content_image/597506.jpg
stated in 14 CFR part 91, section 91.3 should an immediate deviation from the assigned clearance be necessary and time does not permit approval by ATC. 

Generally, when weather disrupts the flow of air traffic, greater workload demands are placed on the controller. Requests for deviations from course and other services should be made as far in advance as possible to better assure the controller’s ability to approve these requests promptly. When requesting approval to detour around weather activity, include the following information to facilitate the request: 

1. The proposed point where detour commences; 

2. The proposed route and extent of detour (direction and distance); 

3. The point where original route will be resumed; 

4. Flight conditions (instrument meteorological conditions (IMC) or visual meteorological conditions (VMC); 

5. Whether the aircraft is equipped with functioning airborne radar; and 

6. Any further deviation that may become necessary. 

To a large degree, the assistance that might be rendered by ATC depends upon the weather information available to controllers. Due to the extremely transitory nature of hazardous weather, the controller’s displayed precipitation information may be of limited value. 

Obtaining IFR clearance or approval to circumnavigate hazardous weather can often be accommodated more readily in the en route areas away from terminals because there is usually less congestion and, therefore, greater freedom of action. In terminal areas, the problem is more acute because of traffic density, ATC coordination requirements, complex departure and arrival routes, and adjacent airports. As a consequence, controllers are less likely to be able to accommodate all requests for weather detours in a terminal area. Nevertheless, pilots should not hesitate to advise controllers of any observed hazardous weather and should specifically advise controllers if they desire circumnavigation of observed weather. 

Pilot reports (PIREPs) of flight conditions help define the nature and extent of weather conditions in a particular area. These reports are disseminated by radio and electronic means to other pilots. Provide PIREP information to ATC regarding pertinent flight conditions, such as: 

1. Turbulence; 

2. Visibility; 

3. Cloud tops and bases; and 

4. The presence of hazards such as ice, hail, and lightning. 

## Approach Control Facility 

An approach control facility is a terminal ATC facility that provides approach control service in the terminal area. Services are provided for arriving and departing VFR and IFR aircraft and, on occasion, en route aircraft. In addition, for airports with parallel runways with ILS or LDA approaches, the approach control facility provides monitoring of the approaches. 

## Approach Control Advances 

## Precision Runway Monitor (PRM) 

Over the past few years, a new technology has been installed at airports that permits a decreased separation distance between parallel runways. The system is called a Precision Runway Monitor (PRM) and is comprised of high-update radar, high-resolution ATC displays, and PRM-certified controllers. [Figure 2-14] 

<img src='content_image/597506.jpg'>

## PRM Radar 

The PRM uses a Monopulse Secondary Surveillance Radar (MSSR) that employs electronically-scanned antennas. Because the PRM has no scan rate restrictions, it is capable of providing a faster update rate (up to 1.0 second) over conventional systems, thereby providing better target presentation in terms of accuracy, resolution, and track prediction. The system is designed to search, track, process, and display SSR-equipped aircraft within airspace of over 30 miles in range and over 15,000 feet in elevation. Visual and audible alerts are generated to warn controllers to take corrective actions. 

