Instrument Flight Rules - Procedures

Procedures

Specific procedures allow IFR aircraft to transition safely through every stage of flight. These procedures specify how an IFR pilot should respond, even in the event of a complete radio failure, and loss of communications with ATC, including the expected aircraft course and altitude.

Departures are described in an IFR clearance issued by ATC prior to takeoff. The departure clearance may contain an assigned heading, one or more waypoints, and an initial altitude to fly. The clearance can also specify a departure procedure (DP), or standard instrument departure (SID) that should be followed unless "NO DP" is specified in the notes section of the filed flight plan.

Here is an example of an IFR clearance, for a Cessna aircraft traveling from Palo Alto airport (KPAO) to Stockton airport (KSCK).

Detailed explanation:

"Cessna 21756"

Verifies that only this specific aircraft is cleared.

"cleared to Stockton Airport"

Clearance Limit: the farthest destination the aircraft is allowed to go under IFR (in most cases it is the destination airport).

"via turn right heading zero-six-zero within one mile of the airport."

The pilot is expected to execute the right turn to 060° without further ATC prompting within one mile of the departure airport.

"Radar Vectors San Jose"

The departure controller will provide directional guidance to the San Jose VOR.

"Then as filed."

After arriving at the San Jose VOR, the pilot will likely resume navigation without ATC prompts along the airways and intersections that were filed in their flight plan.

"Maintain 3,000 ..."

After takeoff, climb to an altitude of 3000 feet above sea level.

"... expect 5,000 five minutes after departure."

Your final altitude assignment is probably going to be 5000 feet above sea level. However, you must follow actual ATC altitude assignments throughout the flight. This portion of the clearance provides a backup if communications are lost, allowing you to proceed to climb and maintain 5000 feet.

"Departure frequency is 121.3, ..."

Contact with NORCAL Departure on the specified communication frequency, after Palo Alto Tower tells you to switch.

"... squawk 4263."

Program your transponder to 4263 so that ATC can positively identify you on radar.

En route flight is described by IFR charts showing navigation aids, fixes, and standard routes called airways. Aircraft with appropriate navigational equipment such as GPS, are also often cleared for a direct-to routing, where only the destination, or a few navigational waypoints are used to describe the route that the flight will follow. ATC will assign altitudes in its initial clearance or amendments thereto, and navigational charts indicate minimum safe altitudes for airways.

The approach portion of an IFR flight may begin with a standard terminal arrival route (STAR), describing common routes to fly to arrive at an initial approach fix (IAF) from which an instrument approach commences. Instrument approaches are categorized as precision and non-precision. A precision approach is one in which both vertical and lateral guidance are given, such as in an ILS or WAAS (LPV) approach. A non-precision approach is one in which only lateral guidance is given, such as a VOR, NDB, or Localizer approach. Due to the fact that they provide vertical guidance, the weather criteria required for precision approaches is less restrictive than it is for non-precision approaches.

In either case, an instrument approach will terminate either in a) the pilot acquiring sufficient visual reference to carry out a normal landing, or in b) a missed approach if the required visual reference is not encountered in time. The point at which the crew of an aircraft has to make a decision to either proceed visually, or "miss" the approach is called decision altitude (DA) or decision height (DH) for precision approaches, and missed approach point (MAP) for non-precision approaches. During precision approaches the altitude of the aircraft is determined by the navigational instruments. For non-precision approaches the crew will descend to specific altitudes during the approach procedure, with the final altitude termed the minimum descent altitude (MDA). Documents describing the approach procedure are frequently called approach plates in reference to single-page sheet that it is printed on.

Some commercial aircraft are equipped with automatic landing systems that allow the aircraft to land without transitioning from instruments to visual conditions for a normal landing. Such autoland operations require specialized equipment, procedures and training, and involve the aircraft, airport, and the crew. Autoland is the only way some major airports such as Paris-Charles de Gaulle Airport remain operational every day of the year. Some modern aircraft are equipped with enhanced vision systems based on infrared sensors, that provide a day-like visual environment and allow operations in conditions and at airports that would otherwise not be suitable for a landing. Commercial aircraft also frequently use such equipment for takeoffs when takeoff minima are not met.

An instrument approach that terminates in a missed approach will continue using missed approach procedure information shown on the approach plate. Typically it describes a transition to a nearby navigational fix, from which the pilot can elect to either attempt the approach again or proceed to an alternate airport. In practice (esp. when flying in radar environment) the missed portion of an approach is rarely flown as published. Instead, ATC will usually assign headings and altitudes that will assimilate the aircraft into the arriving traffic for a repeated approach attempt.