Vector VS Assigned Heading

[sellener777]

Taking off RW 26 somewhere......Clearance assigns "Cleared to airport, fly heading 360, Radar vectors ABC then as filed....."

I understand a vector is when you have been identified on radar and given heading/altitudes.

I understand a vector assures terrain clearance.

The assigned heading is not, by definition a radar vector.

Question) How does a typical pilot assure the heading assigned was/is intended for terrain seperation (among other things). ( I know you can ask, and clarify, and ultimetly terrain seperation is the PIC responsibility). However, I am intrested in the intent of the assigned heading and if terrain seperation is a part of it.

I have heard some talk amongst controllers of Diverse Vector Areas and understand it loosely to be an area where they can "vector" you below MEA's or perhaps in the abscence of radar contact. (which goes against definiton of radar vectors.....perhaps their are different types of vectors?) And perhaps that is the authority in which they assign "headings" prior to takeoff that assure terrain clearance. However, as a pilot, I do not know which aiprots have this established Diverse Vector Area and which do not.

This really makes you think when their is a ODP for the takeoff runway that conflicts with "fly heading 360." I currently understand it to be climb to 400ft 200ft/nm and turn to 360. This is confusing if there exists a ODP stating climb to 1500 before making turns or any other seemingly conflicting procedures.

If a controller could chime in it would be great.

It doesnt seem like a pilot should have to clarify everytime they are given "cleared to airport, fly heading 360, radar vectors ABC...."

It seems like we should know the intent, and what thought process was used, of assigning that heading.

[Peter Grey]

Hello,

This is a good question.

Here is the official pilot/controller glossary definition of a vector:

VECTOR− A heading issued to an aircraft to provide navigational guidance by radar

At most of the airports that PilotEdge covers radar coverage is quite good and for all intents and purposes can be considered to start from 0 AGL. As a result of this most of these airports have DVA's established for them. Per the P/CG a DVA is:

In a radar environment, that area in which a prescribed departure route is not required as the only suitable route to avoid obstacles. The area in which random radar vectors below the MVA/MIA, established in accordance with the TERPS criteria for diverse departures, obstacles and terrain avoidance, may be issued to departing aircraft

I'm going to skip the DVA TERPS requirements, but as long as you climb at a reasonable rate (> 200 ft/nm) you'll miss everything in a DVA. This results in procedures where aircraft are given an initial heading off the ground at a large number of our airports.

In all cases this heading is a DVA and ensures obstacle avoidance. ATC can't assign a heading off the ground that isn't in a DVA without pilot approval (this is extremely rare). Or in simple terms, if you follow the ATC instruction you won't hit anything.

Let me know if you have any questions about this.

[sellener777]

Hello,

This is a good question.

Here is the official pilot/controller glossary definition of a vector:

VECTOR− A heading issued to an aircraft to provide navigational guidance by radar

At most of the airports that PilotEdge covers radar coverage is quite good and for all intents and purposes can be considered to start from 0 AGL. As a result of this most of these airports have DVA's established for them. Per the P/CG a DVA is:

In a radar environment, that area in which a prescribed departure route is not required as the only suitable route to avoid obstacles. The area in which random radar vectors below the MVA/MIA, established in accordance with the TERPS criteria for diverse departures, obstacles and terrain avoidance, may be issued to departing aircraft

I'm going to skip the DVA TERPS requirements, but as long as you climb at a reasonable rate (> 200 ft/nm) you'll miss everything in a DVA. This results in procedures where aircraft are given an initial heading off the ground at a large number of our airports.

In all cases this heading is a DVA and ensures obstacle avoidance. ATC can't assign a heading off the ground that isn't in a DVA without pilot approval (this is extremely rare). Or in simple terms, if you follow the ATC instruction you won't hit anything.

Let me know if you have any questions about this.

So I get what your basically saying, but have a few hangups on details:

1) A DVA is not a circle surrounding an airport with no obstacles penetrating the 200ft/nm climb? Correct? I would think DVA's come in different size and shapes and pies depending on local terrain/obstacles.

So a heading of say 360 to the north would be contained(terrain safely seperated) in a north ish sector, but perhaps a heading of 060 would be outside of the DVA because of a mountain.

2) Other thing is the assigned heading. It does not appear to be a vector by definition as you are not being provided navigational guidance by radar......yet. So I guess Im looking for a reference to why we accept it as terrain seperation. When Im flying and someone asks "who is providing terrain seperation," I normally answer a couple ways...... a) at altitude when vectored of an airway or something I would say terrain is on the controller due to radar vector. b) If I want to get a bit lower then the MEA to cancel IFR they may have a lower altitude via MVA or a DVA still maintaining radar contact ( i assume this would be where u have a published MEA for the area, but because of a special DVA you can give me lower and still see me on radar and able to turn me away from some potential obstacles if needed seen on scope.) c) On a published ODP or SID or Diverse departure(an IAP at the airport and no other guidance from ATC or published DP) I can say because its the procedure.

d) It also makes since that if im performing a diverse departure from an airpot with an IAP and no published ODP or DP that I can accept any heading and fly it and be clear of terrain by definition of a diverse departure.

Where I still am confused is the situation where there is a ODP and clearance gives me a conflicting heading to fly after takeoff. IM 99 percent satisfied that the heading is providing me terrain seperation but want to know where to find the ref material stating that.

Thanks

[sellener777]

Also, while I have your ear.....

THis topic brings up another reason behind knowing the guts of the assinged heading DVA terrain seperation thing. I was flying an assigned heading assigned by clearance after departure that conflicted with the ODP. I lost comms before talking to departure. What is safest course to fly? I concluded that knowing local terrain would be the best thing, but made me even more curious about the assinged heading and the DVA and so forth. How long does the assigned heading assure terrain seperation? Should I turn off assigned heading and get on the airway or stay on assigned heading? Two scenarios: assinged heading flys me into mountain after 10 miles, or assigned heading keeps me away from mountain on my left. I turned to intercept airway but I could have flown into a mountain the heading was keeping me from flying into.

I guess I conclude that the ODP is safest due to lost comm scenario and KNOWING it assures terrain seperation without any need for ATC/radar. I would argue there is inherent risk (very small) in the assigned heading DVA due to lost comm issue and not knowing details behind the DVA and assigned heading.

Anyway thanks for your response, look forward to hearing your input, and realize this is a bit technical but still worthy of discussion.

[Peter Grey]

Ok, I think to allay your concerns I'm going to have to reference you to FAA Order 8260.3B (aka the TERPS).

If you want to follow along: http://www.faa.gov/documentLibrary/medi ... 26_rev.pdf

We are considered with DVAs which is covered in Volume 4 Chapter 2 (start on PDF page 397).

First we do a general check of the area covered by the DVA (46NM from the airport for most airports within PilotEdge) to see if any obstacle penetrate the Obstruction Clearance Slope (this slope starts at 35' at the departure end of the runway and climbs at 152' ft/nm away from that point). There is a separate allowance for the initial climb (runway to 400') which I wont' go over as all this is done for all IFR runways. Note that because IFR aircraft are expected to climb at 200 ft/nm this means for each mile you climb away you gain 48 feet of terrain clearance.

Within PilotEdge you will find an obstacle that violates this area at every single airport, so we have to restrict the departure area using criteria listed in this document.

If you look through this you will find 2 approved methods to make a restricted DVA. We can define "areas around obstructions" that we can't vector into, or approved headings which assure obstacle clearance out to 46NM (at which point you are 9200' AGL and should be well above any MSA).

We use the second method here at PilotEdge. So what we do is take a line from a point that's approximately the runway and head directly into the obstacle that violates the 152 ft/nm gradient. Then we provide a 20 degree buffer. For example if a heading of 360 through 030 would hit hit the side of the mountain, we would not be allowed to vector between 340-050.

Here at PilotEdge we end up using specific headings that both provide obstruction clearance and allow for proper traffic separation, that's why you always tend to get the same heading from an airport.

So let's look at an example regarding your ODP question. Let's use KCMA runway 26, an airport with no SID, but we regularly assign headings from (normally heading 275).

Here is the KOXR Runway 26 ODP:

climbing right turn to 2500 via CMA
R-265. All aircraft climbing left turn direct CMA VOR/

So that makes sense, go west (over water) and once you're above the terrain (highest terrain around CMA is 3100 which is just S of the VOR) turn around to go on course.

So let's DVA CMA (we are going to do this roughly, in reality this is a very exact science). We will start from due North and work our ways clockwise around.

Drawing a circle 46 NM around from CMA we find a big mountain range to the North starting around 18 miles from the airport. 18 NM * 152 ft/nm + 77' (CMA elevation) gives us 2813'. These mountains are well above 4000' so that's not going to work. As we scan from N towards E we continue to find mountains until around a 035 course (where there is gap in the mountains near LHS). At this point the mountains are 34 nm away and only 4300' high. Running it by 34NM * 152 ft/nm + 77 gives a maximum height of 5245', that's above the terrain so we are good to go.

We need a 20 degree buffer so the first heading we could give is 055. As we continue to scan E we fine another mountain range just E of BUR with the high peak at 6560' 46NM away (right at the edge of the ring). Maximum terrain height at this point is 7070' (and the plane should be just above 9000' climbing at 200 ft/nm) so we are still good.

Continuing our scan around we find a peak at 2403' 15NM away on a 080 heading. Quick run through says max terrain height is 2357' so we are good there.

We continue around and find a 3100' peak 10 miles away on a 110 course. This won't work so that defines the south edge of the clear sector (remember the N edge was the mountains near LHS). Give us a 20 degree buffer and we can assign a 090 heading.

So our first safe DVA zone is heading 055-090.

Continuing South that peak is lonely with no other mountains around it so we can add a 20 degree buffer on the other side and start the second ok zone on heading 130. By this point we are over water (or islands with low mountains) so we continue to be doing ok until a course of 290 where we hit a 4000' peak NW of SBA 34 NM away. That terrain is too low to be of issue so we continue and end up hitting a 2326' tower 14 NM away on a course of 295. This ends up being 100' too high to be safe so that defines the edge of the second safe zone. We lob 20 degrees off of 295 and we get 275. Continuing N we quickly run into that same mountain range we started with and all of it is too high to climb above safely.

So our second safe zone is 130-275. Note this zone includes the ODP (and our 275 heading).

With the analysis complete we now know that we can assign a heading between 055-090 or 130-290 and not run an airplane into anything. So why 275?

Well 275 provides ATC with a divergent heading from KOXR which is nearby (and uses a 255 heading for it's departures). This allows us to launch aircraft from both airports at the same time. Anything south of 275 (including the ODP) would conflict with OXR departures, hence why we picked heading 275.

Hopefully that explains the logic behind it all.

To answer the specific questions:

1) A DVA is not a circle surrounding an airport with no obstacles penetrating the 200ft/nm climb? Correct?

Correct, however note we use 152 ft/nm for the obstacles (so that you have a safe buffer of 48 ft/nm). By 46NM your safe buffer is 2208'.

You have to trust that the heading we give is in the DVA (don't worry it is).

Other thing is the assigned heading. It does not appear to be a vector by definition as you are not being provided navigational guidance by radar......yet. So I guess Im looking for a reference to why we accept it as terrain separation.

I would personally debate the vector aspect of it. There is no requirement to be radar identified to meet the "navigation guidance by radar" requirement in my previous post, note that definition does not require an aircraft to be in radar contact. In certain cases we actually assign headings prior to radar contact to allow us to radar identify an aircraft (we take other steps to ensure terrain clearance in this case).

In the specific case of a DVA we are vectoring from a known point (the airport), and as we assume radar is available down to the airport level we will have you on radar well before you start that turn at 400' (even if we haven't told you radar contact by that point).

The non technical reference is AIM 5-2-8 C 2 which states in part:

ATC may assume responsibility for obstacle clearance by vectoring the aircraft prior to reaching the minimum vectoring altitude by using a Diverse Vector Area (DVA) The DVA has been assessed for departures which do not follow a specific ground track.

This is what we are doing in this case.

If I want to get a bit lower then the MEA to cancel IFR they may have a lower altitude via MVA or a DVA still maintaining radar contact ( i assume this would be where u have a published MEA for the area, but because of a special DVA you can give me lower and still see me on radar and able to turn me away from some potential obstacles if needed seen on scope.)

This is actually partially incorrect. In some cases the MVA is lower then the MEA, however we cannot vector into a DVA for anything other then a departure off the ground climbing to the MVA/MEA. Once it reaches the MVA/MEA we are bound by that altitude.

c) On a published ODP or SID or Diverse departure(an IAP at the airport and no other guidance from ATC or published DP) I can say because its the procedure.

A DVA is a diverse departure (note the name "Diverse vectoring area").

d) It also makes since that if im performing a diverse departure from an airpot with an IAP and no published ODP or DP that I can accept any heading and fly it and be clear of terrain by definition of a diverse departure.

It does make sense but this can't generally happen. A DVA is unlikely to have be done at an airport without an ODP (which is different from an airport with no ODP due to no obstructions in which case a DVA isn't needed as there are no restrictions). An airport cannot have an IAP without an ODP (or determination that no obstructions exist requiring an ODP).

I was flying an assigned heading assigned by clearance after departure that conflicted with the ODP. I lost comms before talking to departure. What is safest course to fly?

Assuming an IMC scenario, assigned heading till above the MSA/MEA/OROCA, then on course in accordance with relevant regs.

How long does the assigned heading assure terrain seperation? Should I turn off assigned heading and get on the airway or stay on assigned heading?

25-46 NM (46 for most airport in PE airspace), No, stay on the heading to MSA/MEA/OROCA then proceed on course. If you pass the airway above airway MEA (or even MOCA in this case) you could turn onto it if navigation signal is acceptable.

As a final note AIM 5-2-8 provides the pilot version of all of this stuff and is a good read for these types of cases.

Let me know what else you have questions on.

[sellener777]

Hey thanks a bunch. Best clarification I've heard! Appreciate the time you took to respond. Now send me a bill for ground dual given and an IPC.

[Keith Smith]

Eric, some perspective from a controller who reads the forum:

At the end of his post he wrote,”It seems like we should know the intent, and what thought process was used, of assigning that heading.” ... The controller may be using the heading to avoid departure conflicts, special considerations, (TFR, Search and Rescue, etc,) reduced departure delay, or consecutive departure sequencing. The pilot may ask why, but should know that ATC is using the vector to comply with the “safe and expeditious” flow of traffic. Secondly, 7110.65U Para. 5-8-2. Note. Terminal. reads, “A purpose for the heading is not necessary, since pilots operating in a radar environment associate assigned headings with vectors to their planned route of flight.”