Radiocommunications

The key to this section is common sense and good airmanship (as with so many other parts of flying!).

CAR 602.136 Continuous Listening Watch

• maintain listening watch on appropriate frequency
• establish communication with appropriate ATC, FSS, etc. when required

CAR 602.137 Two-way Radio communication Failure in IFR Flight

• in controlled airspace:
• maintain listening watch on appropriate frequency
• squawk 7600
• attempt to contact other ATS facilities or aircraft to relay info
• if unable to make contact, comply with procedures in CAP / CFS (unless other procedures were given by ATC)

Reference also AIM RAC 6.3.2:

• if VMC, or if VMC is encountered, remain VFR and land as soon as practicable (not the same as 'as soon as possible' - use good judgement)
• if IMC:
• Route:
• route last assigned and acknowledged
• if being vectored, go directly to fix/route/airway specified in clearance
• if no assigned route, use advised/expected
• if no advised/expected, use what has filed on flight plan
• Altitude: use highest of:
• altitude last assigned and acknowledged
• minimum IFR altitude
• expected in a further clearance
• Descent and approach: commence descent at most recent time of:
• calculated ETA
• ETA last notified and acknowledged
• EAT last received and acknowledged
• if assigned a hold, commence approach at EAT or EFC
• if cleared for a STAR, proceed to FAF via
• published routing
• from radar vectors direct fix for straight-in or full procedure
• CLOSED RNAV STAR as published for straight-in
• OPEN RNAV STAR as published to DTW and then turn to FACF to intercept for straight-in

Reference AIM COM 5.15: As a last resort, PIC may attempt to contact ATS using conventional cellphone or satellite phone.

CAR 602.138 Two-way Radio communication Failure in VFR Flight

• in class B, C or D:
• leave airspace (by landing or else shortest route)
• squawk 7600
• inform ATC ASAP of actions taken

Reference also AIM RAC 4.4.8: if you are outside of class B, C, D, you may enter and land if there is no nearby suitable aerodrome available.  See NORDO arrival procedures in AIM RAC 4.4.5.

Air Traffic Surveillance

Reference AIM COM 7.0

Recall: RADAR = RAdio Detection and Ranging (i.e. what's out there, which direction, and how far away?)

Primary Returns

• computes target positions by determining range and azimuth of reflected radio frequency energy
• passive - does not rely on info from aircraft
• uses:
• TSR (terminal surveillance radar) - short range (80 NM) to complement SSR
• PAR (Precision Approach Radar) - approach aid
• ASDE (Airport Surface Detection Equipment) - high def for aircraft and vehicles on manoeuvring areas
• Weather Radar - monitor hazardous weather conditions

Secondary Returns

• determines aircraft range by measuring the interval between transmitting an interrogation to and receiving a reply from an airborne transponder
• uses:
• enroute control - long range (200 NM)
• terminal control - in conjunction with PSR

ADS-B (Automatic Dependent Surveillance - Broadcast)

• uses aircraft avionics, satellites and/or ground infrastructure to relay a range of aircraft parameters to ATC
• automatic (no external stimulus required) but dependent (relies on aircraft avionics)

Traffic Alert and Collision Avoidance System (TCAS)

Reference AIM RAC 12.16

TCAS uses transponder interrogation and return signals to determine if aircraft around you pose a threat.  In order to detect these aircraft, they must be equipped with an operating Mode A, C, or S transponder.  Note: Mode A transponders will provide range and bearing only - no altitude info.

TCAS I provides TAs only.  
TCAS II provides TAs and RAs.

Some notes:

• Traffic Advisories (TAs) and Resolution Advisories (RAs) are only provided in the vertical plane (azimuth information is not reliably accurate)
• pilots should only alter their flight in the event of a RA (not a TA).  
• notify ATC ASAP of any deviation from your clearance.  Also notify them when you are clear of the conflict and returning to the cleared altitude
• See also CAR 602.31 (3) and (4) Compliance with ATC instructions and clearances

AIM RAC 12.16.6 (a) "Although TCAS will never be a complete substitute for a good lookout, good situational awareness and proper radio procedures, it has been proven to be a valuable tool in providing information on potential collision hazards."

Inertial Navigation Systems (INS)

Basic Principle: measures acceleration against time to determine speed and direction

How: uses accelerometers, in a gimbal assembly, to sense all vertical and horizontal accelerations to provide position and steering information.

Information Provided:

• steering information to autopilot
• aircraft attitude information for flight instruments
• antenna stabilization for airborne weather radar
• horizontal navigation data

GPS Approaches

Recall the basic operation of GPS: it triangulates your position by measuring distances from satellites by precise timing of radio signals.  4 satellites are required to obtain a 3D position fix. 

Reference AIM COM 3.14

GPS approaches are generally more efficient because they allow pilots to bypass procedure turns and proceed directly to the FAF.   GPS approaches must be retrieved from a current avionics database.  Pilot-generated waypoints are not approved for approach procedures.  There are two types of GPS approaches: stand-alone and overlay.

Stand-Alone

• approach design is usually based on a 'T' pattern 
• charted as "RNAV (GPS) RWY XX"

Overlay

• the underlying navaids do not have to be monitored
• you can use the GPS when the traditional navaid is out of service

There is always the requirement for a RAIM check (for +/- 15 minutes of the ETA) Without it, you have no assurance of the accuracy of the GPS position!

If you want to take credit for a GPS approach at an alternate aerodrome (AIM COM 3.14.12):

• there must be a usable approach at the planned destination which is served by a functioning traditional aid
• the published LNAV minima are the lowest landing limits for which credit may be taken when determining alternate weather minima requirements (not LNAV/VNAV or LPV)
• approach-level RAIM must be available at the ETA for the alternate
• periodically during the flight, and at least once before the mid-point of the flight to the destination, verify that approach-level RAIM is expected to be available at the planned alternate at the ETA

Note: There are GPS and WAAS NOTAM files which can advise of outages / failures

Instrument Landing System (ILS)

Reference AIM COM 3.12

Localizer

• valid and reliable signal coverage 35 degrees on either side of front course centre line up to 10 NM from transmitter
• 10 degrees up to 18 NM from transmitter for front and back courses
• 3-letter identifier
• starts with 'I' if aligned within 3 degrees of runway heading
• starts with 'X' if more than 3 degrees
• CDI needle deflection is 2.5 degrees from centre to full-scale

Glideslope

• beam depth is 1.4 degrees (0.7 above and below)
• standard glidepath is 3 degrees

Backcourse - Localizer only

• beware of reverse sensing!
• with an HSI, the track bar must be selected to the outbound course on localizer back course approaches in order to obtain positive track bar sensing

VHF Omnidirectional Range (VOR)

How does it work?

• it depends upon a phase difference between two signals transmitted simultaneously from a ground station
• position sensitive, NOT azimuth (i.e. no matter what direction you are facing, your instruments will give you the same VOR information about your position)
• line of sight: reception distance = 1.23 x sqrt(altitude above station)

Components:

• Omni Bearing Selector (OBS) >> select radials "FROM top, TO bottom"
• Course Deviation Indicator (CDI needle) >> centre to full scale is 10 degrees
• TO / FROM indicator >> directional ambiguity when crossing a radial 90 degrees from what is set on OBS

Tolerances:

• airway radials maintained by TC within +/- 3 degrees
• VOR checkpoint +/- 4 degrees
• dual VOR check +/- 4 degrees on ground or in air
• visual check over landmark +/- 6 degrees

To calculate distance (NM) from station:

• (groundspeed x time in minutes) / degrees of bearing change

Distance Measuring Equipment (DME)

Operating Principle: the measurement of the time between the transmission of an aircraft interrogating signal and the receipt of a matched pulse reply signal from a ground station (the 2 signals having different frequencies).

DME operates in the UHF range, but can be collocated with a VOR or ILS, or occasionally NDB. Distance information can also be obtained from TACAN stations by selecting the paired VOR frequency.

DME measures slant range, not distance along the ground. Therefore, the greatest error occurs when flying high and close to the station.

Tolerance at a VOR checkpoint: +/- 0.5 NM

Radio Theory

Radio... what FGU calls the 'modern magic genie' :)

Some basic definitions:

• wavelength: linear measurement of a wave in meters
• cycle: peak to peak vibration period measured in seconds
• frequency: number of cycles per second measured in hertz

Wavelength remains constant, but the amplitude (strength) decreases with distance from the transmitting station.

Frequency Bands:

• Low and Medium Frequency (LF / MF): NDBs
• High Frequency (HF): long range communication
• Very High Frequency (VHF): communication, VOR, ILS
• Ultra High Frequency (UHF): DME, glideslope of ILS

Characteristics:

• LF/MF/HF
• ground waves: follow the surface of the earth; can bend and be attenuated (higher frequencies = more attenuation = less reception distance)
• sky waves: travel up into the atmosphere and are reflected back to earth from the ionosphere
• skip distance: the distance between the transmitting antenna and the point where the skywave first returns to the surface of the earth
• skip zone: the space between the end of ground wave coverage and the point at which the first sky wave is returned to earth
• VHF
• line of sight

Comm and nav systems will get their own separate posts soon - stay tuned!