50FT Obstacle landing.

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TopGun1234
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50FT Obstacle landing.

#1 Post by TopGun1234 » Sun Feb 25, 2018 10:28 pm

When landing with a 50ft obstacle, is there a rule of thumb that states how high you should clear the obstacle? I'm in a C172. The FTM doesn't list a specific height.

Thanks,
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Schooner69A
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Re: 50FT Obstacle landing.

#2 Post by Schooner69A » Mon Feb 26, 2018 7:54 am

I'm not sure anything is specified. Your comfort zone, I guess.

I did a check out in a 172 years ago and in overflying a real obstacle (trees short of the runway) during a short-field landing demonstration, my "examiner" noted "You were pretty close to the tree tops". To which I replied: "If I'd have been in a helicopter, the skids would have been IN the tree tops"...


John
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Blackdog0301
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Re: 50FT Obstacle landing.

#3 Post by Blackdog0301 » Tue Feb 27, 2018 4:23 pm

Back when I was instructing, I’d usually give them a height ASL (which was roughly 50AGL) that I wanted them to cross the threshold at. If they were right bang on their altitude, I couldn’t really tell them they were off, but I did point out the fact that they probably scratched some paint on the belly as a result. So obstacle +50 feet on the altimeter is what I’d usually teach. Seemed to work very well.
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Re: 50FT Obstacle landing.

#4 Post by photofly » Tue Feb 27, 2018 4:32 pm

The point of the exercise is not to clear the obstacle by any fixed amount, but, to “select the most suitable touchdown zone and specify a touchdown point;” then clear the obstacle safely and “touch down at the specified touchdown point (+200/–50 feet)”.

It’s about predicting your own performance and matching your flying to your prediction, and not about aceing the shortest touchdown over the obstacle in history.
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ahramin
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Re: 50FT Obstacle landing.

#5 Post by ahramin » Tue Feb 27, 2018 10:24 pm

Well the 50 foot obstacle landing distance in your POH is based on clearing a 50 foot obstacle by 0 feet.
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Re: 50FT Obstacle landing.

#6 Post by CpnCrunch » Wed Feb 28, 2018 10:24 am

For the flight test, the examiner just wants you to imagine there is a tree or something similar at the threshold...so as long as you're somewhere in the region of 50ft that's fine. If there is an actual obstacle, just leave as much of a gap as you're comfortable with.
height ASL (which was roughly 50AGL) that I wanted them to cross the threshold at
I'm not sure it's a good idea to be looking at your altimeter on short final, and it probably isn't going to be accurate enough anyway.
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Re: 50FT Obstacle landing.

#7 Post by lownslow » Wed Feb 28, 2018 1:05 pm

photofly wrote:
Tue Feb 27, 2018 4:32 pm
It’s about predicting your own performance and matching your flying to your prediction, and not about aceing the shortest touchdown over the obstacle in history.
It's been a while since I did trig but on a 3* glide path you should be at fifty feet AGL just under a thousand feet before your aiming point. Since a VFR circuit is more courteous with a little steeper approach you'd probably be around fifty feet AGL maybe 800 feet prior to your aiming point then a bit of float and touch down smoothly after about a two hundred foot flare, but monitor your own performance to hone your consistency then as photofly said just pick your aim point accordingly.
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Re: 50FT Obstacle landing.

#8 Post by Blackdog0301 » Wed Feb 28, 2018 7:29 pm

CpnCrunch wrote:
Wed Feb 28, 2018 10:24 am
height ASL (which was roughly 50AGL) that I wanted them to cross the threshold at
I'm not sure it's a good idea to be looking at your altimeter on short final, and it probably isn't going to be accurate enough anyway.
Well yes, but simply imaging a 50ft obstacle that isn’t there isn’t easy for a new pilot either. It was more about picking an aim point, fly an approach (at as constant of a descent as possible) and then just as you’re coming up to where your imaginary obstacle is, take a quick peak down to see where you sit. Never had a student fail that exercise with this method.
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Re: 50FT Obstacle landing.

#9 Post by C.W.E. » Wed Mar 28, 2018 2:17 pm

Where do you look to judge your height at 50 feet?
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Re: 50FT Obstacle landing.

#10 Post by dpm » Sun Apr 01, 2018 9:31 am

lownslow wrote:
Wed Feb 28, 2018 1:05 pm
photofly wrote:
Tue Feb 27, 2018 4:32 pm
It’s about predicting your own performance and matching your flying to your prediction, and not about aceing the shortest touchdown over the obstacle in history.
It's been a while since I did trig but on a 3* glide path you should be at fifty feet AGL just under a thousand feet before your aiming point. Since a VFR circuit is more courteous with a little steeper approach you'd probably be around fifty feet AGL maybe 800 feet prior to your aiming point then a bit of float and touch down smoothly after about a two hundred foot flare, but monitor your own performance to hone your consistency then as photofly said just pick your aim point accordingly.
If you have an actual obstacle, then as long as it appears to be moving slightly downwards in your windshield, you'll clear it with a bit of a margin (modulo any windshear or downdraft). If you're carrying ~10% over stall, you'll be able to zoom 10–20ft to clear if you do encounter that downdraft or shear. I agree with other posters that short final is no place to be fixating on your altimeter or counting runway markings—it's the time for basic stick and rudder flying.
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