Altimeter IFR Certification and G5's

[skykrawler]

Most know the G5 altimeter and airspeed cannot be used as replacements for primary instruments.   Why do, and is it necessary, for shops to do a separate altimeter certification for the G5?   There has been an additional $100 charge for the G5 on my last two IFR certs.

[CChris]

All altimeters in the plane must be certified for IFR, so that means both G5s, even if one is used primarily as HSI, and any other altimeter you might have in the panel.

[EricJ]

The G5 can be a bear to calibrate the altimeter, so I think many are left in a less-than-accurate state.    My IFR guy just asked me if I cared about the G5, and I said, "No, the air instrument is primary."   He's fine with that so we just went with the air altimeter.

[CChris]

Part 91.411 states that:

(a) No person may operate an airplane, or helicopter, in controlled airspace under IFR unless—

(1) Within the preceding 24 calendar months, each static pressure system, each altimeter instrument, and each automatic pressure altitude reporting system has been tested and inspected and found to comply with appendices E and F of part 43 of this chapter;

So I understand that regulation requires "each and all" to be tested.

[N201MKTurbo]

My G5 is installed as an HSI. I occasionally switch it to ADI mode for the jollies of it. 
 

I don’t get it certified as an altimeter, but when they do the cert test, I switch it to ADI mode to see how it performs. It is dead nuts on. It would pass if it was getting it certified.

[ricardo-sf]

As mentioned the regs require all pitot static instruments to be certified for ifr flight. 
 

 

[EricJ]

If an instrument isn't primary many may not consider it needs to be treated as a primary instrument.   I think that's where the various shops may differ.  My IFD shows altitude, too, but it doesn't get tested for IFR cert, either.

[Vance Harral]

Not to be pompous about it, but I likely have more data points on G5 calibration than most pilots posting here.  That's because I instruct at a couple of flight schools/flying clubs, where every aircraft has a dual G5 setup.  Between that and instruction in owner aircraft, I've flown about a dozen airplanes in the last couple of years with G5s.  Most of these airplanes have never had their G5s calibrated through a static system check, because the shops and/or the aircraft owners know the instrument is not primary for altitude.  Despite @CChris's argument - which I agree with - the owners generally just don't want to pay for the calibration, and the shops don't want to try to bill for it unless explicitly requested.

Here's where it gets interesting: based on these data points, I am convinced there is a consistent error in the "bad" direction of an uncalibrated G5 with respect to altitude, at least at field elevations here in the Denver metro area (generally around 5000').  Every single uncalibrated G5 I've flown with indicates higher than their certified mechanical counterpart.  The difference ranges from +50 to +120 vs. the certified instrument, with not a single one of them indicating lower.  This is an eye opener when/if you watch an instrument pilot shoot a practice approach down to 200' minimums using the G5 altitude, and subsequently point out they have descended to within 100' of the ground.

I'm never surprised when different altimeters indicated different values, but I am surprised by the apparent net error in G5 altitude across many data points.    Because of what I've seen, I've made it a standard part of my avionics instruction, and a point of particular interest in instrument instruction, to point out that not only is G5 altitude not certified primary, but that if you use altitude from an uncalibrated G5 on an instrument approach, you are quite likely to bust minimums - and not by just a few feet, but perhaps in excess of 100'.

Anyway, I paid directly out of my own pocket to have the local shop calibrate the G5s in our partnership airplane, and would do so regardless of the outcome of arguments about whether it's legally required.  I also won't fly low IMC in an airplane that hasn't had the calibration done.  That beautiful EFIS display tends to draw the eyes of most of the pilots I fly with, and most of them keep using the G5 altitude no matter how many times I remind them it's not primary.  I just let that go with folks that lack an instrument rating, but it gives me the heebie-jeebies with airplanes and pilots that are purportedly going to fly IMC.  For me, that's the number one reason I recommend paying the shop extra to calibrate the non-primary G5 altimeter.  I don't think doing so is being anal-retentive.  I feel like it's required to correct what appears to be a consistent bias in the design of the instrument, in the "dangerous" direction.

 

[N201MKTurbo]

13 hours ago, ricardo-sf said:

As mentioned the regs require all pitot static instruments to be certified for ifr flight. 
 

 

So, you are saying my VSI and airspeed needs to be certified for IFR?

[skykrawler]

Regarding G5 altitude calibration.....that is a required step for installation under the STC.   If calibration wasn't checked and corrected then shame on the installer.  I installed the G5 as a backup attitude instrument and eliminated the stupid Precise Flight standby.

My G5 has been certified twice now - when the primary altimeter was certified and its more accurate and it didn't require the calibration data to be changed.  In fact the G5 continues to be accurate at altitudes above 12000 where the analog instrument error increases.

I think the "each altimeter instrument"  was meant to apply to aircraft with independent altimeter systems at two crew stations. 

[JimB]

I don't know why anyone would think calibrating the G5s is difficult. I have done a bunch. It's just part of the 91.411/.413 check. As a digital instrument, once it is calibrated, it stays pretty consistent. 

[PT20J]

My shop charges a flat rate for the certs and checks all altimeters installed: Aspen and mechanical when I had that, and G3X and G5 now. 

[EricJ]

2 hours ago, JimB said:

I don't know why anyone would think calibrating the G5s is difficult. I have done a bunch. It's just part of the 91.411/.413 check. As a digital instrument, once it is calibrated, it stays pretty consistent. 

There's been a fair amount of experience that some of them resist calibration, even in healthy static systems, unless the tester is connected directly to the instrument (i.e., it is disconnected from the aircraft static system and connected only to the tester).    Since the software in the G5 manages the calibration, if it isn't happy the calibration can't be completed.   If it resists calibration even this way, it gets a bit difficult to do.   The owner of a local avionics/instrument shop told me that they'd had a fair amount of trouble this way.

Clearly they don't all do that, but I can see somebody living with a less-than-perfect calibration if they have that kind of trouble with it.   

[JimB]

21 minutes ago, PT20J said:

My shop charges a flat rate for the certs and checks all altimeters installed: Aspen and mechanical when I had that, and G3X and G5 now. 

Yes. Flat rated at $450 for the transponder/encoder and all the altimeters installed in the aircraft. G5s, GI-275s, G1000, G3X, standbys and mechanical. Biggest issue we run in to is tracking down static leaks and it doesn't matter if the aircraft is new or old. Usually its pretty easy and it doesn't add to the cost but sometimes it can take a lot of time. 

[IFLYIFR]

Jim’s, does your flat rate mean $450 for all the instruments you listed in your post or $450 for each of the instruments?


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