ELECTROSTATIC SENSITIVE DEVICES

Handling of microelectronic devices

The voltage and current requirements for microelectronic devices are of a very low magnitude.  It is therefore necessary to observe strict precautions to avoid damage or destruction when carrying out functional testing and fault diagnosis.  There are some devices whose circuits can, by the very nature of their construction, be damaged or destroyed by “Static Electricity” discharges resulting simply from the manner in which they are handled.

These device are referred to as “Electrostatic-Sensitive Devices” (ESD).  The type of devices that are most susceptible to damage by static electricity 


On aircraft precautions

When replacing Line Replacement Units (LRUs), containing ESDs on aircraft, the following safety precautions must be observed.

1.       All electrical power from the system should be removed by pulling the system circuit breaker(s).

2.       If the power is not removed during LRU removal or installation, transient voltages may cause permanent damage.

3.       After the removal of an LRU from its rack, a conductive shorting dust cap must be installed on each of its electrical connectors.  Under no circumstances must the electrical pins in the connectors be touched by hand.

4.       The conductive dust caps from the unit to be installed can be use on the unit being removed.

5.       The removed unit is then transported with the conductive dust caps fitted.

Aircraft are often fitted with racks containing removable circuit boards, or cards, which often contain ESDs.

During the removal and replacement of the cards, the following procedure is to be followed:

1.       The body of the operator must be grounded by using the wrist strap provided, connected to the appropriate ground jack.

2.       The card is removed using the top and bottom, or left and right, extractors on the card.  Touching the connectors, leads or edge connectors of the card must be avoided.

3.       The removed card is placed in the conductive bag, which is then secured, in accordance with the manufacturer’s approved procedure.

Airspeed indicator

The airspeed indicator or airspeed gauge is an instrument used in an aircraft to display the craft's airspeed, typically in knots, to the pilot.




The airspeed indicator is used by the pilot during all phases of flight, from take-off, climb, cruise, descent and landing in order to maintain airspeeds specific to the aircraft type and operating conditions as specified in the Operating Manual.

During instrument flight, the airspeed indicator is used in addition to the Artificial horizon as an instrument of reference for pitch control during climbs, descents and turns.

The airspeed indicator is also used in dead reckoning, where time, speed, and bearing are used for navigation in the absence of aids such asNDBs, VORs or GPS.

The airspeed indicator is especially important for monitoring V-Speeds while operating an aircraft. However, in large aircraft, V-speeds can vary considerably depending on airfield elevation, temperature and aircraft weight. For this reason the coloured ranges found on the ASIs of light aircraft are not used - instead the instrument has a number of moveable pointers known as bugswhich may be preset by the pilot to indicate appropriate V-speeds for the current conditions

Along with the altimeter and vertical speed indicator, the airspeed indicator is a member of thepitot-static system of aviation instruments, so named because they operate by measuring pressure in the pitot and static circuits.

Airspeed indicators work by measuring the difference between static pressure, captured through one or more static ports; and stagnation pressure due to "ram air", captured through a pitot tube. This difference in pressure due to ram air is called impact pressure.

The static ports are located on the exterior of the aircraft, at a location chosen to detect the prevailing atmospheric pressure as accurately as possible, that is, with minimum disturbance from the presence of the aircraft. Some aircraft have static ports on both sides of the fuselage or empennage, in order to more accurately measure static pressure during slips and skids. Aerodynamic slips and skids cause either or both static ports and pitot tube(s) to present themselves to the relative wind in other than basic forward motion. Thus, alternative placement on some aircraft.

Icing is a problem for pitot tubes when the air temperature is below freezing and visible moisture is present in the atmosphere, as when flying through cloud or precipitation. Electrically heated pitot tubes are used to prevent ice forming over the tube.

The airspeed indicator and altimeter will be rendered inoperative by blockage in the static system. To avoid this problem, most aircraft intended for use in instrument meteorological conditions are equipped with an alternate source of static pressure. In unpressurised aircraft, the alternate static source is usually achieved by opening the static pressure system to the air in the cabin. This is less accurate, but is still workable. In pressurised aircraft, the alternate static source is a second set of static ports on the skin of the aircraft, but at a different location to the primary source.

Lightning detectors vs. weather radar

Lightning detectors and weather radar are used together to detect storms. Lightning detectors indicate electrical activity, while weather radar indicates precipitation. Both phenomena are associated with thunderstorms and can help indicate storm strength.

The first image on the right shows the life cycle of a thunderstorm:

• Air is moving upward due to instability.
• Condensation occurs and radar detects echoes above the ground (colored areas).
• Eventually the mass of rain drops is too large to be sustained by the updraft and they fall toward the ground.

The cloud must develop to a certain vertical extent before lightning is produced, so generally weather radar will indicate a developing storm before a lightning detector does. It is not always clear from early returns if a shower cloud will develop into a thunderstorm, and weather radar also sometimes suffers from a masking effect by attenuation, where precipitation close to the radar can hide (perhaps more intense) precipitation further away. Lightning detectors do not suffer from a masking effect and can provide confirmation when a shower cloud has evolved into a thunderstorm.

Lightning may be also located outside the precipitation recorded by radar. The second image shows that this happens when strikes originate in the anvil of the thundercloud (top part blown ahead of the cumulonimbus cloud by upper winds) or on the outside edge of the rain shaft. In both cases, there is still an area of radar echoes somewhere nearby.

Lightning detection

A lightning detector is a device that detects lightning produced by thunderstorms. There are three primary types of detectors: ground-based systems using multiple antennas, mobile systems using a direction and a sense antenna in the same location (often aboard an aircraft), and space-based systems.

Large airliners are more likely to use weather radar than lightning detectors, since weather radar can detect smaller storms that also cause turbulence; however, modern avionics systems often include lightning detection as well, for additional safety.

For smaller aircraft, especially in general aviation, there are two main brands of lightning detectors (often referred to as sferics, short for radio atmospherics): Stormscope, produced originally by Ryan (later B.F. Goodrich) and currently by L-3 Communications, and the Strikefinder, produced by Insight. Lightning detectors are inexpensive and lightweight, making them attractive to owners of light aircraft (particularly of single-engine aircraft, where the aircraft nose is not available for installation of a radome).

Primary Flight Display (PFD)

A primary flight display or PFD is a modern aircraft instrument dedicated to flight information. Much like multi-function displays, primary flight displays are built around an LCD or CRT display device. Representations of older six pack or "steam gauge" instruments are combined on one compact display, simplifying pilot workflow and streamlining cockpit layouts.

Mechanical gauges have not been completely eliminated from the cockpit with the onset of the PFD; they are retained for backup purposes in the event of total electrical failure.


While the PFD does not directly use the pitot-static system to physically display flight data, it still uses the system to make altitude, airspeed, vertical speed, and other measurements precisely using air pressure and barometric readings. An air data computer analyzes the information and displays it to the pilot in a readable format. A number of manufacturers produce PFDs, varying slightly in appearance and functionality, but the information is displayed to the pilot in a similar fashion.

The center of the PFD usually contains an attitude indicator (AI), which gives the pilot information about the aircraft's pitch and roll characteristics, and the orientation of the aircraft with respect to the horizon. Unlike a traditional attitude indicator, however, the mechanical gyroscope is not contained within the panel itself, but is rather a separate device whose information is simply displayed on the PFD. The attitude indicator is designed to look very much like traditional mechanical AI's. Other information that may or may not appear on or about the attitude indicator can include the stall angle, a runway diagram, ILS localizer and glide-path “needles”, and so on. Unlike mechanical instruments, this information can be dynamically updated as required; the stall angle, for example, can be adjusted in real time to reflect the calculated critical angle of attack of the aircraft in its current configuration (airspeed, etc.). The PFD may also show an indicator of the aircraft's future path (over the next few seconds), as calculated by onboard computers, making it easier for pilots to anticipate aircraft movements and reactions.
To the left and right of the attitude indicator are usually the airspeed and altitude indicators, respectively. The airspeed indicator displays the speed of the aircraft in knots, while the altitude indicator displays the aircraft's altitude above mean sea level (AMSL). These measurements are conducted through the aircraft's pitot system, which tracks air pressure measurements. As in the PFD's attitude indicator, these systems are merely displayed data from the underlying mechanical systems, and do not contain any mechanical parts (unlike an aircraft's airspeed indicator and altimeter). Both of these indicators are usually presented as vertical “tapes”, which scroll up and down as altitude and airspeed change. Both indicators may often have “bugs”, that is, indicators that show various important speeds and altitudes, such as V speeds calculated by a flight management system, do-not-exceed speeds for the current configuration, stall speeds, selected altitudes and airspeeds for the autopilot, and so on.
The vertical speed indicator, usually next to the altitude indicator, indicates to the pilot how fast the aircraft is ascending or descending, or the rate at which the altitude changes. This is usually represented with numbers in "thousands of feet per minute." For example, a measurement of "+2" indicates an ascent of 2000 feet per minute, while a measurement of "-1.5" indicates a descent of 1500 feet per minute. There may also be a simulated needle showing the general direction and magnitude of vertical movement.
At the bottom of the PFD is the heading display, which shows the pilot the magnetic heading of the aircraft. This functions much like a standard magnetic heading indicator, turning as required. Often this part of the display shows not only the current heading, but also the current track (actual path over the ground), current heading setting on the autopilot, and other indicators.
Other information displayed on the PFD includes navigational marker information, bugs (to control the autopilot), ILS glideslope indicators, course deviation indicators, altitude indicator QFE settings, and much more.

Aircraft Data Network (ADN)

Aircraft Data Network (ADN) is a concept introduced by the ARINC Airline Electronics Engineering Committee (AEEC) in the ARINC 664 Specification. The specification proposes data networking standards recommended for use in commercial aircraft installations. The standards provide a means to adapt COTS networking standards to an aircraft environment. It refers to devices such as bridges, switches, routers and hubs and their use in an aircraft environment. This equipment, when installed in a network topology, can provide effective data transfer and overall avionics performance. The ARINC 664 specification refers extensively to the set of data networking standards developed by the Internet community and IEEE. The specification also applies the concepts of Open Systems Interconnection (OSI) standards.
The specification is organized in multiple parts, as follows:

• Part 1 - Systems Concepts and Overview;
• Part 2 - Ethernet Physical and Data-Link Layer Specifications;
• Part 3 - Internet-based Protocols and Services;
• Part 4 - Internet-based Address Structure and Assigned Numbers;
• Part 5 - Network Domain Characteristics and Functional Elements;
• Part 6 - Reserved;
• Part 7 - Deterministic Networks (this part is commonly referred to as the AFDX Specification)
• Part 8 - Upper Layer Protocol Services

Glass cockpit

A glass cockpit is an aircraft cockpit that features electronic instrumentdisplays. Where a traditional cockpit relies on numerous mechanical gauges to display information, a glass cockpit uses several displays driven by flight management systems, that can be adjusted to display flight information as needed. This simplifies aircraft operation and navigation and allows pilots to focus only on the most pertinent information.

Early glass cockpits, found in the McDonnell Douglas MD-80/90, Boeing737 Classic, 757 and 767-200/-300, and in the Airbus A300-600 and A310, used Electronic Flight Instrument Systems (EFIS) to display attitude and navigational information only, with traditional mechanical gauges retained for airspeed, altitude and vertical speed. Later glass cockpits, found in the Boeing 737NG, 747-400, 767-400, 777, A320 and later Airbuses, Ilyushin Il-96 and Tupolev Tu-204 have completely replaced the mechanical gauges and warning lights in previous generations of aircraft.

The average transport aircraft in the mid-1970s had more than one hundred cockpit instruments and controls, and the primary flight instruments were already crowded with indicators, crossbars, and symbols, and the growing number of cockpit elements were competing for cockpit space and pilot attention. As a result, NASA conducted research on displays that could process the raw aircraft system and flight data into an integrated, easily understood picture of the flight situation, culminating in a series of flights demonstrating a full glass cockpit system.

The glass cockpit has become standard equipment in airliners, business jets, and military aircraft, and was even fitted into NASA's Space Shuttle orbiters Atlantis, Columbia, Discovery, and Endeavour, and the current Russian Soyuz TMA model spacecraft that was launched in 2002. By the end of the century glass cockpits began appearing in general aviation aircraft as well. By 2005, even basic trainers like the Piper Cherokee and Cessna 172 were shipping with glass cockpits as options (which nearly all customers chose), and many modern aircraft such as the Diamond Aircraft twin-engine travel and training aircraft DA42, and Cirrus Design SR20 and SR22 are available with glass cockpit only.

As aircraft operation becomes more dependent on glass cockpit systems, flight crews must be trained to deal with possible failures. In one glass-cockpit aircraft, the Airbus A320, fifty incidents of glass-cockpit blackout have occurred. On 25 January 2008 United Airlines Flight 731 experienced a serious glass-cockpit blackout, losing half of the ECAM displays as well as all radios, transponders, TCAS, and attitude indicators. Partially due to good weather and daylight conditions, the pilots were able to land successfully at Newark Airport without radio contact. Airbus has offered an optional fix, which the US NTSB has suggested to the US FAA as mandatory, but the FAA has yet to make it a requirement. A preliminary NTSB factsheet is available.