Years ago, following a "dive and drive" mishap, a major airline had to remind its pilots that a non-precision approach must be flown with great precision. In my distant past, I think the U. Air Force must have lost a few airplanes to "dive and drive" because our evaluation criteria required crews be busted for even an inch of deviation below the MDA. For most limits we allowed momentary deviations with signs of a positive correction, but the MDA was a brick floor, none were allowed to go below it until the runway was sighted and the airplane was in a position to land. Leveling off at the MDA can be problematic if there are distractions or turbulence. Keeping the airplane at the MDA until the runway is sighted is another issue.
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If you wish to contribute or participate in the discussions about articles you are invited to join SKYbrary as a registered user. Aerodrome operating minima AOM are calculated by operators based on information supplied by national authorities in their AIPs.
This information typically consists of approach and departure procedures which assure safe separation between the aircraft and known obstacles located close to the intended flight path of the procedure in question. The procedures themselves are based on obstacle clearance domains constructed using internationally accepted standards. This is especially true in respect of Circling Approaches where the assumed radius of turn and minimum obstacle clearance are markedly different see below.
These values are calculated differently and therefore, may result in different AOM. Table 1 shows the lowest value of visibility assumed by each method:.
The circling approach area has been expanded to provide improved obstacle protection. As a result, circling minima at certain airports may increase significantly. TERPS These distances, dependent on aircraft category, are also based on the circling altitude which accounts for the true airspeed increase with altitude. From May 2, , the FAA started publishing new instrument approach plates that include an enlarged segment of airspace to protect aircraft during circling approaches.
The new airspace also offers pilots additional obstacle clearance while considering their MSL altitude above the MDA, which affects true airspeed. The boundaries of protected airspace for circling approaches are defined by arcs drawn from the threshold of each runway at an airport.
The higher the speed of the aircraft, the larger the arc. Under the new criteria that radius will increase by 65 percent, to 2. Chart providers U. Terminal Procedures and Jeppesen both plan to use new chart symbology to identify the updated approaches.
Charts without the new designation will continue to be guided by the old, smaller-radii criteria. Both systems assume a 25 kt The latter is shown on Table This is believed to have been a major factor in the following fatal accident, which resulted in considerable loss of life: B, vicinity Busan Korea, Additionally, pilots not aware of the increased bank angle expected in US TERPS calculations might, in certain circumstances, stray outside the circling area due to the increased circling radius.
It is therefore essential that pilots understand these differences and are aware of the basis of calculations for all airfields at which they intend to operate, including alternates. The basis for calculation of minima is usually printed on the approach plate see Further Reading: Jeppesen Chart Basics - a presentation. National authorities or operators may require adjustments to be applied to operating minima to compensate for these differences. For details refer to the relevant documents listed below.
Continuous Descent Final Approach (CDFA)
Such procedures are used to allow aircraft to land and take off when instrument meteorological conditions IMC impose instrument flight rules IFR. Chapter 4 of Annex 14 to the Convention on International Civil Aviation "[establishes] a series of obstacle limitation surfaces that define the limits to which objects may project into the airspace" surrounding an aerodrome. These surfaces may be used as a tool for local governments in assessing building development. Where buildings may under certain circumstances be permitted to penetrate the OLS, they cannot be permitted to penetrate any PANS-OPS surface, because the purpose of these surfaces is to guarantee pilots operating under IMC a descent path free of obstacles for a given approach. In the very first commercially available off the shelf instrument procedure design software conforming to ICAO document Pans-Ops was programmed. Prior to this all procedure design was done with pencil, tracing paper and a calculator. From Wikipedia, the free encyclopedia.