Altimeter Setting

[Jim Hall]

While watching Utube fsx landings I noticed the altimeter reads zero at touchdown which seems to me a great thing. Mine shows the corrected altitude of the runway. How do you make it read zero at touchdown?

[alverthein]

My planes never are at zero as the warning message says for me to reset and I hit the B key to adjust the reading to the current height at the runway's correct position including sea level height...You must also reset when going above 18,000 feet or descending below 18,000 feet...This works for me and the airplane is "Happy" when it lands...I don't believe everything I see on YouTube.

[mallcott]

While watching Utube fsx landings I noticed the altimeter reads zero at touchdown which seems to me a great thing. Mine shows the corrected altitude of the runway. How do you make it read zero at touchdown?

 

As runway altitudes are ALWAYS measured above mean sea level (AMSL) and because they are NOT fixed, immutable numbers, they are called `elevation` and not altitude.

Your altimeter will vary according to temperature and pressure, while Runway Elevation is based on an averaged datum that doesn't take into account day-to-day variations (Sea level varies according to time, tide, season and gravitational and weather effects so it isn't fixed either). A Standard Day (or ISA) can be defined:

https://en.wikipedia.org/wiki/Standard_day

 

So, with a moving sea, a static runway and changing altitude the only time those will coincide for a `zero = zero` setting is on an ISA day when temperature, pressure and humidity precisely matches the Standard Day.

 

For this reason you never EVER set the altitude for the runway to `0`as you no longer have any idea just how far you are above that runway, on that day, in those conditions. Makes for an invaluable opportunity to discover what arriving under a runway feels like. :o

 

However, what you CAN do is set the actual altitude of the runway (from charts or the GPS data) and from that deduce what the density altitude is for the area, before you take off. Useful if one finds oneself at a non-radio field, some distance from the nearest weather reporting station. If the field elevation is 1,000ft you can set your altimeter to 1,000 ft and read off the pressure reading.

[mrzippy]

Could you, perhaps, be looking at the radar altimeter as opposed to the barometric one? The radalt will give the exact distance from the rec/transmitter antenna (usually belly mounted) to the ground.

[mallcott]

Could you, perhaps, be looking at the radar altimeter as oppose to the barometric one? The radalt will give the exact distance from the rec/transmitter antenna (usually belly mounted) to the ground.

 

Correct. In addition to defining what altitude is versus elevation, a radar `altimeter` is actually an `elevation` device that will give the aircraft height above the surface (usually immediately below the aircraft).

 

God knows what they must have been smoking before they defined a virtual fixed point for a runway or field as an `elevation`, then the device that measures that actual variation as a fixed relative elevation as an `altimeter`... :rolleyes:

 

The curious aviation dichotomy of sense v. stupidity... :pilot:

[ark1320]

If you put the QNH value in the altimeter's Kollsman window, the altimeter indicates your altitude above mean sea level. If you put the QNE value in the Kollsman window, the altimeter will indicate your height above the airport. QNE is used more frequently in Europe than in the US. You can set the QNE value for an airport by adjusting the altimeter to read zero while sitting on the runway. For a destination airport, the value has to be provided by local air traffic control.

Al

[il88pp]

I used to do this for a while when still practicing landings in the cessna and beech:

set fixed weather, 29.92.

 

Then park at an airport. Turn the altimeter knob until it reads zero ft.

Take off, fly a pattern, and land at the same airport. The altimeter will read zero again on touchdown.

 

But! Land at a different airport, and it willl of course NOT read zero.

Land at a different airport a few times anyway, and you will appreciate the 'zero at sea level' a lot more.

 

If the weather changes then at that same airport it will also no longer indicate zero on touchdown.

[mallcott]

If you put the QNH value in the altimeter's Kollsman window, the altimeter indicates your altitude above mean sea level. If you put the QNE value in the Kollsman window, the altimeter will indicate your height above the airport. QNE is used more frequently in Europe than in the US. You can set the QNE value for an airport by adjusting the altimeter to read zero while sitting on the runway. For a destination airport, the value has to be provided by local air traffic control.

Al

 

Actually I believe you are confusing QNE with QFE:

 

Q Field Elevation

QNauticalEquivalent

QNauticalHeight

 

QNE is height above sea level at the `equivalent` standard 1013 and has nothing to do with your height above the airport, UNLESS conditions are ISA.

 

Perhaps the old adage is better to avoid creating confusion:

QNE = Now Easy: always 29.92

QNH = the ground is very HARD, set altimeter correctly!

QFE = simply Field Elevation

 

And while this used to be true the advent of WAAS and GPS is forcing pilots in Europe toward a more common standard so that `my` 1,500 ft is the same as `your` 1,500 ft for the purpose of sufficient en route clearance with reduced vertical separation minima and airspace infringement. There are exceptions in wide open spaces with voluminous uncontrolled airspace, but in most places in Western Europe you can cruise for an hour at 1,500 ft above the ground, and fly straight into 1,600 ft terrain. CFIT (Controlled Flight Into Terrain) is nearly always attributed to pilot error, and in many of those cases it will be uncertainty over whether what one is seeing is QNH or QNE - or QFE in your case Al.

Precisely the point at which increasing workload or diminishing visibility means your attention is turned.

 

Contrary to the way it is depicted in most flight simulator packages QNH is normally set according to a regional, NOT local setting, and will be adjusted to represent the lowest forecast pressure expected in that region, so it will always failsafe to UNDER-read the actual setting - always better to be 50 feet above your `programmed` altitude than fifty feet below! The way to read all these pressure changes one gets from weather packages in the sim is to be thankful for the frequency pf updates - and use them!

 

We haven't brought Flight Levels into the equation and now would seem to be a good time to: Flight Level simply is the reported altitude at the standard 1013/29.92 setting. When everyone uses this setting, all altitudes will be fixed in relation to one another. Great whenever and wherever obstacle or terrain clearance isn't necessary, but potentially a CFIT if it is. WAAS and RVSM is seeing an inexorable decrease in the elevation (see what I did there!) at which FL is adopted as a common standard - in parts of the Southern UK it's as low as 3,000 feet because there are no obstacles at that height that are attached to the ground, so passing 3,000 ft you set 29.92/1013 and take all relative heights from there.

 

in the sim it's a global 18,000 feet - well beyond most GA, and in tubeliner territory where IFR is mandatory and tight control over altitude is a given. In the Real World, and in Europe, there is almost no circumstance under which QFE provides `better` information on altitude than QNH/QNE

[mallcott]

I used to do this for a while when still practicing landings in the cessna and beech:

set fixed weather, 29.92.

 

Then park at an airport. Turn the altimeter knob until it reads zero ft.

Take off, fly a pattern, and land at the same airport. The altimeter will read zero again on touchdown.

 

But! Land at a different airport, and it willl of course NOT read zero.

Land at a different airport a few times anyway, and you will appreciate the 'zero at sea level' a lot more.

 

If the weather changes then at that same airport it will also no longer indicate zero on touchdown.

 

Yes the only real reason for using QFE is for very localised pattern/circuit work when its a simpler equation in a busy circuit with high exterior workload (eyes out) to set zero-zero and then just use the altitude setting for relevant points, typically 500, 800 and 1,000 ft.

 

But the issue is you must change the sight picture as soon as you leave the immediate area when you need to set QNH, then remember it was set you QNH not QFE when you return to base and enter the pattern at 1,000 ft, which is no longer AGL on the altimeter so will require a different sight picture for the instrument scan - if the airfield is at 500 ft you will enter the pattern at 1,500 ft rather than the previous 1,000...

 

One can see how for a student things might get a bit fraught, particularly in a high workload environment when one needs to be certain to fly at the correct height, joining, descending or turning short final.

 

FAR better to fix QNH and adjust to the field elevation mentally, for consistency, leaving QNE for FL's.

[lnuss]

While watching Utube fsx landings I noticed the altimeter reads zero at touchdown which seems to me a great thing. Mine shows the corrected altitude of the runway. How do you make it read zero at touchdown?

 

It's quite possible that you saw a British video. It seems that in the UK they have multiple altimeter setting styles (QNE and QNH, I believe), and they set their altimeters so they'll read zero on the airport they're using.

 

In the U.S. (and much of the rest of the world) altimeters are set so that they'll indicate relative to mean sea level (MSL), and show the touchdown height above MSL when on the ground. For example, I don't think that you could actually move the Kollsman window setting far enough to have the altimeter reading zero at Denver, and I guarantee that can't happen at Leadville (almost 10,000 feet up). Since it wouldn't make sense to have settings be set one way in part of the country and differently in another part, all are set relative to MSL.

 

It also would seem strange to me to have the altimeter set so that it reads zero at the approach end of runway 29 (5595') (Jeffco or KBJC) but 76 feet at the approach end of runway 11 (5671'). There are many other examples.

 

So we don't mess with QNE/QNH -- it's just an altimeter setting.

[jlaurie]

Perhaps look at the main altimeter not the radar altitude one. That one shows how far above the surrounding terrain you are while the main altimeter, when properly adjusted for local barometric pressure shows how far above sea level you are . . .

 

While watching Utube fsx landings I noticed the altimeter reads zero at touchdown which seems to me a great thing. Mine shows the corrected altitude of the runway. How do you make it read zero at touchdown?