photofly wrote: ↑Wed May 08, 2019 5:10 pm
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Alternatively, If you do it "my way", perhaps this is what happens: then you abort at 30kts and have a thousand feet to stop. You try again and abort at 40kts, and have 800 feet to stop, of which you use 500. You try again and abort at 45kts, and but end up stopping 50' from the fence.

Alternatively in your scenario you could wind up in the ditch at the end of the runway because the last 150 ft of the runway was slick as warm snot and instead of stopping with 50 ft to spare you went off the end. FWIW my personal experience has been that for some reason the last bit of an unprepared runway surface is often slicker than the mid part of a runway.

Ultimately any numbers in the POH only represents a starting point which then need to be adjusted for both expected variables and what the pilot is actually experiencing during the takeoff run.

The 70/50 rule does not replace good pilot decision making before and during the takeoff run. For me it served as one indicator of how the takeoff is progressing and like Iflyforpie, I have found in the real world it works pretty well.

However the reality is that short bush strips represents a significant increase in risk because of uncontrollable or unrecognizable factors. This must be emphasized in flight training
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Returning to the thread question, the challenge remains. How best to prepare PPL students for dealing with an actual short field after they get their license. My method has been trying to provide as much context to the challenges of short field work, factors that could apply and strategies for dealing with them, and of which one will be the 70/50 rule of thumb as one way to assess how the takeoff is progressing.

However the greatest service I think I have provided my students is the fact that I am a hard ass and insist on accurate precise flying.
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Big Pistons Forever wrote: ↑Wed May 08, 2019 6:10 pm Alternatively in your scenario you could wind up in the ditch at the end of the runway because the last 150 ft of the runway was slick as warm snot and instead of stopping with 50 ft to spare you went off the end.

Yes, that could happen, depending on how close to the edge you want to push things. There are no guarantees for a safe takeoff, or a safe abort. All you can do is take steps to minimize the risk where you can, and understand the risk where you can't. I don't find the 50/70 rule contributes to either, but I accept you feel differently. I've made my own suggestions for doing that, and I'd like to read others.

Sorry, Photo, and BPF - I’ve managed to delete the majority of a useful thread. Urgent call in to tech services to see if it can be resurrected

Hmmm.... the 70/50 rule. If you haven't reached seventy percent of your takeoff speed after using 50 percent of the runway, you should abort.

Sounds like an acceleration check speed to me.

As used on thousands of takeoffs of CF-5s and CF-104s.

Back in the day on those aircraft, every time you signed out to go flying, you noted the line check speed in ops.

As you blasted down the runway, you noted your speed at the 2000 foot marker. At or above the line check speed, GO! Below, STOP.

Basically a modified 70/50 rule.

Good enough for me then, good enough for me now...

Don't know what the CF-18s are using... Might be some magic in the cockpit. Any '18 drivers on site?