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Old 03-31-2010, 07:00 AM   #1  
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Default Takeoff obstacle avoidance & runway analysis

Ok, here is the scenario, on an 800XP, FAR 135 recurrent ride; the check pilot presented this situation: VMC departure (clear and 20) from RWY 15 from Addison, TX (KADS).

In front of me I have the Obstacle Departure Procedure (HUBBARD Departure), the computer generated runway analysis and a made up NOTAM indicating that the first 2000 feet of the runway is closed leaving 5205 ft. available for takeoff. The current runway analysis indicates an obstacle limiting weight of 26,990 lbs (NOTAM obstacle limiting weight). After going through the charts in the AFM I found that the runway limiting weight is 27990 lbs., with 5202 ft. of runway.

This is where it becomes gray. Do I takeoff using the obstacle limiting weight of 26,990 lbs. or because it is VMC and I can see and avoid the “multiple building beginning 1085’ from departure end of runway, 21’ left of centerline, up to 321’AGL/956’MSL” and go with the runway limiting weight of 27990 lbs. and make my destination without a fuel stop.

My answer was the more conservative, and to make the fuel stop. This was accepted, however after vast research and looking at several closed threads that never really addressed this precise issue (of obstacle clearance analysis and VMC departures), the question still lurks in the back of my mind. It would probably be acceptable for FAR 91 operations to takeoff with the heavier weight, but for 135 and 121, I don’t see a definitive regulation as to why this cannot be done.

Additionally, looking into the Instrument flying handbook, it say’s to see and avoid obstacles thus eliminating the need for an obstacle restrictive runway. (does this only apply for FAR 91?) Then it talks about escape route procedures and so forth. Also looked into the FAA instrument Check Pilots handbook and came up short there as well.

So where is the definitive answer as to why you cannot see and avoid obstacles under FAR 135 and 121?
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Old 03-31-2010, 08:52 AM   #2  
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I would say that your AFM runway numbers are derived only for a specific Density altitude and prescribe how much runway the aircraft would need to take off under those conditions considering accelerate stop/go distance, balance field length etc.

An AFM can give you climb limit weights as a guideline but can not account for every airports unique obstacles. This is why we use runway analysis like APG to derive takeoff weights in the real world. The computer runway analysis will be limiting in this scenario for part 135 and 121 because it DOES take into account the surveyed plane surrounding the specific airport. Every takeoff must be assumed to have the OEI performance associated with that airport.

The computer analysis or APG or whatever service you use will offer weights that are higher provided you use the OEI DP that would be provided SHOULD you bag one on departure. These weights will give you TERPS obstacle clearance ability for you particular aircraft. That being said, if its VMC, then you can just climb to 1500 feet AGL or the prescribed Obstacle Clearance Altitude and then see and avoid to go run your checklists and return to the airport. VMC does not exclude you from having to have the single engine performance required by TERPS for obstacle clearance. It just allows you to see and avoid and possibly just stay in the traffic pattern to return to the airport at pilots discretion. I hope this helps or at least doesnt make it more confusing

In short; yes you must adhere to the limiting weight, no you do not have to follow the OEI ODP in the event of an engine failure in VMC. And I dont know the exact place where it states all of this because I dont have a TERPS or FAR with me right now but its all in there somewhere : )

I fly part 91 and we still use APG because I need to prove to myself that we can maintain obstacle clearance, however I dont think it is required.
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Old 03-31-2010, 11:13 AM   #3  
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You CAN 'see and avoid' flying 135.

135.379 lays out the obstacle clearance requirements. If you can't comply with the pulished DP, then you can maneuver visually to satisfy the reg.

AC 120-91 provides further guidance on the subject.
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Old 04-01-2010, 07:13 AM   #4  
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Originally Posted by AKASHA View Post
You CAN 'see and avoid' flying 135.

135.379 lays out the obstacle clearance requirements. If you can't comply with the pulished DP, then you can maneuver visually to satisfy the reg.

AC 120-91 provides further guidance on the subject.

135.379 has nothing to do with the published DP. 135.379 is all about runway requirements and the Part 25 takeoff flight path, which becomes critical in the event of an engine failure, and has nothing to do with weather conditions.
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Old 04-01-2010, 09:26 AM   #5  
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135.379 is totally relevant to tracer997's scenario. And nothing was said about losing an engine, which is off-subject. As I read it, the question is simply...

"If I am too heavy to meet the climb gradient on the ODP, can I still take-off at the heavier weight and maneuver visually to avoid obstacles under Part 135... where is the reg??"

135.379 states obstacle clearance requirents both within and outside of the airport boundary. And AC 120-91 reminds us that "operators MUST COMPLY with 14 CFR requirements regarding the development of takeoff performance data and procedures." That is, 135.379.
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Old 04-01-2010, 09:40 AM   #6  
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Originally Posted by AKASHA View Post
135.379 is totally relevant to tracer997's scenario. And nothing was said about losing an engine, which is off-subject. As I read it, the question is simply...

"If I am too heavy to meet the climb gradient on the ODP, can I still take-off at the heavier weight and maneuver visually to avoid obstacles under Part 135... where is the reg??"

135.379 states obstacle clearance requirents both within and outside of the airport boundary. And AC 120-91 reminds us that "operators MUST COMPLY with 14 CFR requirements regarding the development of takeoff performance data and procedures." That is, 135.379.
Thus, 135.379 and AC 120-91, which apply only to OEI, are totally irrelevant to his question.

The issue is, "where is the controlling obstacle along the ODP route?" Answer: It is not published.

There may be many obstacles along an ODP path that penetrate the basic 40:1 path, but only one that dictates the charted climb gradient.

If the controlling obstacle is within 3 miles of the departure end of the runway then an alternative ceiling and visibility will be charted, which can be used in conjunction with the ODP (but usually not with any SIDs). The problem is, if there is an optional ceiling and visibility published in the takeoff minimums, it has little use unless a VCOA (visual climb over airport) procedure is also charted (those are fairly new, thus most airports don't have them). And, a VCOA itself is fraught with hazards unless the pilot is provided a good plan on how to use it safely.
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Old 04-01-2010, 11:51 AM   #7  
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The way I read it, tracer simply wants reference to a 135 regulation that allows an aircraft to depart a runway and maintain your own obstruction clearance (ie 'see and avoid') rather than fly the published ODP.

I would agree that performing a visual climb over the airport (even if not published) might be one way of maintaining obstruction clearance on your own. But I also suggest that you can fly your own departure path and accomplish the same, as long as you request and receive a clearance to do so.
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Old 04-01-2010, 12:30 PM   #8  
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The way I read it, tracer simply wants reference to a 135 regulation that allows an aircraft to depart a runway and maintain your own obstruction clearance (ie 'see and avoid') rather than fly the published ODP.

I would agree that performing a visual climb over the airport (even if not published) might be one way of maintaining obstruction clearance on your own. But I also suggest that you can fly your own departure path and accomplish the same, as long as you request and receive a clearance to do so.
The change to 91.175 a couple of years ago requires 121 and 135 operators to either use the ODP (or SID if assigned) or use an FAA-approved company departure procedure; such as an OEI path.

ATC really doesn't have much jurisdiction except to the extent such a visual climb would occur at a Class D airport.

I certainly wouldn't want to do visual avoidance on a departure procedure under Part 135 without the advance concurrence of the FSDO holding the certificate.

Part 91 is altogether different. ODPs and takeoff minimums are optional, only SIDs, when assigned, are mandatory.
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Old 04-01-2010, 03:41 PM   #9  
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I certainly wouldn't want to do visual avoidance on a departure procedure under Part 135 without the advance concurrence of the FSDO holding the certificate.
And there lies the answer. Check your Ops Specs for authorization (or lack thereof). Our Ops Specs allows for it with provisions. I was wrong to assume that is the case for tracer.
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Old 04-01-2010, 04:55 PM   #10  
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I appreciate the input(s). So if I had 135 (or even 121) Ops Specs that permit VMC departures, I could forget the computer generated or APG runway analysis which shows a lesser weight because of the obstacles. I still may be runway limited because of temp and PA. But is is probably going to be a better weight and thus eliminating a fuel stop.
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