Why publish close-in obstacles

[Checks]

I can't figure out why the FAA publishes close-in obstacles under the "T" in the front of the IFR plates.

How am I supposed to avoid a 16ft tree 300ft away from the DER?

Any comments?

 

[midlifeflyer]

Wild guess. So you know it's there?

 

[JAFI]

Would you rather know it is a 16 foot tree, 200 foot tower, or a 1500 foot mountain and where it is or just go blast off with out knowing at all?

 

[Checks]

Ok, let me change the question to this:

Do you actually read and plot all the close in obstacles?
Do you do anything different during your takeoff knwoing thereis a tree 16ft tall 300ft away?

Personally, I look and say "Oh, just some small, less than 200ft, obstacles" I dont change anything. Should I?

 

[puddlejumper]

This comes from the website of CAVU Companies, creator of the EFBPro Aircraft Performance Calculator:

[FONT=arial, Arial, Helvetica]Lets look at an example; an obstacle is 140 feet above the runway and 2000 feet from the runway end. The reference point above a dry runway is 35 feet (15 feet for a wet runway, effectively increasing the required gradient). Therefore, the geometric rise of 115 feet (140-35) divided by the run of 2000 feet renders a required net gradient of 5.75%. Add in the Part 135 requirement (35 feet clearance) and the resulting required net gradient is 7.0%. Assuming a twin engine jet, the required gross gradient becomes 7.8%.[/FONT]

In their [FONT=arial, Arial, Helvetica]"Aircraft Performance Calculations- Methods and Myths"[/FONT] video, they address, somewhere in the 1+15 presentation, close-in obstacles and figuring your net takeoff flight path to clear them.

One of these days, I hope to be able to discuss this sort of thing intelligently, but for now, I will just copy and paste.

 

[FurloughedAgain]

Thank goodness for airport analysis for those of us who are too dumb to understand all of the math, but who would still like to take off at a weight so as to avoid hitting said tree should the poop hit the fan.

 

[MauleSkinner]

For the vast majority of my takeoffs, I don't worry about outclimbing them, because I can see and avoid.

For the vast minority, I make darn sure I can outclimb 'em when I rotate into the clouds.

Fly safe!

David

 

[midlifeflyer]

Ok, let me change the question to this:

Wait. The answer two of us gave was that it's information about the area in the departure/takeoff/maneuvering are that one might what to simply =know=. Like anything else, what one chooses to do with knowledge (including, "I really don't have to change anything") is pretty much up to them.

If you change the question to, "What if I don't give a crap about knowing," then there's really no answer to that one.

 

[Checks]

The truth is that you don't change any of your IFR departure procedures based on a tree 16ft AGL, 300ft off DER, 260 to the left of the DER. I was hoping maybe I was missing something but it looks like I am not. Those close in obstacles are a waste of time and ink.

 

[Basil]

A few excerpts from FAA Order 8900.1 Flight Standards Information Management System (FSIMS)

A. Definition of Obstacle. Any object inside the airport boundary which is within a horizontal distance of 200 feet of the flightpath or outside the airport boundary within 300 feet of the flightpath, must be considered an obstacle for takeoff computations.

Authorizations for lower-than-standard takeoff minimums are based on the operator adjusting airplane takeoff weight to avoid obstacles in the takeoff flightpath if an engine fails on takeoff.

Obviously applies only to 91K/135/121, but looks like the computation should be done when using lower-than-standard T/O mins.

Only you can decide if it's smart to depart under 91 with 500 RVR and not know if you can clear the close-in obstacles. What would you expect if you were the pax?

 

[MauleSkinner]

The truth is that you don't change any of your IFR departure procedures based on a tree 16ft AGL, 300ft off DER, 260 to the left of the DER. I was hoping maybe I was missing something but it looks like I am not. Those close in obstacles are a waste of time and ink.

How about this?...the airport is KACP.

trees, 1300 ft. from runway, on centerline, 50 feet AGL/159 MSL.

That's a line of trees, and the trees to the sides are taller...that's 233 ft/mile to lose your belly beacon. There's absolutely no way you can take off from this runway, be at your minimum of 35' over the DER, meet the minimum climb gradient of 200 ft/mile, and not hit trees.

Fortunately, it's a relatively short runway, so I was always limited by runway length, not climb gradient.

Fly safe!

David

 

[Checks]

For the plane I fly, a Sa-227, it is no problem clearing those trees. I did the calculations.

 

[JAFI]

For the plane I fly, a Sa-227, it is no problem clearing those trees. I did the calculations.

Single engine (new or very tired), at gross weight, on a 95 degree day? or under what conditions? The problem should not just be if everything is working in your favor - because the question should be what if nothing is working in your favor and what kind of risk are you looking at. If it is a 16 foot tree 90 degrees off runway heading or at the end of the runway, it may matter or it may not. That is why they publish the information - so you are informed enough to make a decision.

JAFI

 

[MauleSkinner]

For the plane I fly, a Sa-227, it is no problem clearing those trees. I did the calculations.

So did mine...but if the runway was long enough that I could carry enough fuel to go where I wanted to go without making a fuel stop, I wouldn't be able to.

Fly safe!

David

 

[Checks]

I am usually restricted by Acel-stop and/or climb gradient. In every case that I can find, if I meet acel-stop and my required 2.0 climb gradient(If weather above 1000/3) then these close in obstacles do not mean anything to me. I am would like to find a situation it does but I have been able to find one.
I imagine it is the same for most jets.

 

[HSDriver]

From the AIM

The reason they are published is to prevent having to impose steep climb gradients at every airport...

4. Obstacles that are located within 1 NM of the DER and penetrate the 40:1 OCS are referred to as “low, close-in obstacles.” The standard required obstacle clearance (ROC) of 48 feet per NM to clear these obstacles would require a climb gradient greater than 200 feet per NM for a very short distance, only until the aircraft was 200 feet above the DER. To eliminate publishing an excessive climb gradient, the obstacle AGL/MSL height and location relative to the DER is noted in the “Take-off Minimums and (OBSTACLE) Departure Procedures” section of a given Terminal Procedures Publication (TPP) booklet. The purpose of this note is to identify the obstacle(s) and alert the pilot to the height and location of the obstacle(s) so they can be avoided. This can be accomplished in a variety of ways, e.g., the pilot may be able to see the obstruction and maneuver around the obstacle(s) if necessary; early liftoff/climb performance may allow the aircraft to cross well above the obstacle(s); or if the obstacle(s) cannot be visually acquired during departure, preflight planning should take into account what turns or other maneuver may be necessary immediately after takeoff to avoid the obstruction(s).