This is the second instalment in our set of articles on different runways and their requirements.
Airfield rules series
Instrument Flight Rules (IFR) are a set of regulations under which a pilot operates an aircraft in weather conditions not clear enough to see where they are going. IFR are used for instrument piloting and non-visual runways.
IFR are defined by the International Civil Aviation Organisation (ICAO) or a local governing authority, such as the Federal Aviation Administration (FAA) in the US. Each country’s aviation authority has a set of regulations that dictate how aircraft are operated when the pilot cannot navigate using an outside visual reference.
IFR pilot must rely upon and follow their onboard instruments inside the cockpit to safely achieve the different phases of a flight such as departure, navigation and approach.
By checking the weather conditions, the pilot determines if IFR is compulsory. Instrument meteorological conditions (IMC) require the pilot to operate an aircraft under IFR if:
IFR – the basics
IFR approaches let the pilot align a flying aircraft with a runway. It allows a pilot to safely transition from the IFR navigation phase to the IFR approach phase when the weather conditions do not allow the flight crew to have outside references of the airport environment.
The pilot is authorised to descend to a defined altitude or height above the ground and a specific airport distance. These depend on aircraft, pilot rating and on-ground infrastructure equipment (such as airport lighting). It is known as Decision Altitude/Height (DA/DH) or Minimum Descent Altitude/Height (MDA/MDH).
If visual contact has not been acquired at that point, the pilot must initiate a Missed Approach Procedure (MAP). This involves either coming back for another attempt, entering a holding pattern while waiting for the weather to improve, or diverting to the alternate airport. As long the flight crew can get visual references of the runway environment – including the airfield lighting system – they can continue descending to complete a safe landing.
What are the lighting types on an IFR runway?
There are different rules and regulations for ICAO and FAA IFR runways, but they have some standard requirements.
Medium or high-intensity runway lights are required depending on Runway Visual Range (RVR) based minimums. Runway threshold and end lighting are also a must. Taxiway lighting needs to be emitting blue light and positioned along the edges of each taxiway to define the taxiway’s lateral limits. The location and colour output rules are the same as for a VFR runway.
Runway Edge Identification Lighting (REILs) should be installed at the threshold of a precision approach runway in most circumstances. This provides rapid and positive identification of the approach end. The system consists of a pair of synchronised flashing lights.
ICAO and FAA require Precision Approach Path Indicators (PAPIs). PAPIs are a visual aid that provides guidance information to help a pilot acquire and maintain the correct approach.
An approach lighting system must be implemented to give visual guidance for circling, offset, and straight-line approaches to help lower visibility minimums. This can be in the form of a MALSR, SSALR or ALSF configuration depending on the operational and environmental needs of the individual site as well as regional airport guidelines.
What are the types of IFR approaches?
IFR approaches will be higher or lower in height depending on the type of approach required, predominately determined by the weather conditions measured at the airport. The more complex the type of approach required, the more stringent the aircraft’s requirements, flight crew and airport infrastructure.
There are two types of IFR approaches, including:
Ground-based aids and satellite generated navigation data displayed in the cockpit make it possible for the pilot to decide if precision or non-precision IFR should be used. They need the vertical and horizontal guidance displayed on the cockpit instruments to follow the correct approach path for landing.
Non-precision approaches require only horizontal guidance. Therefore, its MDA/MDH will be placed at a higher altitude, and less complex requirements will be required to complete this approach. There must be better weather conditions and visibility at the airport to finish landing.
Our next instalment in the airfield rules series will look into CAT I airports.