Obstacle Departure Procedure - U42

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dougwells

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Doug Wells
I was doing some sim training with an IFR student today. Our home airport is U42 (just south of Salt Lake City International, KSLC) and we were practicing taking off from U42 and then shooting approaches about 30 miles north at Ogden airport (KOGD). Around here, the normal departure procedure is to fly the ITOFO1.FFU departure or take off VFR and pick up the IFR clearance in the air.

Because of the mountainous terrain that we fly in, we spend ALOT of time talking about ODPs and how to safely depart unfamiliar airports. We've talked about why following the published missed approach is generally not a good idea (not at the same altitude and starting point as the published procedure).

As this is our home airport, we are quite familiar with the obstacles. My clever student points out that the missed approach waypoints for GPS Y are a great way to track safely out of the airport (and much more direct) towards her flight plan's first waypoint...STACO.

I think her plan in this specific case is fine...what do you think?

Here are the details...Flightplan:
U42-STACO-JOSIF-KOGD.

She wants to fly the route listed in the published miss from U42 GPS Y Approach to get to STACO. From local flying, we know that taking off from runway 34 and climbing at about 350 feet per nautical mile (easy in her plane, turbocharged Saratoga with retractable gear), will keep her clear of obstacles.

If her clearance is "cleared as filed", could she use this missed approach path to get her to STACO? I'm quite sure controllers would be expecting her to shoot the published textual ODP that calls for her to go to the local VOR (TCH) and then to STACO so a heads up to the controller would be in order.

I suggested we shoot the published ODP as the FAA could have listed the missed approach waypoints for U42's GPS Y if they wanted but they obviously chose not too (why? I do not know...). Also, I think shooting the published missed in general is not a good idea when an ODP exists and I don't want to start bad habits....BUT....I do think its not a bad option at all. What do you think?

Thanks - Doug
 
If your IFR clearance doesn't specify a heading or route other than "as filed" I think you're OK but my experience at SLC tells me you're not likely to get such a clearance due to traffic conflicts with SLC traffic. Until you reach the MVA and are given vectors, you're always on your own for terrain avoidance. An ODP is one way to assure that but it's not the only way. I would suggest determining your actual separation from the ground and/or obstacles to establish minimum climb gradients and target altitudes before trying this in IMC (assuming you get permission). Just because your climb rate was sufficient on the day you flew it in VMC doesn't mean the next time will work as well. Things like higher weight, high DA, tailwinds, downdrafts, and airframe ice could change the picture dramatically and unless you have some kind of metric you won't know that you're too low until you hit something.
 
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Since the Class B of SLC goes to the surface just north of U42, following the missed approach route would take her into Class B airspace. As you said, make sure SLC approach/departure knows what you're doing, and blesses it. I don't see an issue from a terrain clearance standpoint.
 
dougwells said:
<SNIP>
Because of the mountainous terrain that we fly in, we spend ALOT of time talking about ODPs and how to safely depart unfamiliar airports. We've talked about why following the published missed approach is generally not a good idea (not at the same altitude and starting point as the published procedure).

<SNIP>
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Doug- I think I'm not understanding something in this sentence...Why isn't following the published missed approach a good idea? I'd think it has terrain clearance built into it. What am I not understanding?
 
Cap'n Jack said:
Doug- I think I'm not understanding something in this sentence...Why isn't following the published missed approach a good idea? I'd think it has terrain clearance built into it. What am I not understanding?
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Nonexpert answer:

A missed approach procedure presumes that you are starting at the MDA/DA, and are flying (have airspeed/groundspeed already). From that point forward you are presumed to have a minimum climb gradient (feet per mile).

A takeoff from a static position is not the same as flying at the MDA/DA with regards to the starting altitude and ability to climb. Going missed, you have a 200 ft AGL or more head start, and at 1.3 VSO you actually have a bit of airspeed you can trade for VX/VY instantaneously while transitioning to a full power climb.

ODP's perhaps are designed with a different set of assumptions with regards to climb gradient.

edit to add:
From the AIM (5-2-6, b, 1):

Unless specified otherwise, required obstacle clearance for all departures, including diverse, is based on the pilot crossing the departure end of the runway at least 35 feet above the departure end of runway elevation, climbing to 400 feet abouve the departure end of runway elevation beofre making the initial turn, and maintaining a minimum climb gradient of 200 feet per nautical mile, unless required to level off by a crossing restriction, until the minimum IFR altitude.

And further reading not from the AIM, while the Missed procedure uses the same gradient, unless otherwise specified, its also being executed at the missed approach point, which may be at, or before, or sometimes after the threshhold. Different scenario than sitting still on the runway with zero starting speed.
 
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Cap'n Jack said:
Doug- I think I'm not understanding something in this sentence...Why isn't following the published missed approach a good idea? I'd think it has terrain clearance built into it. What am I not understanding?
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The published missed approach procedure provides terrain clearance starting at the MAP, in this case at runway 34 threshold. For the approach in question, a standard climb rate for the missed approach segment is used, 200 feet of climb per NM. However, it starts at the MDA and rises from that point. Protection is applied based on a 40 to 1 slope, which is 152 ft/NM, in other words an obstacle can not penetrate the 40 to 1 slope. Since the required climb rate is 200 feet per NM, the protection during the climb increases at a rate of 48 feet per NM.

But the protection surface starts at the MDA altitude and at the MAP location, in this case 5060 Ft MSL or 454 feet above the threshold. The runway is 5860 ft long, so at the other end of the runway, the protection surface is another 146 feet higher, or about 600 feet above the departure end.

In the standard departure procedure, the aircraft is expected to be 35 feet above the departure end of the runway. From this point, a standard protection surface assumes the same 40 to 1 for obstacle clearance or a higher rate of climb per nautical mile will be specified. In this case, the ODP requires a rate of climb of 353 feet per NM for runway 34, so there must be obstacles or airspace issues (probably both).

So, if one uses the RNAV (GPS) RWY 34 approach, missed approach procedure, they would have to climb to an altitude where they intersected the protection offered by the missed approach procedure. They would start out with a 565 foot deficit at the departure end (600 -35) and would have to make that up plus the 200 feet per mile before they would be protected from further obstacles on the procedure. In the mean time, they would not be protected.

Assuming a climb at 120 Kts and 1000 feet per minute no wind, this would work out to 500 feet per nautical mile, or a convergence rate of 300 ft per nautical mile. A tail wind would exacerbate things as the climb rate would have to be able to compensate for the loss of forward distance verses altitude. I wouldn't want to assume more than 400 feet per nautical mile, or a convergence of 200 feet per nautical mile. In other words it would take around 3 miles off the end of the runway before you would climb to obstacle protection afforded by the missed approach procedure. No way would I do this without intimate knowledge of the terrain in this area, especially if the conditions were IMC to the ground.

Of course, if they lift off well before the end of the runway and are higher than 35 feet AGL while crossing the end of the runway, they will have less of a deficit to make up. If one has local knowledge of the terrain and has flown the missed approach procedure before to determine if they had adequate terrain clearance, they might be safe in using it as an alternative departure procedure. If conditions are visual until climbing to the protected altitude, that increases your odds of not hitting something.

At these altitudes, a turbo-charged or turbo normalized aircraft with good performance for the conditions would be a must.
 
John Collins said:
Of course, if they lift off well before the end of the runway and are higher than 35 feet AGL while crossing the end of the runway, they will have less of a deficit to make up. If one has local knowledge of the terrain and has flown the missed approach procedure before to determine if they had adequate terrain clearance, they might be safe in using it as an alternative departure procedure. If conditions are visual until climbing to the protected altitude, that increases your odds of not hitting something.

At these altitudes, a turbo-charged or turbo normalized aircraft with good performance for the conditions would be a must.
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John, what do you think of flying a pattern at or above the circling MDA while keeping the runway in sight, then flying the published miss procedure. Ground clearance wise that shouldn't be any different than a miss from a circle to land.
 
Why wouldn't you just do the published ODP instead of flying the missed approach procedure since they are predicated on different starting conditions? It would be OK in VMC but in IMC it seems a little bit like making up your own procedure, at least to me.
 
Note that ATC must provide separation from all other IFR aircraft for the published ODP, whether that's explicitly in your clearance or not. Anything else may require precoordination with ATC. And, as noted above, the published missed approach may not provide obstacle clearance if initiated from the runway rather than the MAP at DH/MDA. All in all, I'm with those who said just fly the ODP. I just don't see any reason not to do so since it's already published, and guarantees both obstacles and separation from other IFR aircraft.
 
Everskyward said:
Why wouldn't you just do the published ODP instead of flying the missed approach procedure since they are predicated on different starting conditions? It would be OK in VMC but in IMC it seems a little bit like making up your own procedure, at least to me.
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The reason given in this particular instance is that the ODP goes south and the flight was to the north. Of course there are lots of situations where the published ODP goes the "wrong" direction for the flight but in many of those the "wrong" direction is the only viable direction so there's not much point in making your own procedure. Also there are cases where the published ODP is really unworkable due to conflicts with traffic in and out of a nearby major airport. In the published ODP for U42 has that exact problem although I don't think the published miss procedure to the north offers any advantages there. I had a couple long discussions with the TRACON supervisor regarding IFR departures from U42 and given the area's current limitations (primarily the narrow north/south vallley) there's no path for departing IFR traffic from U42 to follow that doesn't conflict severely with SLC traffic.

But a key point is that unlike approach procedures, we pilots (at least part 91 pilots) have the option of using whatever departure procedure we want as long as we realize that we are then entirely responsible for terrain avoidance until ATC takes that over by assigning a heading or course to fly. And if you are diligent in the design of your own ODP this can be done safely (with the possible exception of a tower or other structure being added in a way that inteferes with your plan).
 
What Lance says is true, but if you do anything other than the published ODP, and you'll be in controlled airspace (especially in IMC), make sure you coordinate your other plan with ATC, because they hate surprises.
 
To change the situation a bit...

Someone breaks out of minimums to see the approach and runway environment and continues the approach- maybe their wheels just touch. They have to go around (maybe someone drove a plane onto the runway, or they see a bunch of deer or something).

The best thing to do on the go around then, is to follow a departure procedure until you have enough clearance to do something else, like talk to ATC so they can vector you to try again?
 
Similar situations arise when you abandon a circle to land or a "fly visual to airport" segment after the DA. The advice of following an ODP or DP makes sense in these cases, but how often is it part of your briefing before the approach. If it isn't, your not going to be looking it up on the miss.
 
Cap'n Jack said:
Someone breaks out of minimums to see the approach and runway environment and continues the approach- maybe their wheels just touch. They have to go around (maybe someone drove a plane onto the runway, or they see a bunch of deer or something).

The best thing to do on the go around then, is to follow a departure procedure until you have enough clearance to do something else, like talk to ATC so they can vector you to try again?
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That may be so. The FAA recently added a bit of discussion on this to AIM Section 5-4-21 "Missed Approach," paragraph h:
h. Missed approach obstacle clearance is predicated on beginning the missed approach procedure at the Missed Approach Point (MAP) from MDA or DA and then climbing 200 feet/NM or greater. Initiating a go-around after passing the published MAP may result in total loss of obstacle clearance. To compensate for the possibility of reduced obstacle clearance during a go-around, a pilot should apply procedures used in takeoff planning. Pilots should refer to airport obstacle and departure data prior to initiating an instrument approach procedure. Such information may be found in the "TAKE-OFF MINIMUMS AND (OBSTACLE) DEPARTURE PROCEDURES" section of the U.S. TERMINAL PROCEDURES publication.
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