Avionics Service

Our dedicated team of experienced avionics technicians will provide you with:

  • The highest standard of avionics service
  • Factory (OEM) approved parts only
  • Comprehensive detail of any repairs or service performed
  • Personalized service

Our many service centre agreements with leading avionics manufacturers ensure that your aircraft equipment is in the hands of professionals trusted throughout the industry. Pacific Avionics & Instrument's technical staff is committed to resolving your avionics problem in a timely and cost-efficient manner and have you "back in the air" as soon as possible.



Airborne Radar Systems

An acronym for RAdio Direction And Ranging.

Airborne RADAR is a complex system of high power X-Band pulses being transmitted out a swept dish or phased array antenna, reflected back from the condensation in the clouds and received by the same swept dish or phased array antenna. The receiver times the received pulses relative to the transmitted pulses and displays a representation of the condensation on the RADAR display.

Monochrome RADARS indicate cloud density using levels of grey. Color RADARS relate cloud density using colors.

Most RADAR systems allow the flight crew to 'point' the antenna down to map the ground allowing the crew to 'see' through the clouds to find ground features.

Some RADAR systems will also overlay mapping information, or display beacons for tracking.

Latest generation RADAR systems will also map wind shear, and the vertical components of the weather and interface weather information onto ARINC 429 data busses for display onto the EFIS system.

Most general aviation RADAR systems employ a two component system comprising a receiver/transmitter/ antenna + panel mounted indicator. Air Transport systems are generally three components; Antenna, Receiver/Transmitter, and panel mounted indicator.

Care and Handling of Radar System

RADAR systems require special handling. The transmitter of most RADAR systems employ a device called a magnetron. This device uses a very large permanent magnet. Some shipping companies class magnetic devices as dangerous goods as the magnet can affect the shipping aircraft's compass systems. Another potential hazard is the proximity of the magnetron to the RADAR indicator. CRT's use a scanned electron beam (or beams for color units). These beams are directed by electromagnets on the yoke of the CRT. If a permanent magnet is held in close proximity of the CRT a magnetic 'hot spot' may be induced into the CRT. This will cause the beams to converge creating a distorted display. If a CRT has been affected it must be de-gaussed with special coil to equalize the charge across the CRT display.

Shipping

Our policy is to maintain a 3' separation between the RADAR indicator, and RADAR transmitter. These units should also be shipped in separate containers



Navigation/Communication

Aircraft Communications

Pilot's communicate with Air Traffic Control on a Two-Way radio in the VHF frequency spectrum, 118.000 to 135.975 Mhz. In North America the 'channels' are separated by 25 Khz providing 760 communication 'channels'.

Usually aircraft have at least 2 comm radios. Usually the radios are identical to provide the pilot with commonality in operation. The radio is standard simplex operation using the same frequency for both receiving and transmitting.

Most aircraft and helicopters have an intercom system allowing the pilot and copilot to communicate with each other. Some intercoms are hands free with a voice activated intercom, others require the crew members to 'push-to-talk'. The intercom is a critical link in the cabin communication equation. We recommend and install only the best TSO'd intercoms.

Installation Issues

The most variable part of the communication radio installation is the antenna. The antenna is installed in one of the world's harshest environments. The sealing of the antenna to the aircraft skin is critical. Any moisture allowed under the base of the antenna is the first ingredient of corrosion. Corrosion under the antenna first of all goes un-noticed during inspections with obvious structural ramifications, secondly degrades the bonding of the antenna. This bonding is as important as the radiating element. Without a good bond the radiated signal has no reference. Reflected signals are increased reducing the amount of radiated power, and possibly damaging the final stages of the radio transmitter.

Aircraft Navigation

Consisting of:

  • VOR (VHF Omni Range)
  • ILS (Instrument Landing System)
  • ADF (Automatic Direction Finder)
  • GPS (Global Positioning System)
  • LORAN C (Long Range Navigation 'C')

The navigation system on board our aircraft may have one or all of the components listed above. Aircraft operations in IMC will obviously necessitate safer navigation systems.

Our technicians understand that whether IFR or VFR the lives of the flying public depend upon the serviceability of the aircraft navigation system. Our policy is to return the unit under test to the original manufacturer's specifications. We do not take any liberties in design or calibration, or take any short-cuts in calibration procedures. We use only the latest revision of the OEM Component Maintenance Manual, and the recommended, in-calibration, avionics test equipment to service your equipment.

GPS is the latest game in world-wide navigation. We have stepped up to the plate and procured the latest test equipment to support GPS service. With this test equipment we can now test the receiver sensitivity of the GPS receivers. This is unique since the GPS signal levels are below the normal noise floor of the earth's atmosphere. We also have facilities to re-radiate the GPS signals within our shops to test real-time the capabilities of the GPS systems to track all visible SV's (Space Vehicles).



Pulse Equipment

Transponder/DME Commonly referred to as PULSE equipment. Transponders and DMEs are almost always classed in the same category due to their common frequency spectrum, and similarities in signal types. Transponder:

These avionics systems are the airborne component of the ATCRBS (Air Traffic Control Radar Beacon System), and SSR (Secondary Surveillance Radar) system. Transponders are also an integral part of TCAS (Terminal Collision Avoidance Systems). A mode A/C transponder receives interrogations from the ground based radar and replies with either the code selected on the transponder or the encoded altitude. The selected code is an octal code, and is either a standard code for the procedure being flown (VFR=1200 for example) or an ATC assigned code. Some codes are for emergency use; 7700=emergency, 7600=no radio, 7500=hijack. The encoded altitude is derived from either an encoding altimeter, or a dedicated blind encoder. The altitude is encoded as a Gillham Code. The transponder transmitted altitude is always referenced to Standard Day (barometric setting of 29.92 inHg), and is converted by the computer system within the ATC ground based RADAR. The transponder may also be interrogated by a TCAS equipped aircraft flying in relative proximity to provide the TCAS aircraft with the interrogated aircrafts relative position and altitude.

Mode S transponders are capable data linking, and unique aircraft identification coding.

Airborne transponders produce a 100-500 watt pulsed signal at 1090Mhz, and receive replies on 1030Mhz. The latest generation transponders use a solid state transmitter. Older units use a high voltage cavity, which is a style of vacuum tube.

Common Problems:
  • Alignment: The alignment of the receiver/decoder and transmitter are critical for serviceable performance of the transponder. We have two dedicated benches for Transponder and DE service. All transponder transmitters are aligned and tested in accordance with their approved maintenance manuals.
  • Cavity drifting: The cavity transmitter tube is a vacuum tube excited by a high voltage power supply. As the cavity ages its calibration and linearity drifts. We test all cavity based transponders using our line stretcher to test the cavities VSWR characteristics. If it is ‘out of spec’, it needs to be replaced.
  • Code Slipping: Erroneous codes can be caused by either switch problems, or logic problems. ATC will report that the wrong code is being received or that your 1500’ approach reads out 41,000’. Logic troubleshooting can be laborious. We have veteran technicians that are up to the task.
DME:

Distance Measuring Equipment computes distance by measuring the time it takes for a transmitted pulse to go from the aircraft to a ground based receiver, and back to the aircraft. The measured distance is the ‘slant range’, or distance plus altitude hypotenuse. The ground speed is also computed by the DME by averaging the change in distance. Distance is displayed in NM to the station, and either time to/from station or ground speed.

The DME transmitter produces 100–500 watt pulsed signals. The DME is frequency paired to a DME enabled VOR (military designation is a TACAN), or ILS. The channeling of the DME is usually done by the NAV frequency selector. The DME transmits and receives in the 900-1200Mhz band. The equipment manufactured within the past 20 years primarily uses solid state transmitters. Earlier equipment employed a vacuum tube type transmitter.

Common Problems:

  • Low Power: If either the transmitter or receiver is weak the DME will have poor range. With our test equipment and experience we can isolate the problem and effect a serviceable repair.
  • Receiver: Because the frequency of the DME signal is so high, the troubleshooting of the receivers is very difficult. We have dedicated test equipment including signal generators, spectrum analyzers, and digital oscilloscopes to assist our experienced technicians.
  • Transmitters: As with the DME receivers the signals are in the microwave spectrum. The DME transmitters usually use stripline wave guides, and very fast solid state electronics. Troubleshooting transmitters is difficult and alignment usually requires high frequency sweep generators.


Radio Altimeters

The radio altimeter (RAD ALT) system provides the pilot with accurate indication of the aircraft’s height above the terrain, usually in the range of zero to 2500 feet AGL (Above Ground Level). A radio altimeter system consists of a receiver-transmitter, indicator, and transmit and receive antennas. (Some systems employ a single antenna for both the receive and transmit function.) Because the system operates at radar frequencies (C band, 4.3 GHz), radio altimeters are sometimes called radar altimeters. Radio altimeters differ from barometric altimeter systems in that they measure height above terrain, rather than barometric altitude.

Most radio altimeters use an FM modulated system to determine altitude, although some use a more traditional radar pulse system. The receiver-transmitter (RT) outputs a signal to the transmit antenna, which travels to the ground, and is reflected back to the receive antenna. Processing circuits in the RT compare the transmitted and received signals, which differ in timing due to the distance traveled to the ground and back. The indicator in the cockpit displays the calculated height above ground. The indicator commonly has a Decision Height (DH) control, allowing the pilot to set a height above ground at which a visual or audible alert is activated. In addition to the DH alerting capability, most radio altimeters RTs also provide up to six discrete outputs indicating when the descending aircraft passes through pre-set altitudes.

Radio altimeter outputs can interface with other aircraft components and systems (such as autopilot and ground proximity warning systems). Faulty operation of the radio altimeter can affect these interconnected systems resulting in fault conditions, flags and warnings. Proper servicing and calibration of radio altimeters is essential to reliable operation of these aircraft systems. Servicing radio altimeters requires specialized equipment to accurately simulate altitudes and signal strengths on the test bench. Investing in such equipment enables us to test, repair and calibrate a wide range of radio altimeter components.

A properly calibrated radio altimeter indicates zero feet at the moment the aircraft contacts ground. This requires taking into account the height of the antennas above ground (at touchdown), the length and propagation delays of the antenna cables, and the inherent delays in the RT. The sum of all these delay factors is termed the Aircraft Installation Delay (AID). The RT usually employs external strapping to select the correct AID for that particular aircraft installation, using specified antenna cable lengths. Strapping connections and antenna lengths must match the installation requirements of the aircraft, or the altitude will not accurately indicate zero at touchdown. After touchdown, the weight of the aircraft may cause the radio altimeter to read slightly below ground level. (The less common pulse-type systems usually have a zero foot calibration adjustment accessible through the case of the RT.)

An improperly aligned RT can result in spurious altitude outputs above 2500 feet AGL, creating nuisance flags and warnings. Some radio altimeters may produce spurious or inaccurate altitude outputs or flag conditions when the aircraft passes over unusually abrupt terrain changes or unusual surfaces (such as water). Improperly sealed, painted or bonded antennas can also adversely affect radio altimeter outputs and sensitivity. When the radio altimeter system operates unreliably, antenna bonding and cable integrity should be assessed, if the RT and indicator bench test normally. Radio altimeter antennas should only be refinished or repainted to manufacturers’ specifications.



Additional Support

Along with the other avionics products that we support some of the other systems and components that our avionics department specializes in are:

  • Autopilot's
  • Chadwick balancers
  • Emergency locator beacons
  • Emergency aircraft lighting modules
  • Emergency stand-by battery systems
  • Static inverters
  • Annunciator panels
  • Warning system
  • Aircraft strobe light system
  • Aircraft NiCad batteries

With our many years experience and our ability to solve unique problems if you have any needs, at any time, for our services with any of the above please give our service representatives a call or drop us a line.