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This is a follow up question to the earlier question about landing a
DA40. Can you please provide more detail on your settings starting
with abeam the numbers downwind?
I'm a student pilot in a DA40 and my problem is that in order to end
up 400 AGL base to final I pull back the throttle to 9" MP abeam the
numbers. However, I then end up with too great a sink rate once I go
full flaps on final.
When you wrote 12" MP, is that your setting abeam the numbers? What
altitude are you at base to final.
Any help you can provide is appreciated?
-- George Swetlitz, May 31, 2006
Tal's answer below makes a lot of sense for a flight instructor in GA planes. If you own an airplane, however, or you are flying a slow-to-respond jet, or you are flying instruments, it makes sense to use a catalog of power settings and "fly by the numbers, then tweak".
First of all, I would have 500' AGL as a goal for base-to-final, rather than 400' AGL. Depending on weight, usually around 10-11 inches of manifold pressure will accomplish this goal. Then when you put full flaps in, at perhaps 300' AGL, you'll have to add power up to 15-17" to stay on a reasonable glide slope.
I suggested 12" for you because I thought maybe you'd want to try flying a slightly wider/longer pattern and getting stabilized on final with a fair amount of power in. If you want to land extremely short, this is not a good technique, but if you want to land very smoothly (and still very comfortably on a 2500'+ runway), power and a longer shallower approach make sense. The old-timers will tell you that you shouldn't fly the 3-degree VASI in a single-engine plane because you won't make the runway if the engine quits. That is true, but it is very rare for an engine to quit during final approach.
One interesting thing for you might be to go to an airport with an ILS and 5000'+ runway and fly the VASI or PAPI all the way down from 1000' AGL. Get totally stabilized at 70 knots from 500' AGL. See how it feels. When you get that solid, go back to flying standard patterns and try to make the last 300' of the square pattern feel like the last 300' of the ILS approach.
-- Philip Greenspun, June 1, 2006
To answer the question on flaps and slips below... you can slip with full flaps and it won't hurt the airplane. On the other hand, if you have a runway longer than 2000' you might ask yourself "Why am I needing this slip and wouldn't a go-around be a better idea?" If you are just going from normal airport to normal airport, the slip should never be required. Why are slips taught for the Private certificate then? I'm not actually sure! The FAA doesn't say why they want you to know this stuff, just that you have to know it. If your engine quits and you need to put the airplane into a corn field, the slip could be a life-saver (you won't have multiple chances to set up for a perfect spot landing). If you are flying an airplane without flaps, you might need the slip. But for a plane like the DA40 with fairly effective landing flaps, the slip should never be necessary and adding it means that you've destabilized your approach.
-- Philip Greenspun, June 14, 2006
I'm merely a private pilot, and Philip can surely contribute more on this subject, but when I fly downwind I'm keeping track of my altitude and airspeed, and as I'm turning base I start my descent and stop tracking my altitude. The one and only instrument I follow is the airspeed indicator, for all the other parameters I look outside (just as I'm not checking the heading indicator to confirm I'm flying in the right direction or the attitude indicator to cofirm I have the appropriate final approach attitude). I don't know at which altitude I'm turning base-to-final, as I'm merely trying to keep the right glide path, and how far from the threshold I turn base varies significantly with factors such as traffic and so on.
All of that is obviously for VFR, which is a good thing, as I'm not IFR certified.
-- Tal Reichert, May 31, 2006
Thanks -- this has been helpful.
Philip -- do you know if there are any limitations on flap settings for forward slips in the DA40? I didn't see anything in the POH.
-- George Swetlitz, June 4, 2006
Slips are taught for a number of reasons.
For one thing, it can help you clear the area in front of and below the nose.
Second, it can help you get down if you don't have access to the flaps (equipment/electrical failure).
Third, not all airplanes have flaps, and after certification the student will be legally entitled to fly some of those planes.
Fourth, it can be useful during emergencies, as you pointed out.
Fifth, it can be the only way to land at some airports. Think about the wake turbulence from runway 19R at SNA. If you're landing on runway 19L, you can either go around 50 times in a row, or keep the plane a bit high to stay above the wake turbulence from that 757 and then slip it down once you're clear.
I could go on all day about the benefits of slips.
-- Ron Rapp, July 16, 2006