San Francisco Rwy 28R - LDA approach (offset track)

[Will]

My airline was based out of KSTL, so I frequently flew the LDA RWY 30L approach, which actually brought the aircraft in closer to the runway threshold before turning than the KSFO approach (2.6 nm vs. 3.4 nm) and with a lower decision height.  Give it a try, Hardy, and tell me what you think.

The instructions were to always fly the approach to the missed approach point before turning towards the runway, so if you were assigned the LDA approach, you always flew the whole thing including the turn at the very end.  I never noticed any variation between operators.  It was a nice ride.

[Zinger]

SFO handles heavy traffic, therefore utilizing both parallel runways concurrently, whose lateral separation is around 1000 feet. To enable efficient flow, the procedures below were put in place.  Aircraft are prohibited from flying into an approach neutral zone between the runway extended centelines. PRM requires a specific pilot training. Without it the pilot must contact FAA prior to departure to obtain a reservation.

1. PRM is essentially straggering approaching aircraft so that wings are not rubbed. Its weather limitaions are ceiling 2100 feet and visibility 4 statute miles. The pilot must monitor a second tower frequency on which only the tower is allowed to transmit, reducing tower wait times between transmissions, thereby affecting immediate message receipt by the pilot.
2. The LDA 28R DME utilizes a 5 degree localiser right offset, thereby increasing lateral separation from 28L traffic.  MAP is at  DARNE, 3.4NM from the threshold, altitude 1140 feet. The pilot must report visual contact with the  preceding aircraft  as soon as practicable and before MAP, maintaining LDA till DARNE to not penetrate NTZ. After which a 4 degree left correction to threshold is visually flown,  and the pilot can decide when to visually correct to and fly the centerline to touchdown. I'm not aware of a 2.6NM guideline Will mentioned.

Where and how the aircraft intercepts the IAP is entirlely NORCAL TRACON consideration, based on traffic and conditions, not related to one carrier or another. At SFO a provision exists to allow vectoring to lower than normal altitudes (1600 feet on final), as well as runway sidestepping down to 460 feet altitude.

[Jeroen Hoppenbrouwers]

World Flight 10th anniversary goes KSFO :mrgreen:

[Hardy Heinlin]

OK, having the MAP so high and far away from the threshold, -- that explains a lot :-)

2. The LDA 28R DME utilizes a 5 degree localiser right offset, thereby increasing lateral separation from 28L traffic.

I don't understand this. Just to confirm: What do you mean by "right offset"? Referring to the runway heading, you mean the localizer course is turned right? Or do you mean a lateral right-shift in feet or whatever, not in degrees?

I think if you want more separation from runway 28 LEFT, the course to our runway 28 RIGHT should be turned left, i.e. anti-clockwise (with the rotation center at the LDA antenna).

My database agrees with your statements partially:

- The chart shows the LDA antenna some feet right of runway 28R
- LDA course is 296, runway 28R heading is 283, i.e. LDA is turned right

However:

- The difference between 296 and 283 is not (as you say) 005, but 013
- It doesn't increase traffic separation, it actually crosses the ILS of 28L

What have I misunderstood?


Cheers,

|-|ardy

[Hardy Heinlin]

I see DARNE is right of the 28R extended centerline.

So is that a typo in the database? Is the LDA course 296 wrong? Should it be 278?

That would explain everything.

Darn.

[Zinger]

Charts:
http://www.naco.faa.gov/d-tpp/1006/00375LDAPRM28R.PDF
http://www.naco.faa.gov/d-tpp/1006/00375LDAPRM28R_C.PDF

According to these, LDA localiser heading is 278 degrees, runway heading is 283.

By degrees right offset I mean that in view from top (such as ND), the LDA localiser is offset right / north, to increase the approach clearance from 28L approach traffic. The 28R LDA localiser heading degrees as shown in the previous paragraph are left.
HTH

[Will]

The inbound course of the LDA is 278 degrees: http://flightaware.com/resources/airport/SFO/IAP/LDA+PRM+RWY+28R+(SIM+CLOSE+PAR)/pdf

The course of the LDA is parallel to the approach course of the adjacent runway; that's how they achieve the required separation, through the (constant) lateral offset.

[Zinger]

296 is erroneous, it would make an aircraft flying heading 296 into 28R fly across runway 28L approach line.

[Zinger]

The course of the LDA is parallel to the approach course of the adjacent runway; that's how they achieve the required separation, through the (constant) lateral offset.

Will,
 I disagree about parallel, please check my message detailing the angles above, the LDA is 278, runways are 283 degrees.

[Will]

That's correct, the runways are at 283 degrees, LDA is at 278.

[Hardy Heinlin]

Next time I'll check some approach charts before posting such questions :-)

[Hardy Heinlin]

Are those downloaded charts from 1998?

LDA course was 278 in the year 1998?

The chart says LOC offset 3.01 deg.

That would set the runway to 281 deg.

Add 2 deg for the current year, then the LDA is now 280.


Edit: No, they are from 2010! But they haven't updated the mag var yet? I guess they do that in 5 or 10 year cycles. My true headings are computed using actual geograpic runway threshold coords. My results must be correct as all ILS LOC antenna coords sit exactly on extended runway centerlines (at least for the few hundred airports that I have checked. Their correctness can't be pure coincidence).

[Hardy Heinlin]

The database is correct. It was my fault. My code has added magvar to offset localizers which included the magvar already.

[Hardy Heinlin]

Jeez. No, it wasn't my fault. The database record for the LDA 28R has the correct course, but a wrong magvar for that LDA, namely E34.0 instead of E14.8.

I'm ready for the madhouse.

[Zinger]

But they haven't updated the mag var yet? I guess they do that in 5 or 10 year cycles.

Current average magnetic declination change for SFO is 6 arc minutes a year, makes sense to update it every 10 years, for one degree accumulated change.

[AI744]

Old topic... But here is what DLH has to say....

Loc course 28R is 365m right of RW 28R THR.

LDA DME authorised for DLH LDA PRM is not authorised for DLH aircraft.

Hope that helps