Remedial IR question - Published Departure

[killbilly]

I know this is probably a dumb question, and I think I know the answer to this, but I'm trying to understand WHY it's the answer. I suspect that the answer is: "because TERPS can guarantee obstacle clearance this way" but I don't know that for sure.

Take a look at procedures for YKM....specifically, the GROMO FOUR departure. GROMO FOUR

Each of the runways requires a climbing turn to GROMO and then you fly the appropriate transition, or, if you want to go southeast, you fly the arc to something like OHAWY and then SUNED.

What I'm not understanding is why, if I want to go southeast, I still have to go to GROMO and then fly the arc? The altitude required is 6300. If I can climb to 6300 before GROMO then clearly I can make 6300 before OHAWY, intercept R-108, and fly that to SUNED.

Is this because the only way they can guarantee clearance is to get to GROMO at 6300 FIRST, and then fly that 9nm arc? It seems like - especially if I'm taking off on runway 9, it would be simpler/less maneuvering to pick up R-108 and then proceed.

I'd appreciate wiser/more experienced thoughts on this. Like I said, I think it's because TERPS probably ensures clearance this way, but I'm wondering if that's the case or if I'm making assumptions.

 

[Roger Roger]

I know this is probably a dumb question, and I think I know the answer to this, but I'm trying to understand WHY it's the answer. I suspect that the answer is: "because TERPS can guarantee obstacle clearance this way" but I don't know that for sure.

Take a look at procedures for YKM....specifically, the GROMO FOUR departure. GROMO FOUR

Each of the runways requires a climbing turn to GROMO and then you fly the appropriate transition, or, if you want to go southeast, you fly the arc to something like OHAWY and then SUNED.

What I'm not understanding is why, if I want to go southeast, I still have to go to GROMO and then fly the arc? The altitude required is 6300. If I can climb to 6300 before GROMO then clearly I can make 6300 before OHAWY, intercept R-108, and fly that to SUNED.

Is this because the only way they can guarantee clearance is to get to GROMO at 6300 FIRST, and then fly that 9nm arc? It seems like - especially if I'm taking off on runway 9, it would be simpler/less maneuvering to pick up R-108 and then proceed.

I'd appreciate wiser/more experienced thoughts on this. Like I said, I think it's because TERPS probably ensures clearance this way, but I'm wondering if that's the case or if I'm making assumptions.

Because the procedure is written for the lowest common denominator, what is it 300’ per mile? And has to provide positive clearance for that climb gradient. If you exceed that and hit 6300 early you just request direct.

 

[killbilly]

Because the procedure is written for the lowest common denominator, what is it 300’ per mile? And has to provide postage clearance for that climb gradient. If you exceed that and hit 6300 early you just request direct.

405' per NM if you're departing east, but your point is noted. Thanks. That makes sense.

 

[Lawman]

405' per NM if you're departing east, but your point is noted. Thanks. That makes sense.

I think he’s referencing the default “must advice ATC” climb gradient.

Individual airports can be terp’d to a different standard (like something buried in a weird place in the Alps or something) but then it risks cutting off a large portion of available customers/users. Better to design and terp to as low a common standard as possible.


Sent from my iPhone using Tapatalk

 

[killbilly]

Ok. Good stuff.

My instrument skills/knowledge went to hell in the last year. Talk about a perishable skill. Before I started studying for the -II I booked some time in the Redbird and tried to fly a couple of basic ILSs with light winds.

Had it been a real flight, it would have been a more-or-less safe landing with minimal damage to aircraft and a group of alive but terrified passengers. That was the baseline that had me exiting the sim, looking at the other CFIs standing around and saying, "Which one of you knuckleheads would like to re-teach me instrument flying?"

 

[Roger Roger]

405' per NM if you're departing east, but your point is noted. Thanks. That makes sense.

The direct distance from KYKM to GROMO is 5 NM. At 405 fpnm, and airport elevation of 1099, you’d only be at 3100 by GROMO. Let’s say you can get to 1000’ in the turn, and you’re still 2000’ below your 6300’ number. Most turbines are going to blow those climb gradients out of the water, but the procedures are written for everything from a 150 on up.

FYI if my quickie math is right at 400 fpnm you’d be at OGZOF before hitting 6300’.


Oops, forgot to double the radius. Between ogfaw and ogxob.

 

[killbilly]

The direct distance from KYKM to GROMO is 5 NM. At 405 fpnm, and airport elevation of 1099, you’d only be at 3100 by GROMO. Let’s say you can get to 1000’ in the turn, and you’re still 2000’ below your 6300’ number. Most turbines are going to blow those climb gradients out of the water, but the procedures are written for everything from a 150 on up.

Gotcha. Thanks!

I'm guessing your PC-12 would exceed those gradients pretty easily?

 

[ppragman]

Gotcha. Thanks!

I'm guessing your PC-12 would exceed those gradients pretty easily?

Easily. Fully loaded 675SHP Caravan climbing at 120KIAS makes that 405fpnm a whopping 810fpm... which is starting to get marginal

 

[Roger Roger]

Gotcha. Thanks!

I'm guessing your PC-12 would exceed those gradients pretty easily?

Running the numbers on the PC12 app, it spits out a climb gradient at max gross weight from 1000-6500 of only about 500 fpnm. But the AFM climb profile is quite a bit faster IAS/slower VS than what we use IRL.

 

[ppragman]

Running the numbers on the PC12 app, it spits out a climb gradient at max gross weight from 1000-6500 of only about 500 fpnm. But the AFM climb profile is quite a bit faster IAS/slower VS than what we use IRL.

I always climbed at 120 through 10k if memory serves, basically Vy unless in ice

 

[Roger Roger]

I always climbed at 120 through 10k if memory serves, basically Vy unless in ice

With the -67P engine on the NG I do 120 until clean, then accelerate to 150 and keep that until about 20k, then you typically have to start dialing it back to keep 500 fpnm. The book is something crazy like 165 kias to 10k, then 160 to 15k.

 

[gotWXdagain]

Ok. Good stuff.

My instrument skills/knowledge went to hell in the last year. Talk about a perishable skill. Before I started studying for the -II I booked some time in the Redbird and tried to fly a couple of basic ILSs with light winds.

Had it been a real flight, it would have been a more-or-less safe landing with minimal damage to aircraft and a group of alive but terrified passengers. That was the baseline that had me exiting the sim, looking at the other CFIs standing around and saying, "Which one of you knuckleheads would like to re-teach me instrument flying?"

It’s better to pull a Jerry in the sim than the real thing.

 

[Cheese7]

The altitude required is 6300. If I can climb to 6300 before GROMO then clearly I can make 6300 before OHAWY, intercept R-108, and fly that to SUNED.

Disclaimer: I'm not an experienced instrument pilot, so hopefully the experts will fact-check this post. Here goes:

Yes, I think you're correct with your answer of "because TERPS can guarantee obstacle clearance this way", but what do you mean by "the altitude required is 6300"? Where are you getting this number from? It looks like 6300' is when your minimum climb gradient of 380 fpnm is no longer in effect, but this only applies when you are flying on the published route. This altitude means nothing if you fly off the route. If you're going to fly off the published route, you need to be at the MOROCA for that lat/long block, which is 8,700' (from the IFR Low Enroute Chart). Unless you are at/above 8,700', there is no guarantee that you won't fly into the side of a mountain.

If you are in radar coverage (which you probably will be), then you can request direct to wherever/whenever (example: direct OHAWY when you are halfway between the airport and GROMO), but I don't think there is any way for them to clear you direct unless you are above the MVA. I don't think there is any way to know what the MVA is for that area without asking a controller, but the MVA could be greater than 6300', so in that case, I don't see how they could clear you direct. This is one reason for the departure procedures.

Another thing you could do would be to request a different departure procedure in your clearance. The ZILLA THREE ODP has a less steep climb gradient and more direct routing to the YKM R-108 (if you are heading southeast). They may or may not clear you for this procedure for whatever reason, but it's worth asking for to save time/gas.

 

[MidlifeFlyer]

Yes, I think you're correct with your answer of "because TERPS can guarantee obstacle clearance this way", but what do you mean by "the altitude required is 6300"? Where are you getting this number from? It looks like 6300' is when your minimum climb gradient of 380 fpnm is no longer in effect, but this only applies when you are flying on the published route.

I think he just means the "altitude required" to not hit anything before you an switch to the standard climb gradient is 6300. If not, I think you are right. The SID does not contain any altitude assignments or restrictions. The full route clearance would include a "climb and maintain" altitude likely higher than 6300.

But I'm not sure I understand your "this only applies when you are flying on the published route" comment. The scenario is he was assigned the SID. Unless he gets a different instruction, he'd better fly the published route to the transition! It's his clearance.

What I'm not understanding is why, if I want to go southeast, I still have to go to GROMO and then fly the arc?

Because you were assigned the SID. It's not an ODP, just for terrain. It's also for traffic management - like avoiding that large restricted area only 7 NM away to the northeast. In the real world, you might well start getting vectors, but if you are own-nav, they want you to circle to the south before proceeding southeast toward the PAPPS or SUNED transitions.

 

[Cheese7]

The scenario is he was assigned the SID. Unless he gets a different instruction, he'd better fly the published route to the transition! It's his clearance.

Agreed! But it seemed like the OP wanted to leave the SID's route after getting to a certain altitude (6,300'). I think they are assuming that 6,300' is some sort of min altitude.