Part 135 Operators - Airport Obstacle Analysis

C150J

C150J

Well-Known Member
I'm going to re-open Pandora's Box here, so I apologize in advance. At my previous 121 employer, we had aircraft-specific procedures in place to satisfy 91.175 and AC120-91. All FAA guidance indicates that ODPs/SIDs are not designed for engine/equipment failure, and that other procedures must be used in lieu of the TERPS criterion.

My question:

- If you currently work for a 135 operation, do you have airport obstacle analysis (APG, Aerodata, etc.)?


I know this debate is mostly academic and a lot "goes out the window" in an emergency (e.g., whether your'e even going to follow a convoluted procedure in day VMC), but it's amazing to me how airlines spend thousands on something that a lot of 135 operations seemingly don't.


I'm putting my helmet on.

J.
 
We do not have the APG or obstacle analysis at our operation.

Places that would require, Aspen, etc, we dont fly in regularly enough to merit the cost.
 
The company I used to work for is working on this issue right now. In the past they didn't give it much thought, until the FAA called them on it a few months ago. I believe they are using APG to get the data.
 
Crockrocket94 said:
Educate me, I have never heard of part 135 operators requiring some sort of APG etc. Any references?
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There are some elements of 91.175 and AC 120-91 that direct the operator to have procedures - other than TERPS - that deal with OEI departures. I'm out, but will find them for you later.
 
Crockrocket94 said:
Id like to see it, as ive been unaware of such analysis requirements.
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Let me preface this with the fact that I'm open to interpretation on this, but most of the "academics" I've discussed this with believe that it's an overlooked requirement in the 135 world.

Here are some elements:

From 91.175:
4) Notwithstanding the requirements of paragraph (f)(3) of this section [this discusses ODPs], no pilot may takeoff from an airport under IFR unless:
(i) For part 121 and part 135 operators, the pilot uses a takeoff obstacle clearance or avoidance procedure that ensures compliance with the applicable airplane performance operating limitations requirements under part 121, subpart I or part 135, subpart I for takeoff at that airport;

Subpart I is a part 25 requirement, dictating obstacle clearance by 35' vertically during the takeoff (defined to 1500') and several lateral requirements.

Now, you may be saying to yourself "this says nothing about OEI and only applies to non-emergency scenarios." However, going further, we see this:

“TERPs and OEI [One-Engine Inoperative] are independent and exclusive.”
- AFS 400

"Extraordinary circumstances, such as a mechanical or electrical malfunction, may
prevent an aircraft from achieving the 200 ft/NM minimum climb gradient assumed by
TERPS. In these cases, adequate obstacle clearance may not be provided by
published instrument procedures. Operational procedures contained outside
TERPS guidelines are required to cope with these abnormal scenarios." - TERPS

http://www.faa.gov/about/office_org...afs420/acfipg/closed/media/Hist 08-01-279.pdf

So, to me, it appears that OEI contingencies *are* required to truly satisfy 91.175. Some also argue that they can extrapolate the single-engine "tab data" and, if it meets/exceeds a SID's climb gradient, can legally depart. The FAA argues that this is incorrect, as part 25 certification standards base OEI performance on flight segments (e.g., 1st, 2nd, 3rd segments, etc.), not a smooth rise-over-run gradient from DER. This makes some sense, as a close-in obstacle might require much more than a 0% net climb as mandated in part 25 for two-engine aircraft.
 
I want to add that this type of logic coincides with other differences between 91 and 121/135 requirements:

- 0/0 takeoffs vs. controlling visibility
- wet footprints vs. equal-time points
- knowingly taking off with no single-engine climb performance vs. having being weight-limited with an aircraft-specific escape procedure
 
Sorry, I totally forgot to mention AC 120-91, which outlines acceptable means to comply with 135.367 and 135.379, 135.398. It does state "Operators may use other methods if those methods are shown to provide the necessary level of safety and are acceptable to the Federal Aviation Administration (FAA)," but as I said before, it has been argued that extrapolating 2nd-segment climb data and comparing it to TERPs guidelines is unacceptable.
 
C150J said:
Sorry, I totally forgot to mention AC 120-91, which outlines acceptable means to comply with 135.367 and 135.379, 135.398. It does state "Operators may use other methods if those methods are shown to provide the necessary level of safety and are acceptable to the Federal Aviation Administration (FAA)," but as I said before, it has been argued that extrapolating 2nd-segment climb data and comparing it to TERPs guidelines is unacceptable.
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Not something we use or has been required/ recommended by our POI.
 
turbomax97 said:
Not something we use or has been required/ recommended by our POI.
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This appears to be the case with many 135 POIs. I wonder why virtually all 121 certificate management units interpret this as a hard requirement, yet we're all here having this conversation.

Again, I'm trying to keep an open mind on this. It just amazes me that this was such a large - and expensive - part of 121 flying that some 135 operators/FAA POIs don't focus on.
 
I still read it as if the operator/pilot has determined a safe backup plan for when something happens, and as long as they meet either terps or part 25 certification then you're fine.

Our VII cannot meet 3.3 out of higher altitude with any considerable amount of fuel on board. So we either go light, or wait for VMC.
 
Crockrocket94 said:
I still read it as if the operator/pilot has determined a safe backup plan for when something happens, and as long as they meet either terps or part 25 certification then you're fine.

Our VII cannot meet 3.3 out of higher altitude with any considerable amount of fuel on board. So we either go light, or wait for VMC.
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This is the common misconception that most 135 pilots have AND places like SimCom, Simuflite, FSI don't do any of us any favors either.

The relevant regulation is 135.379 (keep this on track, we are talking part 25 jets, king airs and such are a different story)

Importantly from that reg is this 135.379 (d)(2)
(2) For an airplane certificated after September 30, 1958 (SR422A, 422B), that allows a net takeoff flight path that clears all obstacles either by a height of at least 35 feet vertically, or by at least 200 feet horizontally within the airport boundaries and by at least 300 feet horizontally after passing the boundaries.
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The AIM and the above referenced AC cover the TERPS argument about using ODP and SIDs for OEI obstacle avoidance (simply, it doesn't work legally).

The premise is simple, as a pilot we don't have access to the necessary data to compute a take off path, taking into account all obstacles, to comply with 135.379. Yes, at probably 90% of the airports we all fly into or out of, the data is not necessary and climb at V2 to 400 or 1500 feet is sufficient and the APG type data will reflect that. But the point isn't that, the Regs and multiple citations from the Feds in both the AIM and an AC require this data for ALL operations not just Aspen et al.

Part 25 jets, operating under 135 simply are NOT allowed to take off and climb visually at a weight that would prevent them from maintaining obstacle clearances, 135.379 says nothing about visual avoidance. Notice it says nothing about VFR or IFR, VMC or IMC either.

Now someone will grab a chart and point to some ODP or SID that has some language about crossing over the field in visual conditions and such, or with a certain ceiling and vis your climb gradient is this. That's fine and dandy but we still have to abide by 135.379. Those "other" procedures are just like LPV mins or 600 RVR mins, if you don't have the approval or whatever, just because it is on the chart, doesn't make it legal or available to you.


Keep this in mind as well. Almost every POH/AFM/WHATEVER has some language about interpolating but almost all forbid extrapolation. A lot of people, I'm looking at you 142 schools, think it is one to take your takeoff data at the top of the SID and apply that V2 and say you can maintain V2 to the top. That is extrapolation, not interpolation and it doesn't work. V2 isn't some magic thing that makes you climb in a straight line, performance diminishes with altitude.
 
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