IFR Terrain Clearance Case Study - KMMH

C150J

C150J

Well-Known Member
Hi guys,

Just trying to get a discussion going concerning IFR in mountainous regions. First and foremost, I would like all of us to take off our "135/121/91/91.X Fractional" hats and just think about actual terrain clearance. Consider us /G, so don't worry too much about identifying intersections, either. I will try to ask the question in its simplest form.

Here's you're departure field:
KMMH
Mammoth Yosemite
http://skyvector.com/airport/MMH/Mammoth-Yosemite-Airport
ODP - http://naco.faa.gov/d-tpp/0910/SW2TO.PDF


Say it's IMC with 600 overcast. You're going to SFO, so you're planning on V381 - NIKOL - V244 (don't worry about the rest of the routing). You follow the ODP:

MAMMOTH LAKES, CA
MAMMOTH YOSEMITE TAKE-OFF MINIMUMS: Rwy 9, 500-2 or std. with a min.
climb of 400'per NM to 10700. Rwy27, 5000-5 or std.
with a min. climb of 450' per NM to 11800. DEPARTURE PROCEDURE: Rwy 9, climbing left turn heading 050° to intercept BIH R-307. Rwy 27, climbing
right turn to heading 095° to intercept BIH R-307. All aircraft proceed via BIH R-307 to BIH VOR/DME, then via BIH R-322 (V381) to NIKOL Int then via assigned route.

In a non-radar environment, how do you ensure terrain clearance? For those that have operated in and out of MMH and other mountainous airports, how low are the MVAs? Can a radar facility "see" you running down the valley? I realize that there is a minimum climb gradient (400-450 up to 10,700/11,800), but unlike a lot of "flatter" airports, these gradients don't get you above surrounding terrain, nor the MEAs in the area.

I apologize if this is a dumb question. I'm just trying to bolster my knowledge of mountainous and non-radar IFR ops.
 
C150J said:
Hi guys,

Just trying to get a discussion going concerning IFR in mountainous regions. First and foremost, I would like all of us to take off our "135/121/91/91.X Fractional" hats and just think about actual terrain clearance. Consider us /G, so don't worry too much about identifying intersections, either. I will try to ask the question in its simplest form.

Here's you're departure field:
KMMH
Mammoth Yosemite
http://skyvector.com/airport/MMH/Mammoth-Yosemite-Airport
ODP - http://naco.faa.gov/d-tpp/0910/SW2TO.PDF


Say it's IMC with 600 overcast. You're going to SFO, so you're planning on V381 - NIKOL - V244 (don't worry about the rest of the routing). You follow the ODP:

MAMMOTH LAKES, CA
MAMMOTH YOSEMITE TAKE-OFF MINIMUMS: Rwy 9, 500-2 or std. with a min.
climb of 400'per NM to 10700. Rwy27, 5000-5 or std.
with a min. climb of 450' per NM to 11800. DEPARTURE PROCEDURE: Rwy 9, climbing left turn heading 050° to intercept BIH R-307. Rwy 27, climbing
right turn to heading 095° to intercept BIH R-307. All aircraft proceed via BIH R-307 to BIH VOR/DME, then via BIH R-322 (V381) to NIKOL Int then via assigned route.

In a non-radar environment, how do you ensure terrain clearance? For those that have operated in and out of MMH and other mountainous airports, how low are the MVAs? Can a radar facility "see" you running down the valley? I realize that there is a minimum climb gradient (400-450 up to 10,700/11,800), but unlike a lot of "flatter" airports, these gradients don't get you above surrounding terrain, nor the MEAs in the area.

I apologize if this is a dumb question. I'm just trying to bolster my knowledge of mountainous and non-radar IFR ops.
Click to expand...

I don't know if a lot of airplanes are going to climb at 450 ft climb gradient at 8k ft msl plus.
 
C150J said:
In a non-radar environment, how do you ensure terrain clearance? For those that have operated in and out of MMH and other mountainous airports, how low are the MVAs? Can a radar facility "see" you running down the valley? I realize that there is a minimum climb gradient (400-450 up to 10,700/11,800), but unlike a lot of "flatter" airports, these gradients don't get you above surrounding terrain, nor the MEAs in the area.

I apologize if this is a dumb question. I'm just trying to bolster my knowledge of mountainous and non-radar IFR ops.
Click to expand...

Down here in southeast its non-radar below something like 8,000 IIRC (its been awhile since I've IFR'd down here). Anyhow, radar can't see you so "ensuring terrain clearance" comes down to knowing your exactly position, and knowing if you're going to hit anything at the altitude you're at along your current course. If so, how long until you hit anything. Situational Awareness is the key. If you takeoff, and hit the airway, and keep on trucking without thinking about your AGL altitude, you may run into trouble, because center can't see you most of the time.

The biggest thing for me was knowing how high the terrain was going to be along my route of flight. E.g. "Ok, I have to be at 3,500 to clear this first set of hills by 500', then I have to be at 7,600 to clear the second set of hills, then there's a peak out here at 56DME that I have to be up above 10,000 to miss. For the most part its not too hard, and infact its harder down in the states because of density altitude, but really, situational awareness is the key.

If you find that you're not able to make your minimum climb gradient on the ODP while you're in flight (which could happen, shouldn't but could), then make a 180 and follow it back down if you're \G. Not the funnest way to go, and definitely an emergency situation, but doable if necessary, and better than smacking the ridge.
 
C150J said:
these gradients don't get you above surrounding terrain, nor the MEAs in the area.
Click to expand...

I'm not quite clear on what you're asking, but your required climb gradients don't go away once you reach the altitude specified in the ODP, they just reduce to the standard 200 ft/nm.
 
tgrayson said:
I'm not quite clear on what you're asking, but your required climb gradients don't go away once you reach the altitude specified in the ODP, they just reduce to the standard 200 ft/nm.
Click to expand...

Thanks for all of the responses. I'm just trying to get an idea of how one would "defensively fly" IFR out of an airport surrounded by mountainous terrain. For the most part, it sounds like breaking out a sectional is the best way to evaluate one's clearance. I just find it interesting that TERPS will go into excruciating detail about some stuff (protected areas on approaches, missed approaches, etc.), yet very little about climbing to MEAs is really discussed.
 
C150J said:
I just find it interesting that TERPS will go into excruciating detail about some stuff (protected areas on approaches, missed approaches, etc.), yet very little about climbing to MEAs is really discussed.
Click to expand...

Have you looked at the TERPS requirements? Routes are in section 1203 and climb gradients in 1205. There are some quantitative requirements for ODP obstacle clearance. The volume of information is lower than approaches, true, but the problem to solve is simpler too. You won't hit anything by climbing too fast. ;)

I see the sectional of little use unless you are departing an airport that has not been evaluated for instrument departures, or you are unable to maintain required climb gradients. After you pass the point to where the greater than standard climb gradients are required, a 200 ft/nm will keep you clear of obstacles until you read minimum IFR altitudes. This doesn't mean MEA, but rather the IFR altitudes in 91.177. In mountainous areas, the ODP may terminate when you're 2,000 ft above the nearest obstacle within a 4 nm radius of the aircraft, even though you might be below published MEAs.
 
Wait...I'm confused. You seem to think that if you follow the ODP and the minimum climb gradients, you're still at risk of hitting something. That's simply not true.
 
Roger said:
Wait...I'm confused. You seem to think that if you follow the ODP and the minimum climb gradients, you're still at risk of hitting something. That's simply not true.
Click to expand...

I'm certainly aware of that, but I don't think I would blast off into IMC in such a situation without doing some due diligence... just trying to get an idea of how people would go beyond the TERPS and plan such flights. I wouldn't necessarily feel comfortable after satisfying the ODP.
 
C150J said:
I'm certainly aware of that, but I don't think I would blast off into IMC in such a situation without doing some due diligence... just trying to get an idea of how people would go beyond the TERPS and plan such flights. I wouldn't necessarily feel comfortable after satisfying the ODP.
Click to expand...
Maybe I'm dangerous, but I would feel comfortable satisfying the ODP and other IFR rules. After all if you can't trust the charts and the climb gradients (both the published ones and the standard ones) what CAN you trust?
 
Roger said:
Maybe I'm dangerous, but I would feel comfortable satisfying the ODP and other IFR rules. After all if you can't trust the charts and the climb gradients (both the published ones and the standard ones) what CAN you trust?
Click to expand...

Not dangerous at all! Just thinking about personal OEI procedures (especially in a single-engine plane!), personal minimums for accomplished such a flight without GPWS, etc.
 
C150J said:
Not dangerous at all! Just thinking about personal OEI procedures (especially in a single-engine plane!), personal minimums for accomplished such a flight without GPWS, etc.
Click to expand...
OEI procedures in a single in the mountains in IMC
-run the restart flow
-make peace with God
 
C150J said:
Hi guys,

Just trying to get a discussion going concerning IFR in mountainous regions. First and foremost, I would like all of us to take off our "135/121/91/91.X Fractional" hats and just think about actual terrain clearance. Consider us /G, so don't worry too much about identifying intersections, either. I will try to ask the question in its simplest form.

Here's you're departure field:
KMMH
Mammoth Yosemite
http://skyvector.com/airport/MMH/Mammoth-Yosemite-Airport
ODP - http://naco.faa.gov/d-tpp/0910/SW2TO.PDF


Say it's IMC with 600 overcast. You're going to SFO, so you're planning on V381 - NIKOL - V244 (don't worry about the rest of the routing). You follow the ODP:

MAMMOTH LAKES, CA
MAMMOTH YOSEMITE TAKE-OFF MINIMUMS: Rwy 9, 500-2 or std. with a min.
climb of 400'per NM to 10700. Rwy27, 5000-5 or std.
with a min. climb of 450' per NM to 11800. DEPARTURE PROCEDURE: Rwy 9, climbing left turn heading 050° to intercept BIH R-307. Rwy 27, climbing
right turn to heading 095° to intercept BIH R-307. All aircraft proceed via BIH R-307 to BIH VOR/DME, then via BIH R-322 (V381) to NIKOL Int then via assigned route.

In a non-radar environment, how do you ensure terrain clearance? For those that have operated in and out of MMH and other mountainous airports, how low are the MVAs? Can a radar facility "see" you running down the valley? I realize that there is a minimum climb gradient (400-450 up to 10,700/11,800), but unlike a lot of "flatter" airports, these gradients don't get you above surrounding terrain, nor the MEAs in the area.

I apologize if this is a dumb question. I'm just trying to bolster my knowledge of mountainous and non-radar IFR ops.
Click to expand...

If KMMH had an approach control quality radar on the airport, ATC could be of no help with avoidance of close-in obstacles below the MVA. With such a radar, the MVA sectors could be smaller and lower than the present Oakland Center MIAs (centers use MIAs, TRACONs use MVAs) but such an MVA would likely still be at least 4,000 feet above the airport. And, the real terrain threat as MMH is below 4,000 feet, agl, at least for takeoff on Runway 27. Runway 27 is a very high risk terrain environment. Runway 9, however is not all that demanding for turbine-powered airplanes with good performance.

As to radar coverage, or lack thereof, it doesn't matter once you achieved MEA on V381. The tricky part is turning around over the BIH VOR with higher mountains on both sides of you.

This is a very poorly designed ODP that is very old and predates the RNAV IAP for the airport. The airport would be far better served by an RNAV ODP, thus avoided having to go SE to BIH VOR then reverse course to get established on V381. But, even with a well-designed RNAV ODP departure on Runway 27 would still be a high-risk maneuver in IMC, or even at night.

And, for commercial operators, compliance with OEI requirements on 27 is really tough unless you're flying a high-end Falcon or Gulfstream.

As to radar coverage there is none, not that it would help in the early stages of a departure anyway. And, there is no capability of communicating with the center until well east and line of sight of KBIH where the center frequency of 125.75 is remoted (as well as in the Tonopah area). The center's radar is also located in the Tonopah area and is blocked by the White Mountains below 16,000 to 17,000 in the area of MMH and BIH. Radar coverage improves dramatically once line of sight north of the north end of the White Mountains.

As to assessing the terrain close in to MMH, which the FAA has done for you with the ODP, only a USGS 1:24,000 topo map is up to that task.

I have attached the Oakland Center MIAs for the area, which in no means assures radar coverage:

MMHAreaMIAs.jpg
 
It is NEVER ATC's primary function to keep you out of the rocks, their job is AIR TRAFFIC. They are supposed to keep you from hitting flying metal objects, that is all!

Having had previously operated out of MMH for several years, I can say that you need to know the terrain, and if IMC I'd ensure I could follow that ODP to the letter. There was no IFR procedures back when I went in there, just at BIH, but your "out" would still be to head down that way, make sure you could get across Sherwin grade hills and hover close to the VOR at BIH in the published hold, or descend down.

Fortunately, MMH rarely had weather as you describe!
 
seagull said:
Fortunately, MMH rarely had weather as you describe!
Click to expand...

ATC's control at MMH is tenuous at best. Last winter the FSS RCO wasn't even available so Horizon (their first winter there) had to use the telephone for clearances. It's really a lousy set up for an airport with a Class E Surface Area.

You're right that most of the time the airport is much better weather ceiling and visibility-wise, than a few miles up the road to the town. The airport sits on the edge of a dry zone, similar to Mono Lake.

But, the problem is wind, sometimes lots of wind and sometimes forcing the use of Runway 27. And, when the mountains are socked in with a vigorous storm in the weather can be a lot worse a mile or two off the end of 27. It's an OEI nightmare.

And, when the wind is kicking up the ODP is a trap for those who actually head down to BIH VOR to do the prescribed reversal. That gets you into the jaws of the Owens Valley turbulence; not a nice place to be.

The Part 91-only operator flying high performance equipment (read: robust turbine equipment) is far better off modifying the ODP to avoid going down to BIH, yet not turning to the NE until well above Glass Mountain (11,200' terrain point on section NE of the airport).

Wonders could done with a well-designed RNAV ODP for this airport. I suspect Horizon Air has designed their own departure procedure and had it approved by the FAA. That would be easy since it it a one-in-one-out airport anyway (and has to share airspace with KBIH.)

That area really needs the new gee-wiz radar beacon augmentation system that the State of Colorado is installing around the busier central Rocky Mountain airports. But, California doesn't have the money.
 
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