Sunday, June 03, 2007

Day 11: Feeling Positive

Today's Lessons
  • Block Test IV
  • VFR Arrivals
  • VFR Departures
If there's one way to sum up today's lessons, it would be "positive control".

Here's an example: Cessna 172PT calls in from the Spartan Aviation FBO. Now, you could tell him "CESSNA 172PT, TAXI TO RUNWAY 28R" and just leave it at that. However, that opens up a can of worms, since he could get to 28R from a million different directions. He could go via taxiways Golf-Bravo-Alpha... or Hotel-Juliet-India-Charlie-Bravo-Alpha... or.... you get the idea. And when you've got landing traffic or traffic coming out of the terminal, there's a very good possibility you could wind up nose-to-nose. On top of that, that clearance was a straight "taxi to runway XX" clearance, meaning he can cross anything along the way - including active runway 16. Big no-no.

Instead, use positive control. You're the controller. You are in control. So, you know...control!

It's a longer transmission, but it leaves no question for either you or the pilot as to where that aircraft should be going. He's going to head via Golf, turn left at Bravo, and hold short of Runway 16. Once he gets clearance to cross, he will proceed to Charlie, turn right, and hold short of Runway 28R for an intersection takeoff. It leaves out any mystery, and allows you to plan ahead.

Practical Exercises

We did some scenarios today on the board, which allowed us to explore different options for getting traffic in and out of our airport.

I think one of the strongest things you can develop is a sense of timing based on aircraft speed and performance. To be successful in this job, you need to have a good understanding of what each airplane's performance envelope is and what kind of speed they will be flying at during different phases of flight. This will help you anticipate more and gauge how much time you have to get an airplane in or out.

Here's an example:
You've got: 1) A Baron holding short of 28L who just called ready for takeoff, 2) a Cherokee N8PM abeam the numbers on downwind for 28L, and 3) another Cherokee N8DS that just called in 6 miles east, inbound straight-in for 28L as well.

Ok, for starters, both Cherokees are slow-movers. The one on downwind is probably making around 80-90 knots, and the one 6 miles out is probably at 90-100 knots. Let's round them to 90, which gives us a distance-per-minute of 1.5NM. The Baron, as a twin, is signifigantly faster.

At 1.5NM per minute and 6 miles away, Cherokee N8DS will take 4 minutes to reach the airport, so he's barely even a factor unless we really screw something up. So we back-burner him for now and turn our attention back to Cherokee N8PM on downwind and our twin-engine friend, the Baron. Cherokee 8PM has to fly 1 mile past the runway threshold to intersect the base leg. Then he has the base leg itself, which is another mile. Then the final leg - 3 miles total. That gives us 2 minutes.

Armed with those 2 minutes, we go "BARON 123, ACADEMY TOWER, TRAFFIC CHEROKEE ON DOWNWIND, RUNWAY 28L, CLEARED FOR TAKE OFF." Out the gate goes the Baron - he's wheels up and gone. Since we're oh-so-confident in how many minutes we have, before the Baron even begins rolling we can call N8PM: "CHEROKEE 8PM, ACADEMY TOWER, TRAFFIC, DEPARTING BARON RUNWAY 28L, RUNWAY 28L, CLEARED TO LAND."

At the point when 8PM is turning final, 8DS should be at least 2 minutes behind him. At this point, you can go ahead and clear him to land. "CHEROKEE 8DS, ACADEMY TOWER, NUMBER TWO BEHIND CHEROKEE ON FINAL FOR RUNWAY 28L, RUNWAY 28L, CLEARED TO LAND."

Voila! Problem solved. When 8PM comes in over the threshold, he'll have a whole 3 miles between him and the Cherokee behind him. This meets the 3000 foot Cat I separation 6-fold. And, we didn't have to delay the Baron at all.

No comments: