Airborne_Again wrote:
LSZS doesn’t have a TA (VFR airport)
Strictly speaking yes, but that’s what the Bizjet pilots flying there seem to use.
You’re right about Sion being 17000’: LSGS AD 2.24.10-5
Peter wrote:
Are there any autopilots which have ALT mode and which don’t do that?
S-TEC 30 doesn’t do it. I’m dealing with this one every flight…..
Edited to add: normally the changes are very small, but there are of course exceptions. One is the – always present – difference between the coastal airports and the high desert ones here in SoCal. Just now: KCMA (Camarillo) 30.09 / 1018.96 hPA, KWJF (Lancaster) 30.22 / 1023.37 hPA
That’s not even 5 hPA, less than 150 ft – who cares? Who has any issue with that?
Jan_Olieslagers wrote:
That’s not even 5 hPA, less than 150 ft – who cares? Who has any issue with that?
Nobody. Just wanted to show that the whole ‘constant changing of altimeter settings’ issue is overblown ;-)) 90% of the time the difference is much smaller.
PS: these two airports are about 50 nm apart.
In the US, a great many little unattended airports have ASOS or AWOS to provide automated altimeter settings to anyone in the area, so in my VFR travels it’s rare that I couldn’t get a local setting when needed. No need to talk to anyone. There are no ‘official’ sources of data, or maybe better said they are all official, so any of them is as good as the other. Mostly I don’t need the data en-route anyway because I’m VFR and talking to nobody on the radio, or alternately I’m talking to somebody who gives me a setting when I make contact. So it’s not something you think about a lot. Today I set my altimeter four times, twice on the ground and twice in the air during two hours of flying and one of those times I set it to field elevation. For me it would feel strange to reset the altimeter just because I’m passing through some some arbitrary altitude – I’ve never flown above TA and I think I’d find it annoying.
Airborne_Again wrote:
The KAP140 does have altitude preselect but I still think that altitude hold is independent of both the encoder and QNH. But I’ll check as soon as I get the opportunity.
On the KAP140 you set the pressure on start up directly on the unit. This is to make sure the altitude preselect correspond with the actual altitude.
If you in ALT hold mode change the pressure setting the Autopilot will climb or decend accordingly.
The altitude encoder is only measuring standard altitude.
pmh wrote:
On the KAP140 you set the pressure on start up directly on the unit. This is to make sure the altitude preselect correspond with the actual altitude.
If you in ALT hold mode change the pressure setting the Autopilot will climb or decend accordingly.
The altitude encoder is only measuring standard altitude.
Yes, I know all that. What I am not convinced of is that it will actually climb or descent when you change the pressure setting. Have you actually tried it?
Airborne_Again wrote:
Yes, I know all that. What I am not convinced of is that it will actually climb or descent when you change the pressure setting. Have you actually tried it?
I fly with KAP140 and confirm that it climbs/descends, as pressure is adjusted on the autopilot panel.
loco wrote:
I fly with KAP140 and confirm that it climbs/descends, as pressure is adjusted on the autopilot panel.
I fly with KAP140 too. I’ll have to try this sometimes. When you cruise on flight levels most of the time, you don’t get to see these nice details of how your autopilot works. 
My S-Tec doesn’t do this. It has its own pressure sensor.
