What Is The Lowest AGL You Will Slip Prior To Landing

One other comment. I slipped until about a second before touchdown on the engine fire on departure drill in the sim while doing training for a part 135 operation. The instructor accepted it as satisfactory on the first attempt. It was sorta funny because the monitor for my side window was out so I had to look across the cockpit and the left seater to judge the approach. A caravan descends very nicely in a slip…
 
Checkout_my_Six said:
What about with flaps?.....o_O
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Emoji noted, but still, a very-Cessna question. :)

Slips with flaps aren't even a debate topic in the low-wing Piper world — we just do 'em (with both wing variants). They give the plane nice, falling-rock aerodynamics if you have to lose a lot of altitude fast, and recovery to a normal descent rate is almost instant when you uncross the controls.

It can freak out the passengers (and ATC too, sometimes, seeing the altitude unwind on their scopes), so always best to give some warning.
 
Using a slip does not make an approach "unstable". A slip is just another tool in the toolbox, just like flaps are a tool, the throttle is a tool. I can slip an airplane all the way down final and still be stabilized. Truth is, too few pilots practice and use slips, or are afraid of them. I make sure all of my students not only know what a slip is, but use them and get comfortable with them.
 
If you're too high on final, and have already cut power and applied full flaps, there are three cheats left to get you down without accelerating:
  • Raise the nose almost to the stall and mush down (tricky, and dangerous in gusty winds)
  • Zigzag (will confuse anyone behind you and look goofy from the ground)
  • Slip (for the win!)
 
Zigzagging is preferred in Florida. Alligators can’t turn fast.
 
midwestpa24 said:
I can slip an airplane all the way down final and still be stabilized.
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Yes, but if you come out of the slip prior to the flare, you are by definition unstabilized.

note that I’m not arguing against slips in any form. I think the FAA didn’t think through the whole stabilized approach concept, which is nothing new for them.
 
MauleSkinner said:
Yes, but if you come out of the slip prior to the flare, you are by definition unstabilized.
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You might be able to push that back to the round-out before the flare, but point well taken.
I think the FAA didn’t think through the whole stabilized approach concept, which is nothing new for them.
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Agreed (and Transport Canada, too). Stabilised approaches make sense for big planes with lots of inertia — I imagine that if you're coming in short or too steep in a medium or heavy, a last-second configuration change at 50 ft AGL just changes your attitude and/or noise level when you smash into the ground — but it makes little sense for our light aircraft. It's like saying you should follow the same procedures for docking a canoe as you would for an aircraft carrier.
 
MauleSkinner said:
Yes, but if you come out of the slip prior to the flare, you are by definition unstabilized.

note that I’m not arguing against slips in any form. I think the FAA didn’t think through the whole stabilized approach concept, which is nothing new for them.
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Can you point me to where a stabilized approach as defined by the FAA precludes a slip.
A slip does not change the plane configuration, at least for me it has never adjusted the flaps, gear or prop control.

Tim

Sent from my HD1907 using Tapatalk
 
tspear said:
Can you point me to where a stabilized approach as defined by the FAA precludes a slip.
A slip does not change the plane configuration, at least for me it has never adjusted the flaps, gear or prop control.

Tim

Sent from my HD1907 using Tapatalk
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Since a the sole purpose of a forward slip (the topic of this thread) is to steepen the approach path, it would "destabilise" the approach from the FAA's or Transport Canada's POV if you did it partway through your final leg, just like dropping flaps or landing gear on short final. (Granted, if you held the same forward slip for your entire final leg, right down the the rollout, you could claim it's equivalent to flaps.)

That would not apply to a sideslip for crosswind correction just before touching down, of course, but that's not the kind of slip we've been discussing.

Like @MauleSkinner wrote, it's yet another example of why the "stabilised approach" dogma isn't a good fit for light pistons. We just don't need to be on exactly the same descent path for 2–5 miles like the big iron does. We have little inertia, our engines don't take 5 seconds to spool up to respond to a power change, etc etc
 
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tspear said:
Can you point me to where a stabilized approach as defined by the FAA precludes a slip.
A slip does not change the plane configuration, at least for me it has never adjusted the flaps, gear or prop control.

Tim

Sent from my HD1907 using Tapatalk
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https://www.faa.gov/news/safety_briefing/2018/media/SE_Topic_18-09.pdf
A pilot is flying a stabilized approach when he or she establishes and maintains a constant angle glidepath towards a predetermined point on the landing runway.
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Nothing in there about configuration, only approach angle. A forward slip, by definition, changes the approach angle, so unless you carry the slip all the way to the flare, you are destabilizing the approach.

also note that in the Private Pilot ACS, all landings EXCEPT the forward slip to landing have a stabilized approach as a “skill” criteria.
 
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Interesting, all the previous definitions I recall reading dealt with configuration not glide slope.

Tim

Sent from my HD1907 using Tapatalk
 
tspear said:
Interesting, all the previous definitions I recall reading dealt with configuration not glide slope.
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The AFH doesn’t define it in the non-turbine chapters, but in the Turboprop chapter, it says
In a stabilized approach, the airplane, depending on design and type, is placed in a stabilized descent on a glidepath ranging from 2.5 to 3.5°. The speed is stabilized at some reference from the AFM/POH—usually 1.25 to 1.30 times the stall speed in approach configuration. The descent rate is stabilized from 500 fpm to 700 fpm until the landing flare.
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The Jet chapter adds some other components...
The five basic elements to the stabilized approach are listed below.
• The airplane should be in the landing configuration early in the approach. The landing gear should be down, landing flaps selected, trim set, and fuel balanced. Ensuring that these tasks are completed helps keep the number of variables to a minimum during the final approach.
• The airplane should be on profile before descending below 1,000 feet. Configuration, trim, speed, and glidepath should be at or near the optimum parameters early in the approach to avoid distractions and conflicts as the airplane nears the threshold window. An optimum glidepath angle of 2.5° to 3° should be established and maintained.
• Indicated airspeed should be within 10 knots of the target airspeed. There are strong relationships between trim, speed, and power in most jet airplanes, and it is important to stabilize the speed in order to minimize those other variables.
• The optimum descent rate should be 500 to 700 fpm. The descent rate should not be allowed to exceed 1,000 fpm at any time during the approach.
• The engine speed should be at an rpm that allows best response when and if a rapid power increase is needed.
Every approach should be evaluated at 500 feet. In a typical jet airplane, this is approximately 1 minute from touchdown. If the approach is not stabilized at that height, a go-around should be initiated.
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So either the FAA actually defines the same term differently for different airplanes, or they’re really crappy at technical writing. Well, ok...the second one is kind of a given. ;)
 
tspear said:
Interesting, all the previous definitions I recall reading dealt with configuration not glide slope.

Tim

Sent from my HD1907 using Tapatalk
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I got my PPL and IR years before the "stabilised approach" thing took hold for light pistons in Canada and the U.S., but my understanding is that your aiming point should be the same for the entire approach, and that implies a constant descent slope (the prohibition on configuration changes is just to support that).

For IFR here in Canada, it's even more explicit: we're expected to hold a constant descent slope now for the whole final leg of even a non-precision approach during an IFR flight test or biennial IPC (no more dive and drive), and to help with that, Nav Canada approach plates usually publish the glide-path crossing altitude for every nautical mile and over the FAF.


D

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David Megginson said:
For IFR here in Canada, it's even more explicit: we're expected to hold a constant glide path now for the whole final leg of even a non-precision approach during an IFR flight test or biennial IPC (no more dive and drive), and to help with that, Nav Canada approach plates usually publish the glide-path crossing altitude for every nautical mile and over the FAF.
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Based on the (admittedly few) times I’ve seen pilots fly approaches that way, it turns a constant descent into several segments with different descent angles. I’m not really sold on it. ;)
 
MauleSkinner said:
Based on the (admittedly few) times I’ve seen pilots fly approaches that way, it turns a constant descent into several segments with different descent angles. I’m not really sold on it. ;)
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I can comment only on myself, but I find it useful for tiny adjustments in my descent (e.g. I'm 50 ft high or low crossing a mile point). Of course, if it's an RNAV+V approach, I can just follow the pseudo-glidescope needle anyway.
 
You can safely slip a plane right to landing. I do it frequently in my AA-5, and also with my AA-1A. Very useful to kill speed and lose altitude. The AA-1A will forward slip like a greased anvil. Nothin' to be skeered of if done competently. Kinda fun.
 
In smooth air, I'd often slowly remove the slip during the roundout so that the slip wasn't fully removed until a few inches off, and just before touchdown. Did it for fun more than anything. It also kept the runway in sight practically until the wheels touched.

Here, I also committed the sin of slipping left wing down in a right x-wind. ;)

 
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whifferdill said:
Here, I also committed the sin of slipping left down in a right x-wind. ;)
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I tend to be guilty of that too, it's just so natural to transition from the left bank turning final to a left slip even though the crosswind is usually from the right. I really should make it a point to slip right more often.
 
MauleSkinner said:
But putting an aircraft in or out of a slip is changing the angle of the glide path (beyond any reasonable definition of bracketing, just to head off that argument), and therefore does not meet that definition of a stabilized approach.
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True but the concept of a stabilized approach in a light ga airplane flying visual approaches is counterproductive if rigidly applied.
 
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