The only exception is when that State specifically approves a lower value — Page 56, Lesson 89

I want to walk you through a key regulatory principle that governs how low we can go when operating into an aerodrome. This is about aerodrome operating minima — the minimum visibility and cloud ceiling conditions required for a take-off, approach, or landing. Here's the core rule: the minima we use shall not be lower than any minima that may have been established for that aerodrome by the State in which the aerodrome is located. In other words, if the local aviation authority — say, the DGCA in India or the FAA in the United States — has published a minimum visibility or decision height for that airport, we cannot go below it. The only exception is when that State specifically approves a lower value. So the State's minima act as a floor that we cannot undercut without their explicit permission. Now, there is a technological caveat. The use of a head-up display, or HUD, a head-up display landing system, HUDLS, or an enhanced vision system, EVS, may allow operations with lower visibilities than are normally associated with the aerodrome operating minima, which we abbreviate as AOM. So if the aircraft is equipped with these advanced systems, the operator may be permitted to use lower minima than the standard published values — but again, only if the State approves. There's also an important note here: this paragraph does not prohibit in-flight calculation of minima for a non-planned alternate aerodrome, provided that calculation is carried out in accordance with an accepted method. So if you're in flight and you need to divert to an airport that wasn't on your flight plan as an alternate, you can compute the minima for that airport on the spot — as long as you follow a method that has been accepted by the regulator. Now, when an operator establishes the aerodrome operating minima for any particular operation, they must take full account of a comprehensive list of factors. Let me walk through each one. First, the type, performance and handling characteristics of the aeroplane. A large jet and a small turboprop have different approach speeds, different stopping distances, and different handling qualities — all of which affect the minima. Second, the composition of the flight crew, their competence and experience. A crew that has recently trained on the approach type or has extensive experience in that aerodrome may be able to operate to lower minima than a less experienced crew. Third, the dimensions and characteristics of the runways which may be selected for use. A wider, longer runway with good surface friction allows lower minima than a short, narrow, or contaminated runway. Fourth, the adequacy and performance of the available visual and non-visual ground aids. This includes things like the instrument landing system, precision approach radar, approach lighting, and runway edge lights — if they are high-performance and serviceable, the minima can be lower. Fifth, the equipment available on the aeroplane for the purpose of navigation and/or control of the flight path during the take-off, the approach, the flare, the landing, roll-out and the missed approach. So we consider the autopilot, flight director, autothrottle, head-up display, and any other systems that help guide the aircraft through each phase of the operation. Sixth, the obstacles in the approach, missed approach and the climb-out areas required for the execution of contingency procedures and necessary clearance. If there are tall obstacles near the runway, the minima must be high enough to ensure safe obstacle clearance during a missed approach or a go-around. Seventh, the obstacle clearance altitude or height for the instrument approach procedures. This is the minimum altitude or height above the runway threshold that ensures you clear all obstacles on the approach path. Eighth, the means to determine and report meteorological conditions. The operator needs reliable weather reporting — from an aerodrome weather station, a tower report, or an automated system — to know whether the actual conditions meet the minima. And ninth, the flight technique to be used during the final approach. Whether you are flying a coupled autoland, a manual approach with flight director guidance, or a visual approach — each technique has different accuracy and workload, and that affects the minima you can safely use. So in summary: the State's minima are the absolute floor unless the State approves lower values, advanced vision systems may allow lower minima, and the operator must consider nine specific factors when setting the minima for each operation.