Altimeter Calibration Height

"Neil Gould" wrote:
The original question asked whether the altimeter is set to indicate
the altitude at the wheels or "at the level...",
and if that question has been definitively answered, I missed it.

Assuming an aircraft of large vertical dimension...

If the point of an altimeter is to directly display to the pilot how far
the lowest point on the aircraft is above surface obstructions (or wheels
above a runway), then I would presume the altimeter would be calibrated so
that when the aircraft rests on the ground it reads the same altitude as
that ground level.

If the point of an altimeter is to directly display to the pilot the
altitude to fly so that the aircraft is as far as possible from other
aircraft also obeying 91.159, then I would presume the altimeter would be
calibrated so that when the aircraft rests on the ground it reads the same
altitude as the ground level plus half the height of the aircraft.

And so on for other uses (e.g. keeping the distance of the top of aircraft
safely below a cloud ceiling of known altitude).

If the point of an altimeter is to directly display to the pilot how far
the lowest point on the aircraft is above surface obstructions (or wheels
above a runway), then I would presume the altimeter would be calibrated so
that when the aircraft rests on the ground it reads the same altitude as
that ground level.

If there's much of a flare, the pilot might be surprised.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

The accuracy of the displayed altitude is such that neither of these can be
depended on. In other words, it doesn't really matter because we are not
juding flare by indicated altitude nor are we using it to vertically
separate planes by merely a few hundred feet.

But, I would love to hear from a pilot of a big plane on what occurs when
they set the altimeter based on field elevation rather than by barametric
pressure. From the lack of better information, I am presuming that there is
a noticable difference in the indicated altitude.

--
-------------------------------
Travis
Lake N3094P
PWK
"Jim Logajan" wrote in message
.. .
"Neil Gould" wrote:
The original question asked whether the altimeter is set to indicate
the altitude at the wheels or "at the level...",
and if that question has been definitively answered, I missed it.

Assuming an aircraft of large vertical dimension...

If the point of an altimeter is to directly display to the pilot how far
the lowest point on the aircraft is above surface obstructions (or wheels
above a runway), then I would presume the altimeter would be calibrated so
that when the aircraft rests on the ground it reads the same altitude as
that ground level.

If the point of an altimeter is to directly display to the pilot the
altitude to fly so that the aircraft is as far as possible from other
aircraft also obeying 91.159, then I would presume the altimeter would be
calibrated so that when the aircraft rests on the ground it reads the same
altitude as the ground level plus half the height of the aircraft.

And so on for other uses (e.g. keeping the distance of the top of aircraft
safely below a cloud ceiling of known altitude).

"Jim Logajan" wrote in message
.. .

Assuming an aircraft of large vertical dimension...

If the point of an altimeter is to directly display to the pilot how far
the lowest point on the aircraft is above surface obstructions (or wheels
above a runway), then I would presume the altimeter would be calibrated so
that when the aircraft rests on the ground it reads the same altitude as
that ground level.


If that was the aim the altimeter would have to be calibrated to read the
same altitude as ground level when the aircraft was in a pre-touchdown nose
high attitude.