Why 80knots?

Discussion in 'Flight Following' started by AggieMike88, Jul 6, 2020.

  1. AggieMike88

    AggieMike88 Touchdown! Greaser! PoA Supporter

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    The original "I don't know it all" of aviation.
    Watching the different cockpit view videos of 135 and 121 jet operations, a common item is a call out of 80 knots as a speed cross check between pilot positions.

    Why 80 knots over a different airspeed?
     
  2. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    Somewhat arbitrary. We used to do it at 80, now we do it at 100. Don’t really know the reasoning behind the change.
     
  3. Arnold

    Arnold Line Up and Wait

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    Fast enough that a) the transition from tiller to rudder is complete & B the airspeed is believed accurate, and b) slow enough the check does not become a distraction. Usually by agreement between the company and the FAA.
     
  4. Jmcmanna

    Jmcmanna Pre-takeoff checklist

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    This is an educated guess: A lot of turboprop/Jet aircraft’s airspeed indicators start at 60 knots, so at 80 the needle is alive. It is also usually well below V1, so if there is an issue (like the CA and FO’s air speeds don’t match), they have time to safely abort the takeoff.
     
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  5. MauleSkinner

    MauleSkinner Final Approach

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    A couple of the airplanes I’ve flown had inspection requirements if you aborted above 90 knots, so the 80-knot callout was also the transition from “abort for any malfunction” to aborting only for serious stuff.
     
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  6. dmspilot

    dmspilot En-Route

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    Fast enough to ensure the airspeed indicators are working, slow enough for the captain to "analyze the situation and decide to continue or abort" for non-critical abnormalities.
     
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  7. Hacker

    Hacker Pre-takeoff checklist

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    I've been trying to get to the bottom of the origin of the 80-knot check for about 10 years, and still don't have a definitive answer as to what or why. BUT..

    "Patient Zero" in the 80-knot check was potentially a Lockheed test pilot, Jay Beasley.

    It still isn't clear how this propagated over to Boeing and the C-135, then into the 700-series...but this is possibly where the virus started, and has mutated many times over the years throughout the industry to mean many different things and serve many different purposes.
     
    Last edited: Jul 6, 2020
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  8. Pugs

    Pugs Line Up and Wait

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    That's the way it was in the EA-6B. "80 knots off nose wheel steering, 100 kts high speed (abort criteria) and 145 (usually) rotate" was the checks. It happened quickly.

    Gear up airborne and 185 kts flaps and slats up to be clean by 200 kts.
     
  9. Doc Holliday

    Doc Holliday Cleared for Takeoff

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    Boeings used 80 knots for years, Airbus used 100kts.

    Now individual operators are selecting the speed they see fit. It's just a target number, who knows how they came up with them.
     
  10. Kritchlow

    Kritchlow Final Approach

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    We call both 80 and 100. We are off the tiller and on the pedals from the start. (Taxi generally tiller only)
     
  11. jayhawk74

    jayhawk74 Pre-Flight

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    At the 121 airline where I worked 80 kts or higher was considered a high speed abort so brake cooling was a consideration. Also above 80 kts we wouldn't abort for Master Caution lights, again due to high speed abort situations.
     
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  12. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    Red or loud.
     
  13. midwestpa24

    midwestpa24 Pattern Altitude

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    Probably more so on a catapult!
     
  14. Sluggo63

    Sluggo63 Cleared for Takeoff

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    I think everyone is right here. The purpose is multi-fold.

    1. Make sure the airspeed indicators are working and accurate. If, for some reason you miss the 80 knot call and it's 95 knots now, please call "95 knots" so I can cross check that my ASI is showing the same.
    2. It's a verbal recognition that you are out of the low-speed regime or the takeoff and into the high-speed part.
    3. Probably more important for the older engines, but most takeoff data is based on the power being set between 40 and 80 knots, so the 80 knot call was a verbal reminder to stop messing with the throttles trying to set N1/EPR.

    Oddly, in the C-135 (KC-135 to be specific) we called "90 knots." I think that had to do with #3. Power had to be set (by the copilot) between 40 and 80, then he had time to look up and call "90". Who knows. I'd be interested to hear if your research turns up anything more concrete.
     
  15. jayhawk74

    jayhawk74 Pre-Flight

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    In the plane I flew the Master Caution was yellow and the Master Warning was red, an alarm bell would also go off if the Master Warning came on. We would abort for a Master Warning anytime up to V1
     
    Last edited: Jul 7, 2020
  16. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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  17. CharlieD3

    CharlieD3 Cleared for Takeoff

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    I know I have to wait until I'm airborne to call it (80, 'cause I'm old school) in the club's 172, but I do it anyway. After all, I'm a perfeshunal. I'm over 100 hours.

    fly to the scene of the incident, or be recovered at the scene of the tragedy
     
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