What's the difference? Two identical approaches, really different minima.

[MAKG1]

Napa (KAPC) has two RNAV approaches to 36L. Both have all the same waypoints, including the missed approach. Both have LPV minima. The RNAV Z approach is pretty much what you would expect from an LPV approach. The Y has ridiculously high minima -- 1250 and 5, and LPV minima are higher than LNAV. What is the difference, and why does the Y even exist? It can't be obstructions because the paths and altitudes are all the same.

https://skyvector.com/files/tpp/1604/pdf/00281RY36L.PDF
https://skyvector.com/files/tpp/1604/pdf/00281RZ36L.PDF

Edit: I see. Large climb gradient for missed approach on the RNAV Z. Though even a 172 should be able to do that at Vy unless it's really hot.

 

[Kritchlow]

I think you nailed it with the gradient for the missed. Doesn't mean much for a 91 SE operator, but for a 135 ME air carrier it can be a world of difference.

 

[MauleSkinner]

Are you not required to comply with clmb gradients under 91?

 

[John Collins]

Part 91 operators have a one time exclusion during their lifetime to not comply with climb gradients.

 

[John Collins]

The lower DA does not meet the standard climb gradient to avoid obstacles. The one with the higher DA starts off at a higher altitude and meets the standard 200 feet per NM climb gradient.

 

[aterpster]

I think you nailed it with the gradient for the missed. Doesn't mean much for a 91 SE operator, but for a 135 ME air carrier it can be a world of difference.

Are you perhaps thinking of one-engine inop (OEI) requirements? If so, these IAP climb gradients are for normal ops, not OEI.

 

[Everskyward]

Are you perhaps thinking of one-engine inop (OEI) requirements? If so, these IAP climb gradients are for normal ops, not OEI.

But in a single, you need to be able to meet the gradient on the one engine you have...

 

[Kritchlow]

Are you perhaps thinking of one-engine inop (OEI) requirements? If so, these IAP climb gradients are for normal ops, not OEI.

But... A two engine jet can make these gradients 10 X over. A 135 carrier needs to do it SE, which gets very tricky.

 

[Kritchlow]

But in a single, you need to be able to meet the gradient on the one engine you have...

Precisely

 

[MauleSkinner]

But... A two engine jet can make these gradients 10 X over. A 135 carrier needs to do it SE, which gets very tricky.

Determining your single-engine missed approach climb over 2100+ feet is the tricky part in most of the AFMs I've worked with...nonstandard gradient or not.

 

[Kritchlow]

Yeah, so true... Luckily we just hit "enter" and the computer tells us. It would indeed be ugly if you had to pull out a 500 page AFM, then interperlate...

 

[aterpster]

But... A two engine jet can make these gradients 10 X over. A 135 carrier needs to do it SE, which gets very tricky.

Those gradients on the LPV chart are for normal operations only. If you have one engine, they are for one engine. If you have four engines they are for four engines, and so forth.
But, if you are commercial, Part 121 or 135, you have to have an engine inoperative alternative that satisfies the requirements of 121.189 or the Part 135 equivalent language. The IAP presumes a constant gradient. The egine failure take off flight path does not, it has segments.