KSMX terrain avoidance/ODP

KSMX terrain avoidance/ODP

Postby linzhiming » Sun Sep 23, 2018 1:48 am

On a recent flight from KSMX to KOXR with a filed route of RZS VTU, I received the following clearance

"Cleared to Oxnard airport, on departure fly heading 100, radar vectors San Marcus, as filed, [...]"

How would I ensure to stay clear of terrain upon departure? I was particularly worried (and would have been in real life) with that heading assignment given the terrain about 10 NM east of the airfield.

I had expected to get the BULET4.RZS departure and transition, which would have kept me clear of terrain and I had also read the ODP which says "Rwy 30: Climb heading 294; climb direct GLJ VOR, then continue climb to airway MEA via GLJ R-300 to intercept MQO R-137 to MQO VORTAC. Cross MQO VORTAC at or above MEA/MCA for assigned route of flight."

Given that conditions had become VMC, I was comfortable with turning straight on to that heading at 400ft AGL but what should I have done in IMC? Don't say "Query the controller and confirm departure instructions" as I would certainly have done that (and also in real life) if I was unsure :).

Option 1: Request the BUELT4 departure and RZS transition.
Option 2: Fly the ODP. However, the ODP would have me fly all the way to MQO VORTAC before almost performing a 180-turn back towards RZS. Given that the controller would have expected me on heading 100 after departure, I would have told the controller that I wanted to fly the ODP for terrain clearance so that he would understood my intentions although technically I would not have had to advise him of that.
Option 3: Request an abbreviated ODP, i.e. advise controller that I would want to fly the ODP until above his MVA so that he could safely vector me towards the south.

Most importantly, would anyone have accepted a departure on heading 100 in real hard IMC in the hope of the controller vectoring me south quickly enough? What if I couldn't get through to the controller because he was busy or in the case of a comms failure (in which case I would have turned south and then proceeded direct RZS as per FP)? Heading 100 would have made me shudder and think in real IMC and real life, I would have been more comfortable with a heading of 170/180 after departure.
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Re: KSMX terrain avoidance/ODP

Postby kevin meyers » Sun Sep 23, 2018 3:53 am

By assigning you the 100 heading, ATC is taking responsibility for you. If you are assigned a departure heading, that heading has been approved for departure off of that runway. ATC doesn’t pull headings and altitudes our of thin air. They have the data that shows them what is safe. Furthermore, a lot of initial IFR departure headings (especially in busy airspace) are pre-designated by LOAs and SOPs.

With that said, I suppose if you ever feel unsafe about an instruction, as PIC it is your right to decline it. However, in an instance like this, as long as you’re not pointed directly at a mountain (for some very odd reason) and you are certain that ATC assigned you the 100 heading, you can rest assured that you will be clear of terrain and obstacles. If you’re in hard IMC, you’re really trusting the controller at that point (obviously) so you don’t have much of a reason to decline an instruction as you won’t see the big picture that they do.

On the other hand, if you still felt unsafe about the 100 heading, requesting an alternative procedure such as the ODP or SID likely isn’t out of the question. From a legal perspective, it would be difficult for a controller to defend why he told the pilot “no” to their request, then the pilot followed the controller’s instruction and an incident occurred. However, know that requesting a SID or ODP (when already having been assigned a heading) in busy airspace is going to make you a big PITA and for reasons stated above wouldn’t be necessary unless you know something that nobody else did (ie you saw a ton of balloon activity on the 100 heading and you were almost sure you would hit one).
Kevin Meyers
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Dallas, Texas
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Re: KSMX terrain avoidance/ODP

Postby jx_ » Sun Sep 23, 2018 8:05 am

on heading 100, terrain is 20nm flight distance at 4500 feet. Assuming you make the turn at 400 above airport elevation:

field elevation 261
turn started at 661
minimum IFR gradient for radar vector = 200 feet per mile

times 20 miles = 4000
plus height at turn = 661

altitude at terrain point = 4661


You only need to clear obstacles by 35 feet at minimum climb performance. The FAA & ATC does the math on these things before they are allowed in practice.
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Re: KSMX terrain avoidance/ODP

Postby linzhiming » Sun Sep 23, 2018 8:30 am

Hi jx_,

Thanks for checking and you are right that heading 100 wouldn’t lead me straight to the tower and 3253ft elevation point that I was concerned about. At first glance, it looked like that as I didn’t account for the magnetic variation. Heading 100 would roughly lead towards the points with the elevation of 4341 and 4528 ft and I would indeed have a bit to climb until then. On the other hand, as a real-world IFR pilot (although mainly flying GA in Europe and Asia and therefore less familiar with all FAA rules), a heading in the direction of general higher terrain would always put me into a higher alert stage, in case of any screwups or lost comm scenario.

Coming back to Keith’s and your comments about the FAA and ATC taking care of me: Does “On departure fly heading 100” constitute a radar vector and/or departure instruction where ATC would assume terrain clearance responsibilty? I was under the impression that in FAA land only upon positive radar identification (“radar contact”) and issuance of a vector (i.e. a “radar vector”) would ATC assume terrain clearance responsibility. If “Fly heading 100” constitutes an instruction with terrain clearance responsibility, what about “after departure, track to XYZ to join V123” or “after departure, direct XYZ VOR”?

Do all of these represent instructions where ATC assumes terrain clearance responsibility? (In which case, I could be more relaxed about it that I have been in the past - although I would of course still visualise potential hazards in my mind.)

In what cases would I need an ODP then? Is that if the clearance is “Cleared to XYZ airport via ABC, DEF and then as filed”, in which case I got an enroute clearance but no after departure instructions?
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Re: KSMX terrain avoidance/ODP

Postby jx_ » Sun Sep 23, 2018 9:18 am

In specific terms, you are correct, the air traffic controller doesn't take responsibility until you receive a new instruction, however, the radar vector that ATC gave you is preplanned to guarantee 35 foot clearance at the minimum IFR gradient for the heading. If you're curious take a look at the TAKEOFF MINIMUMS booklet and search for "Diverse Vector Area". This will show you the exact minimum climb gradient the vector is planned for if not standard. As a pilot, this would be the minimum I would check if I am concerned about terrain on a vector. SMX does not have a vector listed because it is standard 200 feet per mile.


This is from BUR:

DIVERSE VECTOR AREA (RADAR VECTORS)
ORIG 16147 (FAA)
Rwy 8, heading as assigned by ATC; requires minimum climb of 420’ per NM to 2500.

Rwy 15, heading as assigned by ATC; requires minimum climb of 340’ per NM to 2100.

Rwy 26, heading as assigned by ATC; requires minimum climb of 380’ per NM to 4800.

Rwy 33, heading as assigned by ATC; requires minimum climb of 460’ per NM to 4900.



So if you climb on any ATC assigned heading and make the above gradients, you are guaranteed to not hit anything.


Think of it this way, the only difference between the flight path of an SID/ODP and the flight path of a radar vector off the ground is the SID/ODP usually relies on navigation facilities aligning with the flight path; the vector does not; however both guarantee the same obstacle clearance for a NON-RADAR/uncontrolled aircraft. ATC departure headings are no different in their obstacle clearance requirements, and you are not "trusting" ATC. They are planned out and then issued to ATC facilities as approved for use. Controllers never think about what the gradient or clearances are, they just know they are approved for use. If there are headings approved for an airport without a control tower for instance, ATC can use them just the same as an ODP and the pilot will be guaranteed the same safety margin.
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Re: KSMX terrain avoidance/ODP

Postby jx_ » Sun Sep 23, 2018 10:05 am

1) If “Fly heading 100” constitutes an instruction with terrain clearance responsibility, what about “after departure, track to XYZ to join V123” or “after departure, direct XYZ VOR”?

2) In what cases would I need an ODP then? Is that if the clearance is “Cleared to XYZ airport via ABC, DEF and then as filed”, in which case I got an enroute clearance but no after departure instructions?



#1:

Any and all ATC instructions included in your clearance are covered by the FAA IFR minima rules. So if you receive a heading, that has a minimum gradient. If you receive either of your examples above, a gradient would be applicable for it to be legal. But the confusing part is understanding what happens when you transition from terminal environment to the FAA ATSS. The "Climb Gradient" is only guaranteed to avoid obstacles up to that first valid waypoint. From that point on there may be MOCA/MCA/MEA to deal with. If you are below these you're on your own!!! It is always pilot responsibility to take those items into account when planning a transition to or from the ATSS, unless ATC gives explicit instructions, in which case, ATC will use the MVA at all times until the airplane has established itself on a published segment of a nonradar procedure. So it is quite possible that you could be weight restricted by a MOCA on the airway after you transition to the ATS but not restricted to the first fix. ATC is not responsible to give you a restriction to meet that MOCA if you are still in a climb to the MEA.

So to recap: IFR CLIMB gradient is built into any approved ATC instruction that is specifically included; but it is the pilots responsibility to verify he can make any restrictions on the published ATS route.

In the absence of specific climb instructions from ATC such as "Cleared as filed" or "Cleared via XYZ VOR"; it is always the pilot's responsibility to plan has safe climb to the published route.


ONE EXCEPTION: If ATC clears you for an unpublished route. Then it gets tricky but the simplest explanation is ATC is responsible to get you above the MVA with an approved procedure that guarantees climb gradient.


#2:

In the absence of specific climb instructions, you could opt for the ODP or you could be a real airman and pull out your terrain map, stop watch, and calculator. Up to you, because you're on the hook. ODPs are there for your convenience.
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Re: KSMX terrain avoidance/ODP

Postby jx_ » Sun Sep 23, 2018 11:10 am

and last but not least...


If assigned a heading pilots are allowed to fly the ODP first then turn to the heading if they are not comfortable. I have never seen this in use but you are required to advise ATC that you intend to use the ODP.
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Re: KSMX terrain avoidance/ODP

Postby Keith Smith » Tue Sep 25, 2018 9:17 am

You only need to clear obstacles by 35 feet at minimum climb performance


35ft is the minimum altitude at the departure end of runway before climbing to 400ft AGL before the first turn.

The amount of clearance from terrain that is provided by a DP is 48ft/nm if a standard climb gradient of 200ft/nm is permitted. TERPS uses a 152ft/nm gradient for the terrain analysis. So, that's where the 48ft/nm of clearance comes from.
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Re: KSMX terrain avoidance/ODP

Postby jx_ » Tue Sep 25, 2018 1:34 pm

i'm referring to the margin on the approved heading off the ground.

200 feet per mile or as specified
35 foot clearance
25/46 miles to 1000/2000 above
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