.3. of the FAR/AIM.
Thanks again Bryan for the question. Blue skies!!
- Ryan