Instrument flight

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Instrument flight in poor visibility, view from a Cessna Citation C525

Under instrument flight (colloquially Blindflug ) refers to the control of aircraft in which the flight position without reference to external visually perceptible indication with the aid of flight instruments such as navigation instruments and flight control devices is held on board (exception - the circling and visual approach are instrument approaches under Visual conditions are carried out). Air traffic controllers on the ground provide support with flight operations and flight navigation . An instrument flight must be carried out in accordance with instrument flight rules ( IFR ) and in almost all cases coordinated with air traffic control . In contrast, there is visual flight .


In instrument flight, the flight attitude is maintained exclusively using instruments in the aircraft and navigation is carried out with aids that allow the intended flight path to be maintained regardless of the outward view. This means that flying in clouds and with restricted visibility is also possible. Instrument flight makes air traffic largely independent of the weather and is a prerequisite for adhering to flight plans. Weather conditions that only permit instrument flight are called Instrument Meteorological Conditions (IMC). The flight principles to be observed in instrument flight are summarized in the instrument flight rules (IFR).

For commercial air traffic in Europe, the Operating Instructions Part A (Operations Manual Part A according to EU OPS 1) stipulate the conditions under which visual or instrument flight rules must be flown. The supervisory authority of the respective country must approve the decision of the airline.

Flight plan

A flight that is to be carried out according to instrument flight rules must be made known to air traffic control in good time before departure by submitting a detailed flight plan . (Deadline: between five days at the earliest and one hour before the scheduled departure at the latest).

The flight plan contains navigation-related data such as: estimated departure and arrival times, cruising speed, desired flight route, flight altitude, destination airport and alternative locations.

It also contains information related to the flight and the aircraft such as: aircraft type and number, number of people on board, wake vortex category , maximum flight duration, emergency radio transmitter, emergency equipment and the aircraft color.

A flight according to IFR may be subject to measures to avoid airspace congestion. If the capacity of the airspace or air traffic control is exhausted on the planned route, the flight is assigned a specific time window for take-off (CTOT, Coordinated Takeoff Time), which must be adhered to exactly. These airway slots are allocated by DNM (Directorate Network Management), part of EUROCONTROL . Airport slots are also required for take-offs and landings at "coordinated" airports. In Germany, these are assigned by an airport coordinator authorized by ordinance, and practical monitoring is ensured by the local air traffic control.

Instrument flight rules

In Germany, controlled airspace (airspaces C, D, E) is generally intended for instrument flight . For individual IFR approaches and take-offs, additional approved airfields without air traffic control have been set up Radio Mandatory Zones (RMZ - areas with radio contact obligation). Since December 11, 2014, the Radio Mandatory Zones have replaced the previously existing airspace F in Germany. Defined IFR approach and departure procedures apply for take-off and landing. If a pilot cannot see the runway or the approach lights when approaching the instrument from a specified decision height, he must abort the approach. This amount depends on the equipment / approval of the aircraft and the approval of the cockpit crew. This height is calculated on the basis of the current obstacle situation at the airport and in the approach area by DFS Deutsche Flugsicherung GmbH, which publishes these heights as OCA and OCH in the AIP aviation manual. When using an instrument landing system (ILS), typical heights are between approx. 400  ft and 200 ft above ground for Cat I and up to 100 ft above ground for Cat II . Cat III values ​​(below 100 ft) are not published.

Air traffic control ensures the necessary staggering (compliance with safe distances) between IFR flights with each other through the following measures:

In certain airspaces, even under IFR, the pilot himself is responsible for the separation of other aircraft that operate under visual flight rules.

Flying under IFR conditions is in contrast to flying by visual flight rules (Engl. Visual flight rules , VFR), in which assuming compliance with the minimum visual conditions. To carry out the IFR flight, the pilot needs an instrument flight license and, in the case of German licenses, a general radio communication certificate for the aeronautical radio service (AZF). Entering into instrument meteorological conditions (IMC) without appropriate training quickly leads to a loss of orientation in space and has therefore often been the cause of an aircraft accident .


The statutory minimum equipment for instrument flight for aircraft registered in Germany is set out in the Operating Regulations for Aviation Equipment (LuftBO) and in the Ordinance on Flight Safety Equipment for Aircraft (FSAV). Aircraft that are to be operated in accordance with IFR must have the following minimum equipment:

For the interaction with air traffic control, the navigation and the observance of the approach procedures are additionally required:

For ILS approaches:

  • Display device for joint display of landing course and glide slope (cross pointer instrument)
  • Receiver for radio beacons
  • Glide path receivers
  • Heading receiver

Other countries often have significantly different minimum equipment, for example in the USA (in addition to VFR; see FAR §91.205):

  • for flights above FL240 when VOR equipment is required, DME or RNAV
  • Radio for communication with ATC and navigation equipment that is suitable for the planned flight (difference to Germany: no specific navigation devices are required)
  • Generator with sufficient power
  • adjustable barometric altimeter
  • Gyro horizon ( artificial horizon )
  • Course top
  • Clock with seconds display (analog or digital)

Classic radio navigation is carried out using non-directional radio beacons (NDB) and VHF rotary radio beacons , which allow the course to be determined linearly (i.e. along certain courses). The method of area navigation with the aid of GPS / DGPS is newer , which also enables additional parallel flight routes between the radio beacons. For the landing phase, special transmitters are used as instrument landing systems at the airfields, which provide lateral guidance and a glide path for the approach. The equipment is supplemented by anti-collision systems , weather radar, radar altimeters and the instruments required for visual flights.

See also

Individual evidence

  1. International Civil Aviation Organization (Ed.): Air Traffic Management (Doc 4444) . 16th edition. Montréal 2016.
  2. Federal Ministry of Justice - FSAV § 3
  3. 8.33 kHz program website ( Memento from October 19, 2007 in the Internet Archive ) Retrieved October 24, 2019


Web links