Altimeter settings: QNH versus QFE

At 07:30 01 June 2005, Stefan wrote:
I'd like to add that for aerobatic flight, it is common
to use QFE, for
obvious reasons. But then, aerobatic flights are usually
strictly local.

Stefan

Precisely!

And that is the attitude of hundreds of glider pilots
for the last 40 years. Strictly local. I was taught
that way of thinking in a J-3 cub back in 1953, and
then we used it in a glider club in the 60s.

It works fine if you are in an uncomplicated area and
stay local, but it is OLD THINKING! Hardly anyone
travelled to another site those days - even the Cessna
pilots stayed within 25 miles of the home airport (flat
country).

We have a few of those in our club -- guys who never
venture more than 10 miles away in flat land, but the
instructors don't allow it for students.

I'm surprised at the number of US respondents using
the letters QFE, QNH and that third one, which I have
already forgot. I'm even more surprised that no one
has asked what they mean.


QFE = field elevation
QNH = pressure level indicating altitude above sea
level
Q__ = pressure altitude for a standardized pressure
to use for high altitudes (above 18K in the US)


Now, What does the Q mean?

What are the words for NH and for that other one?

For some real fun if you have a large fleet of gliders, go out one
morning and set all the altimeters to 29.92 (or the current setting)
and see how much variation there is in the altitude read outs. You may
be surprised. I certainly was when I did it.

Nyal Williams writes:

....

QFE = field elevation
QNH = pressure level indicating altitude above sea
level
Q__ = pressure altitude for a standardized pressure
to use for high altitudes (above 18K in the US)

Now, What does the Q mean?

They come from morse code days, and there are hundreds of them
covering all sorts of radio, marine, met, and aviation conditions.
Defined by the ITU way back.

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West Australia 6076
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wrote:
For some real fun if you have a large fleet of gliders, go out one
morning and set all the altimeters to 29.92 (or the current setting)
and see how much variation there is in the altitude read outs. You may
be surprised. I certainly was when I did it.


Even more fun, we set QNH of 500 ft. When the student is not looking,
I'll dial in -500 ft. Most don't catch it - the first time.

Tony V.

The original topic is one with some real merit. I learned to fly with
the field = 0. The field was only about 600' MSL so it wasn't a real
big deal, or so I thought at the time. I have just gotten back into
soaring and I am doing my very best to break that habit, and use field
elevation, which for me is now 300 or so. It is taking a while to break
a 19-year habit, but I'm about there. The people that taught me to fly
didn't think they were doing anything wrong. They have nothing to be
ashamed of, that's for sure. I'm proud to say I know all but one of
them... the one that told me I needed to give up, and that I'd never
learn to fly... a real morale builder.

My point is that maybe instructors should be teaching students to add
the field elevation in their decision making. If they're expected to do
that, they will. If you expect them to be stupid, they will. Some have
stated that they don't have a choice because their airports are too
high. They have to teach this the right way. Their students have to
learn this and all do. If I were an instructor, I would not solo a
student that couldn't do this with proficiency. That student will then
know this as instinct, rather than having to unlearn a bad habit. This
is important in our mobile society. I've been moved twice in 8 years. I
expect to move again this coming winter. I am now comfortable using the
MSL field elevation as a start point, and my opinion is that this
should be universal for all students.

Just my nickels worth... and you thought I just had 2 cents...

Jack Womack

Q codes - an exhaustive list - http://www.wemsi.org/qsigs.html

Ian

As a newly certified glider pilot, Hurray!!! I am accustomed to using
field zero because this is how I was taught, BUT... I fly in Florida.
Our place is only 200'.
However, the thought of eventually going cross country has me
considering dumbing this QFE setting, but a few complications entered
my mind. Not to mention the accuracy of the instuments in club and
commercial planes. Nothing that simple math can't solve of course, but
nonetheless important when trying to operate with others in the flying
environment.
Examples:
Cloud base reported by other pilots as 4000',what are they determining
that on? QFE or QNH.
Signal to tow pilot to release me at 2000'. I pop off sooner.
Towing out and looking out for the magic 200'mark to turn back to field
in a rope break.
Granted, communication with tow pilot, incorporating the math, and of
course using good old "That looks about right" may solves these
mentioned scenarios, but I just thought, would it not be nice if QNH
was universally used by everyone even if my home field is a measley
little 200'MSL.?

First, congrats and welcome to the sport.

Some suggestions per your questions (with the caveat that a discussion
with a CFIG that you trust is undoubtedly a much better source of
guidance!):

The cloud base question gets to the very heart of this issue, however
really only on a theoretical basis - cloud bases have been known to
vary quite a bit, cloud to cloud! And here it gets interesting,
because ceilings are given AGL for the field in question - because
instrument approaches have minimums based on how low the clouds are -
AGL! But cloud heights are given in MSL. Hopefully we aren't in the
situation of shooting an approach to mins in our gliders!

Tows are usually billed in altitude gained on tow - so it's really
difference between takeoff and release altitude. You got to do the
math - but since most pilots seem to like nice even tow numbers (odd,
since the good lift always seems to be at either 900 ft or something
like 1700 ft) it really isn't a demanding calculation to make. Anyway,
just release, and trust me the tow operation will figure out a way to
bill you! Seriously - at a strange field with an odd altitude, just do
the math before hooking up, and when you see that number, you are
there.\\

The "magic" 200 ft - if you still use it, instead of TLAR - is the same
thing, do the math before hooking up as part of your checklist (the E
of CBSIFTCBE, for example) and it will work anywhere.

For those who like a visual reminder, there are moveable "bugs" that
can be attached to the altimeter face that can be set at the field
elevation. Cheap and easy.

Kirk
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