What value is a Pressure Altitude display?

[bcg]

As part of my annual, I'm installing an EDM 930 and as part of that, I'm going through the wiring for probably the first time in 30 years and removing stuff that's no longer needed. One thing I have is a Davtron Pressure Altitude display but, I don't think ever ever actually looked at it. Is there a reason I would want to keep this? I can get PA from my transponder with just a couple of button pushes or set my STEAM altimeter to 29.92 since I use the G5 as my primary altitude display. I'm leaning towards removing the Davtron but, wanted to see if there was some compelling reason to keep it. What would you do?

 

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[N201MKTurbo]

I’d put it on a shelf as a momento of the good old days.

[M20F]

I keep my Davtron so it can disagree with my MVP-50 and give me something to fixate on. 

[Joshua Blackh4t]

1 hour ago, M20F said:

I keep my Davtron so it can disagree with my MVP-50 and give me something to fixate on. 

Haha, agreed.

After installing an AV-30, I am no longer sure of my airspeed or height because its always a bit different than the steam guages. Before I had it, I never had any doubts.

[KSMooniac]

A man with two watches never knows what time it is.

[M20F]

2 minutes ago, KSMooniac said:

A man with two watches never knows what time it is.

Einstein said, "Time is relative". Karl Marx said, "Time was invented by clock companies to sell more clocks".

[KSMooniac]

Years ago I replaced my inop OEM OAT instrument with a Davtron M655 that is a really great unit. OAT in F and C, pressure altitude, density altitude, and voltage.  Nowadays I have another OAT on my JPI EMD 900 9and voltage), and pressure altitude on my GTX-330ES.  This is the year that I'll finally remove the trusty M655 as I need more room on the right sub-panel for the Electroair EIS installation.  I'll miss the easy toggling to get F or C, and density alt.

[A64Pilot]

I swapped my KT-76A for a C to get the pressure altitude display, as I’ve had blind encoders fail I see the value in knowing what altitude ATC thinks your at.

With ADSB which one is primary for ATC? Why is ADSB never required to be calibrated / validated?

But having multiple sources I don’t see the value in, I’d pull it if that’s all it does.

[Pinecone]

I could see a readout of what your blind encoder is sending, but not a stand along pressure altitude device.

But if your encoder is sending out some funky numbers, ATC will query you as to your actual altitude and may tell you to turn off you Mode C if there is an issue.

[0TreeLemur]

On 8/17/2023 at 6:32 PM, KSMooniac said:

A man with two watches never knows what time it is.

I heard this as: "A man with one watch always knows the exact time, right?"

[0TreeLemur]

On 8/19/2023 at 9:00 AM, A64Pilot said:

I swapped my KT-76A for a C to get the pressure altitude display, as I’ve had blind encoders fail I see the value in knowing what altitude ATC thinks your at.

With ADSB which one is primary for ATC? Why is ADSB never required to be calibrated / validated?

But having multiple sources I don’t see the value in, I’d pull it if that’s all it does.

Calibration not necessary because ADS-B doesn't make the news, it just reports it.   Then the FAA ignores it .   I don't believe that the FAA software does anything with it automatically.   I've read that controllers can access your extended squitter info, but generally don't.   The only thing they get by default on their display  is the good ol' mode C altitude readout, which was calibrated when you do your mandatory IFR Cert. test on the pitot-static system.

[0TreeLemur]

On 8/17/2023 at 1:28 PM, bcg said:

What would you do?

It depends on the location of the OAT probe.   One well positioned probe is infinitely more valuable than a poorly positioned probe in the heatstream of the engine.  My EDM-900 OAT probe is located maybe three inspection panels out on the left wing, way outside the heat influence of the engine.   The magnetometer/temp sensor connected to the Aspen Pro is on the tail and consistently reads 4-5 degF higher then the wing mounted probe.  It's not accurate, and throws off the TAS calcs done by the Aspen.

[vorlon1]

On 8/17/2023 at 7:32 PM, KSMooniac said:

A man with two watches never knows what time it is.

A team with two quarterbacks never has one.

[RoundTwo]

29 minutes ago, 0TreeLemur said:

It depends on the location of the OAT probe.   One well positioned probe is infinitely more valuable than a poorly positioned probe in the heatstream of the engine.  My EDM-900 OAT probe is located maybe three inspection panels out on the left wing, way outside the heat influence of the engine.   The magnetometer/temp sensor connected to the Aspen Pro is on the tail and consistently reads 4-5 degF higher then the wing mounted probe.  It's not accurate, and throws off the TAS calcs done by the Aspen.

My Garmin probe was mounted under the avionics bay and runs 4-5 degrees hot as well. It helps with great TAS, but it seems I always have a headwind. It’s now getting moved out under the left wing and should make a big difference.