# Is the term "50 Ft obstacle" just a average?

#### Matthew Black

##### Filing Flight Plan
So basically,, where did we get the 50 Ft term from? Are most trees by runway's approximately 50 Ft? Or is there something deeper I'm missing?

So basically,, where did we get the 50 Ft term from? Are most trees by runway's approximately 50 Ft? Or is there something deeper I'm missing?
It's arbitrary. Just like the Standard Day is arbitrary. Why they picked 50, I dunno, I suppose 50 feet might be like an average tree. I don't measure them, I just hug em. [insert size matters joke]

Missing the trees can be a tall order!

So be careful and don't go barking up the wrong tree!

Leave them trees alone!

where did we get the 50 Ft term from?
Its an arbitrary figure for aircraft performance certification to ensure it will take off and climb within certain parameters. Its even used in helicopter performance certifications.

Its an arbitrary figure for aircraft performance certification to ensure it will take off and climb within certain parameters
Ok, but by how much is are we clearing the FAA tree and still making book performance? Feels like gear through the crown is a 91.13 problem.

but by how much is are we clearing the FAA tree and still making book performance?
Well clear is clear. So if your gear hits the obstacle its on you. However I think your first violation would be 91.103. And just to add not all aircraft use the 50 ft mark. Some certify at 30 or 35 feet, or use a ratio like 1:10.

Ok, but by how much is are we clearing the FAA tree and still making book performance? Feels like gear through the crown is a 91.13 problem.
Actually hitting the obstacle with your gear is likely to be a bigger problem than a regulatory violation.

We also try to avoid hitting the wingtips.

We were discussing a tree off the end of our runway, and concerns that as it grew we’d have to displace the threshold further or adjust the PAPI. One of the guys piped up with “it won’t go over 50 feet. Trees don’t grow higher than that, that’s why the FAA uses 50 feet for takeoff and landing charts.”

He had some other, um, unique, ideas, too.

not all aircraft use the 50 ft mark. Some certify at 30 or 35 feet,
And if the runway isn’t dry, thirings can suddenly be shortened to 15 feet.

Actually hitting the obstacle with your gear is likely to be a bigger problem than a regulatory violation.

Just like golf, depends how much of the tree you hit. Smacking a twig or two at the top of a maple is much different than hitting somewhere along the trunk or a main branch.

Just like golf, depends how much of the tree you hit. Smacking a twig or two at the top of a maple is much different than hitting somewhere along the trunk or a main branch.
True enough. And like gof, if all you hit is a twig, it's a big

Missing the trees can be a tall order!

So be careful and don't go barking up the wrong tree!

Leave them trees alone!
And watch out for that tree……

50' trees are pretty short around here. I've heard instructors say that trees are soft on top, and initially thought they were kidding. Until I saw some folks walk in with little twigs, that were caught in the gear as they clipped the tops.

I'll add that I don't think there's an unmodified 70's era PA-28-150 that exist that can meet the book numbers for climb over obstacle. I think those numbers weren't possible when the aircraft were new, and were rated like the HP ratings of a shop vac from a box store. Or they were using some technique other than climbing out at Vx. Just my 2 cents, maybe my skills are terrible, or the newly rebuilt engines I've flown were weak.

Well clear is clear. So if your gear hits the obstacle its on you. However I think your first violation would be 91.103.
Oh no, not the double posthumous violation?!

Its an arbitrary figure for aircraft performance certification to ensure it will take off and climb within certain parameters. Its even used in helicopter performance certifications.
Agree, I was told when the CAA first started to organize aviation and make it safe they created 'Standards'. The flight manual is full of charts that are set up from these pre-WWII era standards. The 50 ft. obstacle should probably be 100 ft. For example: "Advisory Circular 43.13 contains methods, techniques, and practices acceptable to the Administrator for inspection and repair." Many rules or 'Standards' are there so all aircraft mechanics can agree with previously performed work.

While wanting to increase the gross weight of an amphibious C-206 I had a Cessna engineer tell me that the gross weight of the Cessna 206 was chosen by the 'advertised' performance. They wanted the Flight Manual performance charts to be better then the competition. He said Cessna created a gross weight that would sell the plane and a gross weight increase wouldn't be a problem it would just deflate the performance numbers.

Agree, I was told when the CAA first started to organize aviation and make it safe they created 'Standards'.
You’ll find the first attempts at regulating safety go back further to the days of the Air Commerce regs/bulletins which pre-date the CAA/CARs. Its interesting to see how the rules and regs changed (and some stayed the same) over the years from their inception in the mid-20s to when the FARs first came out. I’ve worked on a number of different aircraft that span those years and it was always an adventure to see which rules were in play during those times. Thankfully, they’ve kept the maintenance regs/rules pretty low key and general to navigate those adventures.

Where is that. I hade to do a double take. Looks just like Rwy 20 at Twin Oaks 7S3.
BQ1 in North Carolina, where the Pik n Pig is located. Climbing over them on departure can be even more interesting.

The 50-foot obstacle has less reality than even the FAA standard passenger (which has been raised from 170 pounds to 190 ).

Just like golf, depends how much of the tree you hit. Smacking a twig or two at the top of a maple is much different than hitting somewhere along the trunk or a main branch.
My dad clipped 10 feet off the top of a cottonwood once about mid-wing.…a little sheet metal and some pop rivets got him through the season.

Sometime, the performance charts are published as "15 meters." And in the same Flight Manual. No sweat. that equals 49.2 feet. But the question is Why cut it that close? When was the last year that the trees were measured? Just add %100 to whatever is noted for trees and you may be OK. I would be more interested in the height of power lines and multi storied buildings.

BQ1 in North Carolina, where the Pik n Pig is located. Climbing over them on departure can be even more interesting.
What looked like slope in the runway caught my eye as much as the ‘groove’ cut through the trees. Is the usual thing there depart downhill and land uphill? And this BQ1 thang. I’m assuming they B bb Q those pigs there. Gotta be a story here.

What looked like slope in the runway caught my eye as much as the ‘groove’ cut through the trees. Is the usual thing there depart downhill and land uphill? And this BQ1 thang. I’m assuming they B bb Q those pigs there. Gotta be a story here.
The Pik n Pig is a great bbq restaurant. The airport is privately owned. Used to technically require permission but all flying into the restaurant were welcome. A few years ago it officially became private ownership/public use and acquired the BQ1 ID. There was some thought of getting an AWOS and "upgrading" to KBBQ, but that doesn't seem to be happening.

Slight grade (@eman1200 insusts there is none), but folks take off and land pretty much based on the winds. When gentle, there is definitely a preference, but it's often to busy for one-in-one-out traffic.

Just recently reopened after a major fire.

The Pik n Pig is a great bbq restaurant. The airport is privately owned. Used to technically require permission but all flying into the restaurant were welcome. A few years ago it officially became private ownership/public use and acquired the BQ1 ID. There was some thought of getting an AWOS and "upgrading" to KBBQ, but that doesn't seem to be happening.

Slight grade (@eman1200 insusts there is none), but folks take off and land pretty much based on the winds. When gentle, there is definitely a preference, but it's often to busy for one-in-one-out traffic.

Just recently reopened after a major fire.

After paying attention the last two times I was there I will agree there is the slightest grade that has absolutely zero play in my decision of which runway to use.

The Pik n Pig is a great bbq restaurant. The airport is privately owned. Used to technically require permission but all flying into the restaurant were welcome. A few years ago it officially became private ownership/public use and acquired the BQ1 ID. There was some thought of getting an AWOS and "upgrading" to KBBQ, but that doesn't seem to be happening.

Slight grade (@eman1200 insusts there is none), but folks take off and land pretty much based on the winds. When gentle, there is definitely a preference, but it's often to busy for one-in-one-out traffic.

Just recently reopened after a major fire.
So they were able to pik their ID. Cool. What came first, the restaurant or the runway?

I have long thought that the 50ft standard is a bad choice....
only baby trees are that tall...and most folks don't know how tall a tree is...and so I recon a lot of folks look at a tree down at the end of the runway and think..."that must be about 50ft".
Seems like maybe 100Ft would be a better number....

Depends on whether you're talking about a privet or a giant sequoia.

I have long thought that the 50ft standard is a bad choice....
You're forgetting the 50 ft figure is only a part of the equation and has really nothing to do with trees. Thats merely the OEMs way of simplifying things for pilots.
The equation is ground roll distance + initial climb distance = clearance of 50 ft obstacle. If the aircraft couldnt prove clearing the 50 ft obstacle for certification then the ground roll had to be longer, the climb steeper, the engines more powerful, etc. in order to clear it.

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Never paid much attention to the 50 ft obstacle,untill I started flying into grass strips with trees around the end of the runway.

So they were able to pik their ID. Cool. What came first, the restaurant or the runway?
I don't know. Before my time.

I have long thought that the 50ft standard is a bad choice....
only baby trees are that tall...and most folks don't know how tall a tree is...and so I recon a lot of folks look at a tree down at the end of the runway and think..."that must be about 50ft".
Seems like maybe 100Ft would be a better number....

Really depends on where in the country you are. I've lived places where any vegetation higher than about 20 feet is pretty exceptional. And that's a pretty big chunk of the country. Where I live now, I have a few mature trees in my yard that are about 30 feet tall. That's fairly typical around here, so 50 feet is probably a good all-around number in this area.

Relatedly, the "standard" for instrument procedure design is 100 feet. This is used within 20,000 feet of the airport, and the 100 ft value is used unless a different "average maximum" tree height is specified by the airport manager or other official source. I've seen these range from 200 feet in the redwood parts of California, to a mere 1 ft in some areas where the highest vegetation is scrub grass.

Really depends on where in the country you are. I've lived places where any vegetation higher than about 20 feet is pretty exceptional. And that's a pretty big chunk of the country. Where I live now, I have a few mature trees in my yard that are about 30 feet tall. That's fairly typical around here, so 50 feet is probably a good all-around number in this area.

Relatedly, the "standard" for instrument procedure design is 100 feet. This is used within 20,000 feet of the airport, and the 100 ft value is used unless a different "average maximum" tree height is specified by the airport manager or other official source. I've seen these range from 200 feet in the redwood parts of California, to a mere 1 ft in some areas where the highest vegetation is scrub grass.
Got me to thinking about MEF’s on Sectional Charts. There is a ‘default’ vegetation height built in.