Low visibility and inclement weather, or Instrument Meteorological Conditions (IMC), limit the visual reference points available to pilots, such as the runway, approach lighting, runway lighting, and hazards such as obstacles, trees, tall buildings, and wind turbines. They also reduce the time available to acquire the runway environment visually. In these conditions, safe operation depends on predefined ATC (Air Traffic Control) procedures that keep aircraft clear of terrain and obstacles.
Normally, procedures are aligned with the runway as a standard method of design, although some approach procedures are offset while still facilitating landing to the intended runway. Departure procedures can also be designed as aligned or offset. ATC procedures are different from instrument flight procedures. ATC uses IFPs in conjunction with pilots by clearing pilots for the approach procedure, for example, while monitoring to ensure the pilot complies with the procedure and, in the event of a communication failure, follows the necessary instructions on the procedure chart.
Instrument Flight Procedure (IFP) design provides that structure. ICAO and CAA materials reflect guidance and regulatory criteria rather than general principles. Instrument Approach Procedures are pre-determined manoeuvres, or flight paths, flown by reference to flight instruments that, within specified margins, safely guide an aircraft from an initial or arrival position to a position where landing can commence, or alternatively to a Decision Altitude (DA), where the missed approach phase is engaged and the aircraft returns to the starting position, holding position, or diversion position.
During the approach to land, the DA is a critical point at which, depending on the pilot’s visibility of the relevant approach lighting and/or runway, the pilot must decide whether to continue the approach and land or, if visibility is insufficient, execute a missed approach procedure, hold, or divert. Before reaching this decision point, visual references become critical to enable the pilot’s decision. Pilots may not descend below the defined DA unless they have the approach lighting and/or runway in sight.
What IFP Design Means
Instrument Flight Procedures (IFP) are published procedures used by pilots flying in accordance with Instrument Flight Rules (IFR), as well as by Air Traffic Controllers. They are strictly calculated paths designed to achieve and maintain an acceptable level of safety, protecting aircraft in flight from obstacles, buildings, trees, and terrain.
Instrument Flight Procedure design establishes standardised routes and minima based on terrain, obstacles, runway configuration, aircraft performance, and available navigation capability. The process includes defining protected airspace, calculating descent profiles, turn limits, and missed approach paths that apply to the procedure. The result is a route that can be flown consistently using onboard instruments while maintaining obstacle clearance. IFP design covers all types of procedures: en-route, arrival, transition in the UK, approach, and departure. For departures, there is a minimum climb gradient and/or minimum climb altitude to be achieved, rather than minima.
These are standard features of ICAO PANS-OPS based procedure design.
The Role Of Visual Aids
Although approaches may be flown on instruments, the final stage of landing still usually depends on acquiring adequate visual references. That is why aerodrome lighting, markings, and other visual aids remain important even in instrument-led environments. For instance, a Clearance to Land Indicator (CLI) provides visual indications to the pilot in support of landing clearance communications received from airport ATC.
A CLI is typically a ground-based light unit positioned so it is clearly visible to pilots on final approach. When activated by ATC, it displays a specific light signal, commonly green, that corresponds to landing clearance. This additional visual signal can help reduce ambiguity if a radio call is missed or unclear.
Visual or non-verbal landing-clearance indicators such as these sit within the wider aerodrome visual environment, alongside approach lighting, PAPIs, runway lighting, and taxiway lighting. These systems define the visual picture presented to the pilot on approach.
Their effectiveness depends on consistency. Visual cues need to work together rather than compete for attention, meaning that lighting intensity, colour, positioning, and function must be coordinated. If an airport’s visual systems are misaligned, pilots may need to prioritise between conflicting cues, which can delay interpretation during a time-critical phase of the flight.
Designing For Different Environments
Procedures are predominantly designed based on terrain and obstacles, airspace, danger, prohibited and restricted areas, environmentally protected areas, nearby towns or villages for noise considerations, ATC and pilot requirements, airport infrastructure including navigation aids and lighting, aircraft equipment, and other relevant operational factors.
IFP designs vary by location because the operating conditions at each airport are unique. Terrain or obstacles may constrain approach paths or missed-approach design, and they can also constrain departure procedures, arrival procedures, and even en-route procedures in some cases.
The runway orientation and length affect how aircraft are aligned in prevailing weather conditions. However, depending on the day, the prevailing wind would normally indicate to ATC which runway is in use, and the procedures designed for that runway would then be applicable.
Traffic type and volume are also important. A small regional airport handling scheduled IFR traffic will have different procedural needs from a military site, training airfield, or aerodrome with a high proportion of general aviation movements.
Surrounding airspace adds another layer of complexity. Procedures need to fit within controlled airspace where applicable, and if the airport has its own controlled airspace, that local controlled airspace as well as adjacent airspace should be considered. They also need to fit around adjacent controlled airspace, neighbouring airports, and established arrival and departure routes.
For these reasons, visual aids should be considered in the same site-specific way. A visual confirmation of landing clearance may be more useful at an aerodrome where pilots are managing mixed traffic, variable communications, or a higher workload during the final stage of approach. At another airport, standard radio procedures and the existing visual environment may already provide sufficient clarity for this not to be needed.
The decision to introduce an additional visual signal, or not, should therefore be based on how the aerodrome actually operates, how pilots receive and interpret information on approach, and whether that signal adds useful clarity within the wider lighting and signalling system.
Find Out More
Where landing clearance needs to be conveyed clearly in all conditions, visual confirmation can support operational consistency. At Copperchase, we supply CLIs and related systems designed for practical use in diverse ATC environments, and Instrument Flight Procedures Design plays an important role in supporting safe operations in low visibility. For more information or to discuss your needs, please contact us .
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