Santa Monica VOR or GPS-A Approach

Sam D

Sam D

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Sam D
1) Why isn't this approach the VOR or GPS Rwy 21 Approach? And why doesn't it have straight in minima? It appears perfectly aligned with the runway.

http://204.108.4.16/d-tpp/0712/05023VGA.PDF

2) While I'm at it...is there a set amount that having an on-field barometer would lower the minimums? My home field is considering an AWOS and and I was curious as to what effect this may have on the minima for the instrument approaches. Is this spelled out in a TERPS publication somewhere?

Thanks,
Sam
 
It's an 'A' approach because there are no straight in mins. There are no straight in mins because the descent gradient is too steep, probably due to the mountains. BTW this doesn't mean you can't fly the approach and land straight in, just that you have to use the circling mins and should expect to be too high for a normal descent to the threshold.
 
I'll take a stab. Even with the overlay, you have no exact course guidance with exception of a magenta line on the GPS moving map. The only way the course would be perfectly flown is by AP on GPS NAV and that's not always an option. The VOR is substantially offset from the end of the runway possibly letting one mislead themselves into its radial as the only guidance. The MDA is 975 feet above the runway for obviously good reason. You're past the runway upon reaching the MAP.

I don't know the area but I'm guessing it will stay up there due to terrain. Circling minimums would still be as high and without precise course guidance and I don't see that changing.

As WAAS continues to expand to more GPS approaches, the MDA may drop down but probably not much (if at all) given there is no circling currently authorized on the north side of the airport (more likely due to the towers). I'm picturing it as a mild version of KASE. KASE is circling only and still has a localizer, meaning the course is within 3° of the runway heading.

With regard to the altimeter setting....

Locally, we have KWDR which has an AWOS-3 on the field but the IAPs require using KAHN altimeter. On my instrument ride, that meant a difference of possibly being 60 feet below legal minimums.

http://204.108.4.16/d-tpp/0712/05360VDGA.PDF

I cannot find a source from the FAA but what I've been able to glean from the Instrument Procedures Handbook, any reporting station not maintained by the FAA or NWS is not an authorized source to be used in an IAP.
 
Not true.

Read the instructions I posted on the KPVF plate above. The CTAF is NOT NWS or FAA personal.

~ Christopher
 
lancefisher said:
It's an 'A' approach because there are no straight in mins. There are no straight in mins because the descent gradient is too steep, probably due to the mountains. BTW this doesn't mean you can't fly the approach and land straight in, just that you have to use the circling mins and should expect to be too high for a normal descent to the threshold.
Click to expand...

Lance,
Correct in the excessive descent assessment. Also, it may have to do with where the FAC crosses or does not cross the runway centerline.

Per TERPS.

413. FINAL APPROACH SEGMENT. The final approach begins where the PT intersects the FAC.
a. Alignment. The alignment of the FAC with the runway centerline determines whether a straight-in or circling-only approach may be established.
(1) Straight-In. The angle of convergence of the FAC and the extended runway centerline shall not exceed 30°. The FAC should be aligned to intersect the extended runway centerline 3000 feet outward from the runway threshold. When an operational advantage can be achieved this point of intersection may be established at any point between the runway threshold and a point 5200 feet outward from the runway threshold. Also, where an operational advantage can be achieved, a FAC which does not intersect the runway centerline, or intersects it at a distance greater than 5200 feet from the threshold, may be established, provided that such a course lies within 500 feet laterally of the extended runway centerline at a point 3000 feet outward from the runway threshold.Straight-in category C, D, and E minimums are not authorized when the final approach course intersects the extended centerline at an angle greater than 15° and a distant less than 3,000 feet (see Figure 38).
(2) Circling Approach. When the final approach course alignment does not meet the criteria for straight-in landing, only a circling approach shall be authorized, and the course alignment should be made to the center of the landing area. When an operational advantage can be achieved, the final approach course may be aligned to pass through any portion of the usable landing surface (see Figure 39).

I'm not sure what method was used for this approach, perhaps both, but whatever the reason, it does not meet straight-in criteria.

gary
 
Re: Q2 -- it's not a "set amount," but there is a table which tells them how much to raise the mins from what they would be with a local altimeter setting depending on how far from the airport the altimeter setting is taken, as well as some terrain/elevation modifiers.
 
lancefisher said:
It's an 'A' approach because there are no straight in mins. There are no straight in mins because the descent gradient is too steep, probably due to the mountains. BTW this doesn't mean you can't fly the approach and land straight in, just that you have to use the circling mins and should expect to be too high for a normal descent to the threshold.
Click to expand...

Both the mountains and the antennae make this approach a circling one. It's my understanding that the maximum descent gradient TERPS allows for a straight-in is 20:1 from the FAF. That's pretty close to 300 feet/nm. Taking the distances from the chart and subtracting the runway length (since the DME is at the far end from the threshold), I get a descent gradient of 400 ft/nm from BEVEY, which is enough to scotch the straight-in right there. Now look at the step-down at CULVE, with a required 1120 altitude (presumably so you can miss that 863-foot tower). CULVE is only 1.6 miles from the theshold. To reach the threshold from there requires a 555 ft/nm gradient which is waaay out of TERPS bounds. Circling it 'tis!

Regards,
Joe
 
Thanks everyone. I learned a lot from the responses. Is there somewhere to find the TERPS guidance online?
 
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