SAMRA/SARON Radio Communications and Aids to Navigation Questions

For a radio wave, wavelength and frequency are related such that

• wavelength and frequency are entirely unrelated properties of a radio wave, regardless of the medium or propagation speed involved.
• wavelength and frequency are inversely related -- as frequency increases, wavelength decreases, for a constant propagation speed.
• wavelength depends only on the transmitting antenna's length, with no relationship to frequency at all.
• wavelength and frequency are directly proportional -- as frequency increases, wavelength also increases.

Explanation: Since a radio wave's propagation speed (the speed of light) is effectively constant, wavelength equals that speed divided by frequency -- so higher frequencies always correspond to shorter wavelengths, and lower frequencies to longer wavelengths, across every frequency band.

TP 690 Section 10 - Radio, Wave Length and Frequency

A PAPI (Precision Approach Path Indicator) uses a row of lights to show the pilot

• the distance remaining to the runway threshold, in nautical miles.
• the exact runway heading, independent of the aircraft's position on the approach.
• whether the aircraft is above, on, or below the designed visual glidepath, through the combination of red and white lights observed.
• the current wind direction and speed at the aerodrome.

Explanation: Each light unit in a PAPI array shows red or white depending on the aircraft's angle relative to that unit's calibrated split; the combination the pilot sees across the row of lights (for example, more white lights than red indicating high, or more red than white indicating low) gives a simple, purely visual indication of position relative to the intended glidepath, with no separate distance or wind information provided.

TP 690 Section 10 - Approach Aids, VASIS/PAPI

Coastal refraction, an NDB/ADF error, occurs because

• the NDB signal bends as it crosses a coastline, travelling at different speeds over land and water, distorting the indicated bearing at an oblique crossing angle.
• coastal refraction affects only VOR signals, since NDB signals are entirely unaffected by any change from land to water beneath their path, unlike VHF-band equipment.
• NDB signals cannot cross a coastline at all, so any bearing indication received while over water must always be discarded as entirely unreliable and unusable.
• the NDB ground station itself must be relocated inland whenever it is found to be affected by coastal refraction, eliminating the error at its source entirely.

Explanation: An NDB's radio wave propagates at a slightly different effective speed over land than over water, and when the signal's path crosses a coastline at other than a right angle, that speed difference bends (refracts) the wavefront -- distorting the ADF's indicated bearing. The error is most pronounced for a shallow (oblique) crossing angle and is one of several well-recognized NDB/ADF error sources alongside night effect and mountain effect.

TP 690 Section 10 - Radio Communications and Aids to Navigation, NDB/ADF

Standard aviation VHF voice communication generally operates as a simplex (rather than duplex) system, meaning

• the aircraft transmits on one frequency while continuously receiving on an entirely different, independent frequency at the same time, by definition.
• only one party (either the pilot or the controller) can transmit on a given frequency at a time, with simultaneous transmissions from both sides resulting in a garbled or blocked signal.
• the terms 'simplex' and 'duplex' describe signal encoding methods only, with no bearing on whether simultaneous two-way transmission is possible, a characterization inconsistent with how the terms are actually used to describe channel capability.
• both the pilot and the controller can transmit and receive simultaneously on the same frequency without any risk of one transmission blocking or interfering with the other.

Explanation: A simplex system shares a single frequency for both directions of communication, meaning only one party can be transmitting (and being clearly heard) at a time -- if both the pilot and the controller key their microphones simultaneously, the resulting transmissions can block or garble each other, which is exactly why standard radio discipline (listening before transmitting, brief and clear exchanges) matters; this is distinct from a duplex system (which uses separate frequencies for each direction, allowing simultaneous two-way conversation) and isn't merely an encoding-method distinction.

TP 690 Section 10 - Radio Communications and Aids to Navigation

When an aircraft is unable to establish direct radio contact with ATC or a flight service station, a common technique is to

• wait silently with no further action, since no method exists for restoring or working around a lost direct communication link.
• abandon the flight and return to the departure aerodrome immediately, with no alternative communication option ever considered appropriate.
• request that another aircraft, able to communicate with both parties, relay messages between the aircraft and the ground station.
• immediately declare an emergency regardless of the actual severity of the communication difficulty, treating any radio contact failure as automatically requiring a distress call.

Explanation: A relay through another aircraft -- one able to hear both the aircraft experiencing the communication difficulty and the ground station -- is a well-established, practical technique for getting a message through when direct contact isn't possible, letting the flight continue to communicate effectively without necessarily declaring an emergency (which is reserved for situations that actually meet the distress or urgency threshold) or abandoning the flight outright; it's a genuine, usable workaround rather than a situation with no available response.

TP 690 Section 10 - Radio Communications and Aids to Navigation

A Ground-Based Augmentation System (GBAS), providing a GNSS Landing System (GLS) precision approach service at some aerodromes, differs from a Satellite-Based Augmentation System (SBAS) in that GBAS

• relies entirely on ground-based primary and secondary surveillance radar returns rather than on any satellite signal whatsoever, making it a wholly separate ground-based surveillance system unrelated to GNSS augmentation or satellite navigation in any respect.
• is simply another name for SBAS, with the two terms describing an identical architecture and coverage area.
• provides no vertical guidance whatsoever, unlike SBAS, which is defined as providing vertical guidance exclusively.
• uses correction and integrity data broadcast from a local ground station covering a single aerodrome (or a small area around it), rather than correction data broadcast from a geostationary satellite covering a wide region.

Explanation: GBAS provides GNSS correction and integrity data from a ground station local to a specific aerodrome (covering that aerodrome and its immediate approach area), supporting a GLS precision approach there, whereas SBAS (such as a wide-area system broadcasting corrections via geostationary satellite) covers a much larger region and supports GNSS approaches more broadly across that coverage area -- both augment basic GNSS, but at very different scales and via different delivery mechanisms.

TP 690 -- Radio Communications and Aids to Navigation: GNSS

A Pilot Report (PIREP), relayed by radio to ATC or a Flight Service Station, is intended primarily to

• provide other pilots and forecasters with timely, first-hand, in-flight observations -- such as turbulence, icing, cloud tops, or other significant weather actually encountered -- that may not yet be reflected in official forecasts or reports.
• report only mechanical or maintenance issues with the aircraft, with no relevance to weather conditions.
• formally request a specific altitude or route change from ATC, functioning as a type of clearance request rather than a weather observation.
• replace the need for a pilot to file a flight plan before departure, a claim with no basis in the regulations, since a PIREP is an in-flight report of observed conditions and has no bearing whatsoever on the separate requirement to file a flight plan before a flight departs.

Explanation: A PIREP is a first-hand, in-flight observation -- of conditions such as turbulence, icing, cloud tops, visibility, or other significant weather -- relayed by radio to ATC or a Flight Service Station and then disseminated to other pilots and to forecasters, providing real-time information that may not yet be reflected in official forecasts, SIGMETs, or AIRMETs and that can materially improve other crews' situational awareness and decision-making.

TP 690 -- Radio Communications and Aids to Navigation: Flight Information Services

Aviation HF voice communication is generally transmitted using single-sideband (SSB) modulation rather than conventional double-sideband AM primarily because SSB

• provides significantly greater range than any VHF communication system regardless of frequency selection, which overlooks the technical or procedural considerations that actually govern this equipment
• makes more efficient use of the limited HF spectrum and transmitter power by not transmitting a carrier or the redundant second sideband
• automatically encrypts the voice signal for security purposes, which overlooks the technical or procedural considerations that actually govern this equipment
• requires no antenna coupler or tuning unit, unlike AM, which overlooks the technical or procedural considerations that actually govern this equipment, regardless of the specific installation

Explanation: SSB transmits only one sideband and suppresses the carrier and the other sideband, concentrating available transmitter power into the information-carrying portion of the signal and using less spectrum than conventional double-sideband AM, which is valuable given the limited and congested HF band.

TP 690 -- Radio Communications and Aids to Navigation: HF single-sideband modulation