Testing the Impossible Turn

Discussion in 'Pilot Training' started by dmccormack, May 5, 2010.

  1. dmccormack

    dmccormack Touchdown! Greaser!

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    So I flew a bit this morning -- cool, clear, calm -- perfect tube-and-fabric weather!

    Had the airplane started up and rolling down the taxiway by 0715 -- air was smooth and cool enough for nice lift.

    I flew around for about 30 minutes, practicing steep turns, turns about a point, slow flight, and low-level flying over the remote hills near the Mon river.

    I climbed up to 1000' AGL and did some more airwork on my way back west. I decided to test out altitude loss with power-idle, 180 degree change of course.

    I entered each at 60 MPH in a climb (standard Vy climb out speed), reduced power to idle, waited a moment (simulating recognition delay) and then commenced turning.

    At 60 MPH in a steep descending turn (about 60 degree bank) there was little G load. I let the speed build after the 90 degree point was reached, then levelled off at 180 opposite heaindg.

    Tried it a couple of times -- 300' altitude loss.

    Of course we all know it takes more than 180 to head back to the runway, but as far as I am concerned, pointed towards the airport = landing area. There is lots of level grass on the field not found around it (Wal Mart and water tower on 300' hill immediately south, prison to the north, town to west, hills and steep valley with stream to east).

    I takeoff from the pavement and land on the grass.

    So I thought through the scenarios on the drive to work. When takinig off form 27, If I lose power anywhere before 300' AGL I'll land straight ahead and most likley stay on the runway.

    300-500' AGL will mean landing on I-79

    >500' AGL and I'll turn back.

    When taking off from 9, the options are limited, but a landing somewhat straight ahead will be in a sloped, mowed hillside.

    The slow speeds mean the airplane will turn inside itself with a sufficiently steep turn.

    It's a worthwhile exercise every pilot should do with each airplane flown.
     
  2. vontresc

    vontresc En-Route

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    Dan, keep the wind in mind when you make the decision whether to turn around or not. If you are taking off into a strong headwind you at be at your turn around altitude but not very far from where you took off. Now you are looking at a downwind landing to a short field.

    Just my $.02 from doing a bunch of "stimulated" rope breaks
     
  3. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Final Approach

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    Will you be able to get it going fast enough to merge with the traffic?:D

    Agree.
     
  4. dmccormack

    dmccormack Touchdown! Greaser!

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    Good point -- though I'm realistically limited to about 12 knots.

    Much more than that and it's simply too much like work.

    I've flown in 15G20, and it was a rodeo. :eek:

    this is a fly-for-fun airplane. :yesnod:
     
  5. Rob Schaffer

    Rob Schaffer Cleared for Takeoff

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    You are about 45 minutes to late in my book :yesnod: I've been flying by 6:30am a lot in the past 6 weeks.
     
  6. dmccormack

    dmccormack Touchdown! Greaser!

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    :D

    I'm an early bird (Up at 0500, out the door by 0615), but slept in a tiny bit due to staying up late (2200!) to watch the Pens put the Big Hurt on the Canadiens.

    :D
     
  7. mantakos

    mantakos Final Approach

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    According to the paper "The Possible Impossible Turn", the ideal bank angle is 45 degrees. If you bank more than this, you take on a lot of induced drag and start to lose more altitude in the turn.

    Note that the altitude loss in the turn is only one part of the equation, you also have to consider whether you have enough altitude to be able to glide back to the airport. In a plane with too little power, your climb will be too shallow, and you'll be too far from the airport to be able to make it back. A headwind helps keep you close to the airport on departure, and also pushes you back to the airport upon return. Turning into a cross-wind can also help keep you from straying too far off the extended centerline, which increases the distance from the airport and the number of degrees you have to turn to get pointed back. And, of course, the longer the runway, the shorter the trip back is.
    -harry
     
  8. brcase

    brcase Cleared for Takeoff

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    Dan,

    Great, I agree this is a great thing to learn about.

    However I think you might have missed part of the situation. Part of the problem is it is more than a 180 degree turn.

    You had it right Climb at your normal climb speed to about 1000 feet, but line up on road when you do so as if you had just departed from that road. Wait at least 2 seconds before initiating the turn, it would probably take you at least this long to decide you needed to turn. Also turn downwind (worst case scenario). Your altitude loss will be your altitude about 1-2 seconds after you line up on the road at you normal approach speed. You would need that 1-2 seconds to stabilize the turn and decent enough to round out, flare and land.

    Of course don't let your self go below 500 feet AGL.

    Then try the same maneuver at your best angle speed, (I know, there isn't much difference in the Chief)

    I too have done it many times in a glider, my rule of thumb in a power plane is that I usually turn crosswind at 500 feet. If I am already turning when the engine quits I can consider returning the runway. Otherwise it the softest cheapest place I can find to land if front of me.

    Brian
     
  9. bobmrg

    bobmrg En-Route

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    I've been watching this thread and wondering what ever became of common sense? No instructor should be teaching how to accomplish the impossible turn...the time would be better spent in instilling the automatic reaction to get the nose down...way down, to be sure that the wing is flying...and turn no more than 60 degrees from runway heading. Choose something inexpensive to hit.

    My guess is that if we held a "turn back" contest involving those posters who advocate trying the impossible turn, we would lose over half of them. Land straight ahead (or nearly so), under control and you will live to talk to the insurance adjuster.

    In the case of an actual engine failure the mind shifts into tunnel-vision mode, and all of these brave statements about bank angle and reaction time go out the window.

    Bob Gardner, Pusillanimous Pilot
     
  10. EdFred

    EdFred Touchdown! Greaser!

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    Only if you train at life that way. I just had an engine quit on me a month ago. There was no tunnel vision.
     
  11. dmccormack

    dmccormack Touchdown! Greaser!

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    So if I'm 3000' AGL I should land straight ahead?

    :rolleyes:

    There is an altitude which provides sufficient energy to manuever for a landing. The FAA gives us 1000' AGL for 180 power off for the Commercial PTS -- and that's heading away from the landing point when the exercises begins (In other words -- you have to do a gliding 180)

    The question is -- what altitude for this airplane changes the emergency response from "Land straight ahead" to "Get back to the airport"?

    Take a look at the departure end of 27, you'll see the options are limited.
     
    Last edited: May 5, 2010
  12. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Final Approach

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    Looks to me like Mr. McCormack did exactly that. Put the nose down.

    And, IMO, the reason that the so called "impossible turn" is such a bad one is that over and over, we teach pilots to pull on the yoke as they roll into a turn in order to maintain altitude (which is part of the check ride, right?). But in this situation, that automatic reaction which has been drilled into our heads results in dead pilots.

    The thing that needs to be taught (again in my own stupid opinion) is not just to turn, not just to find out how much altitude you need, but to put the nose DOWN as you roll into the turn. Practice that over and over. Make the nose down as automatic as pulling during a level turn.
     
  13. dmccormack

    dmccormack Touchdown! Greaser!

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    I think the 45 degree "limit" factors in expertise as well as drag. You're only in the steep (60 degree) bank for a very small period of time, you reduce the total time required to turn, and you keep the airplane as close to the centerline as possible (slow speed + steep turn = small radius)

    As far as low power -- 50 MPH is Vx (which is what I use until I’m 500’ AGL. The reason I’m using Vx for the first few hundred feet is that the steep angle keeps me closer to the airport).

    Assumptions: All this assumes no wind. A headwind will make it all easier. I don’t take off in tailwinds.

    @300 FPM climb = about 2 minutes to 500' AGL
    At 50 MPH I've travelled 8800 feet from the takeoff point (approximately 1000’ from the far end of the runway).
    The paved runway is 3500’ long.
    From that point, I flew over 2500’ of runway.
    So I’m 6300’ from the near end of the runway at 500’ AGL.
    I need to turn 180 degrees and remain aloft long enough to touchdown on the airport grounds (remember, the runway isn’t my goal – a flat, unobstructed place will do).
    Glide ratio of 8:1 means I’ll travel 4500’ horizontally from 500’ AGL.

    1800’ short of the runway. :mad:

    I’ve been turning downwind when I reach 500’ AGL, and am established on downwind about 650’ or so AGL (we want to remain good neighbors and an extended departure leg would put me over town).

    So, while I know I can turn 180 degrees with a 300' altitude loss, the distance from the airport means a "straight ahead" is the best choice until I complete my turn to downwind. Once etsbalished there, i know I can make it to the edge of the grass.

    A good exercise: mental and otherwise! :yesnod:
     
  14. dmccormack

    dmccormack Touchdown! Greaser!

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    I have no choice if I want this Chief to continue flying!

    Exactly right.
     
  15. bigred177

    bigred177 Cleared for Takeoff

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    You can get to 3000 agl in a reasonable amount of time?!?! Last time I flew the Champ I had a passenger and just over 1/4 tank of gas and thought I'd never make it to 3500 msl
     
  16. biskeyboy

    biskeyboy Filing Flight Plan

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    From Rich Stowell:
    1. Remember the number "8" -- This is the increase in the risk factor for death or serious injury when attempting a turnback following an engine failure during takeoff vs. landing straight ahead (or nearly so).
    Source: Transport Canada, "An Evaluation of Stall/Spin Accidents in Canada," TP 13748E, 1999.

    2. Remember the number "62" -- This is the overall success rate (percent) for turnbacks in a turnback-specific study using a simulator and techniques ranging from "pilot's choice" to "optimum turnaround bank/speed/g-load."
    Source: Jett, Brent W., "The Feasibility of Turnback from a Low Altitude Engine Failure During the Take-off Climb-out Phase," AIAA-82-0406, January 1982.

    3. Remember the number "68" -- This is the success rate (percent) for turnbacks in the turnback-specific study AFTER subjects were given specific instructions on how to execute the aerodynamic optimum bank/speed/g-load.
    Source: Jett, Brent W., "The Feasibility of Turnback from a Low Altitude Engine Failure During the Take-off Climb-out Phase," AIAA-82-0406, January 1982.

    4. Remember the number "Zero" -- This is the margin for error when attempting a turnback at the aerodynamic optimum combination of bank, speed, and g-load specified in the paper referenced earlier in this thread. If the turnback happens to work, the pilot will be the "Ace of the Base" for a day; if the turnback fails, there will be a burning hole in the ground that consumes both the occupants and the airplane. It's one of the two extremes, with no middle ground.

    5. Remember the numbers "5, 8, 2" -- In a one year period alone (October 2005-2006), there were a total of 5 accidents in the NTSB database wherein the flight profiles included the intentional practice of simulated engine failures with attempted turnbacks to the runway close to the ground. In each of the five cases, the cockpit contained two pilots: one of the two on board was either a CFI or an FAA Inspector. The results: 5 destroyed airplanes; 8 dead pilots; 2 injured pilots. Interestingly, during that same one-year period, there was only one accident in the database where an instructor and a student were killed during intentional spin training. Yet some in this Forum persist in perpetuating the myth that "spin training" is dangerous (and in general, it is dangerous if conducted by the average flight instructor; not so if conducted by those who specialize). What then does that make the practice of turnbacks close to the ground?
    Source: NTSB database search

    6. Remember the number "43" -- In the five accidents referenced in item 5 above, some of the narratives described repeated attempts at turnbacks prior to the accidents. In those cases, the success rate was calculated: 43 percent of the turnback attempts were successful, with the last attempt of course being a smoking hole in the ground.
    Source: NTSB database search

    7. Remember the number "100" -- This is the success rate (percent) for all of the "straight aheads" attempted in the simulator study of turnbacks. Remember, too, that none of the turnback techniques looked at in that turnback-specific study could match the 100 percent success rate logged when the test subjects chose to proceed straight ahead.
    Source: Jett, Brent W., "The Feasibility of Turnback from a Low Altitude Engine Failure During the Take-off Climb-out Phase," AIAA-82-0406, January 1982
     
  17. rottydaddy

    rottydaddy En-Route

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    I think there's no harm in this, but only to learn what it takes to do it in your airplane should it be the best option. In the rare event that it is the best option, it might help to have simulated such a turn.

    Still, assuming you have enough altitude,the big question is: which will hurt more, potentially- going straight ahead to that golf course, pasture, etc., or landing on the runway, landing long, maybe... with a tailwind, and maybe somebody in position for takeoff, or rolling? That's assuming that you actually pull off the turn itself!

    Obviously, the "impossible turn" should not even be contemplated unless it looks far better than impossible. What makes it "impossible" in most cases where a crash results is that these pilots try to turn when they simply don't have sufficient altitude. But we all know that most aircraft can do it below TPA, so there is such a thing as a "possible" turnaround during initial climb, in some cases.

    Of course you should practice it with lots of extra altitude... unless you are a glider pilot, in which case you have to practice it with... not so much extra altitude. :D
    Even with a glider, there is a minimum altitude, and a very strict sequence that must be followed. For us in the 2-33, it's: 200 AGL minimum, nose below horizon immediately, 45 bank immediately, well-coordinated, spoilers or slip if necessary once you have your spot "made".

    Step 1, the nose down thing, is very very important. If your turn is too wide, or you come about too far downwind, that is bad, but not as bad as racking it over when you are near stall speed low to the ground. This mistake is another deal-breaker (and neck-breaker) in such scenarios, aside from trying to turn around without sufficient altitude. Not surprisingly, "nose down!!" is also Step 1 if you decide to land straight ahead. Wishful thinking for more altitude with up elevator can kill you. this point is also worth remembering if you have determined your airplane needs 300 AGL, and the fan quits at 250. Time to forget the turn and find some decent place in front of you.

    Another tip for those who would try this: in practice or in earnest, if there is a crosswind to any extent, initiate your turn into the wind. Saves you a little extra turning to get lined up... which in turn saves you some altitude. Could make all the difference, if the wind is strong enough. One might know from simulating this at altitude that they can do the 180 in xxx feet, but what about 10-20 degrees more? and what happens if you overshoot, or drift downwind, and have to turn yet again, the other way? It's obviously not a good primary option, even from your "known" minimum altitude.
     
  18. dmccormack

    dmccormack Touchdown! Greaser!

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    Oh, it takes a while. :rolleyes:
     
  19. azure

    azure Final Approach

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    I'm really not sure this is drilled into us as an "automatic reaction", any more than pulling up when you want to go up (or go down less quickly) is an automatic reaction. If I'm getting a little slow on base I push the nose down a little in the turn to final. If everything is just right I won't push but I definitely don't pull up unless I'm fast, and depending on altitude I might push the throttle in a little or pull it out. It's all part of energy management and as in flying in general, tailoring your actions to the particular situation.

    As far as the Impossible Turn is concerned, my first Cardinal checkout instructor 6 years ago wanted to teach me about it but I was skeptical and never took him up on it. Today with my new bird, and considering where I'm based (there are really very few options if you lose an engine on climbout from KVLL), it's definitely something I want to explore to come up with a solid idea of under what altitude and conditions it would be the maneuver of choice.
     
    Last edited: May 5, 2010
  20. Palmpilot

    Palmpilot Touchdown! Greaser!

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  21. PittsDriver

    PittsDriver Cleared for Takeoff

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    Here's the article mentioned that advocates for a 45 degree bank:

    http://jeremy.zawodny.com/flying/turnback.pdf

    It also quotes considerably better results from test using this technique than would be suggested by the post quoting Rich Stowell.

    But, debating bank angles and altitudes is moot if you don't have some game in engine out landings to a spot. What Dan did seems to me to be a pretty decent way to learn your airplane and get a feel for what he might do if confronted with this problem. You'll never convince me to "just land straight ahead" because some rule of thumb said so. You're PIC. Make command decisions and make them work because you've developed some skill at doing so.
     
  22. mantakos

    mantakos Final Approach

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    I've never been able to track down this technical report, so I can't give much credence to the quote. I have to be skeptical that they had enough data to work with to come up with such statistics.

    But if pilots are performing a maneuver that they've never been instructed in, and attempting it in cases where success is not possible, and performing it via incorrect maneuvers, then that could be an argument for training as much as it is an argument for not doing that maneuver.
    The number "62" appears nowhere in that report.
    Neither does the number "68".
    That's not true.
    Which is a good argument for not practicing this close to the ground.
    Sure, because the simulator didn't simulate any trees or buildings to crash into. If the world ahead of you is a computer-generated runway of infinite width and length, then the runway behind you has nothing to offer that improves upon what's ahead of you, so by all means do land straight ahead.
    -harry
     
  23. Palmpilot

    Palmpilot Touchdown! Greaser!

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    If you're at 3000 AGL you have choices available to you, but returning to the runway may not be one of them if you departed straight out. In the absence of sufficient headwind, many general aviation aircraft glide at a steeper angle than they climb, in which case additional altitude hurts instead of helping if your goal is to return to the runway.
     
  24. dmccormack

    dmccormack Touchdown! Greaser!

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    Here's my problem with that study -- why make the "45 degree banked coordinated turn just above the stall velocity as indicated by a blaring stall warning horn"?

    Best glide in my airplane is 60 MPH.

    Why would I fly at 45 MPH?
     
  25. dmccormack

    dmccormack Touchdown! Greaser!

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    Give me one hour of fam flight in any SEL GA airplane.

    Then place me 3000' AGL over near, next to a runway and I will land on the runway.

    As should any commercial-rated pilot.
     
  26. dmccormack

    dmccormack Touchdown! Greaser!

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    Exactly right. :yesnod:
     
  27. mantakos

    mantakos Final Approach

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    Best glide in a 45 degree bank is actually higher than best glide wings level, but in this case you're balancing conflicting goals. Best glide gives you the most distance per altitude loss, but the slower you go the tighter your turn radius is, and the less distance you need to travel. And note that the "optimum" is stall speed for a 45 degree bank, not wings-level stall speed. And, of course, a sensible person would allow margin above that.
    -harry
     
  28. dmccormack

    dmccormack Touchdown! Greaser!

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    Right -- but -- the turn radius difference between 45 and 60 MPH (to say nothing about the increased comfort, familiarity, proficiency during a high stress scenario -- hardly seems worth the risk...?
     
  29. Palmpilot

    Palmpilot Touchdown! Greaser!

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    No, expertise did not enter into the calculation. The 45 degrees was not a limit, it was the bank angle that gave the least altitude loss during the turn. The paper I cited in post #20 describes the assumptions made in deriving that number.
     
  30. dmccormack

    dmccormack Touchdown! Greaser!

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    Did they posit 45 degrees because 60 imposed a load factor (and requisite speed increase)?

    Doesn't have to in a descending turn....
     
  31. dmccormack

    dmccormack Touchdown! Greaser!

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    TV Time Out

    ----------------------

    I'm not advocating turning back in every circumstance.

    I am suggesting we test ourselves and our airplanes and figure out how high we should be before we attempt a turnback.

    Part of my pre-takeoff brief includes "Don't turn back until [feet MSL]" and I point to that altitude on the Altimeter.

    A Chief is a lightweight, low powered airplane that takes 1/2 a day to reach 1000' AGL. So it was important to me that I test and come up with a more reasonable target altitude.

    Your Mileage May Vary.

    ----------------------------------

    End of TV Time Out
     
    Last edited: May 5, 2010
  32. EdFred

    EdFred Touchdown! Greaser!

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    If you are REAL good, you go nose up, put in 1/2 a turn of a spin , nose down, then flare...Wheeeeeeeeeeeeeeeeeeeeeee!

    I've only done this successfully....never.
     
  33. dmccormack

    dmccormack Touchdown! Greaser!

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    You'd still be about a mile from the runway. :rolleyes:

    Are you advocating this? How irresponsible! :nono:
     
  34. Palmpilot

    Palmpilot Touchdown! Greaser!

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    When Rich posted that on the AOPA board, I asked for comments from Steve Philipson, a local instructor who has studied the turnback issue extensively, and I posted them there.

    http://forums.aopa.org/showpost.php?p=752607&postcount=72

    Here they are:

     
    Last edited: May 5, 2010
  35. EdFred

    EdFred Touchdown! Greaser!

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    That's why I don't sign my posts with CFI anymore. :D
     
  36. Palmpilot

    Palmpilot Touchdown! Greaser!

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    If you're within gliding distance of the runway, I don't doubt it.
     
  37. Palmpilot

    Palmpilot Touchdown! Greaser!

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    They didn't posit 45 degrees. They wrote an equation for the altitude loss and then used it to find out what bank angle produced the smallest loss.
     
    Last edited: May 5, 2010
  38. Palmpilot

    Palmpilot Touchdown! Greaser!

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    BTW, I'm not here to tell anyone they should or should not attempt to turn back, but I do think that people should have correct information when they are making their decisions.
     
  39. mantakos

    mantakos Final Approach

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    hm
    Which is why I'd say it's perfectly reasonable to add a margin of airspeed.

    We have to differentiate between "this is what the numbers say provides optimal performance" and "this is what provides the best likelihood of a successful outcome under real-world conditions".
    -harry
     
  40. brcase

    brcase Cleared for Takeoff

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    Brian
    Another factor to consider.

    Downwind landings are seldom practiced and should result in a very flat approach that looks lower and faster than normal. As a result it is very easy to subconsciously climb and slow down to try and make the approach look more normal.

    After experiencing this in an off airport landing in a glider I now equate it to the "leans" when instrument flying. As soon as you look away from the airspeed indicator and stop consciously pushing forward on the stick/yoke you will likely start slowing down.

    Brian