holding pattern
A holding pattern (Engl. Holding pattern ) is a maneuver in aviation to a plane above a fixed point, the fix Holding on further releases to keep you waiting. It is mostly flown in the vicinity of controlled airports on the Standard Terminal Arrival Route in order to stagger incoming traffic if necessary. Reasons for flying a holding pattern are excessive traffic, blocked runways (another aircraft during take-off / landing, snow removal) or bad weather conditions. A holding loop consists of two semicircles and a straight flight in between. Are in a queue a plurality of aircraft held one above the other, so it is also called a holding stack (dt. Stacking ).
Planning a holding by the pilot
A holding must be flown properly for safety reasons . For this, it is necessary that the pilot remains within the prescribed limits both vertically and laterally . In the case of an aircraft or helicopter that is simply equipped for instrument flight , many of these limits have to be determined by calculating them yourself or reading them from instrument flight charts before entering the aircraft . These limits and values include:
- the entry procedure (Special Direct, Direct, Tear Drop or Parallel)
- the MHA (Minimum Holding Altitude) minimum holding height
- the maximum speed depending on turbulence and holding height
- the planned height at which to wait
- the type of holding (right hand = standard holding or left hand = non standard holding)
- the place of the start of the timekeeping for the outbound leg (example: "abeam DLE VOR")
- the duration of the outbound leg in seconds
- the WCA (Wind Correction Angle) windward angle
- the resulting outbound heading (departure heading)
- the so-called gate, a radio stand line with an angle difference of 30 ° (or less for holdings above FL140) to the outbound course.
- the inbound heading (inbound course with activation of the calculated WCA)
In a cockpit with multiple crews, within the framework of the MCC (Multi Crew Coordination), the non-flying pilot (PNF) briefs the PF (pilot flying) on the collection of the limits and values, that is, briefly communicates them.
execution
The holding pattern that is common in instrument flight always begins above the holding fix , an entry point defined by a radio beacon such as VOR or NDB or by means of GPS coordinates. In addition, a holding pattern is defined by a minimum height (MHA - Minimum Holding Altitude) and a course with which this fix must be approached again with each lap (IC - Inbound Course). Depending on the angle which the heading of the incoming aircraft forms with this inbound course, there are four different entry procedures: Direct, Special Direct, Parallel and Offset / Teardrop.
- Standard entry procedures in holding patterns
Direct entry (Sector 3)
Parallel entry (Sector 1)
Offset / teardrop entry (Sector 2)
Finally, according to ICAO PANS-OPS (Procedures for Air Navigation Services - Aircraft Operations), maximum speeds depending on altitude / flight level and any turbulence that may be present are prescribed, which must be observed in the waiting loop. A standard holding is flown through in two right turns. If the holding pattern has to be flown with two left turns in accordance with the navigation documents or on the instructions of the air traffic controller , it is a non-standard holding. In some cases, for noise or other reasons, maximum speeds are still defined for the holding in deviation from ICAO PANS-OPS.
A standard waiting loop at or below FL 140 takes four minutes according to PANS-OPS: one minute for the curve to the outbound leg, one minute on this section, one minute for the curve towards the inbound leg, and again one minute on this section until the fix is achieved again.
A standard queue above FL 140 takes five minutes according to PANS-OPS: one minute for the curve to the outbound leg, 1.5 minutes on this section, one minute for the curve towards the inbound leg, and again one and a half minutes on this section, to the fix is achieved again.
In practice, this can only be achieved when there is no wind at all, which is why the pilot must calculate angle and time corrections for the wind offset before entering, unless aids such as a flight management system are available to him.
Consequences and economic costs
- Emissions of pollutants and CO 2 through combustion ,
- Aircraft noise ,
- longer flight times for passengers and staff,
- Airline costs as well
- external costs .
literature
- ICAO, PANS-OPS, (Doc 8168), Procedures for Air Navigation Services - Aircraft Operations, Volume I - Flight Procedures, pages I-6 (i) ff., As of November 23, 2006, available from http: // www .icao.int
