Aerobatics, altimeter settings and waivered airspace

[Diana]

The recently approved waiver for the aerobatic box at Kansas City (KIXD) had an interesting add-on by the FSDO. The Kansas City FSDO tacked on a waiver for altimeter settings (91.121). Seems like other waivers I've seen haven't had that. I wondered what prompted that?

 

[gibbons]

Interesting. It makes sense but I've never seen it before.

 

[N50909]

I don't know if the requirement is always wavied for his airshow waivers, but anytime Rob peforms at an airshow he sets his altimeter to zero before takeoff. Glancing at the AI after 14 snap rolls isn't the time for mental math.

I'll ask him if it's always waived if you like, but I suspect airshow/competition waivers differ from practice aerobatic boxes.

Or maybe Rob's just a rebel... but a safe one.

 

[Bill]

I don't know if the requirement is always wavied for his airshow waivers, but anytime Rob peforms at an airshow he sets his altimeter to zero before takeoff. Glancing at the AI after 14 snap rolls isn't the time for mental math.

During my brief intro to acro lessons, my instructor always had me set the altimiter to zero before takeoff.

 

[tonycondon]

ah i get it now. the box is based on AGL?, plus for lowish level acro you really only care about agl altitude.

 

[N50909]

During my brief intro to acro lessons, my instructor always had me set the altimiter to zero before takeoff.

We do all our stuff above 3500 MSL (that's our absolute floor... we usually start around 5,000) and terrain is only in the 200-300 foot range around us, so there's no real need to reset the altimeter to zero.

 

[CJones]

Wasn't there a high-profile accident a while back near Seattle related to this? Seems like I remember hearing about someone going down while flying over the bay -- they set their altimeter during practice the previous day, but didn't compensate for hi/low tide and hit the water on the bottom of a maneuver the following day.

Don't know if there's any truth to this or if it's just an OWT.

 

[N50909]

ah i get it now. the box is based on AGL?, plus for lowish level acro you really only care about agl altitude.

I can't speak for Diana's aerobatic box (which I'm assuming starts at 1,500 AGL, but may be spelled out in MSL on the waiver itself... never actually read one... any chance you can post for reference, Diana?), but Rob's airshow waivers are always surface level so that may make a difference.

 

[N50909]

Wasn't there a high-profile accident a while back near Seattle related to this? Seems like I remember hearing about someone going down while flying over the bay -- they set their altimeter during practice the previous day, but didn't compensate for hi/low tide and hit the water on the bottom of a maneuver the following day.

Don't know if there's any truth to this or if it's just an OWT.

I can see that. Occasionally Rob does a show over a site away from an airport. It's difficult to set your altimeter to read zero on the surface in the middle of the box if you don't know the exact elevation... or the pressure of the two locations is different... or in this case the surface is moving. 'Bout the only way I know of to do it with 100% accuracy is skim the surface and set to zero... not always possible. Last time Rob had that case we looked up the elevation on my GPS then did the math. Set altimeter to airport elevation. Show elevation is roughly 80 feet less than field elevation. Set altimeter to -80 feet and err on the high side during manuevers.

 

[gibbons]

Almost everyone I know, including Diana, sets the alt to ground zero when flying acro. But I've never noticed an aerobatic waiver pointing out that rule as one being waved.

The Extra had two altimeters, one I left set to the correct pressure and one I set to zero. It just never occured to me that if you have one altimeter and set it to zero then this rule would need to be waived.

 

[Diana]

ah i get it now. the box is based on AGL?, plus for lowish level acro you really only care about agl altitude.

Yes, it's based on AGL.

Here is a good description of the aerobatic box on the IAC site:

http://www.iac.org/begin/aerobatic_box.html

 

[Diana]

I can't speak for Diana's aerobatic box (which I'm assuming starts at 1,500 AGL, but may be spelled out in MSL on the waiver itself... never actually read one... any chance you can post for reference, Diana?),

I have an aerobatic practice area that is a three mile radius centered over the farm from 1500'AGL to 5000' AGL. I had to get a waiver for the federal airway nearby. Then I had to get a waiver for the lower limit for aerobatics down to 500' AGL directly over our property. That was for air show practice by pilots who had personal waivers that allowed them to fly that low. I don't do aerobatics that low since I don't have a low-level waiver (and because I'm not good enough to do it that low ).

The aerobatic box over the airport at KIXD is like a typical aerobatic box and they had to waive more regulations than I did.

 

[Diana]

I can't speak for Diana's aerobatic box (which I'm assuming starts at 1,500 AGL, but may be spelled out in MSL on the waiver itself... never actually read one... any chance you can post for reference, Diana?)

I don't have mine in my computer or I'd post it. The one I just got from the KC chapter is in a PDF file that might be too big to attach here...it's 4.6 MB.

 

[N50909]

I have an aerobatic practice area that is a three mile radius centered over the farm from 1500'AGL to 5000' AGL. I had to get a waiver for the federal airway nearby. Then I had to get a waiver for the lower limit for aerobatics down to 500' AGL directly over our property. That was for air show practice by pilots who had personal waivers that allowed them to fly that low. I don't do aerobatics that low since I don't had a low-level waiver (and because I'm not good enough to do it that low ).

The aerobatic box over the airport at KIXD is like a typical aerobatic box and they had to waive more regulations than I did.

That answered my next question... what you had to get waived.

 

[Everskyward]

Almost everyone I know, including Diana, sets the alt to ground zero when flying acro.

That doesn't work around here. The altitude of the airport is about 5,600' and the altimeter won't adjust that far.

 

[Diana]

That doesn't work around here. The altitude of the airport is about 5,600' and the altimeter won't adjust that far.

Mari, I never even thought about that situation. What do you do then? I don't remember what John did when I was flying with him out there.

I didn't used to set it to zero, even though several sources recommended doing that. I learned the hard way, it really is good idea (for me anyway) most of the time.

 

[KennyFlys]

That doesn't work around here. The altitude of the airport is about 5,600' and the altimeter won't adjust that far.

I recall those days... July in Loveland and DA was over 13,000.

 

[Everskyward]

Mari, I never even thought about that situation. What do you do then? I don't remember what John did when I was flying with him out there.

We just leave the altimeter at its correct setting. I have never discussed this with John since it never occurred to me that you would set it for anything else. We can't really set it on the ground anyway because we fly from KBJC which is a controlled Class D airport. Also the ground elevation where we practice is about 500 feet lower than the airport so we wouldn't be able to set it that accurately anyway.