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I am a low-time pilot, of approximately 200 hours. I trained on the DA20 and DA40, designs that are derived from the Diamond touring motor glider design(s) of the early 1990s. I anticipate getting my Glider rating this summer in the US. As I've considered getting my glider rating, I've noticed a habit that I've developed that closely matches the "glider pilot mentality" which does not seem so prevalent in my training for ASEL.

I've always preferred using a forward-slip for landing with the engine idle, as opposed to using the throttle to adjust the descent angle. I attribute this to multiple factors, such as being aware of the design history of the DA20, training with its more "glider-like" characteristics, and a general paranoia of the engine quitting on base or final.

This brings me to the following questions: What are the safety considerations for this type of approach? Are there limitations on the use of sideslip on light airplanes?

Edit: Supplement questions, for possible merge or replacement of above. (Taken from my comment below)

  • Instead of puttering in using throttle, why don't we use side slips all the time?
  • Why don't most/more GA aircraft have spoilers or dive brakes?
  • Is the mentality of "every landing is an engine-out landing" creating more danger than it alleviates?
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    $\begingroup$ For what it's worth, in my experience in the U.S. from the late 1950s through the 1990s, we used slips in aircraft with flaps almost exclusively for crosswind correction rather than for altitude correction. However, I was taught how to use slips for altitude loss, and would occasionally do so for practice, typically leaving the flaps up. I did still use slips for altitude loss in a Piper J-3 in the 1960s that didn't have flaps. Regardless of the aircraft type, we had no reluctance with regard to using the engine for glidepath control. $\endgroup$ – Terry Mar 1 '16 at 8:29
  • $\begingroup$ The edits to remove the opinion based elements are good, but I feel that they change the question substantially from the original. $\endgroup$ – J Walters Mar 2 '16 at 14:26
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    $\begingroup$ The spirit of the question is basically: "Instead of puttering in using throttle, why don't we use side slips all the time?" which may evolve into the question "Why don't most/more GA aircraft have spoilers or dive brakes?" . My mentality is that every landing is an engine-out landing, such that when I have a real engine-out emergency, it is no big deal. Is that mentality creating more danger than it alleviates? $\endgroup$ – Steve Mar 2 '16 at 16:33
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    $\begingroup$ @Lnafziger excellent list, will be busy reading those. $\endgroup$ – Steve Mar 5 '16 at 8:51
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Diamond aircraft are very low drag and do not have particularly effective flaps, so sideslipping is certainly an effective way to approach the problem. However there are considerations you need to be aware of:

  • A steeper approach can bring you down on top of another airplane on final approach. Maintaining a more common approach angle is safer as it is less likely to bring you into a potential collision, and keeps you on a path where other pilots are likely to see you
  • Steep sideslips are not particularly comfortable for passengers, the steep angle and different feel can be frightening
  • Having your engine idle for long periods can lead to ice buildup in your carburetor, even with the heat on. It also lets your engine cool down quite a bit. Keeping some revs on keeps things warm up front
  • A steep approach angle makes it harder to round out accurately
  • A mishandled sideslip can lead to a loss of control. If the ball is to one side and you get past the critical AoA you will be executing a snap roll at low altitude, which = bad

There's nothing wrong with using sideslip and keeping up with the technique - it's very useful if you catch a thermal on approach, are given a slam dunk approach, or need to get on the ground fast. For me it's not the best tool for normal approaches when you have alternatives, especially if you come in at a very steep approach angle.

One technique I've heard of for approaches on Diamond single engine airplanes is to use a combination of both: a slight sideslip dirties up the airflow enough to create some useful drag, and power is used to maintain the approach angle.

I can't think of a light airplane you can't sideslip, or any airplane you can't sideslip for that matter (perhaps the Mig 15). Sideslipping was used successfully in the Gimli Glider incident, and that was a 767! There are limitations which will be listed in the aircraft documentation, for instance you should not sideslip a C152 above 20 degrees of flap. If I'm flying a C150/152/170/172 I follow that rule.

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  • $\begingroup$ I don't recall any restrictions on slipping the C152 with flaps. I do recall the 20 degrees of flaps limitation on the C172, however. $\endgroup$ – Fred Larson Mar 1 '16 at 16:19
  • $\begingroup$ A note on carb icing: I have been further spoiled in my training on the DA20's in that they are fuel injected: I've never had to worry about carb heat. But the point on engine cooling is quite valid. $\endgroup$ – Steve Mar 2 '16 at 16:44
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    $\begingroup$ Please update article with authoritative evidence for carb ice with full carb heat $\endgroup$ – rbp Mar 4 '16 at 16:10
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    $\begingroup$ @fred that is not a limitation. Its mentioned but not in the limitations section, and is worded as a "should" $\endgroup$ – user13148 Mar 4 '16 at 16:58
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    $\begingroup$ @Dawn: Agreed.. $\endgroup$ – Fred Larson Mar 4 '16 at 17:19
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When we learned to fly in low-lift airfoil tailwheels, with radial or early flat-4 engines, we always expected an engine failure. Patterns were close-in, power was idled turning base (pace winds), and landings were made 3-point in a full stall. And the trainers (eg Cub, Citabria) didn't have flaps, so you learned slips to landing.

With the advent of nose wheels, better airfoils, and the marked improvement of engines, the rate of non-fuel-exhaustion engine failures declined, and we could make bigger patterns and expect that some power would carry us to the threshold.

What we lost is a sense of what it takes to make it to the runway. And indeed the airplane private PTS only needs to show a simulated engine failure:

enter image description here

The commercial PTS, however, requires that the pilot demonstrate a power-off 180 landing:

enter image description here

which more closely represents how pilots were originally taught, and how tailwheel pilots are still taught, especially those flying radials and early trainers, like the Cub.

That being said, although slips to landing are a normal procedure, they are not the recommended procedure for either airplanes or for gliders (almost all of which have some kind of drag device).

My preference (winds permitting):

  • light tailwheels: power-off 180 to a 3-point
  • high-drag tailwheels: power-off below 300ft to a 3-point
  • nosewheels: low-power (1500 rpm or 15")
  • gliders: sufficient use of drag device for a 10:1 approach

In all cases, I am high rather than low, and close in rather than further out in the pattern.

A no-flap landing in an airplane, which is a normal procedure, requires more airspeed because the stall speed is higher, so the approach is flatter and the airspeed is higher.

No flap landing checklists in airplanes do not specify a slip, although slips are still used as necessary. In my airplane, a no-flap landing requires 10 knots higher airspeed because the flaps are so effective.

In an airplane that has not-very-effective landing flaps, such as the DA20 (which I have never flown), the airspeed differential between take-off flaps and landing flaps would be much smaller, and indeed this is what shows up on the checklist:

enter image description here

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