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Q: IFR flight terrain seperation ( Answered 4 out of 5 stars,   0 Comments )
Subject: IFR flight terrain seperation
Category: Science > Technology
Asked by: jrflylow-ga
List Price: $12.00
Posted: 24 Oct 2006 16:59 PDT
Expires: 23 Nov 2006 15:59 PST
Question ID: 776550
If an instrument-rated pilot files an IFR flight plan, and puts down
/G as his aircraft's equipment suffix, and he requests an off-airway
routing between two points that he defines in the flight plan, is he
also responsible to maintain his own terrain seperation during that
leg of the flight?

Request for Question Clarification by denco-ga on 24 Oct 2006 17:50 PDT
Howdy jrflylow-ga,

Does the following answer your question?

"Vectors Below Minimum Vectoring Altitude"

"/*TER/ Pilots are always responsible for terrain separation.  However, when an
air traffic controller assigns a departure procedure or control instructions
involving altitude assignments, pilots expect that compliance with those
instructions will provide terrain separation.

A pilot has no immediate knowledge of the minimum assignable altitude since ATC
may utilize diverse vector areas, minimum vectoring altitudes, and other
altitudes authorized by FAAO 7110.65, Air Traffic Control. Paragraph 5-6-1
authorizes a controller to vector departing IFR aircraft at or above the
minimum vectoring altitude or the minimum IFR altitude except as authorized for
radar approaches, special VFR, VFR operations, or by Paragraph 5-6-3, Vectors
Below Minimum Altitude. Paragraph 5-6-3 allows controllers to vector IFR
aircraft below minimum IFR altitude (MIA), but only when specific requirements
have been met.

When controllers vector or assign headings to IFR aircraft below minimum IFR
altitude, the FAA assumes responsibility for terrain separation. Controllers
may only vector aircraft, assign direct, or a climb on course when the aircraft
has reached MIA or when terrain and obstruction clearance is being otherwise
assured. FAAO 7110.65 Paragraph 5-6-3, Vectors Below Minimum Altitude,
describes how this may be accomplished when vectors will be provided.

Looking Forward, denco-ga - Google Answers Researcher
Subject: Re: IFR flight terrain seperation
Answered By: byrd-ga on 25 Oct 2006 07:58 PDT
Rated:4 out of 5 stars
Hello jrflylow-ga , 

First of all, I need to state that, per the disclaimer below on this
page, nothing in this answer should be construed in any way as
official information to be relied upon for navigation or flight
purposes, or meeting the requirements of FAR 91.103, which says that
?Each pilot in command shall, before beginning a flight, become
familiar with all available information concerning that flight.? It is
still your responsibility to look up the references given and become
familiar with all the available information, of which some portions
are quoted here in reply to your question.

All right, that understood, if you file IFR as described, and your
flight plan is accepted as filed, and you are cleared to fly direct as
filed, having the proper and current navigation equipment as indicated
by the /G suffix, i.e. ?Global Navigation Satellite System (GNSS),
including GPS or WAAS, with enroute and terminal capability,? then in
my considered opinion yes, ATC maintains responsibilty for issuing
terrain/obstruction clearance in general, with some exceptions, but
always with the understanding that the Pilot in Command has the final
authority and responsibility for the safe operation of any flight, as
per FAR 91.3(a), which states:

?The pilot-in-command of an aircraft is directly responsible for, and
is the final authority as to, the operation of that aircraft.?

This of course includes being aware of the MOCA along your route, and
ensuring you do not descend below it regardless of any clearance. If
ATC should clear you to fly at an unsafe altitude, then it is your
responsibility as PIC, whether flying direct or on a charted route,
VFR or IFR, to communicate your inability to comply and request a
higher altitude.

Here are excerpts from the regs that most directly apply to your question: 


Instructions contained in the Briefing Guide for Air Traffic
Controllers in ?Order 7110.65R  Air Traffic Control February 16, 2006?
which ?Includes Change 1 effective August 3, 2006, Chapter 4, Section
5, state:

Except as provided in subparas a and b below, assign altitudes at or
above the MEA for the route segment being flown. When a lower MEA for
subsequent segments of the route is applicable, issue the lower MEA
only after the aircraft is over or past the Fix/NAVAID beyond which
the lower MEA applies unless a crossing restriction at or above the
higher MEA is issued.

a. An aircraft may be cleared below the MEA but not below the MOCA for
the route segment being flown if the altitude assigned is at least 300
feet above the floor of controlled airspace and one of the following
conditions are met ...


Issue altitude instructions as follows: 
Altitude to maintain or cruise. When issuing cruise in conjunction
with an airport clearance limit and an unpublished route will be used,
issue an appropriate crossing altitude to ensure terrain clearance
until the aircraft reaches a fix, point, or route where the altitude
information is available to the pilot. When issuing a cruise clearance
to an airport which does not have a published instrument approach, a
cruise clearance without a crossing restriction may be issued.

I didn?t reproduce the entire document, but you can read it for yourself, here:  


The Aeronautical Information Manual (AIM) also states,  

4-4-8. VFR/IFR Flights 
" ... When accepting a clearance below the MEA/MIA/MVA/OROCA, pilots
are responsible for their own terrain/obstruction clearance until
reaching the MEA/MIA/MVA/OROCA. If pilots are unable to maintain
terrain/obstruction clearance, the controller should be advised and
pilots should state their intentions.

OROCA is an off-route altitude which provides obstruction clearance
with a 1,000 foot buffer in nonmountainous terrain areas and a 2,000
foot buffer in designated mountainous areas within the U.S. This
altitude may not provide signal coverage from ground-based
navigational aids, air traffic control radar, or communications


Other applicable regulations include: 

 91.177   Minimum altitudes for IFR operations.
(a)	Operation of aircraft at minimum altitudes. Except when necessary
for takeoff or landing, no person may operate an aircraft under IFR
(1) The applicable minimum altitudes prescribed in parts 95 and 97 of
this chapter; or
(2) If no applicable minimum altitude is prescribed in those parts? 
(i) In the case of operations over an area designated as a mountainous
area in part 95, an altitude of 2,000 feet above the highest obstacle
within a horizontal distance of 4 nautical miles from the course to be
flown; or
(ii) In any other case, an altitude of 1,000 feet above the highest
obstacle within a horizontal distance of 4 nautical miles from the
course to be flown.
However, if both a MEA and a MOCA are prescribed for a particular
route or route segment, a person may operate an aircraft below the MEA
down to, but not below, the MOCA, when within 22 nautical miles of the
VOR concerned (based on the pilot's reasonable estimate of that
(b) Climb. Climb to a higher minimum IFR altitude shall begin
immediately after passing the point beyond which that minimum altitude
applies, except that when ground obstructions intervene, the point
beyond which that higher minimum altitude applies shall be crossed at
or above the applicable MCA.


Part 95 -  IFR Altitudes:


Additional references: 

Main page, Aeronautical Information Manual (AIM), ?Official Guide to
Basic Flight Information and ATC Procedures? 

Main page Electronic Code of Federal Regulations (e-CFR) Title 14
Aeronautics and Space:

Main page, Order 7110-65R ?Air Traffic Control?  

If you are a member of AOPA, you can access their library of materials
as well, which contains a wealth of information. Here?s the link to
the main page, in case you don?t alredy have it: 

Revised Aircraft Equipment Suffix Table for FAA Flight Plans: 


Finally, if you would like an official opinion from the FAA on your
question, you may obtain one from your local Flight Standards District
Office (FSDO). Just call and let them know what you need. You may or
may not need to go to the FSDO in person to get the opinion, depending
on whether or not you want it in writing. Here?s a link to a locator
where you can find the FSDO nearest you:


If anything isn?t clear, please let me know in a Request for
Clarification, as I want to be sure you?re happy with the information
received. Also let me know if any links don?t work, and I can try to
repost any troublesome ones.


Search strategy:

I relied upon my own knowledge as a certificated Commercial,
Instrument-Rated pilot, as well as on my personal collection of
bookmarks to official publications, where I looked up the pertinent

Request for Answer Clarification by jrflylow-ga on 26 Oct 2006 13:12 PDT
Hi, thanks for your info.  Clearly, you are correct about PIC always
being aultimate authority on the safety of the flight.  The AIM
reference 4-4-8 was helpful, but it also places the responsiblity on
the shoulders of the pilot for any clearance that he receives BELOW
the MORA or OROCA - this I would assume, would only happen if the
controller made an error.  AOPA says that the pertinent altitudes to
consider are the MORA or OROCA, so they agree with you, but their
interpretation is that the pilot is responsible, in the off-airways
case, whereas the controller would be responsible for an on-airways
routing.  In other words, if I filed a flight plan right through a
mountain on an off-airways route, I could thoretically recieve that
clearance and try to fly it, with the obvious result....  Would you
agree with that?  thanks for the help!

Clarification of Answer by byrd-ga on 26 Oct 2006 14:22 PDT
Hi jrflylow,

You're very welcome! I always enjoy researching aviation related
subjects, as I always learn something myself!

As I understand it, your basic question for clarification is "... if I
filed a flight plan right through a mountain on an off-airways route,
I could thoretically recieve that clearance and try to fly it, with
the obvious result....  Would you agree with that?"  Am I correct in
that assumption?

If so, well I'd have to sort of agree, but mostly disagree.
Technically, ANYthing is *theoretically* possible, so sure, I guess
you could receive a clearance that would fly you into a mountain, and
go ahead and fly it trustingly with the inevitable S M A C K. BUT,
realistically, it's very unlikely you'd receive such a clearance
because there are a number of factors at work here.

First of all, your flight plan with the direct routing would be
accepted, of course, at face value. In practice, in flying it,
however, on an IFR flight plan, you don't just get turned loose to fly
your flight plan, but you are under positive control and receive
separate clearances for each leg.

Therefore, when you arrived at the off route portion of the flight,
you'd be cleared for that portion with not only a "cleared direct" but
also a "maintain altitude" portion to the clearance. If you are under
radar control, which you are while on an IFR flight (provided you
don't have a transponder malfunction), then the controller is
extremely unlikely to give you an altitude clearance through the
middle of a mountain, since published altitudes, including OROCA,
require a minimum of 2000' above a mountain. at this point, if you fly
your assigned alitude, ATC is responsible for terrain clearance.

However, again theoretically, suppose you're flying a C-172 with a
service ceiling of 14,500'and the mountain in your path is at 13,500'
-- well, you're going to have to refuse the altitude clearance and fly
only 1000' above the mountain, below the OROCA. At that point, ATC is
no longer responsible for providing terrain clearance, you are.

I did find a few more resources for you, that might help in clarifying this. 

First, here's a 2004 FAA Air Traffic Bulletin, with a section on
minimum altitude emergencies, that says, in part, "Pilots always share
responsibility for terrain and obstacle avoidance ..... Air traffic
controllers issuing specific altitude instructions and clearances
accept responsibility for terrain avoidance." It goes on to say that
"There should be no confusion as to whether ATC is assuming
responsibility for terrain clearance," and so in your example, IF the
controller cleared you to fly your route at a specific altitude, the
controller would assume responsibility for terrain clearance. If you
refused the clearance and accepted one below the OROCA, then you would
assume responsibility and the controller would so advise you, as per
this bulletin, where it says, "a controller can advise a pilot to
provide his/her own terrain and obstruction clearance ...This type of
statement can be used when confusion might exist."

Further guidance on this issue comes from IACO, of which the U.S. is a
member, and so our regulations mirror the requirements in ICAO

In November 2005 the International Federation of Air Traffic
Controllers' Associations (IFATCA), under ICAO auspices, issued a
Safety Alert on "Separation from Terrain." This Alert includes changes
to existing regulations, and says in part, "When vectoring an IFR
flight and when giving an IFR flight a direct
routing which takes the aircraft off an ATS route, the radar controller shall
issue clearances such that the prescribed obstacle clearance will exist at all
times until the aircraft reaches the point where the pilot will resume own

However, it also says, "The objectives of the air traffic control
service ... do not include prevention of collision with terrain. The
procedures prescribed in this document do not therefore relieve pilots
of their responsibility to ensure that any clearances issued by air
traffic control units are safe in this respect...," and so underscores
the letter and spirit of FAR 91.3, again placing ultimate
responsibility and authority for the flight on the shoulders of the

So, back to your theoretical flight plan. As you know, a flight plan
includes only routing, and not altitudes. It is expected that the
route will take into account both aircraft capability (e.g. service
ceiling) and published altitude information, which includes OROCA. So
when your flight plan is accepted, it is expected that you can and
will fly at a safe altitude, and if you are issued an altitude
clearance by ATC, even on the direct portion of your route, ATC does
assume responsibility for terrain avoidance UNLESS

1) s/he clearly states otherwise and says that you are responsible, or
2) you refuse the clearance, and instead accept one at an altitude
lower than OROCA.

In those cases, you and not ATC are responsible for terrain separation. 

I haven't been able to locate the corresponding FAA FAR revision
and/or AC specifically addressing the information contained in the
IFATCA Alert above, but again, as we have a reciprocal relationship
with ICAO, and that alert is a year old, I'm quite sure it has
regulatory authority w/regard to FAA regs also. Again, if you'd like
an official opinion, I do suggest calling the FSDO, or contacting the
"Office of Rulemaking" in Washington, D.C. The address and phone
number is here:

I hope this helps clarify the issue. Let me know if you need any more assistance. 

Best wishes,

Clarification of Answer by byrd-ga on 27 Oct 2006 05:54 PDT
Hi jrflylow,

Was thinking a bit more about your question, and wanted to clarify
something a bit further lest I really muddy the waters for you. When I
said a flight plan doesn't include altitudes, I worded that badly. I
didn't mean that you don't file altitudes, which of course you do (in
Box 7. Cruising Altitude) but that altitudes are usually a lot more
variable and flexible than routings. Hope that averts any confusion!
This is another reason why it's so important to copy and correctly
read back instructions from ATC, because while your route remains
fairly constant, your altitude is often changing, and so there is an
inherent risk of misunderstanding a clearance, with disastrous

jrflylow-ga rated this answer:4 out of 5 stars

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