Help with QNH

[[email protected]]

hi,
Was wondering if someone could help me with calculating the derated
take-off thrust, if there is a change to the QNH for a given actual
takeoff weight.
I know that the thrust setting depends on temp so if you have a Actual
TOW less than the RTOW it is possible replace the OAT reading to a
higher value and therefore allowing for a reduced thrust setting on
takeoff.
What I don't understand is how this is calculated. Also what happens if
there is a change in QNH. how is this taken into account in the
calculation.

sorry if its a bit vague but got to start somewhere.

[Thomas Borchert]

> sorry if its a bit vague but got to start somewhere.
>

I can't really help you with your question, but just a hint at why
you're getting few answers: QNH is a European term for what in this
mostly American forum is known as "altimeter setting".

If I understand your question correctly, however, your interest is in
the effect of pressure and density altitude on take-off power settings.

--
Thomas Borchert (EDDH)

[Stefan]

Thomas Borchert wrote:

> I can't really help you with your question, but just a hint at why
> you're getting few answers: QNH is a European term

Just nitpicking: No, QNH is *not* a European term. The Q-code system is
defined worldwide. It is true, however, that in today's USA aviation
radio communications, the Q-codes are usually not used.

Stefan

[Thomas Borchert]

Stefan,

> No, QNH is *not* a European term.
>

You're right, of course. It's an ICAO term, and it is used anywhere in
the world but... Same goes for "decimal" instead of "point".

--
Thomas Borchert (EDDH)