Page 24 - TNT Dec 2017

22 • TWIN & TURBINE December 2017
The takeoff minimums at Chicago O’Hare airport.
or sometimes four (KDEN), locations along the runway. These positions are classified as touchdown, mid (midfield), rollout and far-end.
The result is expressed as runway visual range, or RVR, in hundreds of feet or meters. Depending on which LVP is in use, we need a specified minimum number of transmissometers to report (that is, functioning), and the value reported must meet or exceed charted RVR minimums in order to use the desired LVP. Individual operators (through FAA ops specs), or the charted procedure itself, may allow substitution of certain transmissometers for another when one or more are inoperative. For example, the mid substituted for touchdown, or far-end for rollout. In order to review several types of LVP’s, let’s take a flight starting from the ramp, a taxi and takeoff, with a review of the decision to return or divert if we have an issue after takeoff, followed by descent and an approach.
Self-Imposed Restrictions
First, we need to determine if the visibility is adequate for taxi, takeoff and a return. While Part 91 operators may depart with no visibility constraints, self-imposing the published takeoff minimums found on the airport diagram pages is a good idea. These charts may specify how many, and which, transmissometers are available for each runway as well as RVR values required for takeoff. These visibilities, however, are normally well below Category I landing minimums. After takeoff, if we have the required equipment operating – two motors, electrical and hydraulic systems for example, as well as necessary ground equipment and lighting – a return for a Cat II or III approach may be possible. If we’re not able to perform a Cat II or III landing at our departure airport, then a diversion to better weather, like Santa, rather than back to the six, four and blurry airport we just left, would be the plan.
Therefore, when the takeoff visibility is below Cat I mins, select a takeoff alternate within a prudent distance that would allow you, the airplane and your avionics to f ly a single-engine, Cat I approach. A piston twin may not have the ability to fly single-engine to another airport with better weather. If not, then waiting for the takeoff weather to reach Cat I landing minimums would be another prudent, self-imposed restriction.
SMGCS, REL’s, THL’s, SMR and ASSC
Next, review the SMGCS (Surface Movement Guidance Control System) taxi procedure pages. There will be charts for several visibilities to and from the active runway (Less than RVR 1,200 to 600, or RVR 600 to 300, for example). Using in-ground, multi- color lights similar to the runway centerline lights, the charts will depict a unidirectional or bidirectional route, geographic position markings, holding “bars” as well as Runway Entrance Lights and Takeoff Hold Lights (REL’s and THL’s) to the takeoff runway.
Since we seldom use these charts, a slow and thorough review before engine start should be accomplished. While we taxi, ATC will normally monitor surface movement using both SMR (Surface Movement Radar) and the ASSC system (Airport Surface Surveillance Capability). These tools display aircraft and ground vehicles on the airport surface, as well
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