Direct-To and Obstacle Clearance

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Louie1975

Well-Known Member
If you are IFR and in Radar contact, and ATC gives you a direct to clearance, does this assure obstacle clearance? I am (or was) under the impression yes, but from the Instrument Procedures Handbook 4-12 (2007):

"ATC is not always responsible for safe terrain clearance for the aircraft under its jurisdiction. Many times ATC wil issue en route clearances for pilots to proceed off airway direct to a point. Pilots who accept this type of clearance also are accepting responsibility for maintaining safe terrain clearance..."
 
Louie1975 said:
If you are IFR and in Radar contact, and ATC gives you a direct to clearance, does this assure obstacle clearance? I am (or was) under the impression yes, but from the Instrument Procedures Handbook 4-12 (2007):

"ATC is not always responsible for safe terrain clearance for the aircraft under its jurisdiction. Many times ATC wil issue en route clearances for pilots to proceed off airway direct to a point. Pilots who accept this type of clearance also are accepting responsibility for maintaining safe terrain clearance..."
Click to expand...
That is one of those CYA statements which aren't really necessary since you are always taking responsibility for terrain clearance. On an airway, you have a published MOCA, and if a controller happens to give you a lower altitude, which he probably won't, but if he does, it is your responsibility to correct him. Same, and double-so, for off-airway routing. They usually have a minimum vectoring altitude, but that does not necessarily guarantee the required terrain clearance.
 
I'd made this discovery after a few hundred hours of teaching...

I found that every thing in the FAR/AIM can be summarized in two rules:

1. Don't hit anything
2. Sound good on the radio


And the second rule exsists to ensure the first doesn't happen. So any time you have a question about a rule....refer to these two and everything will make sense. At lease that is what I tell myself and my students.
 
There have been a few cases of ATC vectoring aircraft into terrain. I thought a P-3 was lost this way in Hawaii, but I can't find a reference.
 
Louie1975 said:
If you are IFR and in Radar contact, and ATC gives you a direct to clearance, does this assure obstacle clearance? I am (or was) under the impression yes, but from the Instrument Procedures Handbook 4-12 (2007):

"ATC is not always responsible for safe terrain clearance for the aircraft under its jurisdiction. Many times ATC wil issue en route clearances for pilots to proceed off airway direct to a point. Pilots who accept this type of clearance also are accepting responsibility for maintaining safe terrain clearance..."
Click to expand...

No, it does not assure you terrain clearance. The ONLY time ATC assures that is when you're on a radar vector.
 
seagull said:
No, it does not assure you terrain clearance. The ONLY time ATC assures that is when you're on a radar vector.
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Even then, you are only "assured" that the ATC guy didn't mean to vector you into that mountain. He could always screw up, and that has happened at least a couple of times.

What's that old joke? What's the difference between a pilot and ATC? When a pilot makes a mistake the pilot dies. When ATC makes a mistake... the pilot dies.

Incidentally, I was out in a Tweet (T-37, an old military trainer) flying a night IFR ride into an unfamiliar field with a student pilot a few years ago. We were at the MDA on a non-precision approach when tower calls us and says "[callsign], be advised I just got a low altitude warning on you." I immediately yanked back on the stick and climbed about a thousand feet, and then rechecked the altitude on the plate and then queried the altimeter setting. His response was, "Oh, we get an altitude warning on everyone who flies that approach. It's just due to the way our RADAR is set up, but we're required to let you know anyway."

The dude about gave me a heart attack, and I'm wondering why he didn't mention that little factoid before I started the approach! Only time it has ever happened, but very unsettling.
 
fish314 said:
Even then, you are only "assured" that the ATC guy didn't mean to vector you into that mountain. He could always screw up, and that has happened at least a couple of times.
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Agree completely! Always protect yourself, regardless, but at least on a vector ATC can be held responsible for it! Might not help you, but does give them some incentive.

As for the initial post, you can ask for, and receive, approval to fly direct into the nearest mountain, and ATC can legally approve it based on only one factor, that is known traffic.

People need to realize that ATC has only ONE job. Control of AIR TRAFFIC. That means that they separate those aircraft they are in communication with. Nothing more, and assuming more can get you killed. U.S. controllers, like those in other more developed countries, do go above and beyond often, but that also leads pilots to the kind of misconceptions demonstrated in the initial post here. Outside the U.S., well, remember AA at Cali...
 
fish314 said:
Incidentally, I was out in a Tweet (T-37, an old military trainer) flying a night IFR ride into an unfamiliar field with a student pilot a few years ago. We were at the MDA on a non-precision approach when tower calls us and says "[callsign], be advised I just got a low altitude warning on you." I immediately yanked back on the stick and climbed about a thousand feet, and then rechecked the altitude on the plate and then queried the altimeter setting. His response was, "Oh, we get an altitude warning on everyone who flies that approach. It's just due to the way our RADAR is set up, but we're required to let you know anyway."
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Yeah, we almost always get that when we do non-precision approaches into my home field in Houston. I think they're required to say it.. it's basically a CYA thing for them, in case we end up hitting an obstacle. All I do is say something to the affect of "Roger, I'm showing XXX feet, altimeter XX.XX" just to verify I copied it right. They usually just say nothing or "Roger" back.
 
MichaelC said:
Yeah, we almost always get that when we do non-precision approaches into my home field in Houston. I think they're required to say it.. it's basically a CYA thing for them, in case we end up hitting an obstacle. All I do is say something to the affect of "Roger, I'm showing XXX feet, altimeter XX.XX" just to verify I copied it right. They usually just say nothing or "Roger" back.
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Which field in Houston? My experience happened in Georgia or Alabama or Tennessee somewhere... don't remember exactly, but I'm reasonably sure it was one of those states. Of course, since I don't know the exact field, I can't call anyone and ask the question.
 
Good replies....thx. So if you are on an airway, and ATC asks you to proceed direct, I would imagine you look at the OROCA/MOCA? But sometimes that can be higher than the MEAs of the airways you are on. Like because of a mountain in the corner of the quadrant. So you have a situation where you are on an airway that is lower than the MOCA/OROCA. How do you determine Obstacle clearance direct to your fix off airway now? I guess sectional chart? But do transcontinental pilots have sectionals for all over? Or do you just ask to climb to the Oroca/Moca?

With the whole new Next Gen stuff coming out I think the move is more toward Direct and away from Airways, so this is a concern

Then again with technology and synthetic vision this may become less of an issue (unless the screen goes blank)
 
Louie1975 said:
Good replies....thx. So if you are on an airway, and ATC asks you to proceed direct, I would imagine you look at the OROCA/MOCA? But sometimes that can be higher than the MEAs of the airways you are on. Like because of a mountain in the corner of the quadrant. So you have a situation where you are on an airway that is lower than the MOCA/OROCA. How do you determine Obstacle clearance direct to your fix off airway now? I guess sectional chart? But do transcontinental pilots have sectionals for all over? Or do you just ask to climb to the Oroca/Moca?

With the whole new Next Gen stuff coming out I think the move is more toward Direct and away from Airways, so this is a concern

Then again with technology and synthetic vision this may become less of an issue (unless the screen goes blank)
Click to expand...

Honestly, I don't typically check. Most of my cruising is done up in the 20's or 30's, so I figure I'm pretty much ok regardless. When I was flying smaller airplanes and cruising lower, I would just have an idea about how high the terrain was in the immediate area. Then I would check only if it seemed "iffy". Maybe not the 100% correct answer, though, but most towers are shorter than 3000' so once I'm 3000-4000' AGL over the highest peak in the vicinity, I stop really worrying about it. If I plan a flight at low altitudes, then I look at it a lot more closely... but in those cases I am usually planning to go VFR anyways. Of course I also check terrain, MSA and ESA on the take-offs and landings just to get a sense of it. I figure that's the time that I'm most worried about it.

Of course, I was once stationed in an area that had a tethered weather balloon that went up to 15 or 20k, but every controller and pilot for 300 miles knew exactly where that thing was, and it was surrounded by a prohibited area.
 
seagull said:
No, it does not assure you terrain clearance. The ONLY time ATC assures that is when you're on a radar vector.
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We can't give any navigational guidance below our MIA without the pilot's concurrence to provide their own terrain/obstacle separation, provided they are in controlled airspace. In class G airspace, terrain avoidance is purely on the pilot.

Obviously the catch to this is that a controller only really knows the MIA in his/her airspace, and a couple dozen miles into the next sector. So it is possible for a controller to give an aircraft a direct route that is good in his airspace, but may be too low several sectors down the road. At this point, it is the duty of the controllers in the following sectors to ensure aircraft are at a safe altitude.

My best suggestion is just to be aware of the minimum IFR altitudes along your route of flight, and plan an altitude that is good for the entire route of flight, ie., one that doesn't have you having to make a climb to make an MEA somewhere down the road. Also, if you file a particular route because you can't make the MEA/MIA on a more direct route, it generally doesn't hurt anyone's feelings on this end to say you need to stay on your filed route.
 
No, they are not publicly available, and probably for good reason. We can overlay our MIA charts on the scope, so we can usually see the obstacles that they are designed to avoid, how they interact with airports, navaids, airways, sector boundaries, etc. A pilot may not be able to determine the exact location where a higher MIA begins, which could mean they end up flying into a tower or something similar. OROCAs on low altitude charts are typically only a couple of hundred feet higher than our highest MIA in a given area, so for a pilot's purpose, you're not gaining much anyway by having our MIAs.
 
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