It's vertical velocity of the aircraft usually expressed in feet per minute.

When an aircraft climbs, the static pressure in the instrument case decreases, which allows the enclosed capsule to expand.

This in turn moves the needle on the instrument to indicate a corresponding altitude.

During descent, the opposite function applies.

Altimeter errors can originate and vary from:

Instrument Pressure Time-lag Barometric Density Temperature Blocked static port

An orographic cloud is formed as the air rises up the slope and will often envelope the summit.

When the air is humid, some of the moisture will fall on the windward slope and on the summit of the mountain.

Drag penalties (additional weight)

Less controllability

Glideslope: 329.15-335Mhz UHF 8 degrees either side, 10NM

Localiser: 108.10-111.95Mhz VHF 35 degrees either side, 17NM

Yes, some directional control as we still have two functioning engines.

Drag is the component of the total aerodynamic force parallel to the relative airflow.

Drag is generated by any body placed in a flow and it's composed of friction, form, and pressure drag.

Jet engines are designed to achieve their best specific fuel consumption at high rpm, which can only be achieved at high altitudes where the air density is low.

Thrust produced will be low enough to equal the required cruising thrust. Also high altitude gives the best operating conditions for the airframe i.e. minimum drag during the cruise.

Turboprops need relatively dense air for the propellers to work efficiently and at high altitude the density would be too low.

In a high bypass design, the vast majority of the thrust is derived from the ducted fan, rather than from combustion gases expanding in a nozzle.

A high bypass ratio provides a lower thrust specific fuel consumption (grams/sec fuel per unit of thrust in kN using SI units), especially at zero velocity (at takeoff) and at the cruise speed of most commercial jet aircraft.

Nose up