Precision Approaches

INSTRUMENT FLIGHT RULES WORKBOOK

CHAPTER THREE

302. INSTRUMENT APPROACH PROCEDURES

An instrument approach procedure is defined as a series of predetermined maneuvers for the

orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial

approach to a landing or to a point from which a landing may be made visually. A pilot must

execute an instrument approach at his destination whenever the weather will not permit a descent

from the airway and an approach for landing under VFR weather conditions. If the weather will

permit a VFR approach, a pilot on an IFR flight plan has the option of executing a standard

instrument approach or canceling his IFR clearance, proceeding VFR to the destination and

executing a VFR approach and landing.

303. PRECISION APPROACHES

Instrument approaches can be divided into two main types: precision and nonprecision. A

precision approach provides a pilot with both course and glideslope information, while a

nonprecision approach provides course information only. This glideslope and course

information may be provided by on-board instrumentation (Instrument Landing System, or ILS)

or by ground control personnel via two-way radio communications (Precision Approach Radar,

or PAR). PAR and ILS approaches are the two most commonly used precision approaches in

military aviation. The PAR approach is one of the two types of Ground Controlled Approaches

(GCA). The other type of GCA, the Airport Surveillance Radar (ASR) approach, will be

explained in the nonprecision approach section.

304. PAR APPROACH

Precision Approach Radar (PAR) equipment operated by FAA or military personnel detects and

displays azimuth (course), elevation, and range information of aircraft on final approach course

to a runway.

A PAR approach is one in which a controller provides highly accurate navigational guidance in

azimuth and elevation to a pilot. Pilots are given headings to fly to direct them to and keep their

aircraft aligned with the extended centerline of the runway. They are told to anticipate glidepath

interception approximately 10 to 30 seconds before it occurs and when to start descent.

If the aircraft is observed to deviate above or below the glidepath, the pilot is given the relative

amount of deviation by use of terms "slightly" or "well" and is expected to adjust his rate of

descent to return to the glidepath. Trend information is also issued with respect to the elevation

of the aircraft and may be modified by the terms "rapidly" and "slowly"; i.e.," well above

glidepath, coming down rapidly." Range from touchdown is given at least once each mile.

To execute a PAR approach, an aircraft does not require any special navigation equipment. The

aircraft must have an operating two-way radio with constant communication with the ground

controller. Course and glidepath information is received verbally from a ground controller who

is using radar to track the aircraft, and to direct it to maintain the desired course and glidepath. A

pilot can execute a PAR approach without a directional gyro (RMI). Since an aircraft is being

tracked by radar during a PAR approach, the ground controller can tell the pilot when to start and

INSTRUMENT APPROACH PROCEDURES 3-3