Turning obstacles off using APG part 135

Inverted25

Inverted25

Well-Known Member
I am sure this has been discussed here previously but I haven't found it. FAR 135.379 states that you have to be able to clear an obstacle by 35 feet vertically or 200 feet inside airport boundaries or 300 feet outside airport boundaries. We use APG which spits out all the performance calculations for this. Now the question comes to if its VMC outside can you turn obstacles off which is a option, and just climb in VMC conditions if you lose an engine and see and avoid the obstacles. By turning obstacles off it allows a much higher takeoff weight then leaving obstacles on. I am of the opinion that since 135.379 makes no mention of IMC or VMC that the obstacles must be accounted for on every takeoff regardless of weather conditions and therefore turning obstacles off would be a NO GO. Lets hear your thoughts
 
So that way you can see the tree before you hit it?

Seriously though, there's doesn't seem to be a reference to "in IMC." I think there's a LOI on this, but I'm not sure.
 
deadstick said:
So that way you can see the tree before you hit it?

Seriously though, there's doesn't seem to be a reference to "in IMC." I think there's a LOI on this, but I'm not sure.
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The argument being made is that the obstacle performance data per 135.379 assumes a max bank angle of no more than 15 degrees. In reality you can do much more than that to maneuver to clear obstacles in VMC. If there is a LOI I would love to see it. I researched the LOI data base and didn't find one but that doesn't mean I missed it. I typed up a letter to mail to the FAA to hopefully receive a LOI on this very subject matter I plan to mail out tomorrow.
 
We turn it off only to get runway numbers for Special Auth VMC alternate OEI departure procedures in the mountains. These departures typically require no climb at all and you just follow the valley to the next airport.
 
Polymox said:
We turn it off only to get runway numbers for Special Auth VMC alternate OEI departure procedures in the mountains. These departures typically require no climb at all and you just follow the valley to the next airport.
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Interesting haven't heard of these. Would you mind sharing one? Any chance you guys operate in and out of KEGE and have one for that airport?
 
I think you're confusing different things. You always have to plan to avoid the 35 ft obstacle. I'm pretty sure most AFMs already factor this into the takeoff data.
 
Polymox said:
We turn it off only to get runway numbers for Special Auth VMC alternate OEI departure procedures in the mountains. These departures typically require no climb at all and you just follow the valley to the next airport.
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14 CFR 135 does NOT allow you to disregard climb requirements because you're VMC despite what some operators with piss poor performing airplanes like to think and what weak POIs will sign off on (remember POIs do not make regs). The obstacles don't move because you think you're a visual super man. I'd bet your DO and CP also think the charted DP covers close in obstacles.
CFIT99 said:
i didn't think APG gave you the ability to turn off obstacles.....
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It does in some cases. I frequently train a huge 135 operator who uses iPreFlight - their particular settings will allow them to disable obstacles, though they're not allowed to do it for computing performance (merely to see the hit).

iPreFlight is extremely customizable (I'd argue the best performance program available for corporate and charter operators of jet aircraft) and an excellent program WHEN you understand the limitations.
 
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JeppUpdater said:
14 CFR 135 does NOT allow you to disregard climb requirements because you're VMC despite what some operators with piss poor performing airplanes like to think and what weak POIs will sign off on (remember POIs do not make regs). The obstacles don't move because you think you're a visual super man. I'd bet your DO and CP also think the charted DP covers close in obstacles.

It does in some cases. I frequently train a huge 135 operator who uses iPreFlight - their particular settings will allow them to disable obstacles, though they're not allowed to do it for computing performance (merely to see the hit).

iPreFlight is extremely customizable (I'd argue the best performance program available for corporate and charter operators of jet aircraft) and an excellent program WHEN you understand the limitations.
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we use iPreflight too, I just checked our version of the program, we don't have the option to remove obstacles
 
CFIT99 said:
we use iPreflight too, I just checked our version of the program, we don't have the option to remove obstacles
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You have to request the ability to do it from APG by telling them you won't hold them responsible if you turn off obstacles and it doesn't go well.
 
JeppUpdater said:
14 CFR 135 does NOT allow you to disregard climb requirements because you're VMC despite what some operators with piss poor performing airplanes like to think and what weak POIs will sign off on (remember POIs do not make regs). The obstacles don't move because you think you're a visual super man. I'd bet your DO and CP also think the charted DP covers close in obstacles.

It does in some cases. I frequently train a huge 135 operator who uses iPreFlight - their particular settings will allow them to disable obstacles, though they're not allowed to do it for computing performance (merely to see the hit).

iPreFlight is extremely customizable (I'd argue the best performance program available for corporate and charter operators of jet aircraft) and an excellent program WHEN you understand the limitations.
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I agree with you on the 135 not being allowed to turn off obstacles. Just trying to make a better argument against it using the regs. Can you point me in the right direction besides the reg I already quoted.
 
CoffeeIcePapers said:
I think you're confusing different things. You always have to plan to avoid the 35 ft obstacle. I'm pretty sure most AFMs already factor this into the takeoff data.
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We are talking about obstacles specific to a airport. The AFM data wouldn't take into account the mountain at the end of the runway at KEGE. The 35ft reference is the 135 requirement that OEI you must be able to clear a obstacle by either 35 vertically or 200/300 ft laterally.
 
Inverted25 said:
We are talking about obstacles specific to a airport. The AFM data wouldn't take into account the mountain at the end of the runway at KEGE. The 35ft reference is the 135 requirement that OEI you must be able to clear a obstacle by either 35 vertically or 200/300 ft laterally.
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91.175 f4i
 
Inverted25 said:
Interesting haven't heard of these. Would you mind sharing one? Any chance you guys operate in and out of KEGE and have one for that airport?
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Yes, we have one at KEGE, that leads down the valley to KRIL. It requires good VFR, I think 5000-5. As long as you can make the numbers for 2nd segment climb, you can use it to take off at a higher weight than would be normally permitted with the Cottonwood. This is an emergency procedure that you would only fly with an engine failure prior to making the first turn on the cleared SID. This is permitted by 91.175(f)3 where it says "or an alternative procedure."

It is most useful for getting out with decent weight in the summer, seldom used in winter with the weather and better weight limits on the Cottonwood.
 
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