Aerodrome operating minima (AOM) are criteria used by pilots to determine whether they may land or take off from any runway. AOM consist of two parts: one relating to the cloud base and one relating to the visibility and/or RVR (RVR).
The international standards for AOM are defined in ICAO Doc 8168 - Procedures for Air Navigation Services (PANS-OPS) and are employed in most countries throughout the world; however, within North America and at certain other locations, United States Standard for Terminal Instrument Procedures (TERPS) are employed. Although these procedures are similar in many ways, there are important differences. Failure to appreciate these differences appears to have been a factor in a number of fatal accidents. Pilots must determine the standards applied at airports where they intend to operate and make due allowance for any differences.
Where relevant, ICAO definitions etc. are employed in the remainder of this article. The main differences between ICAO-PANS OPS and US TERPS related to circling approaches are described in the article Circling Approach - difference between ICAO PANS-OPS and US TERPS.
AOM are defined as: (ICAO Annex 6 Part 1)
"The limits of usability of an aerodrome for:
a) take-off, expressed in terms of RVR and/or visibility and, if necessary, cloud conditions;
b) landing in Precision Approach and landing operations, expressed in terms of visibility and/or RVR and Decision Altitude/Height (DA/DH) (DA/H) as appropriate to the category of the operation;
c) landing in approach and landing operations with vertical guidance, expressed in terms of visibility and/or RVR and DA/H; and
d) landing in Non-Precision Approach and landing operations, expressed in terms of visibility and/or RVR, Minimum Descent Altitude/Height (MDA/MDH) (MDA/H) and, if necessary, cloud conditions."
AOM are calculated by the operator based on information supplied by the national authority and are published in the Flight Operations Manual.
"In establishing the aerodrome operating minima which will apply to any particular operation, an operator must take full account of: (EU-OPS 1.430(b))
1. the type, performance and handling characteristics of the aeroplane;
2. the composition of the flight crew, their competence and experience;
3. the dimensions and characteristics of the runways which may be selected for use;
4. the adequacy and performance of the available visual and non-visual ground aids (See Appendix 1 (New) to OPS 1.430 Table 6a);
5. the equipment available on the aeroplane for the purpose of navigation and/or control of the flight path, as appropriate, during the take-off, the approach, the flare, the landing, roll-out and the missed approach;
6. the obstacles in the approach, missed approach and the climb-out areas required for the execution of contingency procedures and necessary clearance;
7. the obstacle clearance altitude/height for the instrument approach procedures;
8. the means to determine and report meteorological conditions; and
9. the flight technique to be used during the final approach.
Special provisions apply to Low Visibility Procedures (LVP).
Take-off minima normally consist of a visibility and/or RVR element only; however, if an obstacle exists in the Net Take-off Flight Path (NTOFP) which must be avoided by a visual manoeuvre, the minimum cloud base will also be specified.
The commander may not commence take-off unless the weather conditions at the aerodrome of departure are equal to or better than the AOM specified for:
- Take-off from the runway in use; and,
- Landing at that aerodrome or at a suitable Alternate Aerodrome.
Approach and Landing
Landing minima consist of both visibility and/or RVR, and cloud base elements.
An instrument approach may not be continued beyond the outer marker fix in the case of a precision approach or below 1,000 ft aal in the case of a non-precision approach, unless the reported visibility or RVR is above the specified minimum.
An instrument approach may not be continued beyond the DH/DA or MDH/MDA unless the required visual references for the runway are distinctly visible and identifiable.
Where a landing is to be made on a runway other than the runway to which the approach is being flown, appropriate Circling Approach minima (MDH and visibility) apply.