Bravo Clearance when Departing non-towered Class E under Bravo Shelf?

[kenjr]

...quick question for a flight tomorrow...

First time through the DFW Bravo and I'll be landing at 52F which is under the 1200' shelf. There's a class D airport very close by (KAFW).

Something that's got me confused (first time I've seen this). When you are zoomed out on the VFR sectional the shelf shows 110/30. But in ForeFlight when I zoom in I get the DFW Fly (high detail) and it shows 1200' over the top of 52F? What's the deal here?

What's the usual protocol departing in this situation? 52F has it's own CTAF of course so I'd have to use that to get out of there but field elevation is 600' so I'd have pretty much no time once I get off the ground to call and ensure I had clearance into the Bravo.

I'm guessing call DFW departure or approach and get a clearance/TXPR code prior to departing, use 52F CTAF to get out of there, immediately switch to DFW approach during the climb and follow whatever directions they give with the clearance?

Also curious - when arriving with the airport that close under the shelf, how do they normally handle the handoff to the CTAF? Pattern Altitude is 1600' which is in the Class B so not sure how that would go?

Anyway, maybe this is all a moot point because the actual shelf is 2999' and as long I'm under that I'll have time to contact DFW on my way out of 52F?

Thanks in advance!

 

[MassPilot]

...quick question for a flight tomorrow...

First time through the DFW Bravo and I'll be landing at 52F which is under the 1200' shelf. There's a class D airport very close by (KAFW).

What's the usual protocol departing in this situation? 52F has it's own CTAF of course so I'd have to use that to get out of there but field elevation is 600' so I'd have pretty much no time once I get off the ground to call and ensure I had clearance into the Bravo.

I'm guessing call DFW departure or approach and get a clearance/TXPR code prior to departing, use 52F CTAF to get out of there, immediately switch to DFW approach during the climb and follow whatever directions they give with the clearance?

Also curious - when arriving with the airport that close under the shelf, how do they normally handle the handoff to the CTAF? Pattern Altitude is 1600' which is in the Class B so not sure how that would go?

Thanks in advance!

I would look up the phone number for DFW TRACON and call them ahead of time to ask what they suggest. I've called TRACON's on the phone several times with questions, and they always seemed happy to help. My guess is that they'll suggest you call clearance delivery from the ground, either by phone or radio, and get a squawk code and departure frequency to switch to after you clear the pattern. I know this is normally an IFR procedure, but I've talked to pilots that have successfully used it for VFR flights.

 

[Alexb2000]

...quick question for a flight tomorrow...

First time through the DFW Bravo and I'll be landing at 52F which is under the 1200' shelf. There's a class D airport very close by (KAFW).

Something that's got me confused (first time I've seen this). When you are zoomed out on the VFR sectional the shelf shows 110/30. But in ForeFlight when I zoom in I get the DFW Fly (high detail) and it shows 1200' over the top of 52F? What's the deal here?

What's the usual protocol departing in this situation? 52F has it's own CTAF of course so I'd have to use that to get out of there but field elevation is 600' so I'd have pretty much no time once I get off the ground to call and ensure I had clearance into the Bravo.

I'm guessing call DFW departure or approach and get a clearance/TXPR code prior to departing, use 52F CTAF to get out of there, immediately switch to DFW approach during the climb and follow whatever directions they give with the clearance?

Also curious - when arriving with the airport that close under the shelf, how do they normally handle the handoff to the CTAF? Pattern Altitude is 1600' which is in the Class B so not sure how that would go?

Anyway, maybe this is all a moot point because the actual shelf is 2999' and as long I'm under that I'll have time to contact DFW on my way out of 52F?

Thanks in advance!

I believe you are referring to maximum elevation of an obstacle in MSL in that quadrangle. That is the large 1 and little 2. The Bravo starts at 3000. I usually depart out bound at 2K and come inbound at 2500 (makes traffic working under those tight 3K shelves easier). If you look at Alliance the controlled space is -30. So their airspace goes right up to 2999 and touches the Bravo. If you have flight following they will usually handle the handoff once you get the field visually. If not just tell approach you have the field and would like to cancel.

 

[docmirror]

You don't HAVE to talk to anyone. Floor of the shelf is 3000'. Come in from the north, west, or the south. If coming from the south, I recommend 1800' and be sure your alt is accurate. Fly to the inside of the KAFW surface area, and stay out of the DFW surface area. If coming from the north just stay out of KAFW surface, and call NW regional on unicom. Runway slopes downhill to the south.

If you want to talk to app, that's fine, they'll cancel you when you are 'airport in sight' and you can switch to unicom and make your calls. No need to contact anyone when you take off either. If you want FF, call DEP once airborne, and ask for it.

 

[JasonM]

You are seeing the (MSA) minimum safe altitude (MEF) Maximum Elevation Figure of 1200 ft MSL. Your under the 3000' floor at NORTHWEST 52F.

 

[kenjr]

You are seeing the (MSA) minimum safe altitude of 1200 ft MSL. Your under the 3000' floor at NORTHWEST 52F.

thanks, after looking again I had figured that out.

 

[docmirror]

Watch out for the big towers to the north of the field outside the ring. Around 3000'. Can be hard to miss sometimes, but they are lighted with strobes.

 

[Alexb2000]

You are seeing the (MSA) minimum safe altitude of 1200 ft MSL. Your under the 3000' floor at NORTHWEST 52F.

Not trying to nit pick, but that 12 is not an MSA. It is the highest object within the quadrangle (in this case 1046') with a 100' added for vertical error and rounded up to the nearest hundred. I ONLY mention that because someone flying that altitude could easily hit an obstacle if their altimeter was off.

 

[kenjr]

Not trying to nit pick, but that 12 is not an MSA. It is the highest object within the quadrangle (in this case 1046') with a 100' added for vertical error and rounded up to the nearest hundred. I ONLY mention that because someone flying that altitude could easily hit an obstacle if their altimeter was off.

Thanks - we're coming up from the south so shouldn't even be remotely close to those.

 

[AggieMike88]

Thanks - we're coming up from the south so shouldn't even be remotely close to those.

Be on Flight Following, and Regional Approach will take good care of you. Frequently, Bravo clearance will be given from them without your needing to ask if it makes sense based on your position and direction of flight.

When at 52F, keep your head on a swivel since it is an active airport and has it share of folks who do things "their way".

 

[poadeleted20]

You are seeing the (MSA) minimum safe altitude of 1200 ft MSL.

The term for that big blue number on sectionals is Maximum Elevation Figure (MEF), which provides no obstruction clearance, just the highest obstruction elevation in the box. Minimum Safe Altitude (MSA) is only shown on instrument approach charts, and provides 1000/2000 (normal/mountainous) obstruction clearance above the highest obstruction within the designated circle (normally 25nm) around the depicted fix.

 

[Captain]

The term for that big blue number on sectionals is Maximum Elevation Figure (MEF), which provides no obstruction clearance, just the highest obstruction elevation in the box. Minimum Safe Altitude (MSA) is only shown on instrument approach charts, and provides 1000/2000 (normal/mountainous) obstruction clearance above the highest obstruction within the designated circle (normally 25nm) around the depicted fix.

Flying above the highest obsticle is, in itself, 'obstruction clearance'.

 

[timwinters]

Flying above the highest obsticle is, in itself, 'obstruction clearance'.

Agreed, plus, the MEF is not a the elevation of the highest obstacle as Ron infers.

What it is, according to the FAA's explanation is:

MEFs are determined by taking the point of highest elevation within a quadrangle, adding 100 feet for vertical error, then adding the height of the highest obstacle in the quadrangle or 200 feet, whichever is higher, then rounding up to the next hundred feet.

In studying sectionals, though, you'll notice that the MEF is typically 200' (plus rounding) above the highest obstacle in the quadrant rather than the highest elevation...at least it is around here.

 

[Sam D]

Agreed, plus, the MEF is not a the elevation of the highest obstacle as Ron infers.

What it is, according to the FAA's explanation is:



In studying sectionals, though, you'll notice that the MEF is typically 200' (plus rounding) above the highest obstacle in the quadrant rather than the highest elevation...at least it is around here.

But when the faa is providing an obstacle clearance altitude, they add 1000-2000 feet not a few hundred feet. I think it's an important distraction to make that the vfr charts give you the height of the tallest obstacle and you need to plan around that whereas the IFR chart gives you an altitude you should be safe to fly at.

Or put another way, thinking the the number on the vfr chart will give you obstacle clearance can really ruin your day even with a slightly miss-set altimeter.

 

[timwinters]

Or put another way, thinking the the number on the vfr chart will give you obstacle clearance can really ruin your day even with a slightly miss-set altimeter.

Slightly? It would take 0.2" of "mis-setting" for the altimeter to be off by 200' from the actual altitude. While not a huge error, I would hope folks pay more attention to altimeter settings than to allow that much error.


I agree with your differentiation between VFR and IFR minimum altitudes but the altitudes listed on the sectionals do indeed provide ample obstacle clearance everywhere I've flown. I regularly reference and rely on the MEF on nice VFR days because I like flying as low as possible on nice days when I'm in no hurry.

 

[Alexb2000]

Slightly? It would take 0.2" of "mis-setting" for the altimeter to be off by 200' from the actual altitude. While not a huge error, I would hope folks pay more attention to altimeter settings than to allow that much error.


I agree with your differentiation between VFR and IFR minimum altitudes but the altitudes listed on the sectionals do indeed provide ample obstacle clearance everywhere I've flown. I regularly reference and rely on the MEF on nice VFR days because I like flying as low as possible on nice days when I'm in no hurry.

I believe the more likely scenario is the altimeter is changing rapidly due to weather. Cross under even a mild storm front for example and it will change significantly.

Around DFW the big obstacle is towers. Some are 3K' high. On a hazy day they are almost invisible.

 

[poadeleted20]

Flying above the highest obsticle is, in itself, 'obstruction clearance'.

Sure. But when you add in the uncharted towers up to 200 feet AGL, plus altimeter errors (including instrument, wind effects, and temperature variations), charting errors, and measurement errors (all part of that 200-foot buffer included in the MEF), flying at the MEF is no assurance at all of obstruction clearance. OTOH, an MSA adds 1000/2000 feet to the highest obstruction -- now that's what I call "obstruction clearance".

 

[JasonM]

The term for that big blue number on sectionals is Maximum Elevation Figure (MEF), which provides no obstruction clearance, just the highest obstruction elevation in the box. Minimum Safe Altitude (MSA) is only shown on instrument approach charts, and provides 1000/2000 (normal/mountainous) obstruction clearance above the highest obstruction within the designated circle (normally 25nm) around the depicted fix.

whoops. Sorry fellas. Not sure why I jumped on that term. Maybe due to all the instrument rating videos i'm watching. anyhow, thanks for setting me straight. MEF is absolutely the correct terminology.

 

[oldShar]

When you are planning on being close to the ground, it is appropriate and diligent to make yourself completely aware of where all of the obstacles to flight (short of birds) are located, and avoid those locations --- they are not usually spread out much beyond points within the quadrangle.

 

[Capt. Geoffrey Thorpe]

Towers are easier to spot when you are well below the tops and are looking for them against the sky compared to looking for them against the horizon.

 

[MAKG1]

Slightly? It would take 0.2" of "mis-setting" for the altimeter to be off by 200' from the actual altitude. While not a huge error, I would hope folks pay more attention to altimeter settings than to allow that much error.

You can be low by that much on a cold day, even with a perfectly set altimeter with no other errors. Review your altimeter errors. Altimeter settings are only accurate at the site and altitude of the reporting station.

And there is no accuracy standard for VFR altimeters. They can just be wrong by that much. IFR only requires 75 feet, which is a big hunk of that 200, when you start adding in all the other sources of error.

More importantly, people can and very frequently do build 199 foot towers on the highest terrain, because less than 200 feet means they don't have to mess with expenses like notifying the FAA or obstruction lighting/painting.

 

[SixPapaCharlie]

...quick question for a flight tomorrow...

First time through the DFW Bravo and I'll be landing at 52F which is under the 1200' shelf. There's a class D airport very close by (KAFW).

Something that's got me confused (first time I've seen this). When you are zoomed out on the VFR sectional the shelf shows 110/30. But in ForeFlight when I zoom in I get the DFW Fly (high detail) and it shows 1200' over the top of 52F? What's the deal here?

What's the usual protocol departing in this situation? 52F has it's own CTAF of course so I'd have to use that to get out of there but field elevation is 600' so I'd have pretty much no time once I get off the ground to call and ensure I had clearance into the Bravo.

I'm guessing call DFW departure or approach and get a clearance/TXPR code prior to departing, use 52F CTAF to get out of there, immediately switch to DFW approach during the climb and follow whatever directions they give with the clearance?

Also curious - when arriving with the airport that close under the shelf, how do they normally handle the handoff to the CTAF? Pattern Altitude is 1600' which is in the Class B so not sure how that would go?

Anyway, maybe this is all a moot point because the actual shelf is 2999' and as long I'm under that I'll have time to contact DFW on my way out of 52F?

Thanks in advance!

That's my home field.

When are you going to be there?

 

[JoshJ]

Watch for SUV's

 

[Alexb2000]

Guys just another point of clarification. MEF's are NOT 200' above. They are 100' for vertical error and rounded up to the next hundred. So a 999' tower will show an MEF on the chart as 1100. BUT that 100 extra isn't for us to use to fly over it's for the guy measuring the tower or whatever to make an error. The tower could really be ~1100'. Add this to VFR altimeter error and you could really have a problem.

BTW if we apply this formula to the original question. There are 1049' towers directly to the north of the airport, so round up to 1100' and add 100' to 1200' for vertical error. Even if perfectly measured, zero altimeter error on the gauge and setting, then you only have 150'.

 

[Texastaildragger]

Wouldn't drag it in there. Seems to be a good place to make hard tops into convertibles .

 

[timwinters]

I believe the more likely scenario is the altimeter is changing rapidly due to weather. Cross under even a mild storm front for example and it will change significantly.

We do check the ASOS/AWOS of each airport we pass while out flying, don't we?

 

[poadeleted20]

We do check the ASOS/AWOS of each airport we pass while out flying, don't we?

Can't say what Alex does, but I don't. Of course, I have XM in-cockpit weather, so I'm checking all the stations up and down my route the entire way. But back in the pre-satellite days, I tended to check with Flight Service/Watch for more extensive coverage than just checking the individual automated systems I passed along the way.

 

[timwinters]

More importantly, people can and very frequently do build 199 foot towers on the highest terrain, because less than 200 feet means they don't have to mess with expenses like notifying the FAA or obstruction lighting/painting.

But, if that tower is built on the highest piece of ground in the sector, then the MEF will still provide at least 100' clearance. If it's not, then it's of no concern anyway.

You can see the FAA's math on this at the top of page 3 here.

But you make very good points on both cold weather ops and altimeter error.

I DO keep my plane IFR certified though and know that my altimeter has very little error down low. At 12,000' not so much.

 

[RV10flyer]

Set altimeter. Flew the MEF altitude of 2100' on AP, on a cold winter day, past a 1996' radio tower just to check. I would have hit it 25-50' down from the top if I trusted the MEF. My static system is tested. I use OROCA for my minimums in MVFR and night flights.