Air Law

• The transition altitude is the altitude at or below which aircraft use the local QNH setting. Above this point, they switch to standard pressure (1013.25 hPa or 29.92 inHg).
  → It is used during climb.
  → Its value and the associated changeover procedure are State-specific; the United States and Canada do not use an identical nationwide rule.

• The transition level is the lowest usable flight level at or above which aircraft operate on standard pressure. Below this point, they must use the local QNH setting.
  → It is used during descent.
  → It usually varies depending on the current QNH, but may be fixed at some airports.

• The airspace between the transition altitude and the transition level is called the transition layer.

Note: Level flight is not permitted within the transition layer.
For example, if the transition altitude is 5000 ft and the transition level is FL070, an aircraft would not be cleared to maintain FL060 or 6,000 ft within that layer.

United States and Canada

United States: use 29.92 inHg at and above 18,000 ft MSL. The lowest usable flight level is not automatically FL180 when the altimeter setting is low; ATC may use a higher lowest usable flight level.

Canada: the Standard Pressure Region includes all airspace at and above 18,000 ft, but also low-level airspace outside the Altimeter Setting Region. Standard pressure can therefore be used below 18,000 ft in northern and remote Canadian airspace. Apply the changeover procedure for the region being entered rather than treating 18,000 ft as a universal Canadian transition altitude.

Official references: FAA AIM, Altimeter Setting Procedures; TC AIM RAC, Altimeter Setting and Standard Pressure Regions.

Aircraft approach categories are based on the aircraft’s $V_{AT}$, which is the indicated airspeed at threshold.
Vat is defined as 1.3 × $V_{SREF}$ (stalling speed in landing configuration) at the maximum certified landing weight.

The 5 categories are:

Note: These categories are used to determine approach minima, obstacle clearance requirements, and procedure design.

ICAO Annex 14, Volume I, defines the standard number of longitudinal white threshold stripes according to runway width:

Each stripe is at least 30 m long and approximately 1.80 m wide. The spacing between adjacent stripes is approximately 1.80 m, with a larger central separation between the two stripes nearest the runway centre line.

Therefore, a threshold displaying 8 standard stripes normally indicates a 30 m runway, 12 stripes a 45 m runway, and 16 stripes a 60 m runway.

This remains a visual recognition aid rather than authoritative runway-width data. An alternative marking pattern may be used on certain non-precision approach and non-instrument runways that are 45 m or wider. The published AIP or aerodrome chart should be used to confirm the actual runway width.

Reference: ICAO Annex 14, Volume I, §5.2.4 “Threshold marking” and Figure 5-2.

United States and Canada

United States: FAA aiming-point markings are approximately 1,000 ft from the landing threshold. FAA threshold markings can use eight stripes or the width-related 4/6/8/12/16 pattern.

Canada: TP 312 and the aerodrome's certified layout control. Canadian aiming-point placement can vary with landing distance available and visual-slope-system geometry.

In both countries, markings are a recognition aid only. Use the current aerodrome chart/publication—not stripe counting—to determine runway dimensions.

Official references: FAA AIM 2-3-3; Transport Canada TP 312 material.

The ICAO maximum holding speeds depend on the holding altitude and aircraft category:

Note: These are standard ICAO limits. Local procedures or ATC instructions may specify lower values.

United States and Canada

The North American default holding speeds differ from the ICAO/PANS-OPS table above:

A charted restriction or ATC instruction can require a different/lower speed.

Official references: FAA AIM 5-3-8; TC AIM RAC 10.7.

ICAO wake turbulence categories are based on an aircraft’s Maximum Certified Takeoff Weight (MTOW) and are used by ATC to apply appropriate separation minima to mitigate wake turbulence risk.

Note:
- The "Super" category is not based solely on MTOW, but on ICAO designation found in Doc 8643.
- Wake turbulence categories are filed in the ICAO flight plan (Item 9) using the codes J, H, M, or L.

United States and Canada

Do not apply an ICAO wake or final-spacing number as a universal North American minimum.

United States: FAA facilities may use legacy wake categories or approved consolidated/RECAT categories. The current FAA AIM specifies a 4-minute interval for aircraft taking off behind a Super aircraft in the same-threshold/closely spaced parallel-runway cases it describes. Reduced 2.5-NM final spacing is allowed only under stated runway, surveillance, aircraft and facility conditions; wake separation can require more.

Canada: use the current TC AIM, NAV CANADA procedures and the clearance actually issued. Wake separation and reduced final spacing depend on the aircraft pair, runway geometry and authorized local procedure.

Official references: FAA AIM 7-4 and JO 7110.65; TC AIM RAC.

The ICAO airspace classes (A to G) determine the level of ATC services, separation, and communication requirements provided to aircraft.

Summary of services by airspace class:

Notes:

• Separation = active ATC responsibility to maintain distance between aircraft.
• Traffic information = ATC provides position info, but separation is not ensured.
• Classes F and G are uncontrolled airspace.

Important: The exact usage of each class may vary depending on the state’s AIP.

United States and Canada

United States: Classes A through E are controlled; the United States does not use Class F. Class B requires an explicit ATC clearance. In Classes C and D, two-way radio communication must be established before entry, with the precise acknowledgement/entry rule given in the FAA AIM and 14 CFR.

Canada: Class F is special-use airspace and may be controlled, uncontrolled, or a combination of both. Canadian Class B normally covers controlled low-level airspace above 12,500 ft ASL up to, but not including, 18,000 ft ASL; it is used by IFR and controlled-VFR flights rather than ordinary VFR traffic.

Official references: FAA AIM Chapter 3; Transport Canada, Flying in Canada / TC AIM RAC 2.8.