Pandect Instrument Repair & Overhaul

contact Brian Wilkins

Pandect Instrument Laboratories - PIL

Aircraft Instrumentation, Simulators

t: 01494 526301

enquiries@pandect.demon.co.uk or brian.wilkins@pandect.co.uk

Air Data Instruments

Two of the most important pieces of information for a safe flight are height and speed. Almost from the beginning of powered flight these have been provided to the pilot by instruments that utilise the ambient atmospheric pressure by means of a pilot/static system.

Pitot and static systems

static pressure air data instruments...

The ambient atmospheric pressure at any location is known as the static pressure. T

Pitot pressure air data instruments...

As an aircraft moves through the air it displaces the surrounding air. As it moves forward it compresses the air and there is a pressure increase on the forward-facing parts of the aircraft. This pressure is known as dynamic pressure.

Suppose a cup were to be placed on the front of an aircraft, with its open end facing forward. When the aircraft is stationary the pressure inside the cup will be the same as the surrounding air pressure. In other words it will be static pressure. When the aircraft begins to move forward the air inside the cup will be compressed and dynamic pressure will be added to the static.

pressure altimeters...

The function of pressure altimeters is to indicate the aircraft height above a given pressure datum. It operates on the principle of decreasing atmospheric pressure with increasing height and is, in fact, simply an aneroid barometer that is calibrated to read pressure in terms of height.

airspeed indicators

the pilot needs to know when the aircraft is moving fast enough for take-off, when it is flying close to the stalling speed, when it has accelerated to the speed at which landing gear and flaps must be raised and when it is approaching the maximum safe flying speed, to name but a few. This critical information is provided by airspeed indicators (ASI).

The aircraft's speed relative to the surrounding air is proportional to the dynamic pressure that results from the air being brought to rest on forward facing parts of the airframe.

Airspeed indicators measure dynamic pressure and convert this to an indication of airspeed.

Vertical speed indicators (VSIs)

The vertical speed of an aircraft is otherwise known as its rate of climb or descent and the VSI is alternatively known as the rate of climb/descent indicator (RCDI). The purpose of the VSI vertical speed indicators is to indicate to the pilot the aircraft's rate of climb or descent, typically in feet per minute.

Since it is rate of change of height being indicated it is necessary to create a pressure difference within the instrument whilst a height change is occurring, and to arrange that the magnitude of the pressure difference is proportional to the rate of change of height.

Air data computers (ADCs)

In addition to the four instruments already covered there are numerous systems in modern aircraft that require air data inputs in terms of static pressure, pitot pressure and air temperature. Since most, if not all, of these systems are electronic in operation so it is logical to supply such data in electronic form.

Pressure transducers

Pressure transducers convert pitot and static pressure into suitable electrical signals for transmission to the air data computer. In the case of analogue air data computers ADCs the transducer is often of the electro-magnetic type, the amplified output of which drives a servomotor and operates a synchro system, which in turn operates the analogue instrument displays.

Digital ADCs more commonly utilise piezoelectric transducers that form part of a solid-state circuit.

Gyroscopic Instruments and Compasses

Gyroscopic instruments are of great importance in aircraft navigation, because of their ability to maintain a constant spatial reference and provide indication of the aircraft's attitude. The principal aircraft instruments that use the properties of the gyroscope are directional gyros, artificial horizon or attitude indicators and turn and bank indicators.

Inertial Navigation Systems

Inertial navigation systems are computer-based self-contained systems that provide aircraft geographic position information in terms of latitude and longitude, together with aircraft speed, heading and tracking information. When provided with a TAS input, the system also produces an output wind velocity and direction. They require no external information or reference other than the starting location of the aircraft.

The basis of the inertial navigation system lies in measurement of the aircraft's acceleration in a known direction and this is accomplished with use of accelerometers. These are devices that measure acceleration along a specific axis; normally one measures accelerations and decelerations along the east-west axis and a second measures accelerations and decelerations along the north-south axis.

Powerplant Aero Engines and System Monitoring Instruments

Engine and system monitoring has become increasingly presented to the pilots by electronic displays such as EICAS and ECAM. The type of instruments often found in less sophisticated aircraft and older aircraft, are pressure gauges, temperature gauges, fluid flow gauges (and quantity), rotary speed gauges, torque gauges and vibration gauges.

Pandect are official authorised repair agents for Honeywell, Rockwell Collins, BF Goodrich, as well as supporting units from Thomson CSF (Sextant Avionique), Smiths Industries, Bendix and many others.

Approved to EASA Part 145, FAR Part 145 and ISO 9001:2000 facilities, you can rely on Pandect to provide you with a quality service delivered on time.