Why 80knots?

[AggieMike88]

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?

 

[Greg Bockelman]

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

 

[Arnold]

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.

 

[Jmcmanna]

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.

 

[MauleSkinner]

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.

 

[dmspilot]

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.

 

[Hacker]

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.

"Historically , piston engines at idle rpm while taxiing or holding for takeoff would foul the spark plugs causing uneven firing and roughness when takeoff power is applied. Usually they would start operating normally after a short period at high power. If they didn’t you aborted the takeoff. At Lockheed we concluded that we could stop a P-2 abeam the Fire House but any distance beyond was critical for aborts. At this time the airspeed was usually about 80 knots. This became a useful number which is now industry wide. Since it did become a number it was elected to adapt it to the P-3, although a jet engine is not at all like a piston engine. What makes it important is that someone observes the power output and determines whether to continue or stop. “Call 80 knots for a power check” is sometimes mis-understood that you don’t heck the power until 80 knots. Check the power output with the initial application. If it’s bad at 60 knots, stop the aircraft. It won’t get any better at 80 knots like the P-2 engine might. A P-3 will stop on any Navy runway from an 80 knot speed. "

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.

 

[Pugs]

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.

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.

 

[Doc Holliday]

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.

 

[Kritchlow]

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

 

[jayhawk74]

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.

 

[Greg Bockelman]

Also above 80 kts we wouldn't abort for Master Caution lights, again due to high speed abort situations.

Red or loud.

 

[midwestpa24]

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.

Probably more so on a catapult!

 

[Sluggo63]

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.

It still isn't clear how this propagated over to Boeing and the C-135...

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.

 

[jayhawk74]

Red or loud.

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

 

[Greg Bockelman]

Exactly

 

[CharlieD3]

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