Class A Airspace

[SixPapaCharlie]

Thinking about Class A Airspace. Couple questions:

1. Is the only requirement to be on IFR flight plan?

2. If you are VFR having selected a cruising alt of 17.5 to get that perfect tail wind and you reach over to get your hot dog out of the bag and realize they left off the ketchup and rant a little and realize in the frustration that you are at 18050, is that on par with busting Bravo?
Is it worse?

Also, could a VFR pilot ever get cleared in by ATC if not on an IFR plan
I assume it would be rare for VFR pilots to fly that high anyway (maybe over mountains though ) but just curious about how that airspace is treated given it sort of gets glossed over in training as "Doesn't really apply"

 

[ClimbnSink]

There are vfr mountain wave windows opened in specific places by prior agreement so sailplane pilots can do vfr climbs to stupid heights (30k+ in the East, 40k+ out West.) The record hunting wave cross countries are done over 18k on IFR clearances by sailplane pilots that also have IA. Skydives are occasionally done from class a as well guessing they have something similar to a wave window.

 

[dans2992]

In your hot dog example, if it doesn't cause a loss of separation, they probably would not care. Busting Bravo is probably worse because it is likely much busier and therefore more likely to cause a loss of separation.

I took a (normally aspirated) Comanche to FL210 once. Not that big of a deal, although it was nice to not worry if I had the correct altimeter setting...

 

[jordane93]

Thinking about Class A Airspace. Couple questions:

1. Is the only requirement to be on IFR flight plan?

2. If you are VFR having selected a cruising alt of 17.5 to get that perfect tail wind and you reach over to get your hot dog out of the bag and realize they left off the ketchup and rant a little and realize in the frustration that you are at 18050, is that on par with busting Bravo?
Is it worse?

Also, could a VFR pilot ever get cleared in by ATC if not on an IFR plan
I assume it would be rare for VFR pilots to fly that high anyway (maybe over mountains though ) but just curious about how that airspace is treated given it sort of gets glossed over in training as "Doesn't really apply"

1. You have to be an IR pilot, be on an IFR flight plan, plane has to be equipped for IFR, and you need a Mode C transponder.
2. Not sure. I guess if there is a loss of separation they wouldn't be too happy.
3. No

 

[Jim Logajan]

I would think a review of 91.135 would answer your questions.

 

[frfly172]

Are you actually going to fly in class A,or are you just getting high?

 

[flyingron]

Are you actually going to fly in class A,or are you just getting high?

I've never managed to make it into the class A but I was close once. I was bopping along at the Navion at 17500 showing 260 knots ground speed. It's the highest number I've ever seen.

 

[BillTIZ]

I would think a review of 91.135 would answer your questions.

I had to pull spoilers a push to avoid inadvertent Class A entry. I had been crusing between 17 and 17.5 when I tripped into a super thermal that had me rocketing into the stratosphere.

 

[Clark1961]

I had to pull spoilers a push to avoid inadvertent Class A entry. I had been crusing between 17 and 17.5 when I tripped into a super thermal that had me rocketing into the stratosphere.

I've pulled throttle and pointed the nose down in mountain wave to avoid a Class A excursion. Spoilers would have helped. Of course the associated downdraft was waiting for me...and I had to give up altitude to avoid a stall.

 

[BillTIZ]

I've pulled throttle and pointed the nose down in mountain wave to avoid a Class A excursion. Spoilers would have helped. Of course the associated downdraft was waiting for me...and I had to give up altitude to avoid a stall.

I was in a sailplane going cross country. Spoilers were available.

Roger on the mountain wave effects. You don't need to be "high" to experience wave. I climbed at a steady 500fpm from 3000AGL (6000MSL) to 13500MSL in a glider last month. I had to use spoilers to stop the climb because I had no O2 on board for me or my non pilot pax.

I've had the same experience with up and down draft thermals in powered aircraft at lower altitude. It's not worth fighting to maintain altitude.

 

[NoHeat]

If you are VFR having selected a cruising alt of 17.5 to get that perfect tail wind and you reach over to get your hot dog out of the bag and realize they left off the ketchup and rant a little and realize in the frustration that you are at 18050

I think you could bust Class A even before you got out the hot dog.

That's because altitudes in Class A are measured differently, with the altimeter setting at 29.92 instead of the local setting. Depending on the pressure that day, you could be at 17500 on the local setting but over 18000 on the 29.92 setting. In such a case you might think you are flying a valid VFR altitude, but you are actually busting Class A.

On the flip side, on a different day while ranting at the wiener at 18050 on the local altimeter you might still be below 18000 with a setting of 29.92.

 

[SixPapaCharlie]

I think you could bust Class A even before you got out the hot dog.

That's because altitudes in Class A are measured differently, with the altimeter setting at 29.92 instead of the local setting. Depending on the pressure that day, you could be at 17500 on the local setting but over 18000 on the 29.92 setting. In such a case you might think you are flying a valid VFR altitude, but you are actually busting Class A.

On the flip side, on a different day while ranting at the wiener at 18050 on the local altimeter you might still be below 18000 with a setting of 29.92.

That is a great point.
Thanks.

 

[Captain]

That is a great point.
Thanks.

Not really. When the altimeter setting is 29.91 or lower then they raise the lowest usable flight level. I suppose it's still Class A airspace, but it's not usable.

The point is, if you have the proper altimeter set and you are indicating 17,500' then you are NOT in Class A no matter what the pressure is.

 

[Captain]

I think you could bust Class A even before you got out the hot dog.

That's because altitudes in Class A are measured differently, with the altimeter setting at 29.92 instead of the local setting. Depending on the pressure that day, you could be at 17500 on the local setting but over 18000 on the 29.92 setting. In such a case you might think you are flying a valid VFR altitude, but you are actually busting Class A.

On the flip side, on a different day while ranting at the wiener at 18050 on the local altimeter you might still be below 18000 with a setting of 29.92.

Wrong. See above post.

 

[NoHeat]

I would think a review of 91.135 would answer your questions.

Except as provided in paragraph (d) of this section, each person operating an aircraft in Class A airspace must conduct that operation under instrument flight rules (IFR) ...
(d) ATC authorizations. An operator may deviate from any provision of this section under the provisions of an ATC authorization issued by the ATC facility having jurisdiction of the airspace concerned.


So, if I read that correctly, you are required to be under IFR in Class A, except that the ATC facility can allow you to "deviate" from that requirement.

Is that right?

 

[ClimbnSink]

Except as provided in paragraph (d) of this section, each person operating an aircraft in Class A airspace must conduct that operation under instrument flight rules (IFR) ...
(d) ATC authorizations. An operator may deviate from any provision of this section under the provisions of an ATC authorization issued by the ATC facility having jurisdiction of the airspace concerned.


So, if I read that correctly, you are required to be under IFR in Class A, except that the ATC facility can allow you to "deviate" from that requirement.

Is that right?

I don't think deviate is the right word, VFR is possible with prior written agreements and current notification. For example http://www.williamssoaring.com/pilot-info-wave.html

 

[PPC1052]

There are some altitudes in the class A that require you and your aircraft to be RVSM. But that isn't until fl 290, I think.

 

[Captain]

There are some altitudes in the class A that require you and your aircraft to be RVSM. But that isn't until fl 290, I think.

RVSM is FL290 to FL410 inclusive.

 

[BillTIZ]

I think you could bust Class A even before you got out the hot dog.

That's because altitudes in Class A are measured differently, with the altimeter setting at 29.92 instead of the local setting. Depending on the pressure that day, you could be at 17500 on the local setting but over 18000 on the 29.92 setting. In such a case you might think you are flying a valid VFR altitude, but you are actually busting Class A.

On the flip side, on a different day while ranting at the wiener at 18050 on the local altimeter you might still be below 18000 with a setting of 29.92.

On such days, the lowest usable Flight Level changes, so you will not meet IFR Class A traffic. You can be legal on the local altimeter setting at 17,500 MSL even if 29.92 would put you above FL180. But ATC cannot use FL180.

 

[NoHeat]

Not really. When the altimeter setting is 29.91 or lower then they raise the lowest usable flight level. I suppose it's still Class A airspace, but it's not usable.

The point is, if you have the proper altimeter set and you are indicating 17,500' then you are NOT in Class A no matter what the pressure is.

It's true that the AIM has a table that specifies certain flight levels as unusuable depending on the local altimeter setting, and ATC will follow that as a matter of operating practice.

That practice, however, is not part of the definition of Class A airspace. That's a separate matter.

The procedures followed by ATC within Class A airspace do not define what is Class A airspace.

 

[Captain]

On such days, the lowest usable Flight Level changes, so you will not meet IFR Class A traffic. You can be legal on the local altimeter setting at 17,500 MSL even if 29.92 would put you above FL180. But ATC cannot use FL180.

You explained that much better than me six posts prior. Thanks.

 

[BillTIZ]

It's true that the AIM has a table that specifies certain flight levels as unusuable depending on the local altimeter setting, and ATC will follow that as a matter of operating practice.

That practice, however, is not part of the definition of Class A airspace. That's a separate matter.

There's no table in the AIM or FAR that says Class A starts at altitude X if the local pressure is A, but it starts and altitude Y if the local pressure is B.

To define Class A, that just depends on the altitude with the setting of 29.92. No matter what the local pressure is, no matter whether it's a beautiful sunny day, no matter whether the moon is full or the Packers just lost or the hotdog has no ketchup.

At least that's what I recall from when I studied for the Commercial knowledge test. But I could always be wrong!

Understood, but as long as I'm the local altimeter setting and below 18,000MSL I do not care where Class A is, all I care is that it is still above me.

Aircraft climbing into flight levels change to 29.92 when transitioning through 18,000 ft. Aircraft descending to below Flight Levels set the local altimeter setting when cleared below FL 180, not waiting until they transition.

 

[Captain]

It's true that the AIM has a table that specifies certain flight levels as unusuable depending on the local altimeter setting, and ATC will follow that as a matter of operating practice.

That practice, however, is not part of the definition of Class A airspace. That's a separate matter.

There's no table in the AIM or FAR that says Class A starts at altitude X if the local pressure is A, but it starts and altitude Y if the local pressure is B.

To define Class A, that just depends on the altitude with the setting of 29.92. No matter what the local pressure is, no matter whether it's a beautiful sunny day, no matter whether the moon is full or the Packers just lost or the hotdog has no ketchup.

At least that's what I recall from when I studied for the Commercial knowledge test. But I could always be wrong!

Class A starts at FL180. However, a VFR pilot using local altimiter and indicating 17,500 is not in Class A airspace even if that same pilot were to set 29.92 and indicate 18,300' MSL. The reason is that ATC clears out that airspace by making those altitudes unusable.

There are two choices for ATC and the FAA. Restrict the bunch of folks who are VFR and not talking to you or restrict the bunch of folks who are IFR and talking to you and doing what you say. Turns out it's easier to control folks who are under your control.

So, VFR cats at 17,500 get a pass if their pressure altitude is above 18,000' and Class A cats who want FL180 get bent if the pressure is below 29.91.

 

[warthog1984]

Understood, but as long as I'm the local altimeter setting and below 18,000MSL I do not care where Class A is, all I care is that it is still above me.

Although it's interesting that the same airspace can be both Class E and Class A [or neither, depending on the altimeter] by the different definitions, the important part is that at 17,500 you'd still be legal and ATC will not be sending FL180 jets at you.

 

[roncachamp]

Although it's interesting that the same airspace can be both Class E and Class A [or neither, depending on the altimeter] by the different definitions, the important part is that at 17,500 you'd still be legal and ATC will not be sending FL180 jets at you.

It can't. The floor of Class A airspace is 18,000 feet MSL, not FL 180.

 

[flyingron]

Class A starts at FL180.

No, it starts at 18,000 MSL. 71.33 specifically defines the lower limit of US class A as MSL over most of the US. It has nothing to do with flight levels. In fact, the fact that the transition altitude (where you switch from local altimeter to 29.92) is also 18,000 is independent of the fact that it is class A airspace. The rules for the transition is located in regulations that make specific mention of 18,000 NOT being in any particular airspace class.

In fact, the flight level rules apply even in those places above 18,000 that are not in class A airspace.

 

[NoHeat]

Although it's interesting that the same airspace can be both Class E and Class A [or neither, depending on the altimeter] by the different definitions, the important part is that at 17,500 you'd still be legal and ATC will not be sending FL180 jets at you.

Well said!

 

[roncachamp]

Well said!

 

[flyingron]

Well said!

But incorrect.

Class A starts at 18,000 MSL regardless of what the atmospheric pressure is.
Now it's possible that there's no usable flight level right at 18,000' but that doesn't make it not class A.


Again FLIGHT LEVELS have nothing whatsoever to do with class A airspace. It's coincidental that they both start at 18,000 MSL.