6.01 General Approach Criteria

1. Basic Navigation Requirements

Navigation can be defined as the following of a desired flight path, clear of obstacles and clear of other traffic. Adherence to the selected flight path, the clearance of obstacles and the avoidance of traffic constitute the basic navigation requirements.

During approach these requirements can be met by visual reference or by the execution of an instrument approach procedure.

2. Visual Navigation

When flying by visual reference, navigation must be done visually. In other words, the pilot selects the desired flight path visually, while assessing obstacle clearance and (possibly) traffic separation.

Visual approach limitations

These requirements set the limitations for a visual approach. They are: keep the runway in sight and see and avoid traffic and obstacles. Not many, but they can be very demanding.

Unlike an instrument approach procedure, a visual approach has in principle no specified weather minima for landing, no established tracks, no minimum crossing altitudes and no MDA or DA: there is no procedure which provides for protected airspace.

In fact, when flying outside protected airspace, visual navigation requirements apply. An example of this is operation below the descent limit (DA, MDA).

Visual approach and circling approach

NOTE: 1. The difference between a visual approach and a circling approach is, that for a circling approach protected airspace is provided: for the circling area plus the final and missed approach area associated with the cloud break procedure.

NOTE: 2. Weather minima for VFR flying (ceiling 1500 ft — VIS 8 km) are often assumed to be weather minima for visual approach. However, this is not true in most countries.

3. Instrument Navigation

In instrument navigation, predetermined tracks or radar vectors are available for flight path selection. Obstacle clearance is ensured by minimum crossing altitudes or minimum vectoring altitudes. In most airspace ATS takes care of traffic separation.

4. Instrument Approach and Protected Airspace

For the flight path of an instrument approach, protected airspace has been established.

In establishing protected airspace, consideration is given to the performance of the aircraft category in general and to the ‘performance’ of the individual pilot (see next paragraphs). As far as the latter is concerned, adherence to the published procedure using standard operating procedures should satisfy the requirements.

5. Performance of the Aircraft Versus Protected Airspace

Speed

Aircraft types are divided into 5 categories, based on speed. Speed is considered the most significant performance factor. The reference speed is 1.3 x stall speed (in the landing configuration, at maximum certified landing weight).

Instrument procedures are designed per aircraft category.

Aircraft categories

Company aircraft are categorized as follows:

• SAAB 340, Fokker 50 : CAT B
• F-28, Fokker 100, 737, A310 (except for Circling) : CAT C
• 747, MD-11, DC-10, A310 (Circling) : CAT D

(nice to know: Concorde: CAT D and F-16: CAT E).

Climb during missed approach

For protected airspace calculation, the standard minimum required climb gradient for all aircraft categories under all conditions is fixed at 2.5% (150 ft/NM).

In exceptional cases an increased climb gradient is used. This will be indicated in the missed approach procedure.

6. Performance of the Individual Pilot Versus Protected Airspace

Piloting limitations

There are so called piloting limitations for:

• Track keeping
• ILS fly-up demand
• Maximum and minimum speed
• (Minimum) altitude

Track keeping

Maintain:

• VOR radial within 2.5° on either side of track
• LLZ within 2° on either side of track (1/2 scale deflection; see also NOTE below)
• NDB QDM within 3° on either side of track
• Heading within 15° on either side of nominal heading

Be aware that these values are maximum ones. Protected airspace is determined by applying the Route Sum Square of independent tolerances of piloting error, airborne equipment and ground equipment:

√(a² + b² + c²)

Route Sum Square of tolerances

(a, b and c represent the individual tolerances of ground station, airborne receiver, piloting error).

If ‘a’ should be the pilot tolerance, it must be clear, that continued flight with ‘a’ at maximum deviation could place the aircraft outside protected airspace, if ‘b’ and ‘c’ (which are beyond pilot control) become maximum too.

Conclusion: Continue to fly the needle in centered position in so far as possible.

ILS fly-up demand

Maximum fly-up demand is ‘1/2’ scale.

NOTE: ‘1/2’ scale is ICAO terminology. On our present aircraft this is about one dot deflection.

As future developments are not known, ICAO terminology will be used in this chapter.

Maximum and minimum approach speed

For the various stages of the approach, maximum and minimum speeds are applicable.

* Circling with higher IAS than appropriate, requires application of Circling minima of the next aircraft category.

** CAT B: 140 in Racetrack and Course reversal procedures

Minimum and maximum altitude

• The applicable charts show minimum and (in some cases) maximum altitude.
• Be aware, that temperature deviations are not taken into account in obstacle clearance calculations, including DA / MDA. In relation also to the previously discussed track-keeping tolerance, note that obstacle clearance may reduce to zero at the outer edge of protected airspace.

Temperature and obstacle clearance

In view of the above, be advised to increase published altitudes, if the temperature is well below standard and obstacle clearance becomes a factor to be considered.

True altitude

Explanation:

True altitude might be of importance during flight over high terrain or during various stages of the approach. The pressure altimeter is hardly ever indicating the true altitude. Apart from small errors like position error, instrument error, etc., the pressure altimeter will only be indicating the true altitude when:

• subscale of the altimeter is set to local QNH and
• ICAO standard atmosphere conditions exist.

The (ICAO) standard conditions hardly ever exist, so to find true altitude, temperature and pressure corrections must be made:

Temperature correction

• For each °C above STD temperature add 4 ft for each 1000 ft of altitude from altimeter reading to find true altitude.
• For each °C BELOW STD temperature SUBTRACT 4 ft for each 1000 ft of altitude from altimeter reading to find true altitude.

Alternatively the table in the Regional ROM (yellow pages) may be used: in low temperature conditions raise published altitudes with the tabulated value.

Values are rounded-off to multiples of 20 ft. The table is specifically meant for approach procedures.

QNH correction

• For each hPa that QNH is above 1013.2 hPa (29.92 inHg) add 30 ft to/from altimeter reading to find true altitude.
• For each hPa that QNH is BELOW 1013.2 hPa (29.92 inHg) SUBTRACT 30 ft to/from altimeter reading to find true altitude.

‘When flying from high to low, look out below’.