JF Arrow Altimeter setting

[CristiNeagu]

Here is more information for you:

How to set up your Instrument - Altimeter Settings & Calibration - UK...

QFE – This is the local atmospheric pressure at your current location/airfield. When you calibrate your Instrument or Altimeter using the QFE pressure value your instrument reads (barometric) Altitude above that location, this was traditionally used for Take Off and Landing at airfields to display your height above the runway. Pilots often remember this using the acronym Query Field Elevation. Some Free Fliers use a second altimeter on their instrument set to read 0′ at take off, this is essentially a QFE setting.

Bottom line: Setting your altimeter to the barometric pressure of the airfield will have your altimeter read 0ft, and this setting is called QFE.

[hobanagerik]

@CristiNeagu

Bottom line: Setting your altimeter to the barometric pressure of the airfield will have your altimeter read 0ft, and this setting is called QFE.

My understanding of this would be if I was planning to just practice circuits at that airport, remaining in the pattern, I would just set my altimeter to read 0ft.

[CopperNu]

@hobanagerik

My understanding of this would be if I was planning to just practice circuits at that airport, remaining in the pattern, I would just set my altimeter to read 0ft.

Since you still need to communicate with ATC and other traffic, you’d end up in chaos. That’s why there is a value for everyone to follow below the transition altitude.

[hobanagerik]

Right, so if I were to set mine off by a bit, and another pilot sets theirs right, and we are both in the pattern together, that could be a recipe for one of those high wing/low wing accidents, as we both think we are at 1000ft AGL, but only one of us actually is.

[CristiNeagu]

That used to be the case in the ye olde days (and it was actually the case at the airfield where i had flight training about 10 years ago), but these days everyone uses QNH. But it’s ok to have an altimeter set at QFE for situational awareness, though not if you’re flying IFR cause you need a backup altimeter and a way to crosscheck your instruments.

@hobanagerik

Right, so if I were to set mine off by a bit, and another pilot sets theirs right, and we are both in the pattern together, that could be a recipe for one of those high wing/low wing accidents, as we both think we are at 1000ft AGL, but only one of us actually is.

That danger can still exist if airplanes enter the pattern with old altimeter settings. The problem is that if you’re using QFE at an airport situated at an altitude of, say 500ft, and someone else announces on CTAF that they’re at 1500ft, is that 1500ft above the field? Or above MSL? So the decision was made to standardize everything to QNH.

[Riverrover]

http://www.angelflightne.org/images/Docs/the_altimeter.pdf

[CristiNeagu]

Yep. That article proves me right. As such:

Using the table, you can see that you could mark a barometer so that when the pressure is 28.86 inches of mercury, the instrument would read 1,000 feet; 27.82 inches of mercury 2,000 feet, and so on

That confirms that:

1. Barometer pressure drops with altitude, as i said.
2. That if the barometer reads 29.92inHG at sea level, it would read 21.24inHG on the apron at Telluride (the document cites 21.38inHg at 9,000 ft, and Telluride is at 9,078ft), like i said.

imagine that you parked your airplane at a sea-level airport on an “average” day when the temperature was 59 degrees F and the barometric pressure 29.92 inches of mercury. The altimeter in your airplane would look much like the one in Figure 1 [on top right], except that all three indicators would be pointing straight up, showing that you are at zero altitude.

Since your airport has an automated weather report broadcast, you tune it in and hear that the altimeter setting is 29.42. You turn the adjusting knob until 29.42 shows in the Kollsman window. When you do this, all three needles return to “0,” which is correct since as you sit on the ramp at the sea level airport your altitude is zero.

That confirms that setting the altimeter to the barometric pressure of the airport, the altimeter will read 0ft.

In this case, the altimeter setting amounts to what a barometer at that location would read AT SEA LEVEL at that time. One way to obtain such a reading would be to dig a well down to sea level and lower a barometer to the bottom.

Exactly what i said, almost verbatim, down to the digging a well mention.

The way it’s normally done, however, is to read the station pressure–the actual air pressure at the station–and use a mathematical formula to calculate the altimeter setting.

Again, exactly what i said. The actual air pressure at the tower or the nearest weather station is not directly given to the pilot, like you claimed, it is used to calculate MSL pressure, which is then given to the pilot as the QNH.

I can keep going, but i made my point. The document you found confirms exactly what i said.

[groundlooper]

OP do you have any weather mods installed perhaps?

[hobanagerik]

Just spawned at Sedona. ATIS reports 29.96. Pressing B sets it to 30.02.

[CopperNu]

As I said ATIS is quite often inaccurate. This applies to wind, to cloud layers, to visibility and also the QNH. Even or especially if live weather is used.
Hotkey B still should result in a correct altimeter (which is why I always prefer it instead of dialing in manually) and that looks fine in your screenshot, just 50ft difference.

You can also check the QNH in LittleNavMap but that only works for your current location. LNM should have shown 30.02 in your case.

[hobanagerik]

Agreed, I think ATIS results were just confusing people. LNM actually has 29.95 right now.

Wind is also off. But none of this can be attributed to a faulty altimeter in the Arrow.

Scratch that! I just hit B again, and it is reading 29.95 now. I’ve only been here for about 5 minutes.