Here's the deal - Flying into SFO - cleared for the visual 28L and told to maintain 2,500 and 180kts till 6DME - What DME do you use????? LOC DME or SFO vor? The difference between the two is roughly 1.5-2 miles -I interepreted the clearance as the SFO vor and started down at 6DME from SFO; which puts you on glideslope or right about there - the CA on the other hand started to FREAK out because he/she(will remain nameless and genderless for the sake of argument) had the LOC up and was looking at the DME off the LOC - If you look at any charted visuals into SFO the DME is in reference to SFO not LOC dme - anyone else ever run into this??

 

In that situation everything is referenced to straight-in on the extended centerline, which implies the localizer DME unless otherwise specified. It would be a little odd to have you hold 2500' until you had blown through the GS, but certainly legal on a visual.

 

Completely agree, I've flown the approach many times and it's the loc. But the CA shouldn't get freaked out, all he has to do is look over and say "Oh, you're using the VOR, it's actually the LOC so stay up a little longer and I'll tell you when to start down." Plus staying high in the Bro is a hell of a lot more fun.

Last I check the DME for ILS/LOC 28L is off of I-SFO (loc)?

 

I would say 6DME from the runway, therefore the LOC DME would be the most appropriate.

Consider this: Apply the same clearance to an airport that has a VOR off field.

 

My problem with this is that every charted visual into SFO is based on the SFO vor - The 6DME restriction from what I've noticed has to do with the Class B shelf and San Carlos to the south. 6DME on the LOC 28L leaves you almost Full scale high on the glideslope -however 6DME SFO vor puts you practically on glideslpe - Interesting dillema - the CA I was with yestuday agreed it had to be based on the SFO vor - everyone has a different opinion...any ATC guys?

 

sfo VOR...

 

I thought that was you. You scared the hell out of my student .

If you are over the bay, 7 DME from the VOR, you are clear of any GA traffic. I agree that you should use the LOC DME. Maybe it is worth giving the tower a call to see what they say.

San Carlos is my home airport, and the airspace around there is some of the craziest in the country (like New York and Los Angeles). Bravo starts at 1500 over the field. They give us a little cut out to fly our pattern up to 5 DME from SFO. And if we are landing 12 (calm wind), with a big line of planes (I have been #6 to land at San Carlos), we have turned base at 5.1 DME from SFO.
And it always seems like my closest encounters have been with the Brasilia's (the MRY-SFO and the MOD-SFO) flights.

Anyway, I would use the LOC DME. It gives you that safety margin from the GA aircraft below. And you never know if there is someone who is unfamiliar with the airspace. It is very easy to bust into the Bravo.

 

If you're not on a charted visual, the should be saying miles, not DME.

But since the charted Visuals all refernce 6 DME off SFO, I'd say the controler was referencing the VOR

 

Not sure which one you did?

http://204.108.4.16/d-tpp/0703/00375...GE_VIS28LR.PDF

http://204.108.4.16/d-tpp/0703/00375TIPPTOE_VIS28L.PDF


They both reference the VOR for distance to remain in class B.

 

I agree if you're on the CHARTED visual, use SFO. But I assume he wasn't since he didn't say anything about charted visuals.

Usually they just clear you for the "visual 28R/L", assuming that was the case and the controller said 6 DME you would normally assume that he meant the LOC DME. If the conroller meant 6 DME SFO he should have specified that, given them a charted visual, or told them to keep the speed up until the bridge.

This sounds more like a SFO tribal knowledge kind of thing...ie ATC making assumptions about what the pilots will assume. Lot's of asumptions here...