Basic VFR Instruments

[Airmutt]

FAR 91.205 specifies that an altimeter and airspeed indicator is required for flight. What it does not specify if they have to be P-S driven. So the question is if one were to install say a Dynon D3 would this satisfy the requirement. Yes, I understand that airspeed and altitude displayed are GPS derived. Thoughts, comments???

[melann]

FAR 91.205 specifies that an altimeter and airspeed indicator is required for flight. What it does not specify if they have to be P-S driven. So the question is if one were to install say a Dynon D3 would this satisfy the requirement. Yes, I understand that airspeed and altitude displayed are GPS derived. Thoughts, comments???
My first comment is that §91.205 applies only to "Standard" certificated aircraft unless specified in the operating limitations, such as in Night and/or IFR operations.

[Dana]

Yes, I understand that airspeed and altitude displayed are GPS derived. Thoughts, comments???

If it's GPS derived, it's not airspeed at all, it's groundspeed. As melann pointed out 91.205 doesn't apply to experimentals so it's not actually required, but you really do want a real airspeed indicator.

[Airmutt]

Good point about ground speed. While y’all are correct about the specific language of 91.205, FAA Order 8130.2 does drive you back to 91.205.

[Auburntsts]

Regs aside, this is something you might run past your DAR/inspector. For example, my FSDO inspector insisted on a whiskey compass even though I was “legal” by reg with my EFIS’s magnetometer. I wanted my AWC so I temporarily installed it a compass to pass inspection. Even though you’re in the right, some battles simply aren’t worth fighting.

[Sam Buchanan]

Good point about ground speed. While y’all are correct about the specific language of 91.205, FAA Order 8130.2 does drive you back to 91.205.

The Operating Limitations for our experimental aircraft do not require compliance with 91.205 or any instrumentation for day VFR operations.

Paragraph 8:

8. After completion of phase I flight testing, unless appropriately equipped for night and/or instrument flight in accordance with FAR 91.205, this aircraft is to be operated under VFR, day only.

This has been debated countless times over the years but it is established practice that instrumentation is required per the Op Lims only for night or IFR flight. There may be DARs that insist on instrumentation but they are enforcing regulation that doesn't exist.

Using only GPS-derived instruments for day VFR in an E-AB aircraft is permitted per the Op Lims.

[FlyingRon]

Sam, those are only the specimen limitations. The limitations are what the inspector puts on your actual aircraft.
As pointed out, the guidance for the inspection pretty much mandates 91.205-compliance for initial certification. Yes, you're probably free to rip them out and fly day VFR if you want, but that's not what was being asked.
No, it's not something that "doesn't exist" the guidance is in the same document you are extracting those sample oplims from.

[Dana]

My understanding is that nowadays the DAR has to build the open lims from the FAA order, no?

[Sam Buchanan]

Sam, those are only the specimen limitations. The limitations are what the inspector puts on your actual aircraft.
As pointed out, the guidance for the inspection pretty much mandates 91.205-compliance for initial certification. Yes, you're probably free to rip them out and fly day VFR if you want, but that's not what was being asked.
No, it's not something that "doesn't exist" the guidance is in the same document you are extracting those sample oplims from.

I just now read FAA Order 8130.2J (https://www.faa.gov/documentLibrary/media/Order/FAA_Order_8130.2J.pdf) chapters 2 and 4 and Appendex D (Table D-1) describing the inspection protocol and what is expected when inspecting an aircraft with an experimental airworthiness certificate. The only implication I found that instruments must be installed in the aircraft is the requirement for various V-speeds be recorded during Phase 1. This implies there will be an airspeed indicator.....of some sort (could be a Hall wind meter for a very slow, light aircraft).

For my education......please point out the section(s) of the Order that require an aircraft with an experimental airworthiness be equipped with instruments (in addition to an implied airspeed indicator) for Day VFR operation when the airworthiness certificate is issued.

Thank you.

[Jeff Point]

For my education......please point out the section(s) of the Order that require an aircraft with an experimental airworthiness be equipped with instruments (in addition to an implied airspeed indicator) for Day VFR operation when the airworthiness certificate is issued.
Thats easy. It’s right after the part that mandates AD compliance for E-AB. :)

[Sam Buchanan]

Thats easy. It’s right after the part that mandates AD compliance for E-AB. :)

Aww right, Jeff.........are you saying this is a discussion that will end up in the "Never Ending Debates" section? Good one! :)

How does that full panel work on your Breezy???? :)

[Jeff Point]

I’m here all week, try the veal and tip the waitresses.

[Frank Giger]

Regs aside, this is something you might run past your DAR/inspector. For example, my FSDO inspector insisted on a whiskey compass even though I was “legal” by reg with my EFIS’s magnetometer. I wanted my AWC so I temporarily installed it a compass to pass inspection. Even though you’re in the right, some battles simply aren’t worth fighting.

This is the best real world answer ever given on the subject.

[Joda]

Regs aside, this is something you might run past your DAR/inspector. For example, my FSDO inspector insisted on a whiskey compass even though I was “legal” by reg with my EFIS’s magnetometer. I wanted my AWC so I temporarily installed it a compass to pass inspection. Even though you’re in the right, some battles simply aren’t worth fighting.


This is the best real world answer ever given on the subject.

Yes, this is the best advice. Every DAR will handle this slightly differently, depending on how their managing office directs them. If I were presented with an aircraft that had no instruments at all in it, I would talk with my FAA advisor and decided how HE wants me to handle it. I would not make that decision in a vacuum. I would want something in writing from my FAA office directing me to go one way or the other. That way the FAA makes the decision, not me. I would keep all the written correspondence regarding the issue with my copy of the paperwork for the aircraft, so that regardless of what decision is made I have a record of the dialog that led up to the decision.

[Sam Buchanan]

I agree a consultation with your DAR is the best route if there is something that might raise a flag during an inspection...and that is advice I've given to builders over the years.

The only reason I participated in this thread is because there seemed to be a train of thought that stated the regs and orders are clear-cut about an E-AB having complete instrumentation per 91.205 if it is expected to pass inspection. The experimental op lims and order 8130.2 do not support that position and there have been instances of DARs creating hurdles to certification on their own volition with no regulatory basis to deny certification. That is why I wrote in an earlier post "There may be DARs that insist on instrumentation but they are enforcing regulation that doesn't exist".

I appreciate Joda's input (and was hoping he would respond) and I suspect the unfortunate variability of this matter among FAA managers is intentional...

[robert l]

I think the FAA is kinda like OSHA, they have regulations but in some cases, they don't want to give you a positive yes or no on any one thing. That's why OSHA has the, "General Duty Clause."
Bob, just thinking out loud

[Ron Blum]

FAR 91.205 specifies that an altimeter and airspeed indicator is required for flight. What it does not specify if they have to be P-S driven. So the question is if one were to install say a Dynon D3 would this satisfy the requirement. Yes, I understand that airspeed and altitude displayed are GPS derived. Thoughts, comments???

As has been pointed out by several, these items are not required for EAB aircraft. What is required are limitations and how to identify those limitations. For example, if an engine has an RPM limitation, then one must have a tachometer (a way to tell if that limitation has been exceeded). The basis for all regulations is safety, and there are levels of safety in the regulations. Part 25 is more restrictive than part 23 because the original intent of part 25 regulations were written to protect people paying to be transported.

In addition to 23/25, the regulations are also written to protect the public (those not involved in the activity), passengers (those not in control of operations) and pilots ... and in that order, too. They are also varied for the number of people on board the aircraft ... more people --> more safety/regulations.

So, back to the original question. (If they were required), GPS altitude and speed would not satisfy the requirement. Airspeed and altitude are both pressures. For airspeed, the limitations on your aircraft are based on pressures/forces: Vs, Va, Vne, Vfe, etc. GPS speed does not measure these pressures. For altitude, the level of safety is now upped a level because this one now involves other people/aircraft. Since GPS altitude (a tapeline/geometric altitude) is different than pressure-based altitude, there could be a mid-air collision. For example, your airplane is cruising east at 7,500' GPS altitude and another airplane (on an IFR flight plan) is cruising west at 8,000' pressure-based altitude. This could be the same, physical altitude.

Bottom line: No; GPS data cannot be a substitute for pressure-based airspeed and altitude.

Blue on Top,
Ron

[Airmutt]

But Ron there are electronic devices ( smart watches, phones, tablets) that can sense pressure altitude. I also have a pic of a Volksplane that has an automotive style altimeter installed. I can set baro on my watch and get pressure altitude too. Do those qualify as an altimeter? Setting the requirement discussion aside, where does it state it has to be a static system driven device. And that is really the crux of my question.

[rwanttaja]

This discussion reminds me of an old story about a college student taking a Physics exam. One question was, "Explain how you can determine the height of a building using a barometer."

The student wrote down, "Go to the building superintendent, and say, 'I will give you this fine barometer if you tell me how high your building is'."

The professor marked the answer wrong, and the student challenged it. The prof's boss allowed the challenge, and told the student to answer a modified question: "USING PHYSICS, explain how you can determine the height of a building using a barometer."

The student answered, "Take the barometer to the top of the building, drop it off, and determine the height of the building using the equation 1/2*acceleration*Time^2."

In other words, it depends on the INTENT of the requirement.

Why does an airplane need an airspeed indicator? For a simple indication of the margin above stall. We all know the limitations of this (stall airspeed affected by weight and G-loading), but in GPS-based system can't provide that.

The second reason is 14CFR 91.117, which limits aircraft to 250 knots or less indicated airspeed below 10,000 feet and includes lower limits for certain airspace. Admittedly, it shouldn't be an issue with our Fly Babies and Piets, but it does indicate how an airspeed indicator may be required for other reasons than 91.205.

And, of course, we must remember that GPS is never an "airspeed indicator." So if your Operating Limits require an "airspeed," a GPS won't do.

The second point is the altimeter. In a world where a non-sensitive altimeter is fully legal, a GPS-based altimeter is nominally an acceptable replacement. For those unfamiliar with the term, a non-sensitive altimeter has only one arm and is calibrated in 1000-foot steps, with tick-marks at 200 feet. They often are not adjustable for barometric pressure.

A GPS altimeter *would* provide the same level of service. The problem is, there are places where non-sensitive altimeter isn't a good pick, and that would follow with the GPS-based unit.

My home airport lies under the Seattle Class-B airspace, and if I wish to fly out to the west, I have to pass under an arm where the floor is only 1800 feet MSL. It's a congested area, so there's a 1000-foot minimum altitude. What's worse, the ground elevation starts out as 400 feet, so I've got only a 400-foot altitude window...that's just two ticks on a non-sensitive altimeter. They raised that arm several years back...it used to be 1600 feet, so it would have a one-tick range.

It's the kind of area where you need a reasonable altimeter. Sure, a GPS will provide the needed resolution. But I've got a Mode C transponder and altitude encoder. It's possible that a GPS altitude readout will show me below 1800 feet, but the static-based altitude encoder would show me above. And the ADS-B out would be blabbing my identity. Obviously, I want a my primary cockpit altitude display being static-based altitude.

*If* the GPS senses static, that might be sufficient. But it has to be "plumbable" into an external, reliable static source. I once experimented with a portable altimeter. It sensed the pressure in the gauge itself, but since the cockpit pressure varies by engine power and aircraft airspeed, it really wasn't accurate.

Ron Wanttaja

[Airmutt]

Years ago I flew a friend’s Corben. It had a very nice and expensive sensitive altimeter installed. Unfortunately his static system was a piece of tubing stuck up under the instrument panel. It fluctuated wildly. My trusty baro-altimeter watch has a slower response period and was not effected by the turbulence in the cockpit.
There is an app available where you can plug in local wind speed and direction and it provides TAS. And to make Ron B happy one can even define the airspeed ranges on the display. Is it perfect, no.... but its a free and getting better!!

[Ron Blum]

But Ron there are electronic devices ( smart watches, phones, tablets) that can sense pressure altitude. I also have a pic of a Volksplane that has an automotive style altimeter installed. I can set baro on my watch and get pressure altitude too. Do those qualify as an altimeter? Setting the requirement discussion aside, where does it state it has to be a static system driven device. And that is really the crux of my question.

(for altitude only) No one said that there had to be a conventional static system (static port(s) on the side of the fuselage, on a wing probe, etc.). So, yes, your pressure devices mentioned above (watch, iPad, automotive unit, etc., IF baro adjustable) work, and IF … per the regulations (for certified aircraft) the unit meets the TSO for altimeters (static pressure in -->correct altitude) AND the static system (in your case the cockpit environment and the watch) must be calibratable to +/- 30' per 100 knots (airspeed).

I'll address airspeed in my next reply (to get your quote on that topic).

[Ron Blum]

There is an app available where you can plug in local wind speed and direction and it provides TAS. And to make Ron B happy one can even define the airspeed ranges on the display. Is it perfect, no.... but its a free and getting better!!

I love, love, love your effort! BUT ...

Even if one could input local wind speed and direction (from ASOS or AWOS which is measured or corrected to 10 meters ~33 feet), wind is not a constant and varies with time and altitude in both direction and magnitude. In addition, TAS is not directly relatable to airspeed limitations like Vne, Vfe, Vle, Vs, etc. TAS is temperature dependent. So, one would need to measure temperature (and correct it (temperature) for Mach number). With a lot of effort, you MIGHT get there with altitude, but you are still not there with airspeed. You need to know dynamic pressure (Ptotal - Pstatic) as flight characteristics and structure depends on it.

Regretfully, Ron W's point above about flying under class B airspace layers can be accomplished utilizing GPS altitude because those airspace layers are a tapeline (physical) altitudes (msl and/or agl) and not pressure-based altitudes.

Blue on Top,
Ron "you're making me think (and learn) a lot" Blum.

[Airmutt]

Ron, I assume that you know iPhones since the 6 and up can sense pressure?. If you or Ron are concerned about local static pressure variances you can Bluetooth to a Texas Instruments SensorTag which can be located just about anywhere you want. This device can also provide temperature, humidity, and serve as a magnetometer. Just ordered one to play with. Checkout Belite’s precision altimeter app.
It’s all mute unless someone stands before the FAA/DAR and states my smart watch, phone, tablet etc is my altimeter, VSI, mag compass, and whatever and attempts to move the dial.

[Bill Berson]

I am trying to find out if the requirements are slightly relaxed for EA-B that qualify as Light Sport Aircraft. (less requirements than regular unrestricted EA-B)
The Light Sport rule was intended to be a step between the unrestricted ultralight vehicles and regular aircraft. I found a website that listed various different operating limitations for Light Sport aircraft of three different types: Special Light Sport, Experimental Light Sport Kits or conversion from Special Light Sport, and the uncertificated ultralights that were converted to experimental Light Sport prior to the 2008 deadline.
So now we have EA-B that can qualify for Light Sport as defined in FAR1.1. What can that builder expect for operating limitations and required equipment?

[Dana]

I am trying to find out if the requirements are slightly relaxed for EA-B that qualify as Light Sport Aircraft. (less requirements than regular unrestricted EA-B)
The Light Sport rule was intended to be a step between the unrestricted ultralight vehicles and regular aircraft. I found a website that listed various different operating limitations for Light Sport aircraft of three different types: Special Light Sport, Experimental Light Sport Kits or conversion from Special Light Sport, and the uncertificated ultralights that were converted to experimental Light Sport prior to the 2008 deadline.
So now we have EA-B that can qualify for Light Sport as defined in FAR1.1. What can that builder expect for operating limitations and required equipment?

There is no difference between an E-AB that qualifies as LSA and any other E-AB as far as certification or equipment requirements goes. The only thing that LSA compliance affects is what level of pilot certification is required to fly it.

[Frank Giger]

Dana is dead on the money!

I had to explain this to my boss the other day, who thought that since I'm a Sport Pilot my homebuilt must be an LSA, and was asking about how I met the LSA (ATSM) standards.

So long as the weight and speeds are within the limitations, it falls within the types of aircraft I can pilot, so I built an E-AB within those parameters. It's an E-AB in the same way that an RV-10 is an E-AB.

It's the same with Type Certified aircraft. I can legally pilot a 7AC Champ, for example, which has a gross weight of 1,220 pounds, but not a 7EC Champ, as it has a gross weight of 1,450 pounds.

I'll make no statement on whether or not this is just silly, because it is what it is.

[DaleB]

It's the same with Type Certified aircraft. I can legally pilot a 7AC Champ, for example, which has a gross weight of 1,220 pounds, but not a 7EC Champ, as it has a gross weight of 1,450 pounds.
Oh, THAT isn't anywhere near the top of the silliness pile. If that 7AC has the heavy duty gear on it, it may have a log book entry bumping the gross weight up over 1320 and thus it's obviously FAR too dangerous for you or I (with a Private certificate but no medical) to fly. In fact... it could have been so modified in the 1950s, returned to it's original state and the gross weight dropped back down to 1220, and STILL be entirely too perilous.

Like a lot of rules, it doesn't have to make any sense at all... it just "is".

[Bill Berson]

There is no difference between an E-AB that qualifies as LSA and any other E-AB as far as certification or equipment requirements goes. The only thing that LSA compliance affects is what level of pilot certification is required to fly it.

I am not so sure. The one operating limitation I found that is different is the very operating limitation that requires a category and class rating for the pilot in command. A Sport Pilot doesn't get category and class ratings. They get endorsements.
So that same limitation must or should not apply. So an inspector going down the list of required operating limitations may or should have some discretion. I don't know if they are allowed discretion to apply common sense.

I found this sample LSA operating limitations: http://www.faa-aircraft-certification.com/experimental-lsa-operating.html which is apparently for SLSA, and I am not sure if it applies to all LSA. Or if I can request something like it at EA-B certification. Item 17 is different from a regular EA-B. And item 17 (d) seems to allow a Recreation or Private pilot without category or class rating.

Joe said student solo is still allowed in EA-B, but I don't yet clearly see that privilege in the operating limitations. My last hope was that LSA might have operating limitations that make sense. I may want to be an LSA instructor using my future EA-B and student solo would be needed. I also know my EA-B instruction can't be "for hire". (it would be free)
After all, LSA was supposed to be for training, for crying out loud.

[rwanttaja]

I had to explain this to my boss the other day, who thought that since I'm a Sport Pilot my homebuilt must be an LSA, and was asking about how I met the LSA (ATSM) standards.

So long as the weight and speeds are within the limitations, it falls within the types of aircraft I can pilot, so I built an E-AB within those parameters. It's an E-AB in the same way that an RV-10 is an E-AB.
I like the Light Sport rules, but one of the dumbest things the FAA did was to use the same term to define both Sport-Pilot-Eligible aircraft and the new certification categories. There are "Light Sport Aircraft" by the definition in 14 CFR Part 1, and "Special Light Sport Aircraft" and "Experimental Light Sport Aircraft" certification categories. This has produced endless confusion over the past fifteen years.

Operating Limitations for Experimental Amateur-Built aircraft may be unique to each example, while those for SLSA should be identical for all aircraft of that type.

Ron Wanttaja

[Frank Giger]

Bill, if an aircraft meets LSA criteria, a sport pilot can fly it, regardless of whether it's a Type Certified aircraft, an E-AB, an E-LSA or an S-LSA.


§61.317 Is my sport pilot certificate issued with aircraft category and class ratings?

Your sport pilot certificate does not list aircraft category and class ratings. When you successfully pass the practical test for a sport pilot certificate, regardless of the light-sport aircraft privileges you seek, the FAA will issue you a sport pilot certificate without any category and class ratings. The FAA will provide you with a logbook endorsement for the category and class of aircraft in which you are authorized to act as pilot in command.

It's a distinction without a difference. The operating limitations of an aircraft might state that one must have a type category and class rating, but it's okay - I'm still authorized based on my Sport Pilot certificate.

I'm Single Engine Land, and have both endorsements for aircraft over and under a Vh of 87 knots.

With a few caveats - obviously, both conventional gear and operating in controlled airspace need additional endorsements.

The limitations of the aircraft might exceed the limitations of a Sport Pilot, though. For example, an aircraft might be equipped for flying at night or even IFR. Doesn't matter - a Sport Pilot can't fly in either conditions.

In the case of my little Noop, it's not referred to in any way as an LSA. It's a straight E-AB. It's a single engine land aircraft that meets every criteria of an LSA (weight, cruise speed, stall speed, etc.), so naturally I'm authorized to act as PIC.

Here's something that may make your eyebrows rise - there is no requirement that a Sport Pilot train in an LSA eligible aircraft. It need only be Single Engine Land. Since the Sport Pilot isn't acting as PIC, the door is open to perform a flight review in a Cessna 172, a Citabria, or a Cessna 152 (all of which I've done). A Sport Pilot student must perform his solo flights and initial check ride in one, of course, as he's acting as PIC.

https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&SID=bbbc2ff3bca856b40f9f3d48881b6be0&mc=true&n=sp14.2.61.j&r=SUBPART&ty=HTML#se14.2.61_1303

[rwanttaja]

Since the Sport Pilot isn't acting as PIC, the door is open to perform a flight review in a Cessna 172, a Citabria, or a Cessna 152 (all of which I've done).
Ditto... C172s and a Warrior, for me.

First one (back in ~2006) was interesting. I was apparently the first SP the CFI had encountered.

"You don't have a current medical?"

"No, I'm flying as Sport Pilot, just need a BFR."

"But a 172 isn't an LSA!"

"Doesn't matter."

The CFI had to talk to his boss...but we did fly the review.

Ron Wanttaja

[planecrazzzy]

I have a private... also tailwheel endorsement

Just got my basic flight review in a Cessna 150....

I fly my Experimental that fits LSA...So I don't need a medical...Just my drivers lic.

Gotta Fly...

[Ron Blum]

This device can also provide temperature, humidity, and serve as a magnetometer. Checkout Belite’s precision altimeter app.

It’s all mute unless someone stands before the FAA/DAR and states my smart watch, phone, tablet etc is my altimeter, VSI, mag compass, and whatever and attempts to move the dial.

I think you can get there with pressure-based altitude. The app is really cool. I know James (Belite) well (he's in town). They recently had a really bad fire, and I am not sure if they will be a Phoenix. :(

I like where you're going with talking to the FAA/DAR. This is one reason I formed my own company. Why do we pay $30K for a landing gear actuator when an off the shelf one will do the same job for $300? The same is true for alternators and generators. We need to use what is commercially available from other industries and NOT manufacture 10/year to OEM specifications. There are simple ways around this!

On a similar note, Transport Canada (TC) allows airplanes that are 30+ years old to be DE-certified and placed into an owner maintenance category (the standard AW is destroyed and a new owner maintenance one is made). It is like EAB, but it is NOT EAB. Under their regulations, the owner can do anything that they want to. I have attended several forums on Arduino-based instrument panels … very impressive! And inexpensive!

[Airmutt]

I heard about the fire; never a good thing. At least no one was injured. Didn’t know that they were that badly hurt. Hope they can hang in there and make a comeback.

[Frank Giger]

Oddly enough, coming back on topic, why are we so excited about barometers in an age of GPS?

I've noticed than when my barometer (altimeter) and the GPS altitudes disagree, it's within 100 feet (at most).

Indeed, one would think that GPS would be adopted as the preferred method, with barometers as acceptable, or as a backup. We're relying on old tech because we always have.

Frank "Adjust the altimeter to the field altitude" Giger.

[Ron Blum]

Oddly enough, coming back on topic, why are we so excited about barometers in an age of GPS?

I've noticed than when my barometer (altimeter) and the GPS altitudes disagree, it's within 100 feet (at most).

Barometers measure pressure (and force when multiplied by an area). If a pilot or autopilot were made to fly a hard GPS altitude (tape line altitude), the ride would be extremely rough, and the airplane structure would take a beating.

When one sets their altimeter baro setting, they are correcting the pressure-based altitude to an approximate tapeline altitude (has to be within 50' for IFR flight). This is done so that airplanes flying at low altitude don't hit ground-based objects … and are separated vertically. At high altitude (class A), the baro is set to 29.92 so everyone flies with the same reference. Pressure fluctuations in the Flight Levels (FLs) are much greater.

Ironically, when GPS first came out, the odds of a trans-oceanic mid-air went up greatly because now navigation systems were right on track (little navigation errors). This mandated RVSM (Reduced Vertical Separation Minima) … less errors allowed in the altimeter systems and autopilot control laws. Now the number of tracks has been increased so we can transport more people, more safely, in a smaller volume with higher safety (less odds of a mid-air) and along the shortest routes possible.

Ron "hope this helps" Blum

[rwanttaja]

Oddly enough, coming back on topic, why are we so excited about barometers in an age of GPS?

I've noticed than when my barometer (altimeter) and the GPS altitudes disagree, it's within 100 feet (at most).

Indeed, one would think that GPS would be adopted as the preferred method, with barometers as acceptable, or as a backup. We're relying on old tech because we always have.
I dunno, Frank. Not trying to sound like a recruiter for the tinfoil-hat brigade, but that's a long stretch of technology that needs to work.

You need a properly-running receiver, power for it, an antenna, a 20+ satellite constellation, a properly operating Ground Segment, and the Government's permission (i.e, they can shut down civilian users anytime).

In addition both the good guys and the bad guys do things that affect usability; the bad guys have even lured drones off-course to snag them.

Vishnu help us if they ever get a Nieuport that way. :-)

In contrast, all a barometric altimeter needs is a bit of 1/4" rubber tube. Even if it breaks, you're off just a few hundred feet...not critical for most users. Similarly, setting the device to field elevation before takeoff is probably sufficient for most of GA.

And if you require a barometric pressure-based altimeter as a backup, you're still going to run the rubber hose and calibrate it anyway. And it gives one more gauge that third-world airline captains will choose to ignore.

Ron "I wear size 7 1/2" Wanttaja

[rwanttaja]

Barometers measure pressure (and force when multiplied by an area). If a pilot or autopilot were made to fly a hard GPS altitude (tape line altitude), the ride would be extremely rough, and the airplane structure would take a beating.
Actually, I think most GPSs have an MSL output available. The hiking one I use in the Fly Baby does....

They have a much fancier term than "MSL", of course.

Ron "Luv them four-syllabobble words" Wanttaja

[Frank Giger]

My thinking was that a big, big bunch of us are already using GPS for navigation - heck, it's used for IFR purposes, IIRC. It's pretty darned reliable within CONUS.

It would seem that things like autopilots getting overly fussy is a software issue; and my little Nexus tablet is height above sea level.

Now, I would never say that altimeters should be abandoned - I'm a card carrying member of the Steam Gauge Association, Anti-Glass Panel Chapter 192 - but I find it odd that a major fault of GPS is that it is too accurate.

Even ADSB is taking the altimeter's word for granted, if I understand things.

Granted, I don't have much of a dog in the hunt here - I'll never fly somewhere and have barometric pressures change enough to where being off adjustment matters. Heck, I rarely look at my altimeter, as the difference between 1,500 feet AGL and 2,500 AGL is fairly easy to suss out.* ;)

I'm thinking more about "going places" airplanes that wind up in controlled airspace and being told to fly at particular altitudes a long way away from where they started, or do things like fly over mountain ranges.

* For about eight months both my ASI and altimeter were either inop or just telling blatant lies, and so rightfully ignored until I sorted out the right pitot/static locations. Indeed, in a lot of my flying videos it's very clear the ASI isn't connected to anything.

Frank "Odd Ducks Fly East" Giger

[Ron Blum]

It would seem that things like autopilots getting overly fussy is a software issue; and my little Nexus tablet is height above sea level.

Frank: I did a poor job of explaining why one doesn't want to use GPS altitude for flight path control. GPS Lat/Long information is great for everyone … including autopilots (follow the pink line to your destination … one doesn't fly the route to the accuracy of the GPS). In addition, if one is only using GPS altitude for a rough estimate (1,500' to 2,500') that works, too. Autopilots in RVSM airspace have to maintain altitude within +/-60'.

What doesn't work is when the air is moving up and down (pressure waves). I am bad at examples but here goes. The air has wave similar to the surfaces of lakes and oceans (both water and air are considered fluids). When we fly in turbulence, we try to keep the wings level but let the altitude change … so we don't overstress the airplane. Just as water waves go up and down (and the boat with it), the airplane wants to do the same. Now, anchor a boat with a rope/chain that is as short as possible (vertically straight down). As the waves come by, the boat and its occupants will get beat up (or break up) as the waves try to move the boat up and down. The same is true with airplanes in flight.

Ron "Another try" Blum

[Frank Giger]

Ah, thanks, that makes sense!

And thank you for understanding that when I ask questions like this, A) it really is a question, and B) I need simple explanations, preferably with small words.

[Ron Blum]

Ah, thanks, that makes sense!

Thank you, Frank. Feedback is always good. They say you don't know a subject until you can teach it. I agree.

[Airmutt]

Just found this pic. Please note that there is no P-S driven airspeed or altimeter installed installed. I think I found the answer to my original question. http://eaaforums.org/blob:http://eaaforums.org/2203d849-57bb-451f-b2c4-5728517d9f60

[Ron Blum]

Just found this pic.http://eaaforums.org/blob:http://eaaforums.org/2203d849-57bb-451f-b2c4-5728517d9f60

I can't believe I'm doing this (must like punishment). Dave: I see no picture.

If the picture is of the panel of an EAB airplane, I agree you have found the answer to your question … supported by all the other posts on this thread. No required instruments for EAB airplanes.

[Airmutt]

Will try this again
http://eaaforums.org/blob:http://eaaforums.org/62e9b53d-50f6-4c9b-a693-12b84cf476f2

[Airmutt]

Well, the image keeps getting scrubbed off so here is the link. The aircraft is equipped with nav lights....wonder if it’s approved for night VFR.

https://www.barnstormers.com/listing_images.php?id=1496942 (https://www.barnstormers.com/listing_images.php?id=1496942)

[melann]

Well, the image keeps getting scrubbed off so here is the link. The aircraft is equipped with nav lights....wonder if it’s approved for night VFR.

https://www.barnstormers.com/listing_images.php?id=1496942 (https://www.barnstormers.com/listing_images.php?id=1496942)

Are you sure that the I-K Tech airspeed indicator is not pitot/static driven? I was looking into their instruments at one time and I'm pretty sure that it is.

[Sam Buchanan]

Well, the image keeps getting scrubbed off so here is the link. The aircraft is equipped with nav lights....wonder if it’s approved for night VFR.

https://www.barnstormers.com/listing_images.php?id=1496942 (https://www.barnstormers.com/listing_images.php?id=1496942)

E-AB aircraft don't get "approved" for night or IFR flight. It is the responsibility of the pilot to comply with night and IFR requirements per 91.205.

[Ron Blum]

This is interesting. I know the Garmin 496 has no P-S information. In fact, the manual states that one has to input that data into the unit from the airspeed and altimeter instruments.

The transponder, on the other hand, has to be getting static pressure from somewhere.

-Ron "definitely don't know all the answers" Blum