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50ft-Obstacle Clear

Asked by: 5375 views ,
FAA Regulations, Flight Instructor

In every POH, there is 50ft-Obstacle Clear Distance and I wonder where that 50ft is off from.

I thought 3 types of reference point. 

  1. 50ft from Departing Point (where airplane releases brake)
  2. 50ft from right below airplane (like..... 50 AGL)
  3. 50ft from the obstacle infront of RWY 

Reason I ask this is that RWY is not exact flat, as it has some slope angle, even though angle can be less than 0.1Degree, there must be some altitude difference between Departing point and End of Departure RWY. Therefore I thought, "then... where is the point?" 

I tried to find on book and google, but couldn't find. 

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2 Answers

  1. Best Answer


    Russ Roslewski on Apr 24, 2020

    The 50ft obstacle distance is simply the distance it takes from the start of the takeoff roll (so, brake release), to accelerate, lift off, and climb to 50 ft above the ground. It’s to answer the question, “There is a 50 ft tree on the extended runway centerline XXXX feet away. Can I make it over the tree on takeoff?”

    All of these calculations assume a perfectly level runway. However, many of these tables also have additional adjustment factors stated for a sloping runway, such as “decrease distance by XX% for each YY degrees of downward slope” (or the reverse).

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  2. BLUESKY7593 on Apr 24, 2020

    Thank you ^^

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