Aviation Speak

Hertz is a measurement of frequency based on the number of cycles per second of an electromagnetic wave. Typically, radio frequencies are measured in kilohertz, abbreviated to kHz and equivalent to 1,000 cycles per second, or megahertz, abbreviated to MHz and equivalent to 1 million cycles per second. In aviation you are most likely to deal with MHz, specifically in the VHF or very high frequency range.

VHF is designated as the frequency band between 30 MHz and 300 MHz. Within this band, frequencies between 108 and 118 MHz are used for certain radio navigation aids such as VORs (very high frequency omnidirectional range stations); those between 118 MHz and 136 MHz are used for civil aviation air-to-ground and ground-to-air voice communications.

UHF or ultrahigh frequency is the band of frequencies that falls between 300 MHz and 3,000 MHz. It is used for military air-to-ground and ground-to-air voice communications. Although 300 MHz is technically the start of this band range, the military sometimes uses frequencies as low as 225 MHz, which it still refers to as UHF.

High frequency or HF is something U.S. pilots are unlikely to encounter, although this band of frequencies between 3 MHz and 30 MHz is some- times used for air-to-ground voice communication in other parts of the world.

Glideslope/Glidepath

Many pilots use the terms glideslope and glidepath interchangeably. Actually they are quite different: A glideslope is anything that provides vertical guidance for aircraft during approach and landing; a glidepath is the vertical descent profile used for the approach.

There are several ways to receive glideslope information on which to base your glidepath. The glideslope indicators most familiar to students are visual, ground-based aids, including visual approach slope indicators (VASI) and precision approach path indicators (PAPI). Both provide vertical guidance for a VFR approach or for the visual portion of an instrument approach.

Other sources of glideslope information are used mainly by instrument pilots. Instrument landing systems (ILS) and microwave landing systems (MLS) emit radio signals which instruments inside the airplane translate into a visual indication on the instrument's face. Precision approach radar (PAR) also provides glideslope information. In that case, an air traffic controller tells the pilot his aircraft's elevation relative to the proper glidepath. When making a PAR approach, the pilot follows the controller's verbal instructions and does not have a visual glideslope reference.

The glidepath is your aircraft's vertical path through the air as you descend to land. The glidepath you use may be steep or shallow depending on terrain clearance and obstacles, the use of flaps, and airspeed.