Minimum Descent Altitude/Height
An additional margin is added to the OCA/H for operational considerations, and a MDA/H is specified. Descent below MDA/H should not be made until visual reference has been established and can be maintained, the pilot has the landing threshold in sight, and the required obstacle clearance can be maintained and the aircraft is in a position to carry out a landing.
Visual Flight Manoeuvre
A circling approach is a visual flight manoeuvre. Each circling situation is different because of variables such as runway layout, final approach track, wind velocity, and meteorological conditions. There is no single procedure that caters for conducting a circling approach in every situation. After initial visual contact, the basic assumption is that the runway environment (the runway threshold, approach lighting aids, or other markings identifiable with the runway), should be kept in sight while at MDA/H for circling.
Missed Approach While Circling
If visual reference is lost while circling to land from an instrument approach, the missed approach for the instrument procedure, must be followed. Other aircraft may be attempting the same manoeuvre therefore the missed approach procedure must take the aircraft away from subsequent instrument aircraft. It is expected that the pilot will make an initial climbing turn toward the landing runway and overhead the aerodrome. Then, the pilot will establish the aircraft climbing on the missed approach track. Because the circling manoeuvre may be accomplished in more than one direction, different patterns will be required to establish the aircraft on the prescribed missed approach course depending on its position at the time visual reference is lost.
The VM(C) OCA for the aerodrome is published on the chart for the instrument part of the approach. The fixed margin is added to OCA for each category of aircraft.
Visual Manoeuvre (Circling) Area
PUBLISHED INFORMATION
Radius from end of Runway Highest
obstacle in area
The radius is based on aircraft
category/speed
Area Navigation (RNAV) Approach Procedures Based On VOR/DME
RNAV approach procedures based on VOR/DME are assumed to be based on one reference facility composed of a VOR and co-located DME. Aircraft equipped with RNAV systems which have been approved, may use these systems to carry out VOR/DME RNAV approaches providing that before conducting any flight it is ensured that the RNAV equipment is serviceable, the pilot has a current knowledge of how to operate the equipment so as to achieve the optimum level of navigation accuracy and the published VOR/DME facility upon which the procedure is based is serviceable. The main disadvantage of using RNAV is that it relies on a navigational database to support the computer interpretation of the received information. If this database contains errors computed positions will be in error.
Use of FMS/RNAV Equipment to Follow Conventional Non-Precision Approach Procedures When FMS/RNAV equipment is available, it may be used when flying a conventional non-precision approach procedure, provided the procedure is monitored using the basic display normally associated with the procedure, and the tolerances for flight using raw data on the basic display are complied with.
Track Reversal and Racetrack Procedures
At large aerodromes serving international commercial aviation, radar vectoring to the ILS or self positioning to the ILS is the standard method of commencing an instrument approach. Even in conditions of good visibility and high cloud ceiling, to ensure separation from departing aircraft, IFR is made mandatory by the imposition of Class A airspace and ILS approaches are required.
At low intensity and remote aerodromes, with limited availability of ‘off aerodrome’ navigation aids, a procedure known as the ‘single beacon reversing turn procedure’ is a standard type of procedure. The chart below shows the ILS DME procedure for runway 08 at Luton.
PROCEDURE
An arriving aircraft would usually enter the holding pattern above the LUT NDB(L), the IAF for the procedure, at an altitude above the lowest holding altitude (LHA) and wait for clearance to begin the procedure. When cleared to the LHA in the hold, the aircraft speed will be adjusted and aircraft configuration adjusted. The ATC clearance would be “(callsign)… cleared ILS runway 08 advising turning inbound at 2000 ft” The aircraft leaves the hold on a track of 258°mag to a point on the reciprocal of the ILS localiser at DME range 5 nm. The pilot would advise ATC
“(callsign) turning inbound at 2000 ft”. The controller will then clear the aircraft “(callsign) report established ILS 08”. The aircraft is then flown through a procedure turn that places the aircraft in a position to intercept the localiser beam inbound. Once established on the localiser and reported so, the controller will instruct the pilot to report glidepath descending to the aerodrome controller. The aircraft is flown along the localiser beam until the glidepath is intercepted, and descent is commenced. If at DH the visual criteria is not obtained, the “go around” (missed approach) procedure is flown as published on the chart.
Missed Approach Procedure Holding Pattern
IAF
Procedure Turn IF FAP (there is no defined FAF)
Glidepath interception
MSA
Localiser Ident and Frequency
VM(C) OCA OCA (OCH)
Glidepath information
Track Reversals
There are several different track reversal methods. The diagram below shows:
¾ Procedure turns;
¾ Base turn; and
¾ Racetrack.
Note: In all the procedures, tracks are flown. Therefore pilots must make allowance for the wind.
Track Reversal Procedures 45°/180° Procedure Turn
This is the most common track reversal procedure. At a defined point the aircraft is turned through 45° and then flown straight and level. From the start of the turn, after for 1 min for Cat A
80°/260° Procedure Turn
This procedure is used where airspace is limited. The aircraft is turned through 80° and the bank angle is immediately reversed to turn through 260° in the opposite direction. The turns are made at rate 1 or 25° bank angle whichever is less. In still air, at the completion of the turn the aircraft will be tracking inbound on the reciprocal of the outbound track. In still air, this procedure takes exactly 2 minutes and is often called a 2 minute procedure.
Note: For either procedure, the tracks flown are reciprocal.
Note: The outbound leg is usually flown with reference to the ILS localiser (if the procedure is part of an ILS approach). Flying the reciprocal of the localiser course is not flying the back beam, which is not approved in Europe. The pilot must remember that indications are reversed when flying the localiser in the wrong direction!
Base Turn
Where accurate track guidance is available other than the ILS localiser, for instance VOR information, a base turn can be flown. From on top of the facility the aircraft is established on a defined track which diverges from the reciprocal of the desired inbound track. At a point defined by time, DME distance or interception of information from another aid, the aircraft is established in a turn at rate 1 or 25° bank angle until the inbound track is intercepted.
Racetrack
It is not always convenient for the holding pattern associated with a single beacon procedure to be oriented so that the inbound holding track can be extended directly into the outbound procedure track as in the case of Luton. The picture below shows part of the procedure for Edinburgh including a racetrack shown by the dotted line.
Racetrack Reversing Turn Procedure
From the above picture it is clear that there is no way that the pilot can track outbound on 065°
directly from the holding pattern. In this case, when cleared to commence the approach the aircraft is flown outbound in the holding pattern and the outbound track is maintained to a defined point (in this case DME range 9 nm) at which a rate 1 turn through 180° is initiated to bring the aircraft on to the desired inbound track. On the approach chart this would be specified as an
‘alternative procedure’.
Racetrack Normal procedure without holding
Note: The student must not confuse a racetrack with a holding pattern. The racetrack is only used for track reversal; similarly, a holding pattern is only used for holding.
Dead Reckoning Segment
Where an operational advantage can be obtained, an ILS procedure may include a dead reckoning segment from a fix (usually the IAF) to the localiser. The DR track will intercept the localiser at 45° and will not be more than 19 km (10 nm) in length. The point of intersection of the localiser is the beginning of the intermediate segment and will allow time for establishing on the localiser before descent is required.
Dead Reckoning Segment
Inevitably aircraft will not be able to make a straight in approach and will need to temporarily
‘park’ whilst awaiting clearance to commence the approach procedure. The process of ‘parking’ is known as holding. We have already seen that the single beacon reversing turn procedure usually starts at a holding point and it is usual for the missed approach procedure to end at a holding point. Holding is achieved by the pilot flying the aircraft around a holding pattern. The process of flying around the pattern is called ‘shuttling’. As part of the IRT the student will be required to fly holding patterns to a precise degree, and this will be achieved after a lot of practice. In the Chapters concerned with Approach Control, the student will be introduced to the process known as ‘stacking’, but first the holding pattern needs to be described and the procedures for joining and flying the pattern discussed.
Deviation Warning
Deviations from the procedures for holding may incur the risk of excursions beyond the perimeter