To reject a takeoff after V1 or not?

Dusting off the FAA takeoff safety training aid

I teach Aircraft Performance for commercial pilots (ATPL) and the question that ALWAYS comes when we talk about V1 is:

  • What if  something happens after V1 and the runway is long enough to stop on?

The simple answer is: You fly.
The catch is: What if you think the aircraft can not fly? How do you know if you are right?

Thanks to a report by the Dutch Aerospace laboratory NLR this matter has new fuel in the form of statistical data and a long forgotten safety program.


High speed abort: faster than 80 knots

After call “80” at 80 knots, the takeoff is only aborted for serious events such as engine failure, engine fire, directional controls or an obstructed runway. Some operators choose 70 or even 100 knots but most use 80. This is also because most modern airplanes have a flight phase inhibit for certain warnings at that speed up to 1500 feet AGL.
V1 is usually higher than 80 kts. A typical value for a Challenger 350 is between 119 and 130 kts. Then there is also reaction time:

With a typical acceleration of 3 to 6 knots per second, just 3 seconds for assessing the situation and decision-making, will add 9 to 18 knots to the speed. If the aircraft is close to V1, it now most likely has exceeded it.


The data

For this report a dataset of 135 high speed aborts was analyzed. There are some interesting numbers in there:

In more than 80% of the high speed aborts, the decision was made after V1

Source: NLR report TP-2010-177
  • In 90% of these cases the aircraft could not be stopped on the runway. 
  • In about half of those cases, the decision to abort was correct or unknown
Source: NLR report TP-2010-177

Only 20 to 25% of all rejected takeoffs are caused by engine failure.

The other 75% by something else.

The Takeoff Safety Training Aid

An old FAA training tool exists, called “The Takeoff Safety Training Aid.” The program consists of a detailed article with the title “Pilot Guide to Takeoff Safety” and a movie: “Rejected Takeoff and the Go/No Go Decision”

The movie looks like a VHS-style movie from the previous century (because it is) and can be found on Youtube:

The full description of the Takeoff Safety Training Aid can it be found under this link.


Has the question been solved: What if there is enough runway after V1?
Well, how do you know if it is enough? And also, how do you know if the failure prohibits the aircraft from flying?
There are plenty of cases where the late decision ended badly:

Runway Overrun During Rejected Takeoff in Bedford, MA 5/31/14

Bizarre stuff, good material for lessons on the importance of sop’s.

Ilyushin IL-18 Aborted take off

Runway overrun after rejected take-off, MD-88, Groningen Airport Eelde

On the runway checks were performed. FDR data indicated a stabilizer position change from 6.8 to 7.2 degrees aircraft nose up (ANU). Thereafter the crew initiated a static engine spin-up. Again the stabilizer warning sounded. The crew released the brakes and started the take-off roll. From the CVR it is derived that during the entire take-off roll the warning sounded continuously.
When attempting to rotate the captain experienced a heavy elevator control force. The captain stated that he needed much more than normal back pressure on his control column to lift the nose. He felt ”it was impossible to make the take-off”, and as the nose did not rise he decided to reject the take-off. Post accident analysis revealed that the rejection was initiated at 128 knots.



I guess it remains a problem. Apart from some of the strange decisions above, the only time where it is actually very clear that you can and must stop after V1 is in the sim on a 4 km runway where at Vr you feel that the elevator has “mysteriously” become jammed so you stop on the remaining 3 km of runway….

It isn’t always that obvious:

But sometimes regrettably also very catastrophic

Learjet 60 runway overrun, Columbia Metropolitan Airport, SC (CAE) Friday 19 September 2008

Aviation safety network

According to the report it is a about a 50/50 choice:

Many high speed rejected takeoffs (44%) should not have been conducted. This number is only slightly less than before the introduction of the training aid (51%); Pilots have difficulties in recognising “unsafe to fly” conditions.

ThomsonFly 757 bird strike & flames captured on video

Crazy LORA ranges today, can Tropospheric propagation be the cause?

Records are breaking

July 25, 2019

It is high summer in Europe with record-breaking temperatures (again) today.
Also we are seeing record-breaking ranges on LORA trackers.

This is one of my gps-nodes on the Things network that rides along in a delivery truck.

It passes the dike between Enkhuizen and Lelystad often but it never had any coverage on it, until today.

180 km to Middelburg

Insane propagation, all the way to Zeeland, Friesland an Germany

As a comparison, here is a typical day:

It passed the same road and was only picked up by the gateway in Dronten well after passing Lelystad.

It gets crazier

I was investigating the traffic to my gateway and found a blip from an unusual distance. After following it back to the source I found this:


So what causes this? Is LORA dx-ing today and bouncing of a freak layer that only exists on very hot days? Is it maybe a special pressure system?

Crunching pressure systems?

The pressure is only 1014 hPa, just 1 hPa above standard 1013. Could it be because of that crunch zone we are in between the low pressure to the west of Ireland and the high to the east, the same one that is working as a gear wheel to transport all that hot air our way?

Tropospheric propagation?
Bouncing on the bottom of an inversion

Is there maybe a massive temperature inversion that causes tropospheric propagation or even tropospheric ducting?

The observable characteristics of such high-pressure systems are usually clear, cloudless days with little or no wind. At sunset the upper air cools, as does the surface temperature, but at different rates. This produces a boundary or temperature gradient, which allows an inversionlevel to form – a similar effect occurs at sunrise. The inversion is capable of allowing very high frequency (VHF) and UHF signal propagation well beyond the normal radio horizon distance.

There is a temperature inversion below 1500 feet, but it is now very powerful.
Look what it says on this report by KNMI:

GELDIG 250900/251500 UTC

       09 UTC:    15 UTC:
0500VT 120/05 +28 140/10 +36
1500VT 100/10 +30 140/10 +33 
3000VT 100/10 +27 170/10 +29
FL 050 180/05 +22 200/15 +23
FL 100 230/10 +08 200/10 +09

It seems that this could be enough though because at the moment it is the only way that I can explain how an 868 MHz UHF signal can do dx. The inversion is gone 15 UTC so if that is the cause of the dx then we can expect the conditions to disappear as the day progresses.

Looks like a reasonable explanation. If someone has a better understanding of this then I’m open to input. Temperatures are rising fast now so I’m going to find a place somewhat cooler.

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The Cloud

There is no cloud, it’s just someone else’s computer

This catchphrase is becoming more popular lately. Why? Because it’s not just about storing your data in Dropbox, or handing over all your images to Google for the convenience of it.
Need I still remind you of this and this?

People are returning to personal websites and private servers for several reasons. Let me give you a few:

Timeline manipulation

Facebook decides what you need to see and when. Instagram same thing. Twitter now has a feature where you can undo this but that setting magically flips back after a while.

The sprinkler system

Grumpy old geeks

What if Facebook or Youtube or wherever you are currently putting your stuff suddenly decide that you violate their terms of service or simply change their mind and delete your account (ok well, set it to invisible).

Then what?

My favorite podcasters have this to say about it:

If you build your business on someone else’s lawn, don’t be surprised if they turn on the sprinklers

The grumpy old geeks

Go check them out here.

Works with Nest – not

…. as a service. Until you stop paying the subscription, the service changes it’s mission or just disappears.

Still here?

So I have this blog here that nobody reads or cares about but at least I can find my own stuff back and I know that if I don’t suffer another server crash or get fed up and delete it again, it will still be present and in the same place where I put it.

See you later 🙂
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