Flight instruments

The most common unit for altimeter calibration worldwide is hectopascals (hPa), except for North America and Japan where inches of mercury (inHg) are used.

[2] The altimeter is adjustable for local barometric pressure which must be set correctly to obtain accurate altitude readings, usually in either feet or meters.

As the aircraft ascends, the capsules expand and the static pressure drops, causing the altimeter to indicate a higher altitude.

Hence when the needles were indicating lower altitudes i.e. the first 360-degree operation of the pointers was delineated by the appearance of a small window with oblique lines warning the pilot that he or she is nearer to the ground.

This modification was introduced in the early sixties after the recurrence of air accidents caused by the confusion in the pilot's mind.

Errors include Variation, or the difference between magnetic and true direction, and Deviation, caused by the electrical wiring in the aircraft, which requires a Compass Correction Card.

While reliable in steady level flight it can give confusing indications when turning, climbing, descending, or accelerating due to the inclination of the Earth's magnetic field.

Bearing friction causes drift errors from precession, which must be periodically corrected by calibrating the instrument to the magnetic compass.

The ADI is an Attitude Indicator with computer-driven steering bars, a task reliever during instrument flight.

An RMI is remotely coupled to a gyrocompass so that it automatically rotates the azimuth card to represent aircraft heading.

In newer aircraft with glass cockpit instruments the layout of the displays conform to the basic T arrangement.

They were: This panel arrangement was incorporated into all RAF aircraft built to official specification from 1938, such as the Miles Master, Hawker Hurricane, Supermarine Spitfire, and 4-engined Avro Lancaster and Handley Page Halifax heavy bombers, but not the earlier light single-engined Tiger Moth trainer, and minimized the type-conversion difficulties associated with blind flying, since a pilot trained on one aircraft could quickly become accustomed to any other if the instruments were identical.

Primary flight display, is given a central place on the panel, superseding the artificial horizon, often, with a horizontal situation indicator next to it or integrated with the PFD.

The cockpit of a Slingsby T-67 Firefly two-seat light airplane . The flight instruments are visible on the left of the instrument panel
Schempp-Hirth Janus -C glider Instrument panel equipped for "cloud flying". The turn and bank indicator is top centre. The heading indicator is replaced by a GPS -driven computer with wind and glide data, driving two electronic variometer displays to the right.
Six basic instruments in a light twin-engine airplane arranged in a "basic-T". From top left: airspeed indicator , attitude indicator , altimeter , turn coordinator , heading indicator , and vertical speed indicator