DGCA ATPL Radio Aids flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Wavelength formula

Wavelength in metres equals 300 divided by frequency in MHz. A 120 MHz VHF signal therefore has a wavelength of about 2.5 metres.

Radio horizon

The line-of-sight distance in nautical miles is approximately 1.23 times the square root of antenna height in feet, giving about 200 NM at FL350.

Skywave propagation

HF signals are refracted by the ionosphere and returned to earth, allowing ranges of thousands of nautical miles that vary with time of day and solar activity.

Ground wave

LF and MF signals follow the earth's surface and provide reliable short-range coverage; attenuation increases with frequency and with poor ground conductivity.

VHF airband range

VHF is essentially line-of-sight, so reception range depends on aircraft altitude and terrain, typically about 200 NM at high altitude.

VHF modulation

Civil VHF airband uses amplitude modulation with double sideband, so two simultaneous transmissions produce a heterodyne squeal on the channel.

121.5 MHz

The international aeronautical emergency and distress frequency, used for voice distress and for emergency locator transmitters.

Squelch function

Squelch mutes the receiver output when the received signal falls below a set threshold, suppressing background noise but possibly masking weak transmissions.

HF single sideband

Aeronautical HF voice uses upper single sideband with suppressed carrier, concentrating transmitter power in one sideband for long-range communication.

SELCAL

Selective calling uses coded tones transmitted on the HF or VHF channel to alert a specific aircraft without the crew monitoring continuously.

HF day/night frequency

Higher HF frequencies are used by day and lower frequencies at night because the ionospheric F layer changes height and density.

ADF relative bearing

The ADF indicator shows the angle between the aircraft's magnetic heading and the direction to the NDB; adding heading gives the magnetic bearing to the station.

NDB frequency band

Non-directional beacons transmit in the LF/MF band from 190 to 1750 kHz and are identified by a two- or three-letter Morse code.

Cone of silence

Directly overhead the station the ADF or VOR signal is weak or lost, causing a needle swing or flag; station passage is confirmed by this effect.

VOR frequency band

VOR operates from 108.0 to 117.95 MHz using even tenths of a megahertz; the 108 to 112 MHz portion is shared with ILS localizers.

VOR phase comparison

Conventional VOR compares a rotating variable-phase signal with a fixed reference; the phase difference equals the magnetic bearing from the station.

Doppler VOR

DVOR uses a wide-aperture antenna array with electronic rotation, reducing site and terrain errors and improving accuracy at high elevation angles.

CDI reverse sensing

If the OBS is set to the reciprocal of the actual course, the deviation bar moves opposite to the expected direction, indicating reverse sensing.

DME slant range

DME measures the straight-line distance to the ground transponder; ground range is found from the square root of DME squared minus altitude squared.

DME frequency pairing

DME operates from 960 to 1215 MHz and is paired with a VOR or ILS frequency so that tuning the VOR also tunes the DME.

Localizer frequencies

The ILS localizer transmits from 108.10 to 111.95 MHz on odd tenths, with 90 Hz left and 150 Hz right of the runway centerline.

Glide path frequency

The ILS glide path transmits in the UHF band from 328.6 to 335.4 MHz, with 90 Hz above and 150 Hz below the nominal 3-degree path.

ILS category minima

CAT I requires a 200 ft decision height and 550 m RVR; CAT II 100 ft and 300 m; CAT IIIA 50 ft and 200 m.

Primary radar range

Range equals the speed of light multiplied by the round-trip time divided by two, because the pulse travels to the target and back.

SSR interrogation

Secondary surveillance radar interrogates on 1030 MHz and the transponder replies on 1090 MHz, giving range, identity and pressure altitude.

Weather radar attenuation

Heavy precipitation absorbs and scatters the radar beam, so targets beyond intense cells may be hidden and appear as a shadow.

RAIM

Receiver autonomous integrity monitoring detects and excludes faulty satellites; its availability depends on satellite geometry and must be predicted before flight.

RNP value

The RNP number, such as RNP 0.3, is the lateral containment limit in nautical miles that the navigation system must meet 95 percent of the time.

SBAS augmentation

Space-based augmentation systems such as WAAS and EGNOS broadcast corrections and integrity data, enabling lateral and vertical guidance down to LPV minima.

Radio altimeter principle

The radio altimeter transmits a frequency-modulated continuous wave and measures the delay of the ground reflection, giving height above terrain directly below.

Radio altimeter use

The radio altimeter drives decision-height callouts, autoland flare and ground proximity warnings, and is independent of barometric pressure settings.

TCAS resolution advisory

A TCAS II resolution advisory commands a climb or descent to resolve a conflict; the crew must follow it and notify ATC of the deviation.