Aerodrome Operating Minima (AOM) are essential guidelines that help pilots decide when it’s safe to land or take off from a runway. AOM includes two main components: cloud base and visibility, which can also involve Runway Visual Range (RVR). These criteria are set by international standards outlined in ICAO Doc 8168, known as Procedures for Air Navigation Services (PANS-OPS). While most countries follow these guidelines, North America uses the United States Standard for Terminal Instrument Procedures (TERPS). Although similar, there are significant differences between the two systems. Ignoring these distinctions has been linked to several serious accidents. Thus, pilots must understand the standards at the airports they plan to use and account for any discrepancies.
According to ICAO Annex 6 Part 1, AOM is defined as the limits for safely using an aerodrome for various operations: a) take-off, based on RVR and visibility, along with necessary cloud conditions; b) landing in precision approaches, requiring visibility, RVR, and Decision Altitude/Height (DA/DH); c) landing in approaches with vertical guidance, focusing on visibility, RVR, and DA/H; and d) landing in non-precision approaches, which considers visibility, RVR, Minimum Descent Altitude/Height (MDA/MDH), and relevant cloud conditions.
Operators calculate AOM based on data from national authorities, and this information is published in the Flight Operations Manual. When setting the AOM for any flight, operators need to consider several factors: 1. the aircraft type and its handling characteristics; 2. the flight crew’s experience and competence; 3. the dimensions and features of the runways available; 4. the effectiveness of visual and non-visual ground aids; 5. onboard navigation and control equipment; 6. obstacles in approach and climb-out areas; 7. obstacle clearance heights for instrument approaches; 8. ways to monitor and report weather conditions; and 9. the approach techniques to be used.
There are special rules for Low Visibility Procedures (LVP). Regarding take-off, minima typically consist only of visibility and/or RVR. However, if there are obstacles in the Net Take-off Flight Path (NTOFP), a minimum cloud base must also be established. The pilot cannot initiate take-off unless the weather at the departure aerodrome meets or exceeds the AOM for both take-off from the active runway and landing at that aerodrome or a suitable alternate.
For landing, minima encompass both visibility/RVR and cloud base. An instrument approach cannot proceed beyond the outer marker fix for precision approaches or below 1,000 feet above airfield level for non-precision approaches unless visibility or RVR is above the minimums set. Furthermore, an approach should not continue beyond the Decision Height/Altitude (DH/DA) or Minimum Descent Height/Altitude (MDH/MDA) without clear visual references for the runway. If landing on a different runway than the one being approached, the appropriate Circling Approach minima apply.
