Can a passenger flight stand mid air before landing

  1. Hi guys,
    i see passenger flight standing mid air for some moment(nearly for some 10 to 15 seconds) in sky before landing , can any one explain how it happens..
     
  2. jcsd
  3. Integral

    Integral 7,345
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    Airliners do not stand still in the air.

    Perhaps it is approaching you in such a manner that you cannot sense its motion. This happens when it is heading straight toward you. The only change you can see in under these conditions is a change in size.
     
  4. Pengwuino

    Pengwuino 7,118
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    Yah... when airplanes stop moving in mid air.... they crash and even then its very rare that they actually stop in mid air.

    It really depends on what angle you are watching from, especially if you're moving. If you see it from a back angled position... it really does seem like the airplane is just hovering in mid air but it is definitely moving.
     
  5. HallsofIvy

    HallsofIvy 40,534
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    Remember that an airplane is literally "flying on the wind". In order to stay in the air, its speed relative to the wind must be greater than its stalling speed. It is possible that an airplane will have ground speed 0 if the wind speed is greater than its stalling speed.
     
  6. DaveC426913

    DaveC426913 16,226
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    Theoretically possible, yes. But not with a passenger flight, as the OP mentioned.
     
  7. Danger

    Danger 9,878
    Gold Member

    There's also the size matter. For whatever psychological/physical reason, I find that large objects appear to be moving slower than small ones when they are in fact at the same speed, since the larger farther-away one crosses less angular distance in the same time. If you're used to seeing cars whizzing by up close, a 747 indeed appears to 'float' in comparison.
     
    Last edited: Feb 15, 2006
  8. I guess what he actually meant by "standing mid air" is when vertical velocity is zero, not horizontal.
    I think that pilots use this time to level the plane and prepare for landing. IMO.
     
  9. FredGarvin

    FredGarvin 5,087
    Science Advisor

    Usually, from quite a ways out (20-50 miles) the aircraft are usually in a constant rate of decent. The rate sometimes varies for weather and such, but there really isn't a purposeful time of zero decent except in cruise.

    It is tough to say what the OP meant by his question.
     
  10. DaveC426913

    DaveC426913 16,226
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    I would be interested in hearing about the circumstances of observation. In particular, whether the observer was in a moving vehicle. The vehicle movement and a lack of reference objects to fix the plane relative to the ground could produce a parallax that would make it appear that the plane was temporarily standing still over the runway.
     
  11. chroot

    chroot 10,426
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    I really have no idea what the original poster is asking, as the question is entirely too vague to be given a real answer, but here's my summary of landing an airplane.

    1) All airliners use instrument landing system (ILS) approaches, which provide the pilot a ground track and a glideslope. The aircraft is expected to follow this glideslope all the way across the threshold of the runway.

    2) Once over the threshold, at an altitude of some ten feet, the aircraft brings the nose first level, then nose-high, in what is called the "flare." The aircraft is flying very slowly at this point, so, despite the nose-up attitude, it is in fact still very gradually losing altitude.

    3) Shortly after entering flare attitude, the main wheels should touchdown. The aircraft continues to lose speed (via aerodynamic drag, thrust reversers, speed brakes, whatever) until its nosewheel naturally drops and settles onto the runway, too.

    The touchdown may be affected by so-called "ground effect," a sort of artificial boost in lift caused by the presence of the ground below the wings of the plane. (Wings work by pushing some air downward; when the ground is near, it builds a high-pressure area.) This ground effect can cause an aircraft to "float" above the runway for, in some cases, up to 10-15 seconds, in flare attitude and with proper landing speed. This is almost always caused by flaring too high, but can be made worse by wind conditions. The end result of such a float is usually a sudden, jarring drop of several feet after the aircraft slows enough that its wings no longer generate adequate lift.

    - Warren
     
  12. I have seen this MANY times myself, and I can tell you with absolute certainty that it is an optical illusion. I would suspect that when you experienced this, that you were in a moving vehicle while noticing this odd "suspension"
     
  13. DaveC426913

    DaveC426913 16,226
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    "absolute certainty" you say?

    I've told you a million times - don't hyperbolize!
     
  14. What do you mean? It is an illusion that the airplane is hovering in the air. What's so hyperbolic (no pun intended) about it?
     
  15. FredGarvin

    FredGarvin 5,087
    Science Advisor

    Sid, Dave was pointing out pallidin's use of hyperbole in his "absolute certainty" comment by engaging in hyperbole himself, i.e. he did not tell pallidin a million times. It really has nothing to do with the topic of the thread.
     
  16. DaveC426913

    DaveC426913 16,226
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    Fred, I think sid got that, he just didn't know why I was questioning pallidin's "absolute certainty".

    I'm questioning his absolute certainty because he wasn't there. He wasn't with with Sathishkumarline.

    I'm not just not just bifurcating bunnies here. Pallidin, like the rest of us - can't even be sure of what Sathishkumarline is trying to describe (much of this thread has been devoted to determining the circumstances of Sath's observation). We don't yet even know if Sath was in a moving vehicle, let alone anything else.

    Pallidin stating he knows anything about Sath's observation with any kind of certainty at all, is highly premature.
     
  17. I stand corrected on my use of the terms "absolute certainty" Though I believe my opinion is correct regarding the matter, my use of some terms were not.
     
  18. I can tell you with absolute certainty that hyperbole is appropriate for what to many is a profoundly significant optical illusion. I also suspect that Sathishkumarline was in a moving vehicle while noticing this
    odd :surprised "suspension". Let's hope Sathishkumarline returns soon to confirm or deny our suspicions.
     
    Last edited: Feb 22, 2006
  19. Hi guys , sorry for the late reply :biggrin: ,
    i feel that what i saw should be an optical illusion as "pallidin" says , since i notice this when iam moving in a train in opposite direction to that of the plane , and not when iam moving along the direction of the plane....i notice this when iam moving in MRT(singapore local train)
     
  20. russ_watters

    Staff: Mentor

    Yep, that's an illusion caused by parallax.
     
  21. Integral

    Integral 7,345
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    What reference points you have to gauge its motion? If you have only the sky behind it then you have none, this makes it very difficult to see the motion.
     
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