martes, 31 de mayo de 2016

When Can You Go Below Minimums On An Instrument Approach?

How low can you go? When it comes to instrument approaches, you can go all the way down to the published minimums, without seeing a thing.

But what do you need to go below minimums and land?

FAR 91.175(c) outlines three requirements:

· You must always be able to make a descent to landing on the intended runway using normal maneuvers and a normal descent rate,
· The flight visibility (that you observe) must meet or exceed the minimums published for the approach, and
· You must be able to distinctly identify one of the approved visual references for the runway (often called the "runway environment")

First Off, What Do You Need To See On Your Approach?

You can group runway visual references into two groups:

1. The ones that let you descend down to 100' above the touchdown zone elevation (TDZE).

2. The ones that let you land.

Here are some examples.

What Gets You To 100' Above The Touchdown Zone?

If you can see the white approach light system and nothing else, you can descend down to 100' above touchdown zone elevation, regardless of the type of approach you're flying (even if it's a non-precision approach). But at the 100' point, you need other visual references to descend lower. Here are some examples of approach light systems that get you down to 100' above the touchdown zone.

What Gets You Down To Land?

So what gets your wheels down on the pavement? If you see any of these references, you can descend down to the runway and land:

· The approach light systems's red terminating bars or red side row
   bars (used on ALSF-1 and ALSF-2 systems)
· The runway threshold
· The threshold lights
· The runway end identifier lights (they're the flashing strobes on
  the corners of the runway's approach threshold)
· The visual approach slope indicator (this includes both VASIs and   PAPIs)
· The touchdown zone or touchdown zone markings
· The touchdown zone lights
· The runway or runway markings
· The runway lights
  That's a bit of a mouth full, so here's a picture to better explain:

How Do You Know What To Look For?

Your approach chart shows the lights you'll see in two places. The top of the chart shows the type of approach lighting system for the approach runway. In this case, KTKI has a MALSR on Runway 18.
The airport diagram also shows the type of approach light system in place for the runways, as well as the type of runway lighting. Runway 18 has high-intensity runway lights (HIRL).

Get Some Practice

Whether you're an instrument rated pilot or not, you can get some practical experience recognizing runway lights. At an uncontrolled airport, use CTAF to turn on the lights. Tower controlled airports rarely turn on the lights during the day in visual conditions (VMC). But, if you ask tower to turn the lights on, they're usually happy to do so. And, the more you see the lights, the easier it is to pick them out of the soup when you're down to minimums.

By Colin Cutler

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